View Online
COMMUNICATION
www.rsc.org/dalton | Dalton Transactions
Cleavage of P–S bonds and oxygenation by a trinuclear iron carboxylate: Synthesis and structures of iron clusters containing group 15/16 anions†‡§ Tatiana V. Mitkina,a Yanhua Lan,a Valeriu Mereacre,a Weifeng Shi,a Annie K. Powella and Alexander Rothenberger*a,b
Downloaded by KIT on 01 March 2011 Published on 23 January 2008 on http://pubs.rsc.org | doi:10.1039/B717583C
Received 13th November 2007, Accepted 2nd January 2008 First published as an Advance Article on the web 23rd January 2008 DOI: 10.1039/b717583c
The first reactions of the trinuclear oxygen-centred iron carboxylate [Fe3 (l3 -O)(l2 -piv)6 (H2 O)3 ](piv) (piv = t BuCOO− ) with the neutral ligand precursor [RP(S)(l-S)]2 (R = 4-anisyl) are reported. Metal phosphonates are a class of well-known and extensively investigated compounds. They have attracted a great deal of interest in open-framework chemistry.1 Many complexes have been prepared and their structures as well as their magnetic properties have been determined.2–7 Recently another aspect of metal phosphonate chemistry was described. Kerman and Kraatz investigated the properties of biomolecule-bound thiophosphate.8 It was found that when sulfur is incorporated into the biophosphate, soft donor centres are present, serving as linkers to small metal-containing particles with size-dependent properties.9 Whilst the final goal of these investigations is to functionalize and address biomolecules at particular domains via the attachment of metal-containing clusters, a short-term aim is simply to explore new synthetic routes to metal complexes containing P-chalcogen and mixed O–Pchalcogen anions.10–18 These may provide a better understanding of interactions between S-functionalized DNA with metalcontaining clusters. In nature phosphorothioation, whereby a P–O group is transformed to a P–S group, is carried out by bacterial gene clusters on the DNA backbone.19 In our case, however, sulfur substituents at a phosphorus atom atoms are replaced with oxygen atoms. In previous investigations we described a number approaches, where chalcogen atoms in thio- and selenophosphinic acid anhydrides20–22 were replaced with oxygen.12–16 This can be done by hydrolysis, alcoholysis or by chemical transformations of metal carboxylates and Scheme 1 shows recently prepared examples of chalcogen-P–O anions.12–16 In this work, we were looking for metal-containing starting materials, which may be useful for similar preparations. A wellestablished class of metal salts in the area of single-molecular
a Institut f¨ur Anorganische Chemie der Universit¨at Karlsruhe, Geb. 30.45, Engesserstr. 15a, 76131, Karlsruhe, Germany b Institut f¨ur Nanotechnologie, Forschungszentrum Karlsruhe GmbH, Postfach 3640, 76021, Karlsruhe, Germany. E-mail:
[email protected] † Dedicated to Professor Ken Wade on the occasion of his 75th birthday. ‡ CCDC reference numbers 667685–667686. For crystallographic data in CIF or other electronic format see DOI: 10.1039/b717583c ¨ § Electronic supplementary information (ESI) available: Moßbauer spectra and magnetic susceptibility of 1. See DOI: 10.1039/b717583c
1136 | Dalton Trans., 2008, 1136–1139
Scheme 1 Recently prepared anionic chalcophosphonate derivatives (R = organic group, Ac = acetyl).
magnet chemistry that may serve this purpose are the carboxylate salts of iron.3,23,24 They are easy to prepare, the solubility in organic solvents can be easily adjusted and they are reactive towards neutral P–S ligand precursors. [Fe3 (l3 -O)(l2 -piv)6 (H2 O)3 ](piv) (piv = t BuCOO− ) was prepared¶ by the reaction of [Fe(NO3 )3 ] with pivalic acid t BuCOOH and the mixture was used as a metal and oxygen source in reactions with Lawesson’s reagent (L.R.) [RP(S)(l-S)]2 (R = 4-anisyl) (Scheme 2).
Scheme 2 Synthesis of 1 and 2 (piv = t BuCOO− , R = 4-anisyl, dme = 1,2-dimethoxyethane). Depending on the ratio of starting materials either 1 or 2 can be isolated.
