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Sometimes the Same, Sometimes Different: Understanding Self-Assembly Algorithms in Coordination Networks Y. Maximilian Klein, Alessandro Prescimone, Mariia Karpacheva, Edwin C. Constable Catherine E. Housecroft *

and

Department of Chemistry, University of Basel, BPR 1096, Mattenstrasse 24a, 4058 Basel, Switzerland; [email protected] (Y.M.K.); [email protected] (A.P.); [email protected] (M.K.); [email protected] (E.C.C.) * Correspondence: [email protected]; Tel.: +41-612-071-008 Received: 23 November 2018; Accepted: 8 December 2018; Published: 11 December 2018







Abstract: The syntheses and characterizations of three new ligands containing two 4,20 :60 ,400 -tpy or two 3,20 :60 ,300 -tpy metal-binding domains are reported. The ligands possess different alkyloxy functionalities attached to the central phenylene spacer: n-pentyloxy in 3, 4-phenyl-n-butoxy in 4, benzyloxy in 5. Crystal growth under ambient conditions has led to the formation of {[Co(NCS)2 (3)]·0.8C6 H4 Cl2 }n and {[Co(NCS)2 (4)]·1.6H2 O·1.2C6 H4 Cl2 }n , with structures confirmed by single crystal X-ray diffraction. Both the cobalt(II) center and ligand 3 or 4 act as 4-connecting nodes and both {[Co(NCS)2 (3)]·0.8C6 H4 Cl2 }n and {[Co(NCS)2 (4)]·1.6H2 O·1.2C6 H4 Cl2 }n possess a 3D cds net despite the fact that 3 and 4 contain two 4,20 :60 ,400 -tpy and two 3,20 :60 ,300 -tpy units, respectively. Taken in conjunction with previously reported data, the results indicate that the role of the alkyloxy substituent is more significant than the choice of 4,20 :60 ,400 - or 3,20 :60 ,300 -tpy isomer in determining the assembly of a particular 3D net. The combination of Co(NCS)2 with 5 resulted in the formation of the discrete molecular complex [Co(NCS)2 (MeOH)2 (5)2 ]·2CHCl3 ·2MeOH in which 5 acts as a monodentate ligand. The pendant phenyls and both coordinated and non-coordinated 4,20 :60 ,400 -tpy units are involved in efficient π-stacking interactions. Keywords: tetratopic ligands; 4,20 :60 ,400 -terpyridine; 3,20 :60 ,300 -terpyridine; metal-organic framework; cobalt(II) thiocyanate

1. Introduction Polymeric materials are essential to mankind, both as the crucial biomolecules enabling life processes and as the materials at the core of our socioeconomic structures. Metallopolymers are an important subset of polymers, in which the incorporation of metal centers allows the blending of new properties which are not readily accessed through polymeric structures based only on C, H, N, O, S and P atoms. An important class of metallopolymers are the coordination polymers and networks, in which the metal centers are incorporated through coordination rather than covalent bonds. Specifically, coordination polymers and networks are infinite assemblies in which the metal centers are connected by coordinated organic molecules. The coordination number and coordination geometry of the metal centers provide an exquisite control over the dimensionality as well as the topographical and topological features of the coordination assemblies. Ligands with pyridine nitrogen donors comprise some of the most commonly utilized linkers, for example [1–7], with 4,40 -bipyridine (4,40 -bpy, Scheme 1) used extensively as a rigid organic linker in coordination assemblies. An [M(pytpy)2 ]n+ (pytpy = 40 -(4-pyridyl)-2,20 :60 ,200 -terpyridine) is an expanded 4,40 -bpy since both can

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bind two metal ions and possess similar vectorial properties (Scheme 1) [8]. Newkome and coworkers Polymers 2018, 10, x FOR PEER REVIEW 2 of 15 n+ building blocks with have demonstrated demonstrated the the assembly other have assembly of of metallocages metallocages based based upon upon [M(tpy) [M(tpy)22]]n+ building blocks with other 0 0 00 0 00 vectorial properties properties [9]. By Bychanging changingfrom fromthe the2,2′:6′,2″-isomer 2,2 :6 ,2 -isomer terpyridine to either 3,2 :60 ,3or vectorial of of terpyridine to blocks either 3,2′:6′,3″have demonstrated[9]. the assembly of metallocages based upon [M(tpy) 2]n+ building with other 0 0 00 0 0 00 0 0 00 or vectorial 4,2 :6 ,4 properties -terpyridine :6 ,3or- 4,2′:6′,4″-tpy, or from 4,2 :6the ,4 -tpy, Scheme it shouldbebepossible possible modifyorthe the 4,2′:6′,4″-terpyridine (3,2′:6′,3″Scheme 2) 2) it of should modify [9].(3,2 By changing 2,2′:6′,2″-isomer terpyridine to eithertoto 3,2′:6′,3″consequences of the coordination interactions on the network assembly in a controlled and predictable consequences of the coordination interactions Scheme on the 2) network assembly in a tocontrolled and 4,2′:6′,4″-terpyridine (3,2′:6′,3″- or 4,2′:6′,4″-tpy, it should be possible modify the 0 :60 ,300 - or 4,20 :60 ,400 -tpy both bind metal ions only through the four outer manner. The ligands 3,2 predictable manner. The ligands 3,2′:6′,3″or 4,2′:6′,4″-tpy both bind metal ions only through the four consequences of the coordination interactions on the network assembly in a controlled and N-donors andmanner. there no ligands literature precedent for metal-coordination through the central pyridine predictable The orprecedent 4,2′:6′,4″-tpy both bind metal ions only through the four outer N-donors and isthere is no 3,2′:6′,3″literature for metal-coordination through the central 0 0 00 ring. WeN-donors and have made widespread of 4,2 :6 -tpy of ligands, typically functionalized in outer there is no literature precedent for,4 metal-coordination through the central pyridine ring.others Weand and others have madeuse widespread use 4,2′:6′,4″-tpy ligands, typically 0 -position for the assembly of 1D-coordination polymers and 2D-networks [10–12]. Examples the 4 pyridine ring. We and others have made widespread use of 4,2′:6′,4″-tpy ligands, typically functionalized in the 4′-position for the assembly of 1D-coordination polymers and 2D-networks [10– 0 :6assembly 0 ,400 -tpy ligands of functionalized 3D-architectures incorporating are rare [13] and a[13] very few examples the 4′-position for4,2 the of 1D-coordination polymers and 2D-networks 12]. Examples ofin3D-architectures incorporating 4,2′:6′,4″-tpy ligands are only rare and only a[10– very 0 0 00 Examples of 3D-architectures 4,2′:6′,4″-tpy ligands arereported rare [13] and onlyThe a[14–20]. very of 12]. 2Dand 3D-assemblies directed incorporating by 3,2 :6 ,3 -tpy ligands have been most few examples of 2Dand 3D-assemblies directed by 3,2′:6′,3″-tpy ligands have been[14–20]. reported 0 :60 ,300 -tpy is few examples of 2D-difference and 3D-assemblies 3,2′:6′,3″-tpy ligands have been reported [14–20]. significant difference between a between 4,20 :60 ,400directed -tpy andby 3,2 the effect inter-ring bond The most significant a 4,2′:6′,4″-tpy and 3,2′:6′,3″-tpy is that the effect that C–C inter-ring 0that 0 ,400 The most significant difference between a 4,2′:6′,4″-tpy and 3,2′:6′,3″-tpy is the effect inter-ring rotation has on the mutual directionality of the outer nitrogen donors. For 4,2 :6 -tpy, there C–C bond rotation has on the mutual directionality of the outer nitrogen donors. For 4,2′:6′,4″-tpy, 0 0 00 C–C bond rotation has on the mutual directionality of the outer nitrogen donors. For 4,2′:6′,4″-tpy, is no is change in the orientation of the nitrogen donors, :6 ,3 -tpy there is there no change in vectorial the vectorial orientation of the nitrogen donors,while whilefor for3,2 3,2′:6′,3″-tpy there is there is no change in the vectorial orientation of the nitrogen donors, while for 3,2′:6′,3″-tpy there is significant variation with the interannular bond rotation [11]. This in turn increases the structural significant variation with the interannular bond rotation [11]. This in turn increases the structural significant variation with the3,2 interannular This in turn increases theself-assembly structural 0 :60 ,300 -tpy, bond diversity to be be expected with at the therotation expense[11]. of the the predictability of the the diversity to expected with 3,2′:6′,3″-tpy, at expense of predictability of self-assembly diversity to be expected with 3,2′:6′,3″-tpy, at the expense of the predictability of the self-assembly 0 0 00 algorithm. InInScheme Scheme 2,2, the the 3,2′:6′,3″-tpy 3,2 :6 ,3 -tpyunit unitisis drawn drawn in in an an orientation orientation preorganized preorganized for for the the algorithm. algorithm. In Scheme 2, the 3,2′:6′,3″-tpy unit is drawn 0 in0 an orientation preorganized the 00 -terpyridin-4 0 -yl)ferrocenefor formation of metallomacrocycles, as observed with 1-(3,2 :6 ,3 [21] and formation of metallomacrocycles, as observed with 1-(3,2′:6′,3′′-terpyridin-4′-yl)ferrocene [21] and 5formation of metallomacrocycles, as observed with 1-(3,2′:6′,3′′-terpyridin-4′-yl)ferrocene [21] and 55-(3,20 :60 ,300 -terpyridin-40 -yl)-N,N-diphenylthiophen2-amine [22]. (3,2′:6′,3′′-terpyridin-4′-yl)-N,N-diphenylthiophen[22]. (3,2′:6′,3′′-terpyridin-4′-yl)-N,N-diphenylthiophen- 2-amine 2-amine [22].

