Inorg. Chem. 2007, 46, 9743−9753
Synthesis, Structural, and Magnetic Studies on a Redox Family of Tetrametallic Vanadium Clusters: {VIV4}, {VIII2VIV2}, and {VIII4} Butterfly Complexes Ian S. Tidmarsh,† Emma Scales,† Paul R. Brearley,† Joanna Wolowska,‡ Lorenzo Sorace,*,§ Andrea Caneschi,§ Rebecca H. Laye,*,† and Eric J. L. McInnes*,† School of Chemistry, The UniVersity of Manchester, Manchester M13 9PL, U.K; EPSRC c.w. EPR SerVice Centre, School of Chemistry, The UniVersity of Manchester, Manchester M13 9PL, U.K; Dipartimento di Chimica, UniVersita` di Firenze, and UdR INSTM, Via della Lastruccia 3, Sesto Fiorentino, Italy Received June 7, 2007
The synthesis, crystal structures, and magnetic properties are reported for a redox family of butterfly-type tetrametallic vanadium alkoxide clusters, namely [V2(VO)2(acac)4(RC{CH2O}3)2] (R ) Me 1, Et 2, CH2OH 3), [V2(VO)2(acac)2(O2CPh)2(MeC{CH2O}3)2] (5), [(VO)4(MeOH)2(O2CPh)2({HOCH2}C{CH2O}3)2] (6), [V4Cl2(dbm)4(RC{CH2OH}3)2] (R ) Me 7, Et 8, CH2OH 9), and [V4Cl2(dbm)4(MeO)6] (10). The cluster cores are {VIV4} (6), {VIII2VIV2} (1−5), and {VIII4} (7−10), with examples of both isomeric forms of the of the mixed-valence cores (either VIII or VIV ions forming the butterfly body). Magnetic studies reveal the clusters to be dominated by antiferromagnetic exchange interactions in each case. The magnetic exchange parameters are determined for representative examples of each core type. {VIV4} and {VIII4} have diamagnetic ground states. The two isomeric {VIII2VIV2} types are found to give rise to either an S ) 0 ground state with a number of low-lying excited states due to competing antiferromagnetic exchange interactions (VIII2 butterfly body) or to a well-isolated S ) 1 ground state (VIV2 butterfly body).
Introduction Vanadium-cluster chemistry has extraordinary flexibility due to the range of available metal oxidation states and coordination geometries. However, the literature is dominated by the high-valent, VIV/V chemistry - the important polyoxovanadates and related species.1 Recently, we have been exploring the cluster chemistry of lower-valent states in an attempt to prepare interesting magnetic clusters based on the VIII ion. This d2, S ) 1 ion typically exhibits a large zerofield splitting (ZFS)2 and, hence, is attractive as a building * To whom correspondence should be addressed. E-mail: eric.mcinnes@ manchester.ac.uk. † School of Chemistry, The University of Manchester. ‡ EPSRC c.w. EPR Service Centre, School of Chemistry, The University of Manchester. § Dipartimento di Chimica, Universita ` di Firenze, and UdR INSTM. (1) For example, see: (a) Pope, M. T.; Mu¨ller, A. Angew. Chem., Int. Ed. 1991, 30, 34. (b) Chen, Q.; Zubieta, J. Coord. Chem. ReV. 1992, 114, 107. (c) Zubieta, J. Mol. Eng. 1993, 3, 93. (d) Khan, M. I.; Zubieta, J. Prog. Inorg. Chem. 1995, 43, 1. (2) (a) Tregenna-Piggott, P. L. W.; Weihe, H.; Bendix, J.; Barra, A.-L.; Gu¨del, H. U. Inorg. Chem. 1999, 38, 5928. (b) Krzystek, J.; Fiedler, A. T.; Sokol, J.; Ozarowski, A.; Zvyagin, S. A.; Brunold, T. C.; Long, J. R.; Brunel, L-C.; Telser, J. Inorg. Chem. 2004, 43, 4654.
