complexes with a macrocyclic ligand containing a

PAPER

www.rsc.org/dalton | Dalton Transactions

New dinuclear nickel(II) and iron(II) complexes with a macrocyclic ligand containing a N6 S2 donor-set: Synthesis, structural, MALDI-TOF-MS, magnetic and spectroscopic studies† Cristina Nún˜ ez,a Rufina Bastida,*a Alejandro Mac´ıas,a Laura Valencia,*b Joan Ribas,c José Luis Capelod,e and Carlos Lodeiro*d,e Received 22nd March 2010, Accepted 1st June 2010 First published as an Advance Article on the web 21st July 2010 DOI: 10.1039/c0dt00182a A series of dinuclear Ni(II) and Fe(II) complexes with a Py2 N4 S2 coordinating octadentate macrocyclic ligand L prepared by direct reactions have been studied. The overall geometry and bonding mode have been deduced on the basis of elemental analysis data, infrared, MALDI-TOF-MS, UV-vis spectroscopy, X-ray diffraction, conductivity and magnetic susceptibility measurements. In general both M2+ centres are sited into the macrocyclic cavity coordinated to a pyridinic nitrogen atom, one sulfur atom, two secondary amine groups from the macrocyclic backbone and completing the coordination spheres with two solvent or anionic molecules in a distorted octahedral geometry, except in the case of [Ni2 L(m-Cl)(H2 O)2 ](BF4 )3 ·2H2 O, where the metal ions are sited in the macrocyclic cavity coordinated to a pyridinic nitrogen atom, one sulfur atom, two secondary amine groups from the macrocyclic backbone, one water molecule and one chloride ion acting as a bridge between the two centres in a distorted octahedral geometry. The magnetic properties of the nickel(II) complexes, [Ni2 L(CH3 CN)4 ](BF4 )4 ·3.5CH3 CN (11) and [Ni2 L(m-Cl)(H2 O)2 ](BF4 )3 ·2H2 O (12) has been recorded in the solid state and indicates an unexpected ferromagnetic exchange in both cases, especially in compound 11 because no similar systems are previously reported in the literature presenting this magnetic behaviour. Further complexes with similar ligands are in progress to corroborate this unexpected ferromagnetic behaviour.

Introduction Nickel was long thought not to be a metal of biological importance. This changed in 1975, when Zerner discovered that urease is a nickel enzyme.1 Since then, other important enzymes that depend on nickel for activity have been identified.2 For this reason, the synthesis of complexes oriented to mimic metal sites of different types of metalloproteins constitutes an important branch in both inorganic and organic chemistry. The direct coordination of one or more sulfur atoms to nickel is found in the majority of redox-active bacterial nickel enzymes, and, in most cases, this sulfur is provided by cysteine.3 Examples a Inorganic Chemistry Department, Faculty of Chemistry, University of Santiago de Compostela, 15782, Santiago de Compostela, Spain. E-mail: mrufi[email protected]; Fax: +34 981 597525 b Inorganic Chemistry Department, Faculty of Chemistry, University of Vigo, 36310, Vigo, Pontevedra, Spain. E-mail: [email protected]; Fax: +34 986 813797 c Inorganic Chemistry Department, Faculty of Chemistry, University of Barcelona, Diagonal, 647, 08028, Barcelona, Spain d BIOSCOPE Group, Physical-Chemistry Department, Faculty of Science University of Vigo, Campus of Ourense, E32004, Ourense, Spain. E-mail: [email protected]; Fax: + 34 988 387001 e REQUIMTE-CQFB, Chemistry Department, FCT-UNL, Monte de Caparica, 2829-516, Portugal. E-mail: [email protected]; Fax: + 34 988 387001 † CCDC reference numbers 768499 and 768500 contain the supplementary crystallographic data for [Ni2 L(CH3 CN)4 ](BF4 )4 ·3.5CH3 CN and [Ni2 L(mCl)(H2 O)2 ](BF4 )3 ·2H2 O. For crystallographic data in CIF or other electronic format see DOI: 10.1039/c0dt00182a

This journal is © The Royal Society of Chemistry 2010

include [NiFe] hydrogenases,4 carbon monoxide dehydrogenase,5 a special class of superoxide dismutases that utilizes nickel (NiSOD)6 and acetyl-coenzyme A (CoA) synthase.7 The fundamental properties of NiN2 S2 complexes as metalloligands are that they can bind as mono- or bidentate ligands, a property fundamental to hemilability,8,9 and the additional lone pair on each sulfur donor site imposes an asymmetrical feature to this ligand quite unlike other planar ligands. The coexistence of nitrogen and sulfur atoms in the same molecule could be an advance in the stabilization of Ni(II) complexes. Many works are reported on the uses of mononuclear ligands for Ni(II) complexation10 but as far as we know few examples are reported with molecules capable of forming dinuclear species.11 In this respect, nickel coordination usually changes the colour of the initial ligand solution, and this alteration can be analytically useful. In some cases, the obtained complexes are coordinatively unsaturated or contain labile ligands such as water, which can easily be replaced, thus leading to new optical molecular chemosensors, and follow the recognition events through a colour change. For example, it has already been reported that the addition of halide ions (basic anions) into the solutions of some metal complexes changes either their colour or their fluorescence properties,12 and these features have applications in medicine, analytical, environmental, and industrial processes.13 Many acyclic and macrocyclic ligands have been successfully used in the detection of halide ions.14 Recently, Tamayo and co-workers have published the first macrocyclic nickel complex developed with this purpose.15 Dalton Trans., 2010, 39, 7673–7683 | 7673

Fig. 1 Crystal structure of the [Ni2 L5 (CH3 CN)4 ]4+ cation. Ellipsoids are shown at the 50% probability level. Hydrogen atoms are omitted for ˚ ) and angles (◦ ): Ni(1)–N(1) 1.993(3), Ni(1)–N(1S) 2.075(3), Ni(1)–N(3) 2.092(3), Ni(1)–N(2S) 2.093(3), Ni(1)–N(2) clarity. Selected bond lengths (A 2.162(3), Ni(1)–S 2.4830(11), N(1)–Ni(1)–N(1S) 96.63(13), N(1)–Ni(1)–N(3) 80.07(13), N(1S)–Ni(1)–N(3) 91.77(14), N(1)–Ni(1)–N(2S) 88.87(13), N(1S)–Ni(1)–N(2S) 172.70(13), N(3)–Ni(1)–N(2S) 93.92(13), N(1)–Ni(1)–N(2) 80.03(12), N(1S)–Ni(1)–N(2) 87.69(12), N(3)–Ni(1)–N(2) 159.90(14), N(2S)–Ni(1)–N(2) 88.53(12), N(1)–Ni(1)–S 164.02(9), N(1S)–Ni(1)–S 86.06(10), N(3)–Ni(1)–S 84.10(10), N(2S)–Ni(1)–S 89.98(9), N(2)–Ni(1)–S 115.88(9).

Following our ongoing projects on the synthesis and studies of transition metal complexes with multifunctional applications16 and our research on fluorescence and colourimetric chemosensors,17 we report here the synthesis, structural characterization, spectroscopic and magnetic studies of several new Ni(II) and Fe(II) complexes with the macrocycle ligand L. Particularly, the interactions with halides will also be discussed. See Scheme 1. Only a few coordination compounds of this type have been reported in the literature;18 while polynuclear Ni(II)-compounds featuring double and triple halide bridges are quite commonly studied,19 only five examples of Ni(II)-binuclear complexes having a single m-halide bridge, similar to the presented complexes synthesized and studied in the present work, have been structurally characterised.20