n+ complex is considered as an expanded 4,4′-bpy. Scheme An[M(tpy) [M(tpy)22]2n+ ]n+ Scheme 1. complexisisconsidered consideredas asan anexpanded expanded4,4′-bpy. 4,40 -bpy. Scheme 1.1.An complex

0 :60 ,400 - and 3,20 :60 ,300 -tpy of general ligand types 1 (with 4,20 :60 ,400 -tpy units) Scheme 2. 2. Structures Scheme Structuresofof4,2 4,2′:6′,4″and 3,2′:6′,3″-tpy of general ligand types 1 (with 4,2′:6′,4″-tpy units) 0 0 00 and 2 2. (with units), and and structures of 1a–1d and 2a. green arrows show thethe and 2 (with 3,23,2′:6′,3″-tpy :6 ,3 -tpy units), of ligands ligands 1a–1d andtypes 2a.The The green arrows show Scheme Structures of 4,2′:6′,4″andstructures 3,2′:6′,3″-tpy of general ligand 1 (with 4,2′:6′,4″-tpy units) vectoral orientation the lonepairs pairs involved in inofformation formation of coordination network. vectoral orientation ofofthe lone involved of the theand coordination network. and 2 (with 3,2′:6′,3″-tpy units), and structures ligands 1a–1d 2a. The green arrows show the

vectoral orientation of the lone pairs involved in formation of the coordination network.

0 :60 ,400 - or 3,20 :60 ,300 -tpy domains combines two ditopic metal-binding Covalent linkage Covalent linkageofoftwo two4,2 4,2′:6′,4″or 3,2′:6′,3″-tpy domains combines two ditopic metal-binding domains into a tetratopic ligand as exemplified with general ligands 1two and 2 Scheme in Scheme 2. We domains into a tetratopic ligand as exemplified with thethe general ligands 1 and 2ditopic in 2. We have Covalent linkage of two 4,2′:6′,4″- or 3,2′:6′,3″-tpy domains combines metal-binding have developed a suite of such ligands, typically with 1,4-phenylene spacers functionalized with developed a suite of such ligands, typically with 1,4-phenylene spacers functionalized with alkyloxy domains into a tetratopic ligand as exemplified with the general ligands 1 and 2 in Scheme 2. We alkyloxy groupsa to increase solubility in organic solvents [23]. nature of the groupisiscritical critical groups to increase solubility in ligands, organic solvents [23]. The The nature of spacers the OROR group in have developed suite of such typically with 1,4-phenylene functionalized with in determining the outcome of the self-assembly. For example, the reaction of 1a or 1b (Scheme 2) alkyloxy groups to increase solubility in organic solvents [23]. The nature of the OR group is critical with zinc(II) halides leads to (4,4) nets in which 1a or 1b is the 4-connecting node. However, in the in determining the outcome of the self-assembly. For example, the reaction of 1a or 1b (Scheme 2) with zinc(II) halides leads to (4,4) nets in which 1a or 1b is the 4-connecting node. However, in the

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determining the outcome of the For example, the reaction of 1a orn-octyl 1b (Scheme 2) in with case of 1a, simple 2D-sheets areself-assembly. observed, whereas the presence of the longer groups 1b zinc(II) halides leads to (4,4) nets in which 1a or 1b is the 4-connecting node. However, in the case of 1a, leads to 2D2D parallel interpenetration with the alkyloxy chains in extended conformations and simple 2D-sheets are observed, whereas the presence of the longer n-octyl groups in 1b leads to 2D→2D directed within each corrugated sheet [23,24]. We have also demonstrated that introducing a pendant parallel interpenetration with the alkyloxy chains in extended conformations and directed within aryl group can facilitate face-to-face π-interactions within the solid-state assembly. In the case of each corrugated sheet [23,24]. We have also demonstrated that introducing a pendant aryl group can [Zn2Br4(1c).H2O]n (see Scheme 2 for 1c), 2-fold interpenetrating nbo nets are observed with inter-net . H O] facilitate face-to-face within the solid-state assembly. In as theacase of [Zn2 Br4 (1c) n 2void π-stacking resulting π-interactions in tightly associated interpenetrated nets and, consequence, large (see Scheme 2 for 1c), 2-fold interpenetrating nbo nets are observed with inter-net π-stacking resulting spaces in the lattice [25]. in tightly associated interpenetrated nets of and, as a consequence, void spaces2in the lattice [25]. In this paper, we describe reactions ligands 3–5 (Scheme large 3) with Co(NCS) . Upon interacting In this paper, we describe reactions of ligands 3–5 (Scheme 3) with Co(NCS) . Upon interacting 2 with pyridine donors, Co(NCS)2 typically generates octahedral cobalt(II) centers with transwith pyridineligands donors,and Co(NCS) generates octahedral cobalt(II) centers with trans-thiocyanato 2 typically thiocyanato four pyridine nitrogen donors defining the equatorial plane. It is therefore ligands and four pyridine nitrogen donors defining the equatorial plane. It is therefore expected to expected to act as a 4-connecting node giving access to a range of different networks [26,27]. We have act as a 4-connecting node giving access to a range of different networks [26,27]. We have shown that shown that the reaction of Co(NCS)2 with 1d (Scheme 2) leads to a 3D cds net in which both metal the of Co(NCS) 1d (Scheme 2) leads to 3D cds of netthe in alkyloxy which both metal ligandand are 2 with andreaction ligand are 4-connecting nodes [28]. Increasing thea length chain to Rand = n-octyl 4-connecting [28].byIncreasing the length of the alkyloxy chain = n-octylfrom and replacing replacing the nodes 4,2′:6′,4″a 3,2′:6′,3″-tpy (2a, Scheme 2) switches the to 3DRassembly a cds to anthe lvt 0 :60 ,400 - by a 3,20 :60 ,300 -tpy (2a, Scheme 2) switches the 3D assembly from a cds to an lvt net [20]. In the 4,2 net [20]. In the present work, 3 was selected in order to investigate the effect of lengthening the present 3 was in order to investigate the effect of alkyloxyLigand chain from alkyloxywork, chain fromselected three to five carbon atoms—would thelengthening cds net bethe retained? 4 is three to five carbon atoms—would the cds net be retained? Ligand 4 is comparable with 2a in terms comparable with 2a in terms of the 3,2′:6′,3″-tpy donor set but introduces terminal phenyl domains 0 :60 ,300 -tpy donor set but introduces terminal phenyl domains in the alkyloxy substituents. of in the the 3,2 alkyloxy substituents. Both 3 and 5 possess 4,2′:6′,4″-tpy units, but the inclusion of the pendant Both 3 and 5 possess 4,20 :60 ,4to00 -tpy units, but the inclusion of thearene–arene pendant phenyls in 5 was expected to phenyls in 5 was expected affect the assembly by enabling π-interactions. affect the assembly by enabling arene–arene π-interactions.

Scheme Scheme 3. 3. Structures Structures of of ligands ligands 3–5. 3–5.

2. Materials and Methods 2. Materials and Methods 2.1. General 2.1. General 1 H and 13 C NMR spectra were recorded on a Bruker DRX-500 NMR spectrometer (Bruker BioSpin 1H and 13C NMR spectra were recorded on a Bruker DRX-500 NMR spectrometer (Bruker AG, Fällanden, Switzerland) with chemical shifts referenced to residual solvent peaks (TMS = δ 0 ppm). BioSpin AG, Fällanden, Switzerland) with chemical shifts referenced to residual solvent peaks (TMS Electrospray ionization (ESI) mass spectra were measured on a Shimazu LCMS 2020 instrument = δ 0 ppm). Electrospray ionization (ESI) mass spectra were measured on a Shimazu LCMS 2020 (Shimadzu Schweiz GmbH, Roemerstr., Switzerland) and high resolution ESI (HR-ESI) mass spectra instrument (Shimadzu Schweiz GmbH, Roemerstr., Switzerland) and high resolution ESI (HR-ESI) on a Bruker maXis 4G QTOF instrument (Bruker BioSpin AG, Fällanden, Switzerland); samples were mass spectra on a Bruker maXis 4G QTOF instrument (Bruker BioSpin AG, Fällanden, Switzerland); introduced as MeCN solutions containing 0.1% formic acid or 0.1% trifluoroacetic acid (TFA) for samples were introduced as MeCN solutions containing 0.1% formic acid or 0.1% trifluoroacetic acid electrospray mass spectrometry (ESI MS) and high-resolution ESI MS, respectively. Commercially (TFA) for electrospray mass spectrometry (ESI MS) and high-resolution ESI MS, respectively. available precursors were purchased from Fluorochem (Hadfield, UK), Sigma-Aldrich (Buchs SG, Commercially available precursors were purchased from Fluorochem (Hadfield, UK), Sigma-Aldrich Switzerland), TCI (Eschborn, Germany) or Acros (Chemie Brunschwig AG, Basel, Switzerland) and (Buchs SG, Switzerland), TCI (Eschborn, Germany) or Acros (Chemie Brunschwig AG, Basel, used without further purification. Compound 4b was prepared following the literature and NMR Switzerland) and used without further purification. Compound 4b was prepared following the spectroscopic data were in accord with those reported [29]. literature and NMR spectroscopic data were in accord with those reported [29]. 2.2. Compound 3a 2.2. Compound 3a Compound 3a was prepared by adapting a literature method [29]. 2,5-Dibromohydroquinone was prepared(2.36 by adapting a literature [29]. 2,5-Dibromohydroquinone (2.0 g,Compound 7.47 mmol),3a 1-bromopentane mL, 2.88 g, 18.7 mmol)method and anhydrous K2 CO3 (3.1 g, 22.4 mmol) (2.0 g, 7.47 mmol), 1-bromopentane (2.36 mL, 2.88 g, 18.7 mmol) and anhydrous K2CO3 (3.1 g, 22.4 mmol) were dissolved in dry DMF (100 mL) and the mixture was heated at 100 °C for ca. 15 h. The