10.1021/ic7011183 CCC: $37.00 Published on Web 10/05/2007
© 2007 American Chemical Society
block toward magnetic materials such as single-molecule magnets. Indeed, Christou has reported a {VIII4} cluster that exhibits SMM behavior.3 However, there are very few lowvalent VIII or VIII/IV clusters in the literature4,5 due to the reducing nature of VIII and the inherent stability of the {VIVO}2+ vanadyl and {VVO}3+ ions. We have been successful in preparing several large homovalent VIII 6 and heterovalent VIII/IV 7 clusters by exploiting solvothermal synthetic methods in alcohols, with nuclearities of up to 10 for the former6a and 18 for the latter (VIII16VIV2)7b. However, whereas there are a few important magnetic studies on small (3) Castro, S. L.; Sun, Z.; Grant, C. M.; Bollinger, J. C.; Hendrickson D. N.; Christou, G. J. Am. Chem. Soc. 1998, 120, 2365. (4) (a) Lee, I. S.; Long, J. R. Chem. Commun. 2004, 3234. (b) Fry, F. H.; Dougan, B. A.; McCann, N.; Ziegler, C.; Brasch, N. E. Inorg. Chem. 2005, 44, 5197. (c) Kumagai, H.; Kitagawa, S. Chem. Lett. 1996, 471. (d) Salta, J.; Zubieta, J. J. Cluster Sci. 1996, 7, 531. (5) Mikuriya, M.; Kotera, T.; Adachi F.; Bandow, S. Chem. Lett. 1993, 945. (6) (a) Laye, R. H.; Murrie, M.; Ochsenbein, S.; Bell, A. R.; Teat, S.; Raftery, J.; Gu¨del, H. U.; McInnes, E. J. L. Chem. Eur. J. 2003, 9, 6215. (b) Laye, R. H.; Larsen, F. K.; Overgaard, J.; Muryn, C. A.; McInnes, E. J. L.; Rentschler, E.; Sanchez, V.; Teat, S. J.; Gu¨del, H. U.; Waldmann, O.; Timco, G. A.; Winpenny, R. E. P. Chem. Commun. 2005, 1125.
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Tidmarsh et al. Scheme
1a
a Top: Representation of a {V } butterfly-type vanadium alkoxide core 4 (top), showing possible magnetic exchange interactions between the body (Jbb) and between the body and wingtip (Jwb1 and Jwb2; Jwb1 ) Jwb2 for a regular rhombus) metal ions. Bottom: Metal oxidation states in the cores of 1-10 reported in this work.
VIV clusters,8,9 which give insight into larger systems, interpretation of the magnetic data of large VIII or VIII/IV species is hampered by the lack of data for smaller examples. There are some important studies, including Christou’s tetramer,3 Wieghardt’s remarkably strongly ferromagnetically coupled VIII dimer,10 and a theoretical study on VIII-OVIII coupling by Weihe and Gu¨del.11 However, well-studied examples larger than dimers12 are rare. Mikuriya’s5 {VIII2VIV2} cluster [V2(VO)2(acac)4(OMe)6] was intriguing to this end because as well as being the only VIII/IV tetrametallic cluster reported to date, it is based on the well-known butterfly structural motif (Scheme 1). Related {VV4} and {VIV4} alkoxide-bridged butterfly complexes have been reported: Crans and co-workers’ [(VO)4(MeC{CH2O}3)2(OMe)6]13 and Plass’ [(VO)4(acac)2(Htea)2(OMe)2]14 and [(VO)4(acac)2(L)2(OMe)2]15 [MeC{CH2OH}3 ) tris-(hydroxymethyl)ethane; H3tea ) triethanolamine; H2L ) N,Nbis(2-hydroxyethyl)-N′-(2-pyrrolyl-methylidene)ethylenediamine]. These clusters imply that this butterfly cluster core, bridged by alkoxides, can stabilize a range of oxidation states. Zubieta1d and Mu¨ller16 have noted the ability of alkoxides to stabilize fully reduced, all-VIV, polyoxo(alkoxo)vanadates (7) (a) Laye, R. H.; Wei, Q.; Mason, P. V.; Shanmugan, M.; Teat, S. J.; Brechin, E. K.; Collison, D.; McInnes, E. J. L. J. Am. Chem. Soc. 2006, 128, 9020. (b) Tidmarsh, I. S.; Laye, R. H.; Brearley, P. R.; Shanmugan, M.; San˜udo, E. C.; Sorace, L.; Caneschi, A.; McInnes, E. J. L. Chem. Commun. 