Results and discussion Synthesis and characterisation of L The synthesis of L was attempted through the slow addition of equimolar amounts of 1,5-diamine-3-thiopentane to a methanolic solution of 2,6-diformylpyridine, using the methodology reported previously by Steenland et al.21 Synthesis and characterisation of the complexes The reaction of L with Ni(II) nitrate or perchlorate in ethanol in a 2 : 1 metal : ligand molar ratio yielded white solids whose elemental analysis fits the formulae [Ni2 L](NO3 )4 ·H2 O (1) and [Ni2 L](ClO4 )4 ·2C2 H6 O (2), respectively. The reaction of L with Ni(II) tetrafluoroborate or Fe(II) acetate in dried nitromethane 7674 | Dalton Trans., 2010, 39, 7673–7683

under a N2 atmosphere in a 2 : 1 metal : ligand molar ratio yielded orange and brown solids whose elemental analysis fits the formulae [Ni2 L](BF4 )4 ·7H2 O (3) and [Fe2 L](C2 O2 H3 )4 ·6H2 O (5), respectively. For the heterodinuclear complex the reaction of L with Ni(II) tetrafluoroborate and Fe(II) acetate in nitromethane in a 1 : 1 : 1 Ni(II) : Fe(II) : L molar ratio yielded a brown solid complex whose elemental analysis fits the formula [NiFeL](BF4 )2 (C2 O2 H3 )2 ·H2 O (6). When the orange complex [Ni2 L](BF4 )4 ·7H2 O (3) was dissolved in acetonitrile, a mauve solution was obtained. This solution gave a mauve solid compound whose analytical data was in accordance with four acetonitrile coordinated molecules; therefore, this new complex should be formulated as [Ni2 L(CH3 CN)4 ](BF4 )4 ·3H2 O (4). Mauve crystals suitable for X-ray diffraction with the formula [Ni2 L(CH3 CN)4 ](BF4 )4 ·3.5CH3 CN (11) were obtained by slow diffusion of diethyl ether and nitromethane into an acetonitrile solution of compound [Ni2 L(CH3 CN)4 ](BF4 )4 ·3H2 O (4). The crystal structure of this compound contains the complex cation [Ni2 L(CH3 CN)4 ]4+ (Fig. 1) where two Ni(II) atoms are located inside the macrocyclic cavity coordinated to a pyridinic nitrogen atom, one S atom, two secondary amine groups from the macrocyclic backbone and two acetonitrile molecules in a distorted octahedral geometry. The longest bond distance is established between each metal atom and the S atom, and the shortest occurs with the N pyridine atom. The ligand shows a stepped conformation with the two symmetry related pyridinic ˚ rings parallel (the planes containing the pyridinic rings are 1.98 A away). The structure presents many hydrogen bond interactions between the tetrafluoroborate anions and the amine hydrogens, but no p–p-stacking interactions. This journal is © The Royal Society of Chemistry 2010

Scheme 1 Schematic synthetic route for ligand L.

Fig. 2 Crystal structure of the [Ni2 L5 (m-Cl)(H2 O)2 ]3+ cation. Ellipsoids are shown at the 50% probability level. Hydrogen atoms are omitted for ˚ ) and angles (◦ ): Ni–N(1) 1.995(3), Ni–O(1 W) 2.076(3), Ni–N(3) 2.125(3), Ni–N(2) 2.140(3), Ni–Cl(1) 2.3938(6), Ni–S clarity. Selected bond lengths (A 2.4865(10), N(1)–Ni–O(1 W) 90.86(14), N(1)–Ni–N(3) 80.28(11), O(1 W)–Ni–N(3) 90.27(12), N(1)–Ni–N(2) 78.81(11), O(1 W)–Ni–N(2) 88.27(13), N(3)–Ni–N(2) 159.02(12), N(1)–Ni–Cl(1) 175.85(9), O(1 W)–Ni–Cl(1) 86.64(11), N(3)–Ni–Cl(1) 96.41(9), N(2)–Ni–Cl(1) 104.40(9), N(1)–Ni–S 87.17(9), O(1 W)–Ni–S 175.56(9), N(3)–Ni–S 85.47(9), N(2)–Ni–S 95.25(9), Cl(1)–Ni–S 95.09(3), Ni–Cl(1)–Ni#1 133.48(5). Symmetry transformations used to generate equivalent atoms: #1 -x+1,y,-z+1/2.

When the orange complex [Ni2 L](BF4 )4 ·7H2 O (3) was dissolved in absolute ethanol or water, colourless and blue solutions were obtained, respectively. These solutions yielded white and blue compounds whose empirical formula could not be predicted. Blue crystals suitable for X-ray diffraction with the formula [Ni2 L(m-Cl)(H2 O)2 ](BF4 )3 ·2H2 O (12) were obtained by slow evaporation of a solution of the compound [Ni2 L](BF4 )4 ·7H2 O (3) in the ionic liquid 1-butyl-3-methyl-imidazolium chloride (BMIM). The crystal structure of this compound contains the complex cation [Ni2 L(m-Cl)(H2 O)2 ]3+ (Fig. 2) where two Ni(II) atoms are located inside the macrocyclic cavity coordinated to the pyridinic nitrogen atom, one S atom, two secondary amine groups from the macrocyclic backbone, one water molecule and one chloride ion acting as a bridge between the two metal centres. The geometry ˚ is therefore a distorted octahedral. The Ni(II) ions are 0.046 A out of the square planes (rms 0.0029) which are comprised by the chloride ion and the three nitrogen atoms, whilst the apical This journal is © The Royal Society of Chemistry 2010

positions are occupied by the water molecule and the sulfur atom. The dihedral angle between the planes containing the pyridine rings of the molecule is 63.62(9)◦ showing that the ligand is twisted. It is also folded as the angle between the pyridine N atoms and the chloride ion acting as a bridge is 137.2◦ . The structure presents hydrogen bond interactions between one tetrafluoroborate anion and the water molecules, but no p–p-stacking interactions. The dinuclear complexes 11 and 12, in solution, adopted a form D probably due to steric reasons.16b,16c Crystallographic data of [Ni2 L(CH3 CN)4 ](BF4 )4 ·3.5CH3 CN (11) and [Ni2 L(m-Cl)(H2 O)2 ](BF4 )3 ·2H2 O (12) are summarized in Tables 1, 2 and 3. The latest X-ray crystallographic structure determinations of the active center of NiSOD reveals that the amine of N-terminal His1, the deprotonated backbone amide of Cys2, and the thiolates of Cys2 and Cys6 form a square planar framework of the Ni coordination sphere. This N2S2 ligand field with the metal Dalton Trans., 2010, 39, 7673–7683 | 7675

Table 1 Crystal data and structure refinement for [Ni2 L(CH3 CN)4 ](BF4 )4 ·3.5CH3 CN (11) and [Ni2 L5 (m-Cl)(H2 O)2 ](BF4 )3 ·2H2 O (12)

Empirical formula Formula weight Temperature/K ˚ Wavelength/A Crystal system Space group Unit cell dimensions

˚3 Volume/A Z Density (calculated)/g cm-3 Absorption coefficient/mm-1 F(000) Crystal size/mm3 Theta range for data collection/◦ Index ranges Reflections collected Independent reflections Completeness to theta = Absorption correction Refinement method Data/restraints/parameters Goodness-of-fit on F 2 Final R indices [I > 2s(I)] R indices (all data) ˚ -3 Largest diff. peak and hole/e A

[Ni2 L(CH3 CN)4 ](BF4 )4 ·3.5CH3 CN

[Ni2 L5 (m-Cl)(H2 O)2 ](BF4 )3 ·2H2 O

C18.50 H28.25 B2 F8 N6.75 Ni S 609.62 293(2) 0.71073 Monoclinic P21 /n ˚ a = 13.079(4) A ˚ , b = 114.836(16)◦ b = 18.517(7) A ˚ c = 13.181(4) A 2897.0(17) 4 1.343 0.813 1250 0.36 ¥ 0.12 ¥ 0.07 1.84 a 26.37 -16 ≤ h ≤ 14, 0 ≤ k ≤ 23, 0 ≤ l ≤ 16 24504 5899 [R(int) = 0.0604] 99.5% (26.37◦ ) Empirical (Sadabs) Full-matrix least-squares on F 2 5899/96/447 1.002 R1 = 0.0546, wR2 = 0.1437 R1 = 0.1007, wR2 = 0.1621 0.433 and -0.312

C22 H42 B2 N6 O4 Ni2 F8 S2 Cl 845.23 100(2) 0.71073 Monoclinic C2/c ˚ , a = 90◦ a = 13.856 A ˚ , b = 111.43◦ b = 19.805 A ˚ , g = 90◦ c = 14.725 A 3761.3 4 1.493 1.258 1740 0.25 ¥ 0.07 ¥ 0.04 1.88 a 26.38 -17 ≤ h ≤ 16, 0 ≤ k ≤ 24, 0 ≤ l ≤ 18 16289 3849 [R(int) = 0.0380] 99.9% (26.38◦ ) Empirical (Sadabs) Full-matrix least-squares on F2 3849/0/239 0.987 R1 = 0.0460, wR2 = 0.0946 R1 = 0.0780, wR2 = 0.1030 0.644 and -0.817

