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

The preparation and properties are described of two related Mn 10 clusters with the same [Mn 10 O 8 ] 14+ (10 Mn III ) core. Dissolution of [Mn 4 O 2 (O 2 CPh) 6 (MeCN) 2 (pic) 2 ] ( 1 ) in MeCONMe 2 (DMA) and CH 2 Cl 2 in the presence of picH (picolinic acid) leads to slow crystallization of [Mn 10 O 8 (O 2 CPh) 6 (pic) 8 ] ( 2 ) in 50−55% yield. The same reaction in the presence of dibenzoylmethane (dbmH) instead of picH gives [Mn 10 O 8 (O 2 CPh) 6 (pic) 6 (dbm) 2 ] ( 3 ). Complex 2 ·6CH 2 Cl 2 crystallizes in the monoclinic space group P 2 1 /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 ·3CH 2 Cl 2 crystallizes in the triclinic space group P 1̄ 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 ·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 (μ eff ) per molecule slowly decreases from 14.28 μ B at 320 K to 4.94 μ 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 dc data except at temperatures ≤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.