Decanuclear Manganese(III) Complexes with the [Mn10O8]14+ Core: Structural and Magnetochemical Characterization of [Mn10O8(O2CPh)6(chel)8] (chel = pic, dbm)

Abstract

The preparation and properties are described of two related Mn10 clusters with the same [Mn10O8]14+ (10 MnIII) core. Dissolution of [Mn4O2(O2CPh)6(MeCN)2(pic)2] (1) in MeCONMe2 (DMA) and CH2Cl2 in the presence of picH (picolinic acid) leads to slow crystallization of [Mn10O8(O2CPh)6(pic)8] (2) in 50−55% yield. The same reaction in the presence of dibenzoylmethane (dbmH) instead of picH gives [Mn10O8(O2CPh)6(pic)6(dbm)2] (3). Complex 2·6CH2Cl2 crystallizes in the monoclinic space group P21/n with (at −169 °C) a = 14.987(3) Å, b = 17.177(3) Å, c = 21.250(4) Å, β = 91.48(1)°, and Z = 2. Complex 3·3CH2Cl2 crystallizes in the triclinic space group P1̄ with (at −165 °C) a = 14.892(6) Å, b = 15.537(6) Å, c = 14.697(6) Å, α = 109.82(2)°, β = 97.75(2)°, γ = 111.66(2)°, 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 2·3H2O with a dc SQUID in the range 2.00−320 K and in a 10 kG applied field. The effective magnetic moment (μeff) per molecule slowly decreases from 14.28 μB at 320 K to 4.94 μB 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 dc data except at temperatures ≤6 K. The combined results indicate a ST = 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 ST = 1 (or even ST = 2) ground state cannot be completely ruled out, however, in the absence of data at <2 K.