It turned out that the nature of the crystalline products that can be isolated from these reactions depends on the stoichiometric ratio of the starting materials employed (Scheme 2). Both in 1* and 2†† cleavage of P–S bonds in L.R. occurred. In 1, however, one P–S bond remained intact. Reduction of Fe(III) to Fe(II) apparently took place during the formation of 1 whereas in 2, Fe-centres remain in the formal oxidation state III. This reaction (Scheme 2) has yet to be investigated in more detail like the previously studied reaction between [Fe(OAc)2 ] and L.R.13 Nevertheless, it is already clear that the oxo-centred iron carboxylate [Fe3 (l3 -O)(l2 -piv)6 (H2 O)3 ](piv) is one of many other structurally similar transition metal salts and a promising reagent This journal is © The Royal Society of Chemistry 2008
Downloaded by KIT on 01 March 2011 Published on 23 January 2008 on http://pubs.rsc.org | doi:10.1039/B717583C
View Online
in the chemistry of neutral group 15/16 compounds. For now it is noteworthy, that both 1 and 2 can be reproduced reliably allowing further investigation of their magnetic properties. A preliminary study of the magnetic properties of 1 was carried out in the range of 1.8–300 K. At room temperature, the vT product is 13.85 cm3 K mol−1 . This value is quite low in comparison to the expected value for whichever of the systems containing two spin-only HS/LS Fe(III) ions and five spin-only HS/LS Fe(II) ions. Decreasing the temperature, the vT product continuously increases to reach 20.82 cm3 K mol−1 at 1.8 K. These types of behavior suggest the presence of dominant ferromagnetic interactions between spin carriers leading to a ground state configuration where the spins are not compensated. The final decrease of the vT product at 10000 Oe below 15 K is probably the result of magnetic anisotropy and/or intermolecular interactions. At present, attempts are made to model this complex behaviour with a combination of magnetic ¨ data and Moßbauer spectra. Preliminary results of the latter suggest an intermediate oxidation state of +2.7 and electron delocalisation between Fe(1–3) in 1. An alternative description involves partial oxidation of ligand S atoms in 1 and the presence of Fe(II) centres only. This aspect is currently looked at in more detail and the final results will be reported in a subsequent full paper. In the solid state 1 exhibits a remarkable arrangement of three inner Fe atoms surrounded by sulfido ligands in a tetrahedral fashion (Fig. 1). The sulfido ligands were formed during the course of the reaction from L.R. This inner arrangement is
˚ ) and angles Fig. 1 Solid-state structure of 1. Selected bond lengths (A (◦ ): Fe(1)–S(1) 2.2598(10), Fe(1)–S(2) 2.2707(10), Fe(1)–S(3) 2.2661(10), Fe(1)–S(4) 2.2691(11), Fe(2)–S(2) 2.3153(11), Fe(2)–S(4) 2.3090(10), Fe(2)–S(6) 2.3004(10), Fe(2)–S(8) 2.3011(10), Fe(3)–S(1) 2.2652(10), Fe(3)–S(3) 2.2790(10), Fe(3)–S(5) 2.2885(11), Fe(3)–S(7) 2.2756(11), Fe(4–7)–S 2.4802(10)–2.5238(11), Fe–OP–O 1.989(2)–2.024(3), Fe–ODME 2.226(3)–2.279(3), S(5)–P(1) 2.0809(14), S(6)–P(2) 2.0660(13), S(7)–P(3) 2.0789(14), S(8)–P(4) 2.0695(13), P–O 1.507(3)–1.518(3), O(2)–P(1)–O(1) 114.87(15), O(4)–P(2)–O(5) 114.30(15), O(2)–P(1)–C 108.11(15), O(1)–P(1)–C 107.51(17), O(2)–P(1)–S(5) 110.32(12), O(1)–P(1)–S(5) 111.96(11), C–P(1)–S(5) 103.31(13).