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were dissolved in dry DMF (100 mL) and the mixture was heated at 100 ◦ C for ca. 15 h. The reaction mixture was cooled to room temperature, added to a beaker containing 100 mL of ice-water and stirred for 30 min. The precipitate that formed was separated by filtration and washed with water (3 × 30 mL) and dried in vacuo. Compound 3a was isolated as a white powder (2.85 g, 6.98 mmol, 93.5%). 1 H NMR (500 MHz, CDCl3 ) δ/ppm 7.09 (s, 2H, HC3 ), 3.95 (t, J = 6.5 Hz, 4H, Ha ), 1.81 (m, 4H, Hb ), 1.46 (m, 4H, Hc ), 1.39 (m, 4H, Hd ), 0.94 (t, J = 7.2 Hz, 6H). 13 C{1 H} NMR (126 MHz, CDCl3 ) δ/ppm 150.2 (CC2 ), 118.6 (CC3 ), 111.3 (CC1 ), 70.5 (Ca ), 29.0 (Cb ), 28.3 (Cc ), 22.5 (Cd ), 14.2 (Ce ). In reference [29], 1 H NMR signals were unassigned, and 13 C NMR spectroscopic data were not reported. 2.3. Compound 4a Compound 4a has been reported but we find the following method more convenient. The method was as for 3a starting with 2,5-dibromohydroquinone (1.5 g, 5.6 mmol), 1-bromo-4-phenylbutane (0.96 mL, 3.04 g, 14 mmol) and anhydrous K2 CO3 (2.32 g, 16.8 mmol) in dry DMF (100 mL). Then, 4a was isolated as a white powder (2.67 g, 5.02 mmol, 89.6%). The NMR spectroscopic data agreed with those published [29]. 2.4. Compound 5a Compound 5a has previously been reported [30], but we find the following synthesis more convenient. The method was as for 3a starting with 2,5-dibromohydroquinone (1.5 g, 5.6 mmol), benzyl chloride (1.61 mL, 1.77 g, 14.0 mmol) and anhydrous K2 CO3 (2.32 g, 16.8 mmol) in dry DMF (100 mL). Then, 5a was obtained as a white powder (2.19 g, 4.89 mmol, 87.3%). 1 H NMR spectroscopic data were in accord with those reported [30]. 13 C{1 H} NMR (126 MHz, CDCl3 ) δ/ppm 150.2 (CC2c ), 136.3 (CD1 ), 128.8 (CD3 ), 128.3 (CD4 ), 127.4 (CD2 ), 119.4 (CC3 ), 111.7 (CC1 ), 72.1 (Ca ). 2.5. Compound 3b Compound 3a (1.8 g, 4.41 mmol) and dry Et2 O (150 mL) were added to a dried flask and cooled to 0 ◦ C in an ice bath. n BuLi solution (1.6 M in hexanes, 8.27 mL, 13.2 mmol) was slowly added to the solution of 3a over 20 min and the temperature maintained at 0 ◦ C for 6 h. Dry DMF (1.02 mL, 13.2 mmol) was then added and the solution stirred for 15 h, while warming up to room temperature. The reaction was neutralized with saturated aqueous NH4 Cl solution and extracted with CH2 Cl2 (200 mL). The organic phase was dried over MgSO4 and concentrated in vacuo. Compound 3b was obtained as a yellow solid (1.14 g, 3.72 mmol, 84.4%) and used without further purification. 1 H NMR (500 MHz, CDCl3 ) δ/ppm 10.51 (s, 2H, HCHO ), 7.42 (s, 2H, HC3 ), 4.08 (t, J = 6.5 Hz, 4H, Ha ), 1.87–1.76 (m, 4H, Hb ), 1.52–1.31 (m, 8H, Hc+d ), 0.93 (t, J = 7.2 Hz, 6H, He ). 13 C{1 H} NMR (126 MHz, CDCl3 ) δ/ppm 189.6 (CCHO ), 155.3 (CC2 ), 129.4 (CC1 ), 111.7 (CC3 ), 69.3 (Ca ), 28.8 (Cb ), 28.3 (Cc ), 22.5 (Cd ), 14.1 (Ce ). 2.6. Compound 5b The method was the same as for 3b but starting with 5a (2.0 g, 4.46 mmol) and n BuLi (1.6 M in hexanes, 8.36 mL, 13.4 mmol). Compound 2b was obtained as a yellow solid (1.23 g, 3.55 mmol, 79.6%) and was used without further purification. 1 H NMR spectroscopic data matched those reported [29]. 13 C{1 H} NMR (126 MHz, CDCl ) δ/ppm 189.2 (CCHO ), 155.2 (CC2 ), 135.8 (CD1 ), 129.7 (CC1 ), 128.9 3 (CD2/D3 ), 128.5 (CD4 ), 127.7 (CD2/D3 ), 112.5 (CC3 ), 71.3 (Ca ). 2.7. Compound 3 Compound 3b (0.3 g, 0.98 mmol) was dissolved in EtOH (100 mL), then 4-acetylpyridine (0.45 mL, 0.49 g, 3.92 mmol) and crushed solid KOH (0.22 g, 3.92 mmol) were added in one portion. Aqueous NH3 (32%, 7.8 mL) was added dropwise and the reaction mixture was stirred at room temperature for ca. 15 h. The precipitate that had formed was collected by filtration and washed with water, EtOH