2006, 2560. (c) Shaw, R.; Laye, R. H.; Jones, L. F.; Low, D. M.; Talbot-Eeckelaers, C.; Wei, Q.; Milios, C. J.; Teat, S.; Helliwell, M.; Raftery, J.; Evangelisti, M.; Affronte, M.; Collison, D.; Brechin, E. K.; McInnes, E. J. L. Inorg. Chem. 2007, 46, 4968. (d) Tidmarsh, I. S.; Laye, R. H.; Brearley, P.R.; Shanmugam, M.; San˜udo, E. C.; Sorace, L.; Caneschi, A.; McInnes, E. J. L. Chem.s Eur. J. 2007, 13, 6329. (8) Plass, W. Angew. Chem., Int. Ed. Engl. 1996, 35, 627. (9) Hegetschweiler, K.; Morgenstern, B.; Zubieta, J.; Hagrman, P. J.; Lima, N.; Sessoli R.; Totti, F. Angew. Chem., Int. Ed. 2004, 43, 3436. (10) Knopp, P.; Wieghardt, K.; Nuber, B.; Weiss, J.; Sheldrick, W.S. Inorg. Chem. 1990, 29, 363. (11) Weihe, H.; Gu¨del, H. U. J. Am. Chem. Soc. 1998, 120, 2870. (12) Kanamori, K.; Coord. Chem. ReV. 2003, 237, 147, and references therein. (13) Crans, D. C.; Jiang, F.; Chen, J.; Anderson, O. P.; Miller, M. M. Inorg. Chem. 1997, 36, 1038. (14) Plass, W. Eur. J. Inorg. Chem. 1998, 799. (15) Plass, W. Inorg. Chem. 1997, 36, 2200. (16) Mu¨ller, A.; Meyer, J.; Bogge, H.; Stammler, A.; Botar, A. Chem.s Eur. J. 1998, 4, 1388.
9744 Inorganic Chemistry, Vol. 46, No. 23, 2007
by reducing charge density cf. naked polyoxovanadates. Given our success with stabilizing large VIII and VIII/IV clusters by solvothermal synthesis in alcohols, we reasoned that we should be able to extend the vanadium butterfly family to include {VIII4} and other {VIII2VIV2} species. Mikuriya’s complex was prepared by the reduction of [VO(acac)2] with a thiolate in MeOH/CH2Cl2 (the yield was not reported).5 In this work, we report a much-more facile synthesis, via a solvothermal route and in excellent yields, of four new {VIII2VIV2} clusters. These have analogous alkoxide-bridged butterfly cores, and, moreover, provide examples where the butterfly bodies are VIII (type A, Scheme 1; as in Mikuriya’s compound) and the previously unknown isomeric core, where the VIV ions form the butterfly body (type B, Scheme 1). Furthermore, we report the synthesis of four examples of the all-VIII analogues of this core formally by the substitution of {VIVdO}2+ with the isoelectronic fragment {VIII-Cl}2+ - again by solvothermal methods and in excellent yields. We also report a new example of the all-VIV core. Hence, these complexes represent a unique redox family of compounds. Magnetic studies are presented for examples of the {VIV4}, both forms of the {VIII2VIV2} and the {VIII4} species, allowing the comparison of the magnetic exchange coupling constants and consequent electronic structure throughout the family. Experimental Section Physical Measurements. IR data was measured on KBr pellets on a PerkinElmer FTIR spectrometer. MS measurements were conducted on either a VG Trio 2000 (electrospray) or on a Waters Micro mass TofSpec 2E (MALDI) spectrometer. EPR data were collected on ESP-300 (Q-band) and Elexsys E600 (W band) spectrometers. Variable-temperature magnetic data were measured with a Cryogenic S600 SQUID magnetometer on polycrystalline samples in 1 (300-35 K) and 0.1 ( 2σ(I)] no. of params R(F) wR2 ∆Fmin (eÅ-3) ∆Fmax (eÅ-3)