˚ ] and angles [◦ ] for [Ni2 L(CH3 Table 2 Selected bond lengths [A CN)4 ](BF4 )4 ·3.5CH3 CN

˚ ] and angles [◦ ] for and [Ni2 L5 (mTable 3 Selected bond lengths [A Cl)(H2 O)2 ](BF4 )3 ·2H2 O

Ni(1)–N(1) Ni(1)–N(1S) Ni(1)–N(3) Ni(1)–N(2S) Ni(1)–N(2) Ni(1)–S N(1)–Ni(1)–N(1S) N(1)–Ni(1)–N(3) N(1S)–Ni(1)–N(3) N(1)–Ni(1)–N(2S) N(1S)–Ni(1)–N(2S) N(3)–Ni(1)–N(2S) N(1)–Ni(1)–N(2) N(1S)–Ni(1)–N(2) N(3)–Ni(1)–N(2) N(2S)–Ni(1)–N(2) N(1)–Ni(1)–S N(1S)–Ni(1)–S N(3)–Ni(1)–S N(2S)–Ni(1)–S N(2)–Ni(1)–S

Ni–N(1) Ni–O(1W) Ni–N(3) Ni–N(2) Ni–Cl(1) Ni–S N(1)–Ni–O(1W) N(1)–Ni–N(3) O(1W)–Ni–N(3) N(1)–Ni–N(2) O(1 W)–Ni–N(2) N(3)–Ni–N(2) N(1)–Ni–Cl(1) O(1W)–Ni–Cl(1) N(3)–Ni–Cl(1) N(2)–Ni–Cl(1) N(1)–Ni–S O(1W)–Ni–S N(3)–Ni–S N(2)–Ni–S Cl(1)–Ni–S Ni–Cl(1)–Ni#1

1.993(3) 2.075(3) 2.092(3) 2.093(3) 2.162(3) 2.4830(11) 96.63(13) 80.07(13) 91.77(14) 88.87(13) 172.70(13) 93.92(13) 80.03(12) 87.69(12) 159.90(14) 88.53(12) 164.02(9) 86.06(10) 84.10(10) 89.98(9) 115.88(9)

1.995(3) 2.076(3) 2.125(3) 2.140(3) 2.3938(6) 2.4865(10) 90.86(14) 80.28(11) 90.27(12) 78.81(11) 88.27(13) 159.02(12) 175.85(9) 86.64(11) 96.41(9) 104.40(9) 87.17(9) 175.56(9) 85.47(9) 95.25(9) 95.09(3) 133.48(5)

Symmetry transformations used to generate equivalent atoms: #1 -x+1,y,-z+1/2

incorporation into the backbone nitrogens and thiolate sulfurs is reminiscent of nickel coordination by the A-cluster of acetylcoenzyme A (CoA) synthase (ACS).22 Two distinct conformations for the His1 side chain were observed in the NiSOD active site: one with the axial Ni(III)–Nd His1 coordination to the metal center in its oxidized (resting, or native) state or, alternatively, with the His1 imidazole ring tilted away from the metal (via the rotation around the Cb –Cg bond) in its reduced Ni(II) state. The resting square pyramidal Ni(III) can be reduced to a square planar Ni(II) 7676 | Dalton Trans., 2010, 39, 7673–7683

chemically (with dithionite23 or thiosulfate24 ) or under exposure to X-ray radiation.25 In the case of derived compounds of complex [Ni2 L](BF4 )4 ·7H2 O (3), an N3S1 square planar coordination environment was observed similar to that presented in the reduced Ni(II) state of NiSOD. In order to explore the interaction with the halide family, the halide complexes with the general formula [Ni2 L]X4 ·nH2 O This journal is © The Royal Society of Chemistry 2010

were isolated from the reaction between the complex [Ni2 L](BF4 )4 ·7H2 O (3) and the corresponding tetrabutylammonium halide. The fluoride (7), chloride (8) and bromide (9) complexes show a blue colour, while the iodide (10) complex was green. The IR spectra of all complexes show similar features. The n(C=N) and n(C=C) bands of the pyridine rings are generally shifted to higher wave numbers than those in the free ligand, confirming the coordination of the pyridine groups to the metal ions.26 In the cases of the nitrate complex [Ni2 L](NO3 )4 ·H2 O (1) the spectrum shows a band at 1383 cm-1 , which is associated with the presence of ionic nitrate, showing that the counterion is not coordinated. The IR spectrum of the perchlorate complex [Ni2 L](ClO4 )4 ·2C2 H6 O (2) features absorptions attributable to ionic perchlorate at ca.1100 and 626 cm-1 , indicating that these groups are not coordinated to the metal centres.27 The IR spectra of the tetrafluoroborate complexes shows bands indicating that these groups are involved in hydrogen bond interactions.28 In the spectrum of complex [NiFeL](BF4 )2 (C2 O2 H3 )2 ·H2 O (6) with acetate groups, the vibration bands corresponding to the counterion can not be observed, because of the complexity that exists in the interval 1606–1447 cm-1 , due to the overlap with the bands assignable to the vibration modes of aromatic rings. Only in the spectrum of complex [Fe2 L](C2 O2 H3 )4 ·6H2 O (5) a band around 1554 cm-1 for the symmetric stretching (CO) was observed but no conclusions about the coordination of the acetate group to the metal ion can be made. The molar conductance values for the complexes (3) and (4) measured in acetonitrile and for the complex (6) measured in nitromethane, at 25 ◦ C, lie in the range reported as 2 : 1 electrolytes. This result suggests that two counterions are uncoordinated in solution.29 The molar conductance values for the halidecomplexes, in acetone, lie in the range reported as 1 : 1 electrolytes, for compounds (7) and (8), and between the range reported as 2 : 1–3 : 1 electrolytes, for compounds (9) and (10). FAB, ESI and MALDI-TOF mass spectra for all the complexes indicate the presence of the metal ions in the macrocyclic ligand. The spectra of most compounds display peaks which confirm the formation of the dinuclear metal complexes.

Spectrophotometric studies The electronic spectra of the complex [Ni2 L](BF4 )4 ·7H2 O (3) in water and in acetonitrile were measured at room temperature; the spectra show a band centred at ca. 260 nm associated with the p–p* electronic transition of the pyridine rings,30 and one band centred at 349 and 346 nm respectively, attributed to a metal-toligand charge transfer (MLCT). In the visible region two bands at 537 and 864 nm in water, and at 545 and 831 nm in acetonitrile were observed, respectively. These bands are assigned to the 3 A2g → 3 T1g (F)(n 2 ) and 3 A2g → 3 T2g (F)(n 1 ) d–d transition of Ni(II) ions. The positions of these bands are typical for octahedral Ni(II) complexes.31 Fig. 3 represents the spectrophotometric titration of ligand L with increasing addition of Ni(II) ions in abs. ethanol. The band at 292 nm achieved a plateau with the formation of 1 : 2 L : M complex. This result is in agreement with the dinuclear nature observed in the solid state for all the Ni(II) complexes. This journal is © The Royal Society of Chemistry 2010

Fig. 3 Absorption spectra of an abs. ethanol solution of L as a function of increasing amounts of Ni(BF4 )2 ·6H2 O. The inset shows the absorbance at 292 nm ([L] = 4.32 ¥ 10-5 M, [Ni(II)] = 1.00 ¥ 10-2 M, 298 K).

Taking into account the results obtained by the UV-vis characterization of the complex [Ni2 L](BF4 )4 ·7H2 O (3) in acetonitrile, both nickel(II) atoms are in an octahedral environment, probably due to the presence of coordinated solvent molecules. Keeping this in mind, we have performed several anion titrations in acetonitrile with compound (3) in order to find out the number of ions coordinated in our complex. Four possibilities can be observed (Scheme 2): If halides form bridges in the dinuclear complex, one (A), two (B) or three (C) of them will stabilize the electronic spectra. On the other hand, if the bridges are not formed, the halides probably occupied the apical positions and in this case four of them are needed to stabilize the spectra (D). Fig. 4 represents the spectrophotometric titrations of (3) in acetonitrile in the presence of fluoride, bromide and iodide. In solution, the presence of these anions does not change the colour, but inspection of the insets in all the titrations shows that four equivalents of halides are needed to stabilize the electronic spectra. These results point out that situation D is the most probable and the octahedral environment of each metal is maintained being in agreement with the synthetic solid complexes. On the contrary as reported below for complex [Ni2 L(m-Cl)(H2 O)2 ]3+ , the chloride ion from the ionic liquid forms a bridge between both metal centres. Similar results were reported by Tamayo and co-workers with a mononuclear Ni(II) macrocylic complex after several titrations with the halides, where two bridges between two complex molecules can be established.26 MALDI-TOF-MS studies As a general rule a MALDI-TOF matrix is a small organic compound that absorbs the energy in the UV region (337 nm N2 laser). An advance in the study by MALDI-TOF-MS spectrometry of supramolecular complexes with organic ligands provided with UV chromophores is that the ligand acts at the same time as the ligand and MALDI matrix.32 In this specific case, unfortunately, the presence of two pyridine rings was not enough to allow the study of the metal complexes without any external competitive matrix. Dalton Trans., 2010, 39, 7673–7683 | 7677

Scheme 2 Schematic routes of halide interactions in acetonitrile.