This journal is © The Royal Society of Chemistry 2008
surrounded by a unique arrangement of octahedrally coordinated Fe atoms. The outer Fe atoms are coordinated by O atoms of the new [RPO2 S]2− anion and DME solvent. Each of the S(1–4) atoms bridges two outer Fe atoms completing their octahedral coordination environment and linking them to the inner tetrahedrally coordinated Fe atoms. Remaining electron density in the extended solid state structure of 1 and the size of the void was consistent with an additional water molecule being present and furthermore the presence of a hydroxide anion was ruled out on the basis of the infra-red spectrum of dried crystals which showed no OH bands. Attempts to investigate the reaction mechanism leading to the formation of 1 in detail were made, but ESI-MS and GC-MS of reaction mixtures did not provide further insight. It is known from previous investigations, however, that the formation of sulfide anions in reactions of L.R. with metal carboxylates can happen, in particular when thiophilic metal ions are present.15 With regard to the potential functionalisation of biomolecules that contain thiophosphate, the iron system we have looked at here indicates potential for future work. In 1, iron atoms are coordinated both by oxygen and sulfur donor centres of the new [RPO2 S]− anion. In future possibly Fe(II)–S clusters or neutral coinage metal particles that only attach to sulfur sites in thiophosphate-functionalised biomolecules could be incorporated. For the synthesis of 2, excess [Fe3 (l3 -O)(l2 -piv)6 (H2 O)3 ](piv) was used (Scheme 2). It is likely that pivalato anions and water were involved in the formation of the phosphonato anions. The fact that elemental sulfur was formed indicates the complexity of the reaction mixture and it is assumed that also Fe(II) species are formed. In the solid-state structure of 2 the structural motif of l3 -O atoms present within the starting material is retained (O27–30, Fig. 2). The [RPO3 ]2− anions generated in the reaction occupy three empty sites in the extended iron-oxo-carboxylate cage. Two of the O atoms of [RPO3 ]2− anions are bridging two Fe atoms whilst the remaining oxygen atom is coordinated to one Fe atom. t Bu-groups solubilize the cage arrangement and Ocarboxylate -atoms coordinate one or bridge two Fe atoms (e.g., O17, O18). The remarkable assembly of thirteen carboxylate groups, nine Fe(III) centres and three phosphonato anions has been observed before and its magnetic properties have been investigated.23,25 The clusters [Fe9 (l3 -O)4 (RPO3 )3 (piv)13 ] (R = camphyl, phenyl) are isostructural to 2 and were obtained by the reaction of the phosphonic acid and [Fe3 O(piv)6 (H2 O)3 ]X (X = Cl, piv).23–26 This suggests, that 2 could also be obtained by a more straightforward reaction than the one reported here (Scheme 2). It was shown that a nonsolvated trinuclear oxo-centred iron carboxylates can oxygenate P atoms in the neutral P–S ligand precursor L.R. The reaction is quite complex and subject of ongoing studies. A first result has been the preparation of the novel complex 1. It is believed complexes with mixed P–O/S anions feature interesting magnetic interactions and may stimulate research and serve as models for small particles that can be attached to thiophosphorylated biomolecules. The crystal structures‡‡ were solved and refined with the SHELXTL programme package.27 The SQUEEZE option in PLATON was used to correct for a solvent molecule in 1.28,29 In the lattice disordered components were refined using isotropic temperature factors. Dalton Trans., 2008, 1136–1139 | 1137
View Online
Downloaded by KIT on 01 March 2011 Published on 23 January 2008 on http://pubs.rsc.org | doi:10.1039/B717583C
