Decanuclear manganese(III) complexes with the [Mn10O8](14+) core: Structural and magnetochemical characterization of [Mn10O8(O(2)CPh)(6)(chel)(8)] (chel=pic, dbm)

The preparation and properties are described of two related Mn-10 clusters with the same [Mn10O8](14+) (10 Mn-III) core. Dissolution of [Mn4O2(O(2)CPh)(6)(MeCN)(2)(pic)(2)] (1) in MeCONMe(2) (DMA) and CH2Cl2 in the presence of picH (picolinic acid) leads to slow crystallization of [Mn10O8(O(2)CPh)(6)(pic)(8)] (2) in 50-55% yield. The same reaction in the presence of dibenzoylmethane (dbmH) instead of picH gives [Mn10O8(O(2)CPh)(6)(pic)(6)(dbm)(2)] (3). Complex 2 . 6CH(2)Cl(2) crystallizes in the monoclinic space gpoup P2(1)/n with (at -169 degrees C) a = 14.987(3) Angstrom, b = 17.177(3) Angstrom, c = 21.250(4) Angstrom, beta = 91.48(1)degrees, and Z = 2. Complex 3 . 3CH(2)Cl(2) crystallizes in the triclinic space group <P(1)over bar> with (at -165 degrees C) a = 14.892(6) Angstrom, b = 15.537(6) Angstrom, 14.697(6) Angstrom, alpha = 109.82(2)degrees, beta = 97.75(2)degrees, gamma = 111.66(2)degrees, and Z = 1. The two structures are very similar, differing only in the chelate identity at two positions, and resulting small perturbations in some metric parameters. Variable-temperature magnetic susceptibility data were obtained for 2 . 3H(2)O with a dc SQUID in the range 2.00-320 K and in a 10 kG applied field. The effective magnetic moment (mu(eff)) per molecule slowly decreases from 14.28 mu(B) at 320 K to 4.94 mu(B) at 2.00 K. Data were also collected with an ac SQUID in the range 2.00-30.0 K in a 1 G field oscillating at 250 Hz. The ac data essentially superimpose on the de data except at temperatures less than or equal to 6 K. The combined results indicate a S-T = 0 ground state for 2 with a very low-lying excited state(s) that is (are) populated even at 2.00 K. The possibility of a S-T = 1 (Or even S-T = 2) ground state cannot be completely ruled out, however, in the absence of data at <2 K.