In order to select the correct solvent and MALDI matrix for the MALDI-TOF-MS metal titrations, complex [Ni2 L](BF4 )4 ·7H2 O (3) was studied dissolved in acetonitrile, acetone or absolute ethanol in the presence of dithranol (1,8,9-trihydroxyanthracene) or DHB (2,5-dihydroxybenzoic acid) as a matrix. Dithranol is preferably used as a matrix for coordination or polymeric compounds. However, if the complex studied is not stable enough, the matrix can compete with the metal ion disrupting the initial metal complex. On the other hand, DHB, is used more for protein and peptide systems with higher molecular weight and due to the low molecular weight of the matrix does not show this competitive effect. As seen in the experimental section, the results obtained for complex [Ni2 L](BF4 )4 ·7H2 O (3) in the presence of dithranol or DHB were similar, where the peaks attributed to the species [NiL]+ , [Ni2 L]+ and [Ni2 L(BF4 )4 (dithranol)]+ were observed when dithranol was used as the MALDI matrix regardless of the solvent used. While in the case of using DHB, the peaks attributed to the species [NiL]+ and [Ni2 L(BF4 )3 (EtOH)]+ were observed, in the last case, the peak assignable to the free protonated ligand was still observed. These results suggest that the complex (3) was stable in

7678 | Dalton Trans., 2010, 39, 7673–7683

these conditions. With regard to the solvent, acetonitrile, acetone or absolute ethanol gave the same results and in order to keep the same experimental conditions as in the metal titrations in solution, acetonitrile was selected. MALDI-TOF metal ion titrations were performed and the results are summarized in Table 4. The samples were dissolved in acetonitrile (1–2 mg mL-1 ) and dithranol was used as a matrix. A solid layer of ligand was deposited on the MALDI-TOF-MS plate after drying off the solvent, followed by superposition of a second solid layer of the aforementioned metal ions. Molar ratios (L : M) of 1 : 1 and 1 : 2 were tested. An in situ MALDITOF-MS reaction on-plate takes place upon laser irradiation, and formation of the metal complexes was observed with compound L. For the hetero-dinuclear complexes a drop containing the ligand and the MALDI-matrix was titrated with the corresponding metal ions: first Ni(II) and second Fe(II). Both the mononuclear and the dinuclear peaks were observed after the addition of the corresponding metal ion. Due to the coordination capability mentioned below shown by the matrix, several peaks attributed to the formation of the adducts between the matrix, the ligand and the metal ion were observed.


Fig. 4 Absorption titrations at room temperature of acetonitrile solutions of Ni2 L](BF4 )4 ·7H2 O (3) with tetrabutylammonium fluoride (A), bromide (B), and iodide (C). The insets show the absorbances at different wavelengths ([Ni2 L](BF4 )4 ·7H2 O] = 1.00 ¥ 10-5 M). Table 4 Major peaks observed in the metal titration of L followed by MALDI-TOF-MS Metal titration

L (a.m.u.)

L+M (a.m.u.)

L+2M (a.m.u.)

Ni2+ Fe2+

[LH]+ —447.64 [LH]+ —447.64

[NiL]+ —503.61 [LH]+ —447.77 [FeL]+ —501.68 [FeL(C2 O2 H3 )]+ —620.64 [FeL(X1 )]+ —726.69

Fe2+ /Ni2+

[LH]+ —447.64

[LH]+ —447.77 [FeL]+ —501.68 [FeL(C2 O2 H3 )]+ —620.64 [FeL(X1 )]+ —726.69

— [LH]+ —447.74 [FeL]+ —501.67 [Fe2 L]+ —558.49 [FeL(X1 )]+ —726.64 [Fe2 L(X1 )]+ —782.45 [LH]+ —447.70 [NiL]+ —504.58 [FeL(X1 )]+ —726.62

X1 = matrix = 1,8,9-Trihydroxyanthracene (Dithranol) = C14 O3 H10

These results show the potential utility of this macrocyclic ligand as a metal chelator for these metal ions in the presence of a competitive MALDI-matrix. Magnetic properties of the nickel(II) complexes [Ni2 L(CH3 CN)4 ](BF4 )4 ·3.5CH3 CN (11) and [Ni2 L(l-Cl)(H2 O)2 ] (BF4 )3 ·2H2 O (12). The magnetic properties of complexes (11) and (12) are very similar. Fig. 5 and 6 show the magnetic data as c M T vs. T plot (c M is the molar magnetic susceptibility for This journal is © The Royal Society of Chemistry 2010

two Ni2+ ions) and the reduced magnetization at 2 K (M/NmB vs. H). The value of c M T at 300 K is 3.10 cm3 mol-1 K (11) and 2.21 cm3 mol-1 K (12) which is as expected for two magnetically spin triplets (g > 2.00). Starting from room temperature c M T values increase to 3.55 cm3 mol-1 K (11) and 2.5 cm3 mol-1 K (12) at 30 K and below 30 K they decrease quickly to 1.7 and 1.1 cm3 mol-1 K at 2 K, respectively. This feature—for both complexes—is characteristic of a noticeably intramolecular ferromagnetic interaction with the presence of both D and J¢ Dalton Trans., 2010, 39, 7673–7683 | 7679

Fig. 5 Plots of experimental c M T vs. T and M/NmB vs. H (inset) for complex [Ni2 L(CH3 CN)4 ](BF4 )4 ·3.5CH3 CN (11). The solid lines are the best fits obtained from least-squares regression.

obtained are J = 4.5 cm-1 , J¢ = -0.09 cm-1 , g = 2.36 and |D| = 6.33 cm-1 for complex (11) and J = 3.1 cm-1 , J¢ = -0.11 cm-1 , g = 2.11 and |D| = 9.25 cm-1 for complex (12). The two phenomena (ZFS and J¢) are mathematically related, having the same effect on the low temperature c m T curve (decreasing). It is impossible, thus, to give an exact value of these parameters, being aware that D is always overparametrized. The reduced molar magnetization at 2 K (insert Fig. 5) corroborates that the influence of D and J¢ are important at low temperatures, mainly for complex (12): the M/NmB plot lies below the theoretical Brillouin function for g = 2.36 or 2.11 respectively. The similarity of the magnetic data between (11) and (12) can indicate that the magnetic pathway (intrinsically ferromagnetic) is mainly due to the macrocyclic ligand, making the influence of the bridge m-Cl in complex (12) (a decreasing of the J value: from ca 4.5 cm-1 to ca 3.0 cm-1 , owing to the likely antiferromagnetic pathway created by this bridge) less noticeable. The magnetic properties of analogous compounds presenting Ni(II)–F–Ni(II) and Ni(II)–Cl–Ni(II) systems are discussed in the literature,16c,16d indicating a significant antiferromagnetic exchange in the former.

Conclusions Twelve new dinuclear complexes with a Py2 N4 S2 macrocyclic ligand containing a pair NiNi, FeFe or NiFe as metal centres have been synthesized and characterized. The [Ni2 L(CH3 CN)4 ](BF4 )4 ·3.5CH3 CN and [Ni2 L(mCl)(H2 O)2 ](BF4 )3 ·2H2 O complexes were fully characterized by Xray diffraction. In all cases the ligand is bound to the metal ions by the nitrogen–sulfur donor set of the macrocyclic backbone, and an octahedral environment was observed for each metal ion. From their magnetic properties, intramolecular interactions were observed in both complexes. Taking into account the results obtained by MALDI-TOF-MS spectrometry, ligand L can be explored as a chelating unit for nickel(II) and iron(II) in the gas phase.