* 1: To a stirring solution of [Fe3 (l3 -O)(l2 -piv)6 (H2 O)3 ](piv) (0.351 g, 0.371 mmol) in 10 mL DME was added Lawesson’s reagent (0.150 g, 0.371 mmol). The mixture became black and a dark green precipitate formed. The suspension was stirred overnight, during which time the precipitate was almost dissolved. The resulting solution was filtered off, evaporated under vacuum to one half of the initial volume. The next day large black crystals of 1 were obtained. They were carefully separated from the mother liquor with a syringe, washed with 5 mL DME and 5 mL hexane and dried under vacuum. 0.05 g, yield 17% (based on [Fe3 (l3 -O)(l2 piv)6 (H2 O)3 ](piv) supplied). Mp > 250 ◦ C (decomposed, black solid); Found: C, 31.31; H, 3.97. C44 H68 Fe7 O20 P4 S8 requires C, 31.30; H, 4.06% (corresponds to loss of lattice DME); mmax /cm−1 (Nujol) 1593, 1498, 1291, 1250, 1171, 1121, 1101, 1067, 1023, 1005, 856, 827, 799, 647, 630, 567, 514, 464. †† 2: A solution of [Fe3 (l3 -O)(l2 -piv)6 (H2 O)3 ](piv) (0.702 g, 0.742 mmol) in 15 mL DME was added to Lawesson’s reagent (0.150 g, 0.371 mmol) under stirring. The mixture became black with the formation of a green precipitate. The suspension was stirred overnight and filtered. The filtrate was evaporated under vacuum to one half of the initial volume. During the first week light yellow crystals of elemental sulfur were isolated. They were filtered off, and the filtrate was again left standing. During the second week brown hexagonal plates of the compound 2 were observed. They were carefully separated from the mother liquor by a syringe, washed with 5 mL hexane and dried under vacuum. 0.07 g, yield 12%. Mp > 250 ◦ C (decomposed, black solid); Found: C, 41.22; H, 5.79. C86 H138 Fe9 O44 P3 requires C, 42.34; H, 5.70% (despite repeated attempts, a better analysis for 2 could not be obtained); mmax /cm−1 (Nujol) 1601, 1559, 1504, 1256, 1232, 1144, 1120, 1041, 1013, 968, 829, 787, 604, 530, 477, 442. ‡‡ Crystal data for 1·2DME·H2 O: C52 H90 Fe7 O25 P4 S8 , M = 1886.60, monoclinic, a = 15.2153(8), b = 34.5374(7), c = 15.3203(19), b = ˚ 3 , T = 150(2) K, space group P21 /c (no. 14), 106.522(4)◦ , U = 7718.4(11) A Z = 4, l(Mo-Ka) = 1.646 mm−1 , 38771 reflections measured, 16107 unique (Rint = 0.0523) which were used in all calculations. wR2 (all data) = 0.1080, R1 = 0.0418. 2: C90 H148 Fe9 O44 P3 , M = 2529.64, monoclinic, a = 15.606(3), ˚ , b = 90.34(3)◦ , U = 12030(4) A ˚ 3 , T = 150(2) b = 28.593(6), c = 26.961(5) A K, space group P21 /n (no. 14), Z = 4, l(Mo-Ka) = 1.170 mm−1 , 69741 reflections measured, 26260 unique (Rint = 0.1115) which were used in all calculations. wR2 (all data) = 0.2093, R1 (I > 2r(I)) = 0.0755. CCDC reference numbers 667685–667686. For crystallographic data in CIF or other electronic format see DOI: 10.1039/b717583c
Fig. 2 Solid-state structure of 2. Top: Only a-C atoms of 4-anisyl substituents at phosphorus atoms are displayed; methyl groups of t Bu groups are omitted. Bottom: Structure of the core of 2 without C atoms; only l3 -O atoms O(27–30) and O atoms of phosphonato ligands are ˚ ): Fe–(l3 -O) 1.864(5)–2.027(6), Fe–OP–O labelled. Selected bond lengths (A 1.943(6)–2.307(5), Fe–Opiv 1.964(6)–2.082(5), P–O 1.518(6)–1.549(5).
Acknowledgements We thank the DFG Centre for Functional Nanostructures (W.S.) and the Forschungszentrum Karlsruhe for financial support. A. R. thanks Professor Dieter Fenske for his support.
Notes and references ¶ Fe3 (l3 -O)(l2 -piv)6 (H2 O)3 ](piv) was prepared by a slightly modified literature procedure.24 A slurry of [Fe(NO3 )3 ·9H2 O] (10.0 g, 24.8 mmol) and Hpiv (28.0 g, 274 mmol) was heated and maintained at reflux over 2 h until the elimination of NO2 stopped. Upon cooling to 100 ◦ C, ethanol (85 ml) and water (15 ml) were added slowly under stirring. Overnight, red-brown hexagonal prisms were formed and were filtered off, washed with benzene and hexane and dried in vacuum leading to solvent-free [Fe3 O(piv)6 (H2 O)3 ](piv). Yield 6.5 g (83.4%). Found: C, 44.62; H, 7.47. Calcd. for C35 H69 Fe3 O18 : C, 44.46; H, 7.36%.