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and Et2 O (3 × 10 mL, each). Compound 3 was obtained as a white solid (0.13 g, 0.18 mmol, 18.8%). M.p. = 297 ◦ C. 1 H NMR (500 MHz, CDCl3 ) δ/ppm 8.81 (m, 8H, HA2 ), 8.15–8.07 (m, 12H, HB3+A3 ), 7.16 (s, 2H, HC3 ), 4.07 (t, J = 6.3 Hz, 4H, Ha ), 1.87 (m, 4H, Hb ), 1.37 (m, 4H, Hc ), 1.32–1.19 (m, 4H, Hd ), 0.77 (t, J = 7.3 Hz, 6H, He ). 13 C{1 H} NMR (126 MHz, CDCl3 ) δ/ppm 154.8 (CB2 ), 150.7 (CC2 ), 150.6 (CA2 ), 148.4 (CB4 ), 146.4 (CA4 ), 129.2 (CC1 ), 121.7 (CB3 ), 121.3 (CA3 ), 115.3 (CC3 ), 69.9 (Ca ), 29.27 (Cb ), 28.61 (Cc ), 22.53 (Cd ), 14.02 (Ce ). ESI-MS m/z 754.40 [M + H + MeCN]+ (base peak, calc. 754.39), 713.35 [M + H]+ (calc. 713.36). HR ESI-MS m/z 713.3600 [M + H]+ (calc. 713.3599). 2.8. Compound 4 The method was as for compound 3 but starting with 4b (0.69 g, 1.62 mmol) and 3-acetylpyridine (0.82 mL, 0.89 g, 7.25 mmol), crushed KOH (0.41 g, 7.25 mmol) and aqueous NH3 (32%, 12.4 mL). Compound 4 was isolated as a white solid (0.47 g, 0.56 mmol, 34.7%). M.p. = 253 ◦ C. 1 H NMR (500 MHz, CDCl3 ) δ/ppm 9.38 (d, J = 2.2 Hz, 4H, HA2 ), 8.73 (m, 4H, HA6 ), 8.50 (dd, J = 7.9, 2.0 Hz, 4H, HA4 ), 8.01 (s, 4H, HB3 ), 7.45 (dd, J = 8.0, 7.9 Hz, 4H, HA5 ), 7.17–7.12 (m, 6H, HC3+D3 ), 7.09 (m, 2H, HD4 ), 6.98 (m, 4H, HD2 ), 4.07 (t, J = 6.1 Hz, 4H, Ha ), 2.55 (t, J = 7.5 Hz, 4H, Hd ), 1.87–1.78 (m, 4H, Hb ), 1.75–1.67 (m, 4H, Hc ). 13 C{1 H} NMR (126 MHz, CDCl3 ) δ/ppm 154.9 (CB2 ), 150.7 (CC2 ), 150.4 (CA6 ), 148.6 (CA2 ), 148.1 (CB4 ), 141.9 (CD1 ), 134.8 (CA3 ), 134.6 (CA4 ), 129.5 (CC1 ), 128.45 (CD3 ), 128.4 (CD2 ), 125.9 (CD4 ), 123.8 (CA5 ), 120.3 (CB3 ), 115.5 (CC3 ), 69.7 (Ca ), 35.5 (Cd ), 29.1 (Cb ), 28.0 (Cc ). ESI-MS m/z 837.40 [M + H]+ (base peak, calc. 837.39). HR ESI-MS m/z 837.3901 [M + H]+ (calc. 837.3912). 2.9. Compound 5 The method was as for 3, starting with 5b (1.06 g, 3.06 mmol), 4-acetylpyridine (1.56 mL, 1.7 g, 13.8 mmol), crushed KOH (0.77 g, 13.8 mmol), and aqueous NH3 (32%, 24 mL). Compound 5 was isolated as a white solid (0.87 g, 1.16 mmol, 37.8%). Decomp. > 280 ◦ C. 1 H NMR (500 MHz, CDCl3 ) δ/ppm 8.77 (m, 8H, HA2 ), 8.07 (s, 4H, HB3 ), 7.96 (m, 8H, HA3 ), 7.40–7.33 (m, 10H, HD2+D3+D4 ), 7.31 (s, 2H, HC3 ), 5.19 (s, 4H, Ha ). 13 C{1 H} NMR (126 MHz, CDCl3 ) δ/ppm 154.9 (CB2 ), 150.7 (CC2 ), 150.5 (CA2 ), 147.7 (CB4 ), 146.3 (CA4 ), 136.2 (CD1 ), 129.5 (CC1 ), 129.0 (CD3 ), 128.7 (CD4 ), 127.9 (CD2 ), 121.5 (CB3 ), 121.4 (CA3 ), 116.1 (CC3 ), 72.1 (Ca ). ESI-MS m/z 794.30 [M + H + MeCN]+ (calc. 794.32), 753.35 [M + H]+ (calc. 753.30). HR ESI-MS m/z 753.2967 [M + H]+ (calc. 753.2973). 2.10. {[Co(NCS)2 (3)]·0.8C6 H4 Cl2 }n A solution of Co(NCS)2 (1.75 mg, 0.01 mmol) in MeOH (8 mL) was layered over a solution of 3 (7.13 mg, 0.01 mmol) in 1,2-dichlorobenzene (5 mL). A few pink crystals of [Co(NCS)2 (3)·0.8C6 H4 Cl2 ]n were obtained after 2–4 weeks. Insufficient material was obtained for powder X-ray diffraction. 2.11. {[Co(NCS)2 (4)]·1.6H2 O·1.2C6 H4 Cl2 }n A solution of Co(NCS)2 (3.5 mg, 0.02 mmol) in MeOH (8 mL) was layered over a solution of 4 (8.37 mg, 0.01 mmol) in 1,2-dichlorobenzene (5 mL). Pink crystals of [Co(NCS)2 (4)·1.6H2 O·1.2C6 H4 Cl2 ]n (2.2 mg, 0.0018 mmol, 18% based on 5) were obtained after 2–4 weeks. The bulk sample was characterized by powder X-ray diffraction (Figure S1). 2.12. [Co(NCS)2 (MeOH)2 (5)2 ]·2CHCl3 ·2MeOH A solution of Co(NCS)2 (3.5 mg, 0.02 mmol) in MeOH (8 mL) was layered over a solution of 5 (15.1 mg, 0.02 mmol) in CHCl3 (5 mL). A small crop of pink crystals of [Co(NCS)2 (MeOH)2 (5)2 ·2CHCl3 ·2MeOH] was obtained after 2–4 weeks. Insufficient material was obtained for powder X-ray diffraction

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2.13. Crystallography Single crystal data were collected on a Bruker APEX-II diffractometer (Bruker Biospin AG, Fällanden, Switzerland); data reduction, solution and refinement used APEX2, SuperFlip and CRYSTALS respectively [31–33]. Structure analysis used Mercury v. 3.10 [34,35]. In {[Co(NCS)2 (3)]·0.8C6 H4 Cl2 }n , the dichlorobenzene molecule was refined as rigid body (occupancy = 0.8 per formula unit). In addition, the aliphatic chain showed high thermal motion, and was refined isotropically using chemically reasonable restraints to bond distances and angles. In {[Co(NCS)2 (4)]·1.6H2 O·1.2C6 H4 Cl2 }n , the side chain of the organic ligand is disordered with high thermal motion; as a result, the phenyl ring was refined with rigid body restraints and the whole chain was refined isotropically. Powder diffraction data were collected on a Stoe Stadi P powder diffractometer (Stoe & Cie GmbH, Darmstadt, Germany). {[Co(NCS)2 (3)]·0.8C6 H4 Cl2 }n : C52.80 H47.20 Cl1.60 CoN8 O2 S2 , M = 1005.60, pink block, monoclinic, space group P21 /c, a = 10.3756(6), b = 19.1855(11), c = 16.2699(9) Å, β = 106.881(3)o , U = 3099.2(3) Å3 , Z = 2, Dc = 1.078 Mg m–3 , µ(Cu-Kα) = 3.749 mm−1 , T = 123 K. Total 31,013 reflections, 5731 unique, Rint = 0.033. Refinement of 4672 reflections (282 parameters) with I > 2σ (I) converged at final R1 = 0.1176 (R1 all data = 0.1247), wR2 = 0.1340 (wR2 all data = 0.1341), gof = 0.9888. CCDC 1877183. {[Co(NCS)2 (4)]·1.6H2 O·1.2C6 H4 Cl2 }n : C65.20 H56.00 Cl2.40 CoN8 O3.60 S2 , M = 1217.36, pink block, monoclinic, space group P21 /c, a = 13.7465(6), b = 15.7832(7), c = 16.2872(8) Å, β = 112.147(2)o , U = 3273.0(3) Å3 , Z = 2, Dc = 1.235 Mg m–3 , µ (Cu-Kα) = 3.953 mm−1 , T = 123 K. Total 23,855 reflections, 5937 unique, Rint = 0.035. Refinement of 5459 reflections (313 parameters) with I >2σ (I) converged at final R1 = 0.1460 (R1 all data = 0.1460), wR2 = 0.1415, gof = 0.9888. CCDC 1877182. [Co(NCS)2 (MeOH)2 (5)2 ]·2CHCl3 ·2MeOH: C108 H90 Cl6 CoN14 O8 S2 , M = 2047.77, pink block, triclinic, space group P–1, a = 14.1006(10), b = 14.5250(10), c = 14.5512(11) Å, α =62.394(3), β = 89.108(3), γ = 64.293(3)o , U = 2314.5(3) Å3 , Z = 1, Dc = 1.469 Mg m–3 , µ(Cu-Kα) = 4.035 mm−1 , T = 123 K. Total 26,118 reflections, 8388 unique, Rint = 0.026. Refinement of 7965 reflections (618 parameters) with I > 2σ (I) converged at final R1 = 0.1090 (R1 all data = 0.2656), wR2 = 0.1117 (wR2 all data = 0.2664), gof = 0.9524. CCDC 1877184. 3. Results 3.1. Synthesis and Characterization of Ligands Compounds 3–5 were prepared following the one-pot strategy of Wang and Hanan [36] (right-side of Scheme 4), an approach that requires the appropriate dicarbaldehyde. Precursors 3a–5a (Scheme 4) were prepared by treatment of 2,5-dibromohydroquinone with 1-bromopentane, 1-bromo-4-phenylbutane or benzyl chloride under basic conditions. Subsequent lithiation and treatment with DMF followed by addition of aqueous NH4 Cl yielded the dicarbaldehydes 3b–5b. After work-up, compounds 3–5 were isolated as white solids in yields ranging from 18.8 to 37.8%. In the HR-ESI mass spectrum of each compound, the highest-mass peak corresponded to the [M + H]+ ion (m/z = 713.3600, 837.3901 and 753.2967, respectively). For 3 and 5, this was the base peak, and lower intensity peaks at 357.1841 and 377.1522, respectively, arose from the [M + 2H]2+ ion. In the HR-ESI mass spectrum of 4, the [M + 2H]2+ ion gave the base peak (m/z = 419.1994), and a peak assigned to the [M + 3H]3+ ion (m/z = 279.8021) was also observed. The mass spectra are shown in Figures S2–S4. The 1 H and 13 C NMR spectra of the ligands were assigned by COSY, NOESY, HMQC and HMBC methods, and the atom labelling scheme is defined in Scheme 4. NOESY cross peaks between the signals for protons HA3 and HB3 in 3 and 5 distinguished HA3 from HA2 . Figure 1 displays the aromatic regions of the 1 H NMR spectra and Figures S5–S10 show full 1 H and 13 C NMR spectra.