Experimental section Measurements

Fig. 6 Plots of experimental c M T vs. T and M/NmB vs. H (inset) for complex [Ni2 L(m-Cl)(H2 O)2 ](BF4 )3 ·2H2 O (12). The solid lines are the best fits obtained from least-squares regression.

(intermolecular antiferromagnetic interactions) which are clearly manifested at low temperatures. From the Hamiltonian given in (1)

Hˆ = −2 JS1S2 + DNi

∑S + gm H S 2 ij

B

iz

(1)

i =1, 2

the fit of the susceptibility data has been carried out applying two different approaches: either considering the J¢ intermolecular parameter (by means of molecular-field approach) or D (single ion zero-field-splitting parameter) by a full-diagonalization method using the MAGPACK program.32 The best-fit parameters 7680 | Dalton Trans., 2010, 39, 7673–7683

Elemental analyses were performed on a Fisons Instruments EA1108 microanalyser by the Universidade de Santiago de Compostela. Infra-red spectra were recorded as KBr discs on a BIORAD FTS 175-C spectrometer. FAB mass spectra were recorded using a KRATOS MS50TC spectrometer with 3-nitrobenzyl alcohol as the matrix. Conductivity measurements were carried out in 10-3 mol dm-3 acetonitrile, nitromethane, ethanol or acetone solutions at 25 ◦ C using a WTW LF3 conductivimeter. Matrixassisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) was performed in a MALDI-TOF-MS model Voyager DE-PRO Biospectrometry Workstation equipped with a nitrogen laser radiating at 337 nm from Applied Biosystems (Foster City, United States) from the MALDI-TOF-MS Service of the REQUIMTE, Chemistry Department, Universidade Nova de Lisboa. The acceleration voltage was 2.0 ¥ 104 kV with a delayed extraction (DE) time of 200 ns. The spectra represent accumulations of 5 ¥ 100 laser shots. The reflection mode was This journal is © The Royal Society of Chemistry 2010

used. The ion source and flight tube pressures were less than 1.80 ¥ 10-7 and 5.60 ¥ 10-8 Torr, respectively. The MALDI mass spectra of the soluble samples in acetonitrile or absolute ethanol (1 or 2 mg mL-1 ) such as the ligand and metal complexes were recorded using the conventional sample preparation method for MALDIMS using as matrix dithranol (1,8,9-trihydroxyanthracene) or DHB (2,5-dihydroxybenzoic acid). For the metal titrations by MALDI 1 mL of the metal sample were put on the sample holder on which the chelating ligand had been previously spotted with the matrix dithranol dissolved in acetonitrile. The sample holder was inserted in the ion source. Chemical reaction between the ligand and metal salts occurred in the holder and complex species were produced. Magnetic measurements were carried out in the “Servei de Magnetoqu´ımica (Universitat de Barcelona)” on polycrystalline samples (30 mg) with a Quantum Design SQUID MPMS-XL magnetometer working in the 2–300 K range. The magnetic field was 0.1 T. The diamagnetic corrections were evaluated from Pascal’s constants. Spectrophotometric measurements Absorption spectra were recorded on a Perkin Elmer lambda 35 spectrophotometer. The linearity of the absorption vs. concentration was checked in the concentration range used (1.00 ¥ 10-4 – 1.00 ¥ 10-6 M). All spectrophotometric titrations were performed as follows: the stock solutions of the ligand (ca. 1.00 ¥ 10-3 M) were prepared by dissolving an appropriate amount of the ligand in a 50 mL volumetric flask and diluting to the mark with freshly abs. ethanol, and in the case of compound (3) acetonitrile was used as a solvent. All measurements were performed at 298 K. The titration solutions ([L] = 4.32 ¥ 10-5 M and [3] = 1.00 ¥ 10-5 M) were prepared by appropriate dilution of the stock solutions. Titrations of the ligand L were carried out by addition of microlitre amounts of standard solutions of the Ni(II) ion in abs. ethanol and titrations of compound (3) were carried out by addition of microlitre amounts of standard solutions of the halide ions in acetonitrile. Chemicals and starting materials The synthesis of L was achieved following the literature method.24 2,6-Pyridinedimethanol, 1,5-diamine-3-thiopenthane and hydrated tetrafluoroborate, acetate and the tetrabutylammonium halide salts were commercial products (ABCR or Aldrich). The ionic liquid 1-butyl-3-methyl-imidazolium chloride (BMIM) was a commercial product (SOLCHEMAR). Solvents used were of reagent grade and purified by the usual methods. Synthesis Synthesis of the Nitrate and perchlorate nickel complexes. General procedure. The corresponding metal salt (Ni(NO3 )2 ·6H2 O and Ni(ClO4 )2 ·6H2 O) (0.08 mmol) was dissolved in abs. ethanol (5 mL) and added to a stirred solution of the ligand L (0.04 mmol) in abs. ethanol. The resulting solution was stirred for 4 h. The precipitate was separated by centrifugation, washed several times with cold abs. ethanol and diethyl ether and dried under vacuum. [Ni2 L](NO3 )4 ·H2 O (1). Yield: 68% (Found: C, 32.0; H, 4.8; N, 16.5; S, 7.6. Calc. for C22 H36 N10 O13 S2 Ni2 : C, 32.0; H, 4.4; N, 16.9; S, 7.7%); Conductivity (CH3 CN, 1 ¥ 10-3 M): 302 mS cm-1 This journal is © The Royal Society of Chemistry 2010

(2 : 1); n max /cm-1 1604, 1469 [n(C=N)py and n(C=C)], 1383 [n(NO3 - )]; m/z (ESI) 447 [L+H]+ , 504 [NiL]+ , 566 [NiL(NO3 )]+ , 748 [Ni2 L(NO3 )2 ]+ . Colour: white. [Ni2 L](ClO4 )4 .2C2 H6 O (2). Yield: 62% (Found: C, 29.9; H, 4.4; N, 8.3; S, 6.8. Calc. for C26 H46 N6 O18 S2 Cl4 Ni2 : C, 29.6; H, 4.4; N, 8.0; S, 6.1%); Conductivity (CH3 CN, 1 ¥ 10-3 M): 254 mS cm-1 (2 : 1); n max /cm-1 1606, 1457 [n(C=N)py and n(C=C)], 1143, 1122, 1088, 636, 625 [n(ClO4 - )]. m/z (ESI) 503 [NiL]+ , 584 [Ni2 L(H2 O)]+ , 807 [Ni2 L(ClO4 )2 (C2 H6 O)]+ . Colour: white. Synthesis of the tetrafluroborate nickel complex and the acetate iron complex. General procedure. Ni(BF4 )2 ·6H2 O or Fe(C2 O2 H3 )2 ·6H2 O (0.08 mmol) were dissolved in nitromethane (10 mL) and added drop wise to a nitromethane solution of L (0.04 mmol). The resulting solution was softly heated and stirred overnight under N2 atmosphere. In the case of nickel complex the solution was concentrated in a rotary evaporator until the volume was ca. 5 mL and it led to the formation of an orange precipitate; this solid was isolated, washed several times with diethyl ether and dried under vacuum. In the case of the iron complex, we observed the formation of a precipitate immediately after addition of the metal salt, but the complex was isolated from the treatment of the remaining solution with diethyl ether. The product was washed several times with cold abs. ethanol and diethyl ether, and then dried under vacuum. [Ni2 L](BF4 )4 ·7H2 O (3). Yield: 73% (Found: C, 25.7; H, 4.3; N, 8.0; S, 6.0. Calc. for C22 H48 N6 O7 S2 B4 F16 Ni2 : C, 25.5; H, 4.6; N, 8.1; S, 6.1%); Conductivity (CH3 CN, 1 ¥ 10-3 M): 265 mS cm-1 (2 : 1); n max /cm-1 1605, 1469 [n(C=N)py and n(C=C)], 1123, 1083, 1038, 801 [n(BF4 - )]; UV-vis (H2 O) l = 261 nm (e = 10673 M-1 cm-1 ); l = 349 nm (e = 465 M-1 cm-1 ); l = 537 nm (e = 155 M-1 cm-1 ); l = 864 nm (e = 84 M-1 cm-1 ). UV-vis (CH3 CN) l = 261 nm (e = 5285 M-1 cm-1 ); l = 346 nm (e = 128 M-1 cm-1 ); l = 545 nm (e = 36 M-1 cm-1 ); l = 787 nm (e = 56 M-1 cm-1 ); l = 831 nm (e = 60 M-1 cm-1 ); m/z (ESI) 447 [L+H]+ , 509 [NiL]+ , 623 [Ni2 L(CH3 NO2 )]+ ; m/z (MALDI) (dithranol-EtOH): 509 [NiL]+ , 565 [Ni2 L]+ , 1131 [Ni2 L(BF4 )4 (dithranol)]+ ; m/z (MALDI) (dithranolCH3 (CO)CH3 ): 509 [NiL]+ , 565 [Ni2 L]+ , 591 [NiL(BF4 )]+ , 793 [Ni2 L(dithranol)]+ , 1131 [Ni2 L(BF4 )4 (dithranol)]+ ; m/z (MALDI) (dithranol-CH3 CN): 509 [NiL]+ , 565 [Ni2 L]+ , 589 [NiL(BF4 )]+ , 1131 [Ni2 L(BF4 )4 (dithranol)]+ ; m/z (MALDI) (DHB-EtOH) : 447 [L+H]+ , 509 [NiL]+ , 867 [Ni2 L(BF4 )3 (EtOH)]+ . Colour: orange. Blue crystals suitable for X-ray diffraction with the formula [Ni2 L(m-Cl)(H2 O)2 ](BF4 )3 ·2H2 O (12) were obtained by slow evaporation of a solution of the compound (3) in the ionic liquid 1-butyl-3-methyl-imidazolium chloride (BMIM). [Ni2 L(CH3 CN)4 ](BF4 )4 ·3H2 O (4). Yield: 56% (Found: C, 31.5; H, 5.1; N, 12.1; S, 5.2. Calc for C30 H52 N10 O3 S2 B4 F16 Ni2 : C, 31.9; H, 4.6; N, 12.4; S, 5.7%); Conductivity (CH3 CN, 1 ¥ 10-3 M): 269 mS cm-1 (2 : 1); n max /cm-1 1604, 1446 [n(C=N)py and n(C=C)], 1123, 1105, 1083, 1037, 800 [n(BF4 - )]; m/z (FAB) 559 [Ni2 L]+ , 667 [Ni2 L(BF4 )(H2 O)]+ , 745 [Ni2 L(CH3 CN)4 (H2 O)]+ , 773 [Ni2 L(CH3 CN)3 (BF4 )]+ . Colour: mauve. Mauve crystals suitable for X-ray structure determination with the formula [Ni2 L(CH3 CN)4 ](BF4 )4 ·3.5CH3 CN (11) were obtained by slow diffusion of diethyl ether and nitromethane into an acetonitrile solution of (4). Dalton Trans., 2010, 39, 7673–7683 | 7681