1138 | Dalton Trans., 2008, 1136–1139
1 K. Maeda, Microporous Mesoporous Mater., 2004, 73, 47–55. 2 S. Maheswaran, G. Chastanet, S. J. Teat, T. Mallah, R. Sessoli, W. Wernsdorfer and R. E. P. Winpenny, Angew. Chem., 2005, 44, 5044– 5048. 3 E. I. Tolis, M. Helliwell, S. Langley, J. Raftery and R. E. P. Winpenny, Angew. Chem., 2003, 42, 3804–3808. 4 A. Clearfield, Curr. Opin. Solid State Mater. Sci., 2002, 6, 495–506. 5 M. G. Walawalkar, H. W. Roesky and R. Murugavel, Acc. Chem. Res., 1999, 32, 117–126. 6 A. Clearfield, Prog. Inorg. Chem., 1998, 47, 371–510. 7 A. Clearfield, Curr. Opin. Solid State Mater. Sci., 1996, 1, 268–278. 8 K. Kerman and H.-B. Kraatz, Chem. Commun., 2007, 5019–5021. 9 E. Roduner, Chem. Soc. Rev., 2006, 35, 583–592. 10 D. Fenske, A. Rothenberger and M. Shafaei-Fallah, Eur. J. Inorg. Chem., 2005, 59–62. 11 D. Fenske, A. Rothenberger and M. Shafaei-Fallah, Z. Anorg. Allg. Chem., 2004, 630, 943–947. 12 A. Rothenberger, W. Shi and M. Shafaei-Fallah, Chem.–Eur. J., 2007, 13, 5974–5981. 13 W. Shi, M. Shafaei-Fallah, C. E. Anson and A. Rothenberger, Dalton Trans., 2005, 3909–3912. 14 W. Shi and A. Rothenberger, Eur. J. Inorg. Chem., 2005, 2935–2937. 15 W. Shi, R. Ahlrichs, C. E. Anson, A. Rothenberger, C. Schrodt and M. Shafaei-Fallah, Chem. Commun., 2005, 5893–5895. 16 W. Shi, M. Shafaei-Fallah, L. Zhang, C. E. Anson, E. Matern and A. Rothenberger, Chem.–Eur. J., 2007, 13, 598–603. 17 W. Shi, R. Kelting, M. Shafael-Fallah and A. Rothenberger, J. Organomet. Chem., 2007, 692, 2678–2682. 18 W. Shi, L. Zhang, M. Shafaei-Fallah and A. Rothenberger, Z. Anorg. Allg. Chem., 2007, 633, 440–442. 19 L. Wang, S. Chen, T. Xu, K. Taghizadeh, J. S. Wishnok, X. Zhou, D. You, Z. Deng and P. C. Dedon, Nat. Chem. Biol., 2007, 3, 709–710.
This journal is © The Royal Society of Chemistry 2008
View Online
24 A. S. Batsanov, Y. T. Struchkov and G. A. Timko, Koord. Khim., 1988, 14, 266–270. 25 S. Konar, N. Bhuvanesh and A. Clearfield, J. Am. Chem. Soc., 2006, 128, 9604–9605. 26 A. B. Blake and L. R. Fraser, J. Chem. Soc., Dalton Trans., 1975, 193–197. ¨ 27 G. M. Sheldrick, SHELXTL, University of Gottingen, Germany, 1997. 28 A. L. Spek, J. Appl. Crystallogr., 2003, 36, 7–13. 29 P. Van Der Sluis and A. L. Spek, Acta Crystallogr., Sect. A, 1990, 46, 194–201.
Downloaded by KIT on 01 March 2011 Published on 23 January 2008 on http://pubs.rsc.org | doi:10.1039/B717583C
20 I. P. Gray, P. Bhattacharyya, A. M. Z. Slawin and J. D. Woollins, Chem.–Eur. J., 2005, 11, 6221–6227. 21 M. J. Pilkington, A. M. Z. Slawin, D. J. Williams, P. T. Wood and J. D. Woollins, Heteroat. Chem., 1990, 1, 351. 22 B. S. Pedersen, S. Scheibye, K. Clausen and S. O. Lawesson, Bull. Soc. Chim. Belg., 1978, 87, 293–297. 23 E. I. Tolis, L. P. Engelhardt, P. V. Mason, G. Rajaraman, K. Kindo, M. ¨ Luban, A. Matsuo, H. Nojiri, J. Raftery, C. Schroder, G. A. Timco, F. Tuna, W. Wernsdorfer and R. E. P. Winpenny, Chem.–Eur. J., 2006, 12, 8961–8968.
This journal is © The Royal Society of Chemistry 2008
Dalton Trans., 2008, 1136–1139 | 1139