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Scheme 4. Synthetic routes to 3–5 with numbering for NMR spectroscopic assignments in the experimental section;routes CH 2 units in alkyloxy chains are labelled a, b, c… etc. starting at the OCH2 unit Scheme 4. 4.Synthetic to for NMR NMR spectroscopic spectroscopicassignments assignmentsin in Scheme Synthetic routes to 3–5 3–5 with with numbering numbering for thethe and the terminal phenyl rings areinlabelled D.chains Conditions: (i) RBra,orb, (see Materials and experimental section;CH CH22 units units alkyloxy c… at the OCH unit experimental section; alkyloxy chainsare arelabelled labelled a,benzyl b, cetc. . .chloride . starting etc. starting at the2 OCH 2 Methods), anhydrous K2rings CO3, are drylabelled DMF, 100 °C, 15 h; (ii)(i)nBuLi, Etbenzyl 2O, 0 °C; DMF, warmed to room and thethe terminal phenyl D. Conditions: RBr chloride (see Materials and unit and terminal phenyl rings are labelled D. Conditions: (i)or RBr or benzyl chloride (see Materials temperature, 15 h; (iii)K4-acetylpyridine, KOH, EtOH, aqueous NH23O, , room temperature, 15 h; 3nBuLi, Methods), anhydrous 2CO , dry 100 °C, h; 15 (ii) h; to (iv) room and Methods), anhydrous K23CO dry DMF, 10015◦ C, (ii) nEt BuLi,0Et°C; 0 ◦ C;warmed DMF, warmed to 3 , DMF, 2 O,DMF, acetylpyridine, EtOH, aqueous NHKOH, 3, room temperature, 15 h. temperature, 15KOH, h;15 (iii) EtOH,EtOH, aqueous NH3, room 15 h; (iv) 15 3- h; room temperature, h; 4-acetylpyridine, (iii) 4-acetylpyridine, KOH, aqueous NH3temperature, , room temperature, KOH, EtOH, aqueous NH3, NH room temperature, 15 h. (iv)acetylpyridine, 3-acetylpyridine, KOH, EtOH, aqueous 3 , room temperature, 15 h.

1H NMR 1 H NMR Figure Aromatic regions of of thethe spectraspectra of ligands (500 MHz, CDClMHz, 3, 298 K). See Scheme Figure 1. 1. Aromatic regions of 3–5 ligands 3–5 (500 CDCl3 , 298 K). 4 for atom labels. * = residual CHCl 3 . 1H NMRCHCl SeeFigure Scheme 4 for atom labels.of*the = residual . 1. Aromatic regions spectra of ligands 3–5 (500 MHz, CDCl 3 , 298 K). See Scheme 3 4 for atom labels. * = residual CHCl3.

Crystal Growth 3.2.3.2. Crystal Growth

3.2. Crystal Growth All crystal growth experiments carried out under ambient conditions by layering a All crystal growth experiments werewere carried out under ambient conditions by layering a methanol methanol solution of Co(NCS) 2 over a solution of the ligand in either 1,2-dichlorobenzene or solutionAllofcrystal Co(NCS) a solution were of thecarried ligandout in either chloroform growth experiments under 1,2-dichlorobenzene ambient conditions byorlayering a 2 over chloroform (see Materials and methods). Parallel orfor (see Materials and methods). Parallel using 1,2-dichlorobenzene or chloroformor methanol solution of Co(NCS) 2 over crystal-setups a solution of crystal-setups the ligand in using either 1,2-dichlorobenzene 1,2-dichlorobenzene chloroform for each ligand/Co(NCS) 2 combination were made, and the ratio of Co(NCS)2 : ligand was chloroform (see Materials and methods). Parallel using 1,2-dichlorobenzene each ligand/Co(NCS) combination were made, andcrystal-setups the ratio of Co(NCS) : ligand was eitheror1:1 2

2

for each3ligand/Co(NCS) 2 combination were made,after and the of Co(NCS) 2 : ligand or chloroform 2:1. For ligands and 4, pink crystals were harvested 2–4ratio weeks, although in thewas case

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either 1:1 or 2:1. For ligands 3 and 4, pink crystals were harvested after 2–4 weeks, although in the case 3, few crystals formed.X-ray X-rayquality qualitycrystals crystalswere were only only obtained when of 3,offew crystals formed. when 1,2-dichlorobenzene 1,2-dichlorobenzene was wasused used during during crystal crystalgrowth, growth,and andsingle singlecrystal crystalX-ray X-raydiffraction diffractionestablished establishedthe theassembly assemblyofof coordination coordinationnetworks networks(see (seebelow). below).For Forligand ligand5,5,crystals crystalswere wereonly onlyobtained obtainedwhen whenusing usingaasolution solution ofof55in inchloroform, chloroform,and andX-ray X-raydiffraction diffractionrevealed revealedthe theunexpected unexpecteddiscrete discretecoordination coordinationcompound compound [Co(NCS) 2(5) 2]· 3·2MeOH. [Co(NCS)2(MeOH) ]·2CHCl 2 (MeOH) 2 (5) 22CHCl 3 ·2MeOH. 3.3.{[Co(NCS) {[Co(NCS)2(3)]· ·0.8C }n and {[Co(NCS) ·1.6H O·1.2C 2 (3)]0.8C 6H 4 Cl 2 (4)] 21.2C 6 H2}4nCl2 }n 3.3. 6H 4Cl 2}n2and {[Co(NCS) 2(4)]· 1.6H 2O· 6H4Cl Singlecrystal crystalX-ray X-raydiffraction diffraction confirmed that reactions of Co(NCS) 3 and 4 yielded Single confirmed that reactions of Co(NCS) 2 with 3 and 4 yielded the 2 with the coordination assemblies {[Co(NCS) 0.8C Cl2 }{[Co(NCS) ·1.6H n and {[Co(NCS) coordination assemblies {[Co(NCS) 2(3)]·0.8C 4Cl62}H n4 and 2(4)]·1.6H 2O· 1.2C26O H·41.2C Cl2}n6. H For the 2 (3)]6·H 2 (4)] 4 Cl 2 }n . For the latter, verification that crystal the single crystal was representative of thewas bulk samplefrom was latter, verification that the single was representative of the bulk sample obtained obtained from X-ray diffraction {[Co(NCS) ·0.8C H42}Cl and powder X-raypowder diffraction (Figure (Figure S1). S1). BothBoth{[Co(NCS) 2(3)]· 0.8C 6H6 4Cl n 2 }n and 2 (3)] {[Co(NCS)2(4)]· ·1.6H ·1.2C }n crystallize monoclinicspace spacegroup groupP2 P21/c. Thecobalt(II) cobalt(II) {[Co(NCS) 2O· 1.2C 6H Cl42Cl }n 2crystallize in in thethe monoclinic 2 (4)]1.6H 2O 64H 1 /c.The centerin in each each compound is with trans-thiocyanato ligands and center is in inaasimilar similarsix-coordinate six-coordinateenvironment environment with trans-thiocyanato ligands nitrogen donors from four different ligands defining the equatorial sites. The asymmetric unit in each and nitrogen donors from four different ligands defining the equatorial sites. The asymmetric unit in structure contains oneone cobalt atom andand halfhalf of aofligand 3 or 4. 4.InIn{[Co(NCS) ·0.8C the each structure contains cobalt atom a ligand 3 or {[Co(NCS)2 (3)] 2(3)]· 0.8C66H H44Cl22}}nn, ,the asymmetric unit contains 0.4 C H Cl , while in {[Co(NCS) (4)] · 1.6H O · 1.2C H Cl } , the asymmetric asymmetric unit contains C66 4Cl22, while {[Co(NCS)22(4)]· 22O·1.2C66H44 Cl2}2n,nthe asymmetric unithas has 0.6 0.6 C C66HH4Cl disorderedover overtwo twoorientations orientationsmodelled modelledwith with equal equal occupancies. occupancies. For Forthe the unit 2 2disordered 4 Cl compoundwith withligand ligand4,4,the thepyridine pyridinering ringcontaining containingN1 N1isisdisordered disorderedand andwas wasmodelled modelledover overtwo two compound sitesof ofoccupancies occupancies0.6 0.6and and0.4. 0.4.The TheOOatom atomof ofthe the4-phenyl-n-butoxy 4-phenyl-n-butoxychain chainisisalso alsodisordered, disordered,and and sites wasagain againmodelled modelledover overtwo twosites siteswith withoccupancies occupancies0.6 0.6and and0.4. 0.4.InInthe thediscussion discussionbelow, below,we wefocus focus was onlyon onthe the major major occupancy sites in {[Co(NCS) ·1.6H22O· O·1.2C 1.2C66HH4Cl Cl } . Figures 2 and 3 illustrate n only {[Co(NCS)22(4)] (4)]· 2 } n . Figures 2 and 3 illustrate 4 2 thateach eachof ofligands ligands33and and44binds bindsfour four cobalt cobalt (II) (II) centers, centers, thereby acting as a 4-connecting that 4-connecting node. node. Table Table1 These parameters parametersand andall allother other 1gives givesbond bondparameters parameters within within each each cobalt cobalt (II) coordination sphere. These bond distances and angles in the structures are unremarkable, and do not warrant further comment. bond distances and angles in the structures are unremarkable, and do not warrant further comment.

Figure2.2.The The asymmetric unit in {[Co(NCS) ·0.8C and symmetry-generated 2 (3)] 6H 2 }nsymmetry-generated Figure asymmetric unit in {[Co(NCS) 2(3)]· 0.8C 6H4Cl 2}4 n Cl and atoms atoms to showto show ligand 3 as a 4-connecting node. Symmetry codes: i = − 1 − x, 1 – y, 1 − z; ii = − 1 + x, ligand 3 as a 4-connecting node. Symmetry codes: i = −1 − x, 1 – y, 1 − z; ii = −1 + x, y, 1 + z; iii = y, −11++x,z; 3 1 1 1 1 1 = −1 + x, / − y, / + z; iv = −x, 1 − y, −z; v = x, /y,− /2=+x,z;½ vi− = 3/iii 2 − y, ½ + z; iv =2−x, 1 − y,2−z; v = x, ½ − y, −1/2 + z; vi = −x, ½ + 2 ½ y, – z;−vii y, − ½ x, + z./2 + y, /2 – z; 1 1 vii = x, /2 − y, /2 + z.

