SYNTHESIS, STRUCTURE, AND PROPERTIES OF [MN(SALPN)(ETOH)2](CLO4) AND ITS AEROBIC OXIDATION-PRODUCT [MN(SALPN)O]2

Preparation and isolation of the mononuclear Mn(III) complex [Mn(salpn)(EtOH)2](ClO4) (1a) (H-2salpn = N,N'-bis(salicylidene)-1,3-diaminopropane) were accomplished by air oxidation of a solution containing H-2salpn, NaOH, and Mn(ClO4)2.6H2O in MeOH/EtOH (1:1), followed by addition of Et2O. Compound 1a.EtOH.H2O crystallizes in the triclinic space group P1BAR with a = 11.649 (3) angstrom, b = 13.902 (6) angstrom, c = 19.849 (7) angstrom, alpha = 70.18 (2)-degrees, beta = 70.52 (2)-degrees, gamma = 60.33 (2)-degrees, V = 2726 (2) angstrom 3, and Z = 4. For 1a.EtOH.H2O there are two mononuclear Mn(III) complexes in the crystallographic asymmetric unit. The Mn-O and Mn-N distances for 1 are in good agreement with those found for other Mn(III) Schiff base complexes. The H-1 NMR spectrum of 1 in CD3CN has well-resolved, paramagnetically shifted resonances at 19.8, 11.6, 7.4, -2.8, -24.8, -26.2, and -94.2 ppm. Compound 1 has a Mn(III/II) reduction potential of -0.154 V vs SSCE as measured by cyclic voltammetry in DMSO. Compound 1 was converted into [Mn2O2(salpn)2] (2) by air oxidation in