[Fe2 L](C2 O2 H3 )4 ·6H2 O (5). Yield: 67% (Found: C, 39.4; H, 6.1; N, 9.8; S, 7.4. Calc. for C30 H58 N6 O14 S2 Fe2 : C, 39.9; H, 6.4; N, 9.3; S, 7.1%); n max /cm-1 1578, 1440 [n(C=N)py and n(C=C)], 1554 [n(C–O)]; UV-vis (H2 O) l = 250 nm (e = 22354 M-1 cm-1 ); l = 256 nm (e = 23342 M-1 cm-1 ); l = 261 nm (e = 22614 M-1 cm-1 ); l = 369 nm (e = 5269 M-1 cm-1 ); l = 472 nm (e = 1070 M-1 cm-1 ); m/z (MALDI) 447 [L+H]+ , 501 [FeL]+ , 558 [Fe2 L]+ . Colour: brown. Synthesis of the heterodinuclear Ni–Fe complex. A mixture of Fe(C2 O2 H3 )2 ·6H2 O (0.04 mmol) and Ni(BF4 )2 ·6H2 O (0.04 mmol) was dissolved in nitromethane (5 mL) and added to a stirred solution of the ligand L (0.04 mmol) in the same solvent. The resulting solution was softly heated and stirred for 4 h and concentrated to ca. 5 mL. Diethyl ether was added to the solution and the resulting precipitate was isolated by centrifugation, washed several times with cold abs. ethanol and diethyl ether and dried under vacuum. [NiFeL](BF4 )2 (C2 O2 H3 )2 ·H2 O (6). Yield: 56% (Found: C, 35.9; H, 5.3; N, 10.2; S, 8.0. Calc. for C26 H42 N6 O5 S2 B2 F8 NiFe: C, 35.9; H, 4.8; N, 9.7; S, 7.3%); Conductivity (CH3 NO2 , 1 ¥ 10-3 M): 152 mS cm-1 (2 : 1); n max /cm-1 1606, 1447 [n(C=N)py and n(C=C)], 1038, 1067, 1083 [n(BF4 - )]; UV-vis (H2 O) l = 263 nm (e = 11941 M-1 cm-1 ); l = 354 nm (e = 560 M-1 cm-1 ); l = 490 nm (e = 131 M-1 cm-1 ); l = 850 nm (e = 51 M-1 cm-1 ); m/z (MALDI) 447 [L+H]+ , 509 [NiL]+ , 561 [NiFeL]+ . Colour: brown. Synthesis of halide complexes derived from [Ni2 L](BF4 )4 ·7H2 O (3). General procedure. An acetonitrile solution of the corresponding tetrabutylammonium halide (0.08 mmol) was added drop wise to a solution of (3) (0.02 mmol) in the same solvent (4 mL). The resulting solution was stirred overnight and concentrated to ca. 5 mL. The products were separated by centrifugation, washed several times with diethyl ether and dried under vacuum. [Ni2 L]F4 ·6H2 O (7). Yield: 56%. (Found: C, 34.7; H, 6.4; N, 10.8; S, 8.4. Calc. for C22 H48 N6 O7 S2 F4 Ni2 : C, 34.5; H, 6.3; N, 10.9; S, 8.3%); Conductivity (CH3 COCH3 , 1 ¥ 10-3 M): 183 mS cm-1 (1 : 1); n max /cm-1 1605, 1469 [n(C=N)py and n(C=C)]; m/z (FAB) 503 [NiL]+ , 559 [Ni2 L]+ , 619 [Ni2 L(F)]+ , 651 [Ni2 L(BF4 )]+ , 755 [Ni2 L(F)(BF4 )2 ]+ . Colour: blue. [Ni2 L]Cl4 ·7H2 O (8). Yield: 60% (Found: C, 32.0; H, 5.3; N, 9.9; S, 6.2. Calc. for C22 H48 N6 O7 S2 Cl4 Ni2 : C, 32.0; H, 5.8; N, 10.1; S, 5.8%); Conductivity (CH3 COCH3 , 1 ¥ 10-3 M): 195 mS cm-1 (1 : 1); n max /cm-1 1604, 1445 [n(C=N)py and n(C=C)]; m/z (FAB) 560 [Ni2 L]+ , 597 [Ni2 L(Cl)]+ , 635 [Ni2 L(Cl)2 ]+ . Colour: blue. [Ni2 L]Br4 ·6H2 O (9). Yield: 64% (Found: C, 26.5; H, 4.3; N, 8.4; S, 6.5. Calc. for C22 H46 N6 O6 S2 Br4 Ni2 : C, 26.6; H, 4.6; N, 8.5; S, 6.5%); Conductivity (CH3 COCH3 , 1 ¥ 10-3 M): 222 mS cm-1 (2 : 1– 3 : 1); n max /cm-1 1604, 1446 [n(C=N)py and n(C=C)]; m/z (FAB) 579 [Ni2 L(H2 O)]+ , 607 [NiL(Br)Na]+ , 625 [NiL(Br)Na(H2 O)]+ , 733 [Ni2 L(Br)(BF4 )]+ . Colour: blue. [Ni2 L]I4 ·3H2 O (10). Yield: 59% (Found: C, 23.6; H, 3.5; N, 7.4; S, 5.8. Calc. for C22 H40 N6 O3 S2 I4 Ni2 : C, 23.5; H, 3.5; N, 7.5; S, 5.6%); Conductivity (CH3 COCH3 , 1 ¥ 10-3 M): 245 mS cm-1 (2 : 1–3 : 1); n max /cm-1 ; 1603, 1443 [n(C=N)py and n(C=C)]; m/z (FAB) 668 [Ni2 L(BF4 )(H2 O)]+ , 766 [NiL(I)(BF4 )(Na)2 ]+ . Colour: green. Crystal structure determinations of [Ni2 L(CH3 CN)4 ] (BF4 )4 ·3.5CH3 CN (11) and [Ni2 L(l-Cl)(H2 O)2 ](BF4 )3 ·2H2 O (12). Mauve crystals suitable for X-ray diffraction with the formula 7682 | Dalton Trans., 2010, 39, 7673–7683