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Figure 3. The asymmetric unit in {[Co(NCS) (4)]·1.6H O·1.2C H Cl } and symmetry-generated atoms Figure 3. The asymmetric unit in {[Co(NCS)22(4)]·1.6H22O·1.2C66H44Cl22}nnand symmetry-generated atoms to show ligand 4 as a 4-connecting node. Symmetry codes: i = −1 − x, 2 − y, 1 − z; ii = −1 + x, 1 + y, z; to show ligand 4 as a 4-connecting node. Symmetry codes: i = −1 − x, 2 − y, 1 − z; ii = −1 + x, 1 + y, z; iii iii = −1 − x, 1 / + y, 1 / − z; iv = −x, 1 − y, 1 − z; v = −x, −1 / + y, 3 / − z; vi = x, 3 /2 − y, −1 / + z; = −1 − x, ½1 + y, ½2 −3z; iv =2 −x, 1 − y, 1 − z; v = −x, −1/2 + y, 3/2 − z; vi =2 x, 3/2 − 2y, −1/2 + z; vii = −x, ½ + y, 3/22 − z. vii = −x, /2 + y, /2 − z.

Table 1. Important bond in {[Co(NCS) parameters2 (3)]·0.8C in 6 H{[Co(NCS) 0.8C6H42Cl 2}n·1.6Hand Table 1. Important bond parameters {[Co(NCS) (4)] 4 Cl2 }n and2(3)]· 2 O· {[Co(NCS) 1.2C6 H4 Cl22(4)]· }n . 1.6H2O·1.2C6H4Cl2}n. Bond Parameter Bond Parameter Distance/Å Distance/Å Co1–N1 Co1–N1 Co1–N4 Co1–N4 Co1–N3v Co1–N3v Angle/deg Angle/deg N1–Co1–N4 N1–Co1–N4 N3v–Co1–N1 N3v–Co1–N1 N3v–Co1–N4 N3v–Co1–N4 N3vi–Co1–N1 N3vi–Co1–N1 N3vi–Co1–N4 N3vi–Co1–N4 N1iv–Co1–N4 N1iv–Co1–N4

{[Co(NCS) 2(3)]· 0.8C6H4Cl2}n {[Co(NCS) 2(4)]· 1.6H2O·1.2C6H4Cl2}n {[Co(NCS) {[Co(NCS) 2 (3)]·0.8C6 H4 Cl2 }n 2 (4)]·1.6H2 O·1.2C6 H4 Cl2 }n 2.208 (2) 2.208 (2) 2.062 (3) 2.062 (3) 2.179 (2)(2) 2.179

2.238 (4) 2.238 (4) 2.065 (4) 2.065 (4) 2.169 2.169 (4) (4)

90.18 (10) 90.18 (10) 84.73 (9)(9) 84.73 90.20 (11) 90.20 (11) 95.27 95.27 (9)(9) 89.80 (11) 89.80 (11) 89.82 (10) 89.82 (10)

88.67 88.67 (15) (15) 93.81 93.81 (17) (17) 90.32 90.32 (16) (16) 86.19 86.19 (17) (17) 89.68 89.68 (16) (16) 91.33 91.33 (15) (15)

The The dihedral dihedral angles angles between between the the planes planes through through adjacent adjacent aromatic aromatic rings rings in in coordinated coordinated 33 and and 44 are are given given in in the the first first two two entries entries in in Table Table 2. The The twist twist of of the the ring ring with withN2 N2with withrespect respect to tothe thephenylene phenylene ring covalently bonded bonded arene arenerings ringsand andminimizes minimizesHH…H ring in each compound is typical of covalently . . . Hrepulsions. repulsions. 0 0 00 0 0 00 There are small differences conformations of of the the 4,2 4,2′:6′,4″differences in the conformations :6 ,4 - and 3,2′:6′,3″-tpy 3,2 :6 ,3 -tpyunits unitsin incoordinated coordinated 33 and the {Co {Co44(3)} and {Co44(4)} and 4, as displayed in Figure 4a in the overlay of the (4)} units. units. However, However, both both 33 and function as asplanar planar4-connecting 4-connectingnodes nodesand, and, despite isomeric donor propagates and 4 function despite thethe isomeric donor sets,sets, eacheach propagates into 5.8} cds net (Figures 5 and S12) in which half of the adjacent nodes are mutually perpendicular into {6cds a {65a.8} net (Figures 5 and S12) in which half of the adjacent nodes are mutually perpendicular and and are coplanar resembles thenet 3Dobserved net observed in {[Co(NCS) 2(1d)]· 2C 6H 2}n [28] and, half half are coplanar [26].[26]. ThisThis resembles the 3D in {[Co(NCS) ·2C6 H and, for n [28] 2 (1d)] 4 Cl 24}Cl for comparison, the corresponding dihedral angles forstructure this structure are in given in1.Table 1. the In fact, comparison, the corresponding dihedral angles for this are given Table In fact, unit the cell unit cell dimensions of {[Co(NCS) 2 (3)]· 0.8C 6 H 4 Cl 2 } n and {[Co(NCS) 2 (1d)]· 2C 6 H 4 Cl 2 } n (both in the space dimensions of {[Co(NCS) (3)] · 0.8C H Cl } and {[Co(NCS) (1d)] · 2C H Cl } (both in the space group 2 6 4 2 n 2 6 4 2 n o, U = group aresimilar very similar (a = 10.3756(6), b = 19.1855(11), c =Å, 16.2699(9) Å , β o=, U 106.881(3) P21 /c) P2 are1/c) very (a = 10.3756(6), b = 19.1855(11), c = 16.2699(9) β = 106.881(3) = 3099.2(3) Å3 o 3 3 o 3), 3099.2(3) versus a =b = 10.2136(9), b =c = 19.3452(17), = 16.2214(15) Å , β, U = 107.027(3) U ), = 3064.6(5) versus a =Å10.2136(9), 19.3452(17), 16.2214(15)cÅ, β = 107.027(3) = 3064.6(5), Å revealing Åthat revealing that network can accommodate either n-pentyloxy or n-propoxy chains without the network canthe accommodate either n-pentyloxy or n-propoxy chains without significant perturbation significant perturbation (Figure S11). (Figure S11).

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Polymers 2018, 10, 1369 10 of 15 Polymers 2018, 10, x FOR PEER REVIEW of 15 Table 2. Dihedral angles between pairs of bonded aromatic rings in {[Co(NCS)2(3)]·0.8C6H4Cl2}n10and

{[Co(NCS)2(4)]·1.6H2O·1.2C6H4Cl2}n, and in {[Co(NCS)2(1d)]·2C6H4Cl2}n [28] and Table 2. Dihedral angles between pairs of bonded aromatic rings in {[Co(NCS) 2(3)]·0.8C6H4Cl2}n and {[Co(NCS) 2(2a)]·4CHCl 3}n between [20]. Table 2. Dihedral angles pairs of bonded aromatic rings in {[Co(NCS)2 (3)]·0.8C6 H4 Cl2 }n {[Co(NCS)2(4)]·1.6H2O·1.2C6H4Cl2}n, and in {[Co(NCS)2(1d)]·2C6H4Cl2}n [28] and and {[Co(NCS)2 (4)]·1.6H2 O·1.2C6 H4 Cl2 }n , and in {[Co(NCS)2 (1d)]·2C6 H4 Cl2 }n [28] and Dihedral Angle between Planes/Deg {[Co(NCS)2(2a)]·4CHCl3}n [20]. {[Co(NCS)2 (2a)]·4CHCl3 }n [20]. Compound Ring with N1/Ring Ring with N2/Ring Ring with Dihedral Angle between Planes/Deg with N2 with N3 Planes/Deg N2/Phenylene Ring Dihedral Angle between Compound Ring with N1/Ring Ring with N2/Ring Ring with {[Co(NCS)2Compound (3)]·0.8C6H4Cl2}n 30.7 40.2 Ring 25.3 with N1/Ring Ring with Ring with with N2 with N3N2/Ring N2/Phenylene Ring with N2 with N2/Phenylene {[Co(NCS)2(4)]·1.6H2O·1.2C6H4Cl2}n 34.6 6.4 N3 44.3Ring {[Co(NCS)2(3)]·0.8C6H4Cl2}n 25.3 30.7 40.2 {[Co(NCS) 2(1d)]· 6H 4Cl 2}2n}n 19.5 31.3 40.5 {[Co(NCS) 0.8C 25.3 30.7 40.2 2 (3)]·2C 6H 4 Cl {[Co(NCS)2(4)]·1.6H 2O·1.2C6H4Cl2}n 34.6 6.4 44.3 {[Co(NCS) ·1.6H4CHCl 44.3 55.9 2 (4)] 2 O·1.2C36}H {[Co(NCS) 2(2a)]· n 4 Cl2 }n 29.9;34.6 22.7 12.7;6.4 12.2 58.5; {[Co(NCS) 2C6H4Cl2}n 19.5 31.3 40.5 {[Co(NCS)2(1d)]· 19.5 31.3 40.5 2 (1d)]·2C6 H4 Cl2 }n {[Co(NCS) 2(2a)]· 29.9; 22.7 12.7; 12.2 58.5; {[Co(NCS) ·4CHCl33}}nn 29.9; 22.7 12.7; 12.2 58.5; 55.9 55.9 2 (2a)]4CHCl