1
2
3
4
5
C32H49O16NV4 907.48 0.39 × 0.28 × 0.15
C32H50O16V4 894.48 0.41 × 0.30 × 0.21
C30H46O18V4 898.43 0.44 × 0.41 × 0.40
C30H46O16V4 866.43 0.54 × 0.41 × 0.26
C30H46O18V4 938.49 0.41 × 0.34 × 0.24
monoclinic C2/c 23.992(3) 11.0699(6) 16.632(2) 90 117.814(3) 90 3907.1(7) 4 1.543 100(2) 63.74 12 238 (3284) 2190
orthorhombic Pbca 16.4089(6) 14.1745(5) 16.5690(5) 90 90 90 3853.7(2) 4 1.542 100(2) 63.97 37 290 (5862) 4219
orthorhombic Pbca 15.6887(16) 13.5545(14) 17.3368(19) 90 90 90 3686.7(7) 4 1.619 100(2) 64.06 22 957 (3096) 1942
monoclinic P2(1)/n 10.2091(4) 15.6663(7) 11.3058(5) 90 91.770(3) 90 1807.37(13) 2 1.592 100(2) 63.79 17 947 (5480) 4265
monoclinic P2(1)/n 9.2831(3) 11.1266(4) 19.4966(7) 90 102.773(3) 90 1963.96(12) 2 1.587 100(2) 63.51 5126 (2562) 2282
246 0.0446 0.1090 -0.862 0.505
240 0.0357 0.0978 -0.468 0.890
240 0.0504 0.1093 -0.481 0.688
231 0.0283 0.0763 -0.446 0.762
256 0.0356 0.0976 -0.516 0.393
Table 2. Unit-Cell Details of 6-10
formula fw cryst dimensions (mm) cryst syst space group a (Å) b (Å) c (Å) R (deg) β (deg) γ (deg) U (Å3) Z Fcalcd T (K) 2θmax data collected (unique) data used [I > 2σ(I)] no. of params R(F) wR2 ∆Fmin (eÅ-3) ∆Fmax (eÅ-3)
6
7
8
9
10
C30H52O22V4 968.48 0.35 × 0.30 × 0.15
C74H70O15Cl2V4 1473.96 0.43 × 0.27 × 0.05
C72H66O14Cl2V4 1429.91 0.44 × 0.32 × 0.20
C72.5H67O16.5N1Cl2V4 1490.93 0.50 × 0.25 × 0.20
C66H62O14Cl2V4 1353.82 0.36 × 0.21 × 0.19
triclinic P1h 11.067(8) 12.034(9) 17.256(13) 102.367(14) 94.480(13) 114.203(12) 2012(3) 2 1.599 100(2) 56.4 12 398 (8804) 6891
monoclinic C2/c 24.473(6) 11.0449(15) 25.0270(3) 90 104.667(13) 90 6544(2) 4 1.496 100(2) 63.80 21 436 (6657) 5127
triclinic P1h 11.1495(4) 13.4573(4) 22.8482(8) 78.970(3) 89.538(3) 68.743(3) 3128.88(18) 2 1.518 100(2) 63.79 23 547 (12684) 10 377
tetragonal I4(1)/a 28.1794(14) 28.1794(14) 17.0456(12) 90 90 90 13535.5(13) 8 1.463 100(2) 54.16 38 660 (6941) 4954
monoclinic P2(1)/c 10.7183(16) 25.3971(18) 11.8682(11) 90 108.142(11) 90 3070.1(6) 2 1.464 100(2) 56.32 21 984 (6263) 4256
516 0.0618 0.1681 -1.056 1.021
448 0.0834 0.1741 -0.880 0.714
831 0.0427 0.1172 -0.836 1.032
466 0.0374 0.0991 -0.238 0.774
391 0.0326 0.0795 -0.410 0.379
({HOCH2}C{CH2O}3) 3- ligand of 9, which is disordered over three sites. Hydrogen atoms were added in geometrically calculated positions. Crystal details are summarized in Tables 1 and 2. Synthesis. All of the chemicals were purchased from Aldrich, except for [VO(acac)2], which was purchased from Lancaster, and were used without further purification. [VCl3(THF)3], [V3(O)(PhCO2)6(H2O)3]Cl, and Na(dbm) were prepared by published procedures.19 All of the solvents were from BDH; THF and MeCN (19) (a) Manzer, L. E. Inorg. Synth. 1982, 21, 135. (b) Smith, A. Ph.D. Thesis, The University of Manchester, Manchester, U.K., 1999. (c) Halcrow, M. A.; Sun, J.-S.; Huffman, J. C.; Christou, G. Inorg. Chem. 1995, 34, 4167.