[Ni2 L(CH3 CN)4 ](BF4 )4 ·3.5CH3 CN (11) were obtained by slow diffusion of diethyl ether and nitromethane into an acetonitrile solution of the compound [Ni2 L(CH3 CN)4 ](BF4 )4 ·3H2 O (4). While blue crystals suitable for X-ray diffraction with the formula [Ni2 L(m-Cl)(H2 O)2 ](BF4 )3 ·2H2 O (12) were obtained by slow evaporation of a solution of the compound [Ni2 L](BF4 )4 ·7H2 O (3) in the ionic liquid 1-butyl-3-methyl-imidazolium chloride (BMIM). The molecular structures of the cationic complex are shown in Fig. 1 and 2, respectively, together with the atomic numbering scheme adopted and selected bond distances ˚ ) and angles (◦ ). The details on the X-ray crystal data, (A structure solution and refinement for both crystals are given in Table 1. Measurements were made on a Bruker SMART CCD 1000 area diffractometer in the RIAIDT of the University of Santiago de Compostela, Santiago de Compostela, Spain. All data were corrected for Lorentz and polarization effects. Empirical absorption corrections were also applied for both crystal structures.33 Complex scattering factors were taken from the program package SHELXTL.34 The structures were solved by direct methods, which revealed the position of all non-hydrogen atoms. All the structures were refined on F 2 by a full-matrix leastsquares procedure using anisotropic displacement parameters for all non hydrogen atoms. The hydrogen atoms were located in their calculated positions and refined using a riding model. Both tetrafluroborate anions in the asymmetric unit of [Ni2 L(CH3 CN)4 ](BF4 )4 ·3.5CH3 CN are modelled as disordered in two positions. The unit cell of [Ni2 L(m-Cl)(H2 O)2 ](BF4 )3 ·2H2 O contains four potential anion-accessible symmetry-related cavities centred on the crystallographic twofold rotation axes, filled with disordered anions, probably tretrafluoroborates. The volume of ˚ 3 . Attempts to model treeach cavity is approximately 145 A trafluoroborate molecules in the solvent cavity did not result in an acceptable model. As an alternative strategy, the SQUEEZE35 function of PLATON36 was used to eliminate the contribution of the electron density in the solvent region from the intensity data. The use of this strategy and the subsequent solvent-free model produced much better refinement results than the attempt to model the tetrafluoroborate atoms. Therefore, the solvent-free model and intensity data were used for the final results reported here. A total of 50 e- was found in each cavity, corresponding approximately to one tetrafluoroborate ion per cavity. These anions, together with the half chloride and the tetrafluoroborate anion founded in the asymmetric unit made just the amount necessary to balance the charge of the compound. Where relevant, the crystal data reported earlier in this paper is given without the contribution of the disordered solvent. Molecular graphics were obtained with ORTEP-337 and CAMERON.

Acknowledgements We thank Xunta de Galicia (Spain) (Project PGIDIT07PXIB209039PR), Fundaça˜ o para a Ciência e a Tecnologia/FEDER (Portugal/EU) (Project POCI/QUI/55519/2004 FCT-FEDER), University of Vigo INOU-ViCou K914 and K915 (Spain) for financial support. C.N., A.M., R.B., J.L., and C.L. would like to thank the bilateral programme “Joint Portuguese–Spanish Project 2007” for the agreement number 63/07(Portugal)/HP2006-0119 (Spain). C. N. thanks Fundaça˜ o This journal is © The Royal Society of Chemistry 2010

para a Ciência e a Tecnologia/FEDER (Portugal/EU) programme postdoctoral contract (SFRH/BPD/65367/2009). J.L. and C.L. thank Xunta de Galicia (INCITE) for the Isidro Parga Pondal Research programme. J.R. acknowledges the financial support from the Spanish government (Grant CTQ2009/07264). We acknowledge some of the MALDI-TOF-MS spectra to Dr Luz Fernandes from REQUIMTE, University NOVA de Lisboa.

References 1 B. Zerner, Bioorg. Chem., 1991, 19, 116. 2 U. Ermler et al., Curr. Opin. Struct. Biol., 1998, 8, 749. 3 (a) R. K. Thauer, Science, 2001, 293, 1264; (b) E. I. Steifel and K. Matsumoto, Transition Metal Sulfur Chemistry: Biological and Industrial, ed. ACS Symposium Series 653; American Chemical Society, Washington, DC, 1996, ch. 4. 4 (a) A. Volbeda, E. Garcin, C. Piras, A. L. de Lacey, V. M. Fernandez, E. C. Hatchikian, M. Frey and J. C. Fontecilla-Camps, J. Am. Chem. Soc., 1996, 118, 12989; (b) Z. Gu, J. Dong, C. B. Allan, S. B. Choudhury, R. Franco, J. J. G. Moura, I. Moura, J. LeGall, A. E. Przybyla, W. Roseboom, S. P. J. Albracht, M. J. Axley, R. A. Scott and M. J. Maroney, J. Am. Chem. Soc., 1996, 118, 11155. 5 (a) H. Dobbek, V. Svetlitchnyi, L. Gremer, R. Huber and O. Meyer, Science, 2001, 293, 1281; (b) J. Feng and P. A. Lindahl, J. Am. Chem. Soc., 2004, 126, 9094. 6 D. Nakane, Y. Funahashi, T. Ozawa and H. Masuda, Chem. Lett., 2010, 39, 344. 7 (a) X. Tan, I. V. Surovtsev and P. A. Lindahl, J. Am. Chem. Soc., 2006, 128, 12331; (b) X. Tan, H.-K. Loke, S. Fitch and P. A. Lindahl, J. Am. Chem. Soc., 2005, 127, 5833. 8 A. L. Phelps, M. V. Rampersad, S. B. Fitch, M. Y. Darensbourg and D. J. Darensbourg, Inorg. Chem., 2006, 45, 119. 9 M. V. Rampersad, S. P. Jeffery, M. L. Golden, J. Lee, J. H. Reibenspies, D. J. Darensbourg and M. Y. Darensbourg, J. Am. Chem. Soc., 2005, 127, 17323. 10 (a) E. Szajna, P. Dobrowolski, A. L. Fuller, A. M. Arif and L. M. ` F. A. Berreau, Inorg. Chem., 2004, 43, 3988; (b) A. J. Blake, J. Casabo, Devillanova, L. Escriche, A. Garau, F. Isaia, V. Lippolis, R. Kivekas, V. ¨ Muns, M. Schroder, R. Sillanpäa¨ and G. Verani, J. Chem. Soc., Dalton Trans., 1999, 7, 1085; (c) A. J. Blake, F. A. Devillanova, A. Garau, A. ¨ Harrison, F. Isaia, V. Lippolis, S. K. Tiwary, M. Schroder, G. Verani and G. Whittaker, J. Chem. Soc., Dalton Trans., 2002, 4389; (d) C. ¨ Dietza, F. W. Heinemanna, J. Kuhnigkb, C. Krugerb, M. Gerdanc, A. X. Trautweinc and A. Grohmann, Eur. J. Inorg. Chem., 1998, 1041. 11 (a) L. Xie, X. Zhang, C. Yuan and X. Li, Synth. React. Inorg. M., 2009, 291; (b) S. Sreedaran, K. S. Bharathi, A. K. Rahiman, K. Rajesh, G. Nirmala, L. Jagadish, V. Kaviyarasan and V. Narayanan, Polyhedron, 2008, 27(7), 1867; (c) Y. Q. Tian and J. A. Tong, Chinese Chem. Lett., 1997, 8(2), 107. 12 (a) E. J. Cho, J. W. Moon, S. W. Ko, J. Y. Lee, S. K. Kim, J. Yoon and K. C. Nam, J. Am. Chem. Soc., 2003, 125, 12376; (b) T. Gunnlaugsson, P. E. Kruger, T. C. Lee, R. Parkesh, F. M. Pfeffer and G. M. Hussey, Tetrahedron Lett., 2003, 44, 6575; (c) P. Jr. Anzenbacher, K. Jursikova and J. L. Sessler, J. Am. Chem. Soc., 2000, 122, 9350. 13 (a) C. D. Geddes, Meas. Sci. Technol., 2001, 12, R53–R88; (b) K. L. Kirk, Biochemistry of the Halogens and Inorganic Halides; Plenum Press:, New York, 1991. 14 (a) D. A. Jose, D. K. Kumar, B. Ganguly and A. Das, Org. Lett., 2004, 6, 3445; (b) L. H. Wei, Y. B. He, J. L. Wu, X. L. Wu, L. Z. Meng and X. Yang, Supramol. Chem., 2004, 16, 561; (c) M. Vázquez, L. Fabbrizzi, A. Taglietti, R. M. Pedrido, A. M. González-Noya and M. R. Bermejo, Angew. Chem., Int. Ed., 2004, 43, 1962; (d) C. Suksai and T. Tuntulani, Chem. Soc. Rev., 2003, 32, 192; (e) T. Gunnlaugsson, A. P. Davis and M. Glynn, Chem. Commun., 2001, 2556; (f) D. Jiménez, R. Mart´ınez˜ ´ and J. Soto, Tetrahedron Lett., 2002, 43, 2823. Mánez, F. Sancenon 15 (a) A. Tamayo, J. Casabo, L. Escriche, C. Lodeiro, B. Covelo, C. D. Brondino, R. Kiveka and R. Sillampäa¨ , Inorg. Chem., 2006, 45, 1140; ˜ J. Ribas, B. (b) A. Tamayo, L. Escriche, C. Lodeiro, J. Ribas-Arino, Covelo and J. Casabo, Inorg. Chem., 2006, 45, 7621.