Figure 4. (a) Overlay of {Co4(3)} and {Co4(4)} units in {[Co(NCS)2(3)]·0.8C6H4Cl2}n and Figure (a) Overlay Overlayof of{Co{Co in {[Co(NCS) ·0.8C6 Hand 4 (3)} 2 (3)] 4 Cl2 }n Figure 4. 4. (a) 4(3)} andand {Co4{Co (4)}4 (4)} unitsunits in {[Co(NCS) 2(3)]·0.8C 6H4Cl2}n {[Co(NCS)2(4)]·1.6H2O·1.2C6H4Cl2}n; (b) Overlay of {Co4(4)} and {Co4(2a)} units in and {[Co(NCS) (4)] · 1.6H O · 1.2C H Cl } ; (b) Overlay of {Co (4)} and {Co (2a)} units 2 6H4Cl2}6n; 4 (b) 2 n Overlay {[Co(NCS)2(4)]·21.6H2O·1.2C of {Co4(4)} 4 and {Co4(2a)}4 units in in {[Co(NCS)2(4)]·1.6H2O·1.2C6H4Cl2}n (this work) and {[Co(NCS)2(2a)]·4CHCl3}n [20]. In each overlay, {[Co(NCS) ·1.6H ·1.2C H44Cl Cl22}n}n(this (thiswork) work)and and{[Co(NCS) {[Co(NCS) ·4CHCl }n [20]. In each overlay, 2 (4)] 2O 2 (2a)] {[Co(NCS) 2(4)]· 1.6H 2O· 1.2C66H 2(2a)]· 4CHCl 3}n 3[20]. In each overlay, the atoms atoms of the central central phenylene ring ring superimposed. For For clarity, clarity, only only the the O O atoms atoms of of the alkyloxy alkyloxy the the atomsofofthe the centralphenylene phenylene ring superimposed. superimposed. For clarity, only the O atoms of thethe alkyloxy chains are are shown. shown. chains chains are shown.

Figure 5.Topological Topological representationof of the3D 3D net in in {[Co(NCS)2(4)]· 2O·1.2C6H4Cl2}n generated Figure ·1.6H 1.6H ·1.2C Figure 5. 5. Topological representation representation ofthe the 3Dnet net in{[Co(NCS) {[Co(NCS) 2(4)]· 1.6H 2O· 1.2C 6H Cl22}}nn generated generated 2 (4)] 2O 6H 44Cl using Mercury [34,35] with 4-connecting cobalt and ligand nodes. (3)] The·0.8C netH Cl in using Mercury [34,35] with 4-connecting cobalt and ligand nodes. The net in {[Co(NCS) n using Mercury [34,35] with 4-connecting cobalt and ligand nodes.2 The 6 net 4 2 }in {[Co(NCS)2(3)]·0.8C6H4Cl2}n is the same (see Figure S12). is the same (see Figure S12). {[Co(NCS)2(3)]·0.8C6H4Cl2}n is the same (see Figure S12).

The phenylgroups groups in the4-phenylbutoxy 4-phenylbutoxy chainsin in{[Co(NCS) {[Co(NCS)22(4)] (4)]··1.6H 2O·1.2C6H4Cl2}n do not The 1.6H ·1.2C6 H 2O 44Cl The phenyl phenyl groupsininthe the 4-phenylbutoxychains chains in {[Co(NCS)2(4)]· 1.6H 2O·1.2C 6H Cl22}}nn do do not not play a critical role in the assembly process and are not involved in π-stacking interactions. This is in is play a critical role in the assembly process and are not involved in π-stacking interactions. This play a critical role in the assembly process and are not involved in π-stacking interactions. This is in contrast totothe 3-phenylpropoxy groups in [Zn 2Br4(1c).H2O]n. (see introduction) [25]. Instead, the 1,2in contrast the 3-phenylpropoxy groups in [Zn Br (1c) H O] (see introduction) [25]. Instead, n 2 4 2 . contrast to the 3-phenylpropoxy groups in [Zn2Br4(1c) H2O]n (see introduction) [25]. Instead, the 1,2dichlorobenzene solvate in {[Co(NCS) 2(4)]·1.6H2O·1.2C6H4Cl2}n engages in a face-to-face π-interaction the 1,2-dichlorobenzene solvate in {[Co(NCS) (4)]·1.6H O·1.2C6 H4 Cl2in }n aengages in aπ-interaction face-to-face dichlorobenzene solvate in {[Co(NCS) 2(4)]·1.6H22O·1.2C6H24Cl2}n engages face-to-face with the pyridine ring containing atom N3 (Figure S13). Pertinent parameters are centroid…centroid π-interaction with the pyridine ring containing atom N3 (Figure S13). Pertinent parameters are with pyridine ring containing atom N3of (Figure S13). parameters areangle centroid…centroid andthe centroid…pyridine-plane separations 3.74 and 3.49Pertinent Å , respectively, and an between the centroid . . . centroid and centroid . . . pyridine-plane separations of 3.74 andand 3.49 Å,angle respectively, and and centroid…pyridine-plane of 3.74 3.49 partially Å , respectively, ring planes of 9.7°. However, separations since the ◦solvent siteand is only occupied, oneanmust bebetween cautiousthe an angle between the ring planes of 9.7 . However, since the solvent site is only partially occupied, ring planes of 9.7°. However, since the solvent site is only contacts partiallyshown occupied, one must in over-discussing both these interactions and the Cl…H–C in Figure S13. be cautious one must be cautious in over-discussing both these interactions and the Cl . . . H–C contacts in over-discussing both these interactions and the Cl…H–C contacts shown in Figure S13. shown in Figure S13.

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It is instructive to compare the structures of {[Co(NCS)2 (4)]·1.6H2 O·1.2C6 H4 Cl2 }n (this work) and {[Co(NCS)2 (2a)]·4CHCl3 }n [20]. These compounds both have 3,20 :60 ,300 -tpy donor sets, but differ in the nature of the alkyloxy chain (4-phenylbutoxy versus n-octyloxy). A second difference is the solvent system for crystal growth (1,2-dichlorobenzene versus chloroform). Figure 4b illustrates an overlay of the {Co4 (4)} and {Co4 (2a)} units in {[Co(NCS)2 (4)]·1.6H2 O·1.2C6 H4 Cl2 }n and {[Co(NCS)2 (2a)]·4CHCl3 }n , and reveals a significant difference in ligand conformation. This arises from the larger dihedral angles between the 3,20 :60 ,300 -tpy ring with N2 and the phenylene ring (Table 1). As previously described, {[Co(NCS)2 (2a)]·4CHCl3 }n possesses a {42 .84 } lvt net. It is now clear that the assembly of the lvt net is not simply a consequence of introducing the 3,20 :60 ,300 -tpy in place of the 4,20 :60 ,400 -tpy domain. Unfortunately, we have not been able to obtain good quality X-ray diffraction data from crystals grown from a combination of Co(NCS)2 with 1b (Scheme 2) and are unable, therefore, to verify whether the switch from the cds to lvt net is a consequence of the steric demands of the long n-octyl chain. 3.4. [Co(NCS)2 (MeOH)2 (5)2 ]·2CHCl3 ·2MeOH The discussion above demonstrates that consistent networks can be obtained with a combination of Co(NCS)2 and tetratopic ligands incorporating either 3,20 :60 ,300 - or 4,20 :60 ,400 -tpy metal-binding domains. The observations suggest that the nature of the alkyloxy substituents, rather than the choice of tpy isomer, may be the critical factor in determining the outcome of the coordination assembly. On going from ligand 3 to 5, we gain the potential for π-stacking without significantly lengthening the alkyloxy chain. Layering an MeOH solution of Co(NCS)2 over a CHCl3 solution of 5 produced only a few crystals, and there was insufficient material to obtain powder XRD data for the bulk sample. Single crystal X-ray diffraction revealed the unexpected formation of the discrete molecular coordination compound [Co(NCS)2 (MeOH)2 (5)2 ]·2CHCl3 ·2MeOH. The compound crystallizes in the triclinic space group P–1, and the centrosymmetric structure is shown in Figure 6 with selected bond parameters given in the figure caption. Each ligand 5 acts as a monodentate N-donor ligand and MeOH molecules complete the octahedral coordination sphere of Co1. While {Co(NCS)2 (MeOH)2 (py)2 } (py = pyridine) motifs are well established [37–42], there is only one example in the CSD (v. 5.39 with updates [43]) featuring a monotopic 4,20 :60 ,400 -tpy ligand 6 (Scheme 5) [44]. In this work, crystal growth by layering a MeOH/Co(NCS)2 solution over a solution of 6 in MeOH/CH2 Cl2 with an intermediate MeOH/CH2 Cl2 layer resulted in the formation of [Co(NCS)2 (MeOH)2 (6)2 ]. The preference for this discrete molecular assembly was attributed to the introduction of the sterically demanding pyrenyl group which is involved in efficient intermolecular pyrene . . . 4,20 :60 ,400 -tpy π-stacking interactions [44]. In the case of [Co(NCS)2 (MeOH)2 (5)2 ]·2CHCl3 ·2MeOH, packing interactions (Figure 7) involve centrosymmeric pairs of phenyl rings containing C20 and C20ii (symmetry code ii = 2 − x, 2 − y, 1 − z), pairs of 4,20 :60 ,400 -tpy units containing N2/N4 and N2iii /N4iii (symmetry code iii = 1 − x, 2 − y, −z), and pairs of 4,20 :60 ,400 -tpy units containing N6/N7 and N6iv /N7iv (symmetry code iv = 2 − x, −y, 2 − z). The first two sets of interactions lock together four molecules (Figure 7a). For the phenyl . . . phenyl π-stacking interaction, the separations of the ring planes and centroids are 3.35 and 3.65 Å, respectively. The coordinated 4,20 :60 ,400 -tpy unit with N2/N3/N4 is virtually planar (dihedral angles between the ring planes = 7.4 and 6.0◦ ), and 4,20 :60 ,400 -tpys with N2/N4 and N2iii /N4iii engage in a π-stacking interaction (Figure 7a) with an angle between the ring planes of 6.0◦ and centroid . . . centroid distance of 3.60 Å. For the non-coordinated 4,20 :60 ,400 -tpy unit, the dihedral angles between pairs of rings with N5/N6 and N6/N7 are 24.1 and 3.2◦ , respectively. Figure 7b depicts the face-to-face π-stacking interaction pairs of 4,20 :60 ,400 -tpys containing N6/N7 and N6iv /N7iv (centroid . . . centroid = 3.83 Å). The overall packing in the lattice is, therefore, dominated by efficient π-stacking [45], but, because of the low yield of crystals, we are unable to say whether this leads to a preference for a discrete molecular structure in which three of the four potential metal binding sites of ligand 5 remain non-coordinated, or whether the isolation of crystals of [Co(NCS)2 (MeOH)2 (5)2 ]·2CHCl3 ·2MeOH is serendipitous.