were distilled before use, using standard procedures.20 For the synthesis of all of the compounds, all of the manipulations were conducted under anaerobic conditions (dinitrogen-purged glove box and argon-served Schlenk line), with the exception of 6, which was prepared aerobically. General Procedure for the Synthesis of [V2(VO)2(acac)4(RC{CH2O}3)2] (1-3). [V(acac)3] (0.25 g, 0.72 mmol), [VO(acac)2] (0.190 g, 0.72 mmol), RC(CH2OH)3 [R ) Me 0.086 g (1), Et 0.096 g (2), CH2OH 0.098 (3), 0.72 mmol], and MeCN (9 mL) were (20) Furniss, B. S.; Hannaford, A. J.; Smith, P. W. G.; Tatchell, A. R.; Vogel’s Textbook of Practical Organic Chemistry, 5th Ed.; Longman Scientific and Technical: Sussex, U.K., 1989.
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Tidmarsh et al. placed in a sealed Teflon container (Parr) and heated for 12 h at 150 °C. X-ray quality crystals of the product were filtered from the cooled MeCN and dried in vacuo. [V2(VO)2(acac)4(MeC{CH2O}3)2].MeCN (1): 58% yield. MALDI-MS (dithranol matrix, CH2Cl2 solution), m/z: 866 (molecular ion), 850 (M - O2-), 767 (M - acac-). Anal., observed (Calcd for C32H49O15NV4): C, 42.20 (42.35), H, 5.40 (5.44), N, 1.54 (1.54), V, 22.34 (22.45). Selected IR data (KBr), ν (cm-1): 3468, 2912, 1557, 1354, 1280, 1126, 1034, 971, 784, 547. [V2(VO)2(acac)4(EtC{CH2O}3)2] (2): 74% yield. MALDI-MS (dithranol matrix, CH2Cl2 solution), m/z: 894 (molecular ion), 878 (M - O2-), 795 (M - acac-). Anal., observed (Calcd for C32H50O16V4): C, 42.94 (42.97), H, 5.48 (5.63), V, 22.51 (22.78). IR (KBr), ν (cm-1): 3468, 2913, 1538, 1359, 1280, 1117, 1052, 972, 545, 501. [V2(VO)2(acac)4({HOCH2}C{CH2O}3)2] (3): 78% yield. MALDI-MS (dithranol matrix, CH2Cl2 solution), m/z: 898 (molecular ion), 882 (M - O2-), 799 (M - acac-). Anal., observed (Calcd for C30H46O18V4): C, 40.38 (40.11), H, 5.06 (5.16), V, 21.91 (22.68). IR (KBr), ν (cm-1): 3497, 2911, 1525, 1376, 1117, 1021, 975, 934, 804, 645. Synthesis of [V2(VO)2(acac)4(MeC{CH2O}3)2] (4). The synthesis of 1 was repeated but using THF as solvent. 73% yield. MALDI-MS (dithranol matrix, CH2Cl2 solution), m/z: 866 (molecular ion), 850 (M - O2-), 767 (M - acac-). Anal., observed (Calcd for C30H46O16V4): C, 41.73 (41.59), H, 5.45 (5.35), V, 22.87 (23.52). IR (KBr), ν (cm-1): 3468, 2912, 1557, 1354, 1280, 1126, 1033, 971, 784, 547. Synthesis of [V2(VO)2(acac)2(O2CPh)2(EtC{CH2O}3)2] (5). [V(acac)3] (0.25 g, 0.72 mmol), [VO(acac)2] (0.190 g, 0.72 mmol), EtC{CH2OH}3 (0.096 g, 0.72 mmol), PhCO2H (0.088 g, 0.72 mmol), and MeCN (9 mL) were placed in a sealed Teflon container and heated for 12 h at 200 °C. X-ray quality crystals of 5 were filtered from the cooled MeCN solution, in a 55% yield. MALDIMS (dithranol matrix, in CH2Cl2 solution), m/z: 938 (molecular ion), 922 (M - O2-), 817 (M - O2CPh-). Anal., observed (Calcd for C36H46O16V4): C, 46.15 (46.07), H, 4.96 (4.96), V, 21.87 (21.71). IR (KBr), ν (cm-1): 3450, 2922, 1537, 1398, 1331, 1047, 982, 946, 725, 560. Synthesis of [(VO)4(MeOH)2(O2CPh)2({HOCH2}C{CH2O}3)2]. 