Distorted manganese cubane [Mn4O3Cl]6+ complexes with arenecarboxylate ligation: crystallographic, magnetochemical, and spectroscopic characterization (original) (raw)

1993, Inorganic Chemistry

Synthetic procedures are described that allow access to Mn403C14(OzCR)3(py)3 (R = aryl) complexes, complementing previous work with R = alkyl. Carboxylate exchange of the R = Me complex (2) with the appropriate arenecarboxylic acid leads to preparation of the R = 3S-Clz-Ph (3), Ph (4), 4-F-Ph (3, and 3,5-Fz-Ph (6) complexes. The crystal structure of 3 shows the [Mn403C1I6+ core to be essentially superimposable on that of 2. Crystal data for 3 at -171 OC are as follows: hexagonal, R3, u = 19.056(4) A, c = 28.271(6) A, V = 8888.25 A3, Z = 6, R (R,) = 0.0417 (0.0384) employing 1982 unique data with F > 3.0u(F). Variable-temperature magnetic susceptibility data are presented for 3 at 10.0 kG in the 5-320 K range. The p,rf/molecule value rises from 9.1 p~ at room temperature to a maximum of 9.72 p~ at 60.0 K and then decreases to 8.95 p~ at 5.01 K. Fitting of the data to the appropriate theoretical expression gave the following fitting parameters: J34 = -27.1 cm-I, J33 = +11.1 cm-I, and g = 1.95. These are similar to those for the R = Me complex (2) reported previously and similarly yield a well-isolated S = 9/2 ground state. This was confirmed by variable-field magnetization studies which verified an S = 9/2 ground state experiencing zero-field splitting ( D = 0.50 cm-I). The results of IH and zH NMR studies on 4-6 are presented, together with those for the 4-picoline (7) and 3,5-lutidine (8) derivatives. The observed sp&ra are qualitatively interpreted vis-a-vis the spin delocalization mechanisms that are operative. It is concluded that contact shifts via *-spin delocalization and dipolar shifts are both contributors to the pyridine I H and 2I-E chemical shifts. The greater solubility of the R = aryl derivatives (except 3 and 6) compared to R = alkyl derivatives has allowed better-resolved toluene glass EPR spectra to be obtained for complex 5 than was previously possible for the R = alkyl complexes. ( I ) (aMcCusker, J. K.;Schmitt,E. A.; Folting, K.;Hendrickson, D. N.; Christou, G. Inorg. Chem. 1991,30, 3486. (b) Bouwman, E.; Bolcar, M. A.; Libby, E.; Huffman, J. C.; Folting, K.; Christou, G. Folting, K.;Streib, W. E.; Schmitt, E. A.; McCusker, J. K.; Hendrickson, D. N.; Christou, G. Angew. Chem., Int. Ed. Engl. 1991, 30, 305. (6) (a) Hendricks0n.D. N.; Christou, G.;Schmitt,E. A.; Libby, E.; Bashkin, J. S.; Wang, S.; Tsai, H.-L.; Vincent, J. B.; Boyd, P. D. W.; Huffman, J. C.; Folting, K.; Li, Q.; Streib, W. E. J. Am. Chem. SOC. 1992, 114, 2455. (b) Bashkin, J. S.; Chang, H.-R.; Streib, W. E.; Huffman, J. C.; Hendrickson, D. N.; Christou, G. J. Am. Chem. SOC. 1987, 109, 6502. (8) (a) Caneschi, A.;Gatteschi, D.; Laugier, J.; Ray, P.;Sessoli, R.; Zanchini, C. J. Am. Chem. SOC. 1988, 110, 2795. (b) Boyd, P. D. W.; Li, Q.; Vincent, J. B.; Folting, K.; Chang, H.-R.; Streib, W. E.; Huffman, J. C.; Chrisotu, G.; Hendrickson, D. N. J . Am. Chem. SOC. 1988, 110, 8537. (c) Caneschi, A.; Gatteschi, D.; Sessoli, R.; Barra, A. L.; Brunel, L. C.; Guillot, M. J. Am. Chem. SOC. 1991,113,5873. (d) Schake, A. R.; Tsai, H.-L.; DeVries, N.; Webb, R. J.; Folting, K.; Hendrickson, D. N.;Christou, G. J. Chem.Soc., Chem. Commun. 1992,181. (e) Sessoli, R.; Tsai, H.-L.; Schake, A. R.; Wang, S.; Vincent, J. B.; Folting, K.; Gatteschi, D.; Christou, G.; Hendrickson, D. N.