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Figure 6. Molecular structure of [Co(NCS)2(MeOH)2(5)2]·2CHCl3·2MeOH with solvent molecules and Figure 6. 6. Molecular Molecular structure structure of of [Co(NCS)2(MeOH) (MeOH)2(5) (5)2]]· ··2MeOH with solvent molecules and Figure ·2CHCl 2CHCl333· 2MeOH with with solvent solvent molecules and 22(5)2Co1–O1 Figure 6. omitted. Molecular structure of [Co(NCS) [Co(NCS) (MeOH) 2]·2CHCl= 2MeOH molecules and H atoms Selected bond distances22and angles: 2.138(3), Co1–N1 = 2.090(4), Co1–N2 H atoms omitted. Selected bond distances and angles: Co1–O1 = 2.138(3), Co1–N1 = 2.090(4), Co1–N2 H atoms Selected distances and Co1–O1 == 2.138(3), == 2.090(4), 2.090(4), Co1–N2 i = H atoms omitted. omitted. Selected=bond bond distances and angles: angles: Co1–O1N2–Co1–N1 2.138(3), Co1–N1 Co1–N1 Co1–N2 = 2.167(3) Å , O1–Co1–N2 86.80(12), O1–Co1–N1 = 88.39(15), = 88.06(13), N1–Co1–N2 ii= = 2.167(3) Å , O1–Co1–N2 O1–Co1–N2 = 86.80(12), O1–Co1–N1 = 88.39(15), N2–Co1–N1 = 88.06(13), N1–Co1–N2 = = 2.167(3) Å, = 86.80(12), O1–Co1–N1 = 88.39(15), N2–Co1–N1 = 88.06(13), N1–Co1–N2 i i = 91.61(15), i = 93.20(12)°. =91.94(13), 2.167(3) ÅN1–Co1–O1 , O1–Co1–N2 = 86.80(12), O1–Co1–N1 = 88.39(15),Symmetry N2–Co1–N1 = 88.06(13), = O1–Co1–N2 code i = 1 − x, 3N1–Co1–N2 − y, −z. i i 91.94(13), N1–Co1–O1ii = = 91.61(15), O1–Co1–N2 93.20(12)°. Symmetry code x, 3 −3 y, −z. 91.94(13), 91.61(15), O1–Co1–N2 O1–Co1–N2ii ===93.20(12)°. 93.20(12)◦ .Symmetry Symmetrycode codeii i===111−−− − −z. y, −z. 91.94(13), N1–Co1–O1 N1–Co1–O1 = 91.61(15), x, x, 3 − y,

Scheme 5. The The structure structure of of ligand 66 from from reference [44]. [44]. Scheme Scheme 5. 5. The structure of ligand ligand 6 from reference reference [44]. Scheme 5. The structure of ligand 6 from reference [44].

Figure ]·2CHCl33··2MeOH 2MeOH (solvent (solvent molecules omitted) Figure 7. 7. Packing Packing interactions interactionsin in[Co(NCS) [Co(NCS)22(MeOH) (MeOH)22(5) (5)22]· Figure 7. Packing interactions in [Co(NCS)2(MeOH)2(5)2]· 3·2MeOH (solvent molecules omitted) ii2CHCl ii (a) between pairs of phenyl rings containing C20 and C20 (symmetry code ii =ii 2= − x,x,2 2−−y,y,11omitted) −− z) Figure 7. Packing in [Co(NCS) 2(MeOH) 2(5)C20 2]·2CHCl 3·2MeOH (solvent (a) between pairs interactions of phenyl rings containing C20 and (symmetry code 2 −molecules z) and and ii (symmetry code ii = 2 − x, 2 − y, 1 − z) and (a) between pairs of phenyl rings containing C20 and C20 0 0 00 iii iii ii iii pairs of :6pairs ,4 -tpy units N2/N4 (symmetry code iiiiii (a) between of phenyl rings containing C20 and C20 ==2=1−1−x, 22−2− y,−y,1y,− −−z) z) and pairs of4,2 4,2′:6′,4″-tpy unitscontaining containing N2/N4and andN2 N2iii/N4 /N4iiiiii(symmetry (symmetrycode codeii −x,x, and pairs of 4,2′:6′,4″-tpy units containing N2/N4 and N2iii/N4 (symmetry code iii = 1=−2x, 2 −−y,y,−z) and 0 :60 ,400 -tpy iviv/N7 iv iii (symmetry iv (symmetry (b) of units containing N6/N7 and (symmetry code − 2−− z). pairs of 4,2′:6′,4″-tpy units containing N2/N4 and N2N6 /N4 code iii iv =iv1=−2x, y, 2−z) and (b)pairs pairs of4,2 4,2′:6′,4″-tpy units containing N6/N7 and N6 /N7 code − 2x,x,−−y, z). iv/N7iv (symmetry code iv = 2 − x, −y, 2 − z). (b) pairs of 4,2′:6′,4″-tpy units containing N6/N7 and N6iv iv (b) pairs of 4,2′:6′,4″-tpy units containing N6/N7 and N6 /N7 (symmetry code iv = 2 − x, −y, 2 − z).

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4. Conclusions We have prepared three new ligands containing two 4,20 :60 ,400 -tpy or two 3,20 :60 ,300 -tpy metal-binding domains with the expectation that they would function as 4-connecting nodes in coordination networks. The ligands possess different alkyloxy functionalities attached to the central phenylene spacer: n-pentyloxy in 3, 4-phenylbutoxy in 4, benzyloxy in 5. Reactions with Co(NCS)2 under ambient conditions with MeOH and 1,2-C6 H4 Cl2 as solvents resulted in the formation of {[Co(NCS)2 (3)]·0.8C6 H4 Cl2 }n and {[Co(NCS)2 (4)]·1.6H2 O·1.2C6 H4 Cl2 }n , both of which exhibit 3D cds nets. These data taken along with previously reported related structures suggests that the assembly of a particular net (cds or lvt) with 4-connecting Co and bis(tpy) ligands is independent of the choice of 4,20 :60 ,400 - or 3,20 :60 ,300 -tpy. The role of the alkyloxy substituent appears to be more significant. The combination of Co(NCS)2 with ligand 5 resulted in the formation of the discrete molecular complex [Co(NCS)2 (MeOH)2 (5)2 ]·2CHCl3 ·2MeOH in which 5 behaves as a monodentate ligand. The pendant phenyls and both coordinated and non-coordinated 4,20 :60 ,400 -tpy units engage in efficient π-stacking interactions. However, we are unable to identify whether the isolation of the mononuclear complex is preferred over network assembly, or is a serendipitous result. Further systematic investigations are needed in order to delineate the assembly algorithms in these systems. Supplementary Materials: The following are available online at http://www.mdpi.com/2073-4360/10/12/ 1369/s1, Figure S1: Powder diffraction data for the bulk sample of {[Co(NCS)2 (4)]·1.6H2 O·1.2C6 H4 Cl2 }n . Figures S2–S4: High resolution electrospray (HR-ESI) mass spectra of 3, 4 and 5. Figures S5–S10: 1 H and 13 C NMR spectra of 3, 4 and 5. Figure S11: Overlay of {Co4 (3)} and {Co4 (1d)} units in {[Co(NCS)2 (3)]·0.8C6 H4 Cl2 }n and {[Co(NCS)2 (1d)]·2C6 H4 Cl2 }n . Figure S12: Topological representation of the 3D net in {[Co(NCS)2 (3)]·0.8C6 H4 Cl2 }n . Figure S13: Close contacts involving the 1,2-dichlorobenzene molecule in {[Co(NCS)2 (4)]·1.6H2 O·1.2C6 H4 Cl2 }n . Author Contributions: Y.M.K. and M.K.: synthetic work; A.P.: crystallography; E.C.C.: group leader, project concepts, contributions to manuscript preparation; C.E.H.: group leader, project concepts, manuscript preparation. Funding: This research was funded by the Swiss National Science Foundation (Grant number 200020_162631) and the University of Basel. Conflicts of Interest: The authors declare no conflict of interest.

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