4MeOH(6).[V3(O)(PhCO2)6(H2O)3]Cl(0.25g,mmol),{HOCH2}C{CH2OH}3 (0.035 g, 0.25 mmol), and MeOH (9 mL) were placed in a sealed Teflon container and heated for 12 h at 100 °C. X-ray quality crystals of 6 were formed on standing of the cooled solution for 1 d (31%). Electrospray (in MeOH solution), m/z: 807 (M -OMe-). Anal., observed (Calcd for C30H52O22V4): C, 37.61 (37.20), H, 5.91 (5.41), V, 21.36 (21.04). IR (KBr), ν (cm-1): 3436, 2929, 1532, 1405, 1122, 1024, 966, 723, 656, 558. General Procedure for the Synthesis of [V4Cl2(dbm)4(RC{CH2OH}3)2] (7-9). [VCl3(THF)3] (0.2 g, 0.54 mmol), Na(dbm) (0.26 g, 1.07 mmol), RC(CH2OH)3 [R ) Me 0.064 g (7), Et 0.072 g (8), CH2OH 0.073 (9), 0.54 mmol], and THF (7, 8) or MeCN (9) (9 mL) were heated in a sealed Teflon container for 12 h at 150 °C. X-ray quality crystals of product were filtered immediately from the cooled THF or MeCN solution and dried in vacuo. Filtration must be carried out immediately to avoid the precipitation of NaCl which occurs within a few minutes of opening the Teflon container. [V4Cl2(dbm)4(MeC{CH2O}3)2]‚THF (7): 84% yield. Anal. (%), observed (Calcd for C74H70O15Cl2V4): C, 60.30 (60.30), H, 4.44 (4.79), Cl, 5.00 (4.81), V, 13.63 (13.82). IR (KBr), ν (cm-1): 2919, 1590, 1478, 1320, 1227, 1025, 762, 721, 686, 522. [V4Cl2(dbm)4(EtC{CH2O}3)2] (8): 66% yield. Anal. (%), observed (Calcd for C72H66O14Cl2V4): C, 60.39 (60.48), H, 4.57 (4.65), Cl, 5.12 (4.96), V, 14.11 (14.25). IR (KBr), ν (cm-1): 294, 1589, 1527, 1337, 1227, 1041, 761, 718, 684, 523. [V4Cl2(dbm)4({HOCH2}C-
9746 Inorganic Chemistry, Vol. 46, No. 23, 2007
Table 3. Selected Structural Parameters for 1-4 1 V(1)‚‚‚V(2) V(1)‚‚‚V(2A) V(2)‚‚‚V(2A)
3.237 3.221 3.191
V(1)-O(8) V(1)-O(1) V(1)-O(2) V(2)-O(3) V(2)-O(4)
1.992(2) 1.993(2) 1.979(2) 1.973(2)
V(1)-O(5) V(1)-O(6A) V(1)-O(7A) V(2)-O(6A) V(2)-O(6) V(2)-O(5) V(2)-O(7)
2a 3.244 3.241 3.173
4a
3.244 3.231 3.182
3.236 3.243 3.185
V-O(vanadyl) 1.598(2) 1.6031(13)
1.601(3)
1.6304(11)
V-O(acac) 1.9818(13) 1.9875(13) 1.9708(13) 1.9717(13)
1.989(3) 1.992(3) 1.965(3) 1.969(3)
1.9865(10) 1.9793(10) 1.9753(9) 1.9627(9)
V-O(tris-alkoxide)a 2.008(2) 2.0154(12) 2.318(2) 2.3474(12) 2.016(2) 2.0092(12) 2.070(2) 2.0705(12) 2.067(2) 2.0646(12) 1.953(2) 1.9552(12) 1.956(2) 1.9559(12)
2.023(3) 2.338(3) 2.021(3) 2.082(3) 2.061(3) 1.959(3) 1.966(3)
2.0149(9) 2.3367(9) 2.0229(9) 2.0760(9) 2.0692(9) 1.9584(9) 1.9588(9)
M-O(tris-alkoxide)-M V(1)-O(5)-V(2) 109.61(10) 109.55(6) V(1)-O(7A)-V(2A) 108.39(10) 109.67(6) V(1)-O(6A)-V(2A) 94.39(8) 94.34(5) V(1)-O(6A)-V(2) 94.90(8) 94.27(5) V(2)-O(6)-V(2A) 100.92(9) 100.24(5) aLabeled
3a
109.09(16) 109.06(4) 108.26(15) 109.09(4) 94.29(12) 94.62(3) 94.24(12) 94.15(3) 100.37(14) 100.41(4)
on the basis of the atomic numbering of 1, for simplicity.