˜ E. Oliveira, L. Giestas, L. Valencia, A. Mac´ıas, J. C. Lima, 16 (a) C. Nu´ nez, R. Bastida and C. Lodeiro, Inorg. Chim. Acta, 2008, 361, 2183; (b) C. ˜ R. Bastida, A. Mac´ıas, C. Lodeiro and L. Valencia, Inorg. Chim. Nunez, ˜ R. Bastida, A. Mac´ıas, E. Bértolo, Acta, 2009, 362, 3454; (c) C. Nu´ nez, L. Fernandes, J. L. Capelo and C. Lodeiro, Tetrahedron, 2009, 65, ˜ R. Bastida, A. Mac´ıas, A. Aldrey and L. Valencia, 6179; (d) C. Nu´ nez, Polyhedron, 2010, 29, 126. 17 (a) C. Lodeiro and F. Pina, Coord. Chem. Rev., 2009, 253, 1353; (b) C. Lodeiro, J. L. Capelo, J. C. Mejuto, E. Oliveira, H. M. Santos, B. Pedras ˜ and C. Nu´ nez, Chem. Soc. Rev., 2010, DOI: 10.1039/b819787n. 18 (a) S. Brooker and P. D. Croucher, Chem. Commun., 1997, 459; (b) S. Brooker and P. D. Croucher, J. Chem. Soc., Chem. Commun., 1995, 2075; (c) S. Brooker, Coord. Chem. Rev., 2001, 222, 33; (d) A. C. Marr, ¨ J. E. Spencer and M. Schroder, Coord. Chem. Rev., 2001, 219–221, 1055; (e) V. Lozan, R. Syre and B. Kersting, Z. Anorg. Allg. Chem., 2008, 634, 2330. 19 (a) S. J. Higgins and W. Levason, Inorg. Chim. Acta, 1986, 113, 47; (b) F. J. Rietmeijer, J. G. Haasnoot, A. J. Den Hartog and J. Reedijk, Inorg. Chim. Acta, 1986, 113, 147; (c) J. Reedijk and R. W. M. Tenhoedt, Recl. Trav. Chim. Pays-Bas, 1982, 101, 49; (d) M. M. Brezinski, J. Schneider, L. J. Radonovich and K. J. Klabunde, Inorg. Chem., 1989, 28, 2414; (e) J. Verbiest, J. A. C. van Ooijen and J. Reedijk, J. Inorg. Nucl. Chem., 1980, 42, 971; (f) R. W. M. ten Hoedt and J. Reedijk, Inorg. Chim. Acta, 1981, 51, 23. 20 (a) M. G. B. Drew, D. H. Templeton and A. Zalkin, Inorg. Chem., 1968, 7, 2618; (b) C. Dietz, F. W. Heinemann, J. Kuhnigk, C. Kruger, M. Gerdan, A. X. Trautwein and A. Grohmann, Eur. J. Inorg. Chem., 1998, 1041; (c) L. Bonomo, E. Solari, M. Latronico, R. Scopelliti and C. Floriani, Chem.–Eur. J., 1999, 5, 2040; (d) J. Emsley, M. Arif, P. A. Bates and M. B. Hursthouse, J. Chem. Soc., Dalton Trans., 1989, 1273; (e) J. C. A. Boeyens and E.-L. Oosthuizen, J. Crystallogr. Spectrosc. Res., 1992, 22, 3. 21 M. W. A. Steenland, W. Lippens, G. G. Herman and A. M. Goeminne, Bull. Soc. Chim. Belg., 1993, 102, 239. 22 (a) T. I. Doukov, T. M. Iverson, J. Seravalli, S. W. Ragsdale and C. L. Drennan, Science, 2002, 298, 567; (b) C. Darnault, A. Volbeda, E. J. Kim, P. Legrand, X. Vernede, P. A. Lindahl and J. C. Fontecilla-Camps, Nat. Struct. Biol., 2003, 10, 271; (c) V. Svetlitchnyi, H. Dobbek, W. Meyer-Klaucke, T. Meins, B. Thiele, P. Romer, R. Huber and O. Meyer, Proc. Natl. Acad. Sci. U. S. A., 2004, 101, 446. 23 S. B. Choudhury, J.-W. Lee, G. Davidson, Y.-I. Yim, K. Bose, M. L. Sharma, S.-O. Kang, D. E Cabelli and M. J. Maroney, Biochemistry, 1999, 38, 3744. 24 J. Wuerges, J.-W. Lee, Y.-I. Yim, H.-S. Yim, S.-O. Kang and K. D. Carugo, Proc. Natl. Acad. Sci. U. S. A., 2004, 101, 8569. 25 D. P. Barondeau, C. J Kassmann, C. K. Bruns, J. A. Tainer and E. D. Getzoff, Biochemistry, 2004, 43, 8038. 26 (a) N. S. Gill, R. H. Nuttall, D. E. Scaife and D. W. Sharp, J. Inorg. Nucl. Chem., 1961, 18, 79; (b) S. Aime, M. Botta, U. Casellato, S. Tamburini and P. A. Vigato, Inorg. Chem., 1995, 34, 5825. 27 (a) M. R. Rosenthal, J. Chem. Educ., 1973, 50, 331; (b) B. J. Hathaway and A. E. Underhill, J. Chem. Soc., 1961, 3091. 28 A. S. Quist, J. B. Bates and G. E. Boyd, J. Chem. Phys., 1971, 54, 4896(a) O. L. Casagrande and A. E. Mauro, Polyhedron, 1997, 16(13), 2193. 29 A. K. Livesey and J. C. Brochon, Biophys. J., 1987, 52(5), 693. 30 E. Pretsch, T. Clerc, J. Seibl and W. Simon, Tables of Spectral Data for Structure Determination of Organic Compounds, 2nd ed., SpringerVerlag, Berlin, 1989. 31 A. B. P. Lever, Inorganic Electronic Spectroscopy 2nd Ed, Elsevier, Amsterdam, 1984. 32 L. Fernandes, M. Boucher, J. Fernández-Lodeiro, E. Oliveira, C. ˜ Nunez, H. M. Santos, J. L. Capelo, O. Nieto-Faza, E. Bértolo and C. Lodeiro, Inorg. Chem. Commun., 2009, 12, 905. 33 G. M. Sheldrick, SADABS, Program for Empirical Absorption Correc¨ tion of Area Detector Data, University of Gottingen, Germany, 1996. 34 SHELXTL version, An Integrated System for Solving and Refining Crystal Structures from Diffraction Data (Revision 5.1), Bruker AXS LTD. 35 P Sluis and A. L. Spek, Acta Crystallogr., Sect. A: Found. Crystallogr., 1990, 46, 194. 36 A. L. Spek, PLATON. University of Utrecht, The Netherlands, 2001. 37 L. J. Farrugia, J. Appl. Crystallogr., 1997, 30, 565.

Dalton Trans., 2010, 39, 7673–7683 | 7683