{CH2O}3)2]‚MeCN‚0.5MeOH (9): 72% yield. MALDI-MS (dithranol matrix, THF solution), m/z: 1433 (M+), 1397 (M - Cl-). Anal. (%), observed (Calcd for C72.5H67O16.5N1Cl2V4): C, 58.34 (58.40), H, 4.38 (4.54), N, 1.63 (0.94), Cl, 4.93 (4.76), V, 13.32 (13.67). Synthesis of [V4Cl2(dbm)4(MeO)6] (10). [VCl3(THF)3] (0.2 g, 0.54 mmol), Na(dbm) (0.26 g, 1.07 mmol), and MeOH (9 mL) were heated in a sealed Teflon container for 12 h at 150 °C. X-ray quality crystals of 10 were filtered from the cooled solution and dried in vacuo. 93% yield. MALDI-MS (dithranol matrix, CH2Cl2 solution), m/z: 1317 (M -Cl-). Anal. (%), observed (Calcd for C66H62O14Cl2V4): C 58.26 (58.55), H 4.44 (4.62), Cl, 4.96 (5.24), V, 14.80 (15.08). IR (KBr), ν (cm-1): 2929, 2824, 1591, 1553, 1479, 1320, 1028, 1003, 716, 537.
Results and Discussion Synthesis and Structural Studies. (i). Mixed-Valence {VIII2VIV2} Complexes. The mixed-valence {VIII2VIV2} complexes [V2(VO)2(acac)4{RC(CH2O)3}2] 1-3 (R ) Me 1, Et 2, CH2OH 3) are prepared in excellent yields (5080%) by heating [V(acac)3], [VO(acac)2], and the appropriate RC(CH2OH)3 triol (1:1:1) in MeCN at 150 °C for 12 h, followed by slow cooling to give crystalline products directly from the reaction solutions. The same products are also isolated, but in much lower yields ( ca. 0.65. Conclusions In conclusion, we have prepared a family of clusters based on alkoxide-bridged butterfly cores with oxidation states {VIV4}, {VIII2VIV2} (both isomeric forms), and {VIII4}. These form a unique redox family of cluster species, further
Redox Family of Tetrametallic Vanadium Clusters
extended by known13 diamagnetic {VV4} analogues. The {VIII2VIV2} and {VIII4} species are rare examples of heterovalent VIII/IV and homovalent VIII clusters. These have all been prepared in good yield and from simple starting materials, via solvothermal synthesis. This highlights the utility of these methods in the isolation of low-valent vanadium clusters6,7 - analogous reactions at room temperature or under reflux give only powders from which no clean products could be isolated. Magnetic studies have allowed the magnetic exchange interactions to be determined (unless these parameters are inherently indeterminate). Hence, we have developed a detailed picture of the electronic structures of these low-valent vanadium species and how these change on systematic changes in (i) the metal ion oxidation states and therefore electron count, and (ii) the geometric arrangement of the metal ions, for example between type A and type
B {VIII2VIV2} cores, without gross changes in the metalalkoxo core. It is our hope that this will aid in the understanding of the magnetic properties of high-nuclearity low-valent vanadium systems, particularly given that the {M4(µ3-O)2} fragment is a common building block in larger clusters. Acknowledgment. We thank the EPSRC, the Ramsey Memorial Trust (RHL), and the EC (NMP3-CT-2005-515767 “Magmanet”) for funding. Supporting Information Available: Crystallographic cif files and thermal ellipsoid plots for 1-10 and details of Kambe´ analyses. This material is available free of charge via the Internet at http://pubs.acs.org. IC7011183
Inorganic Chemistry, Vol. 46, No. 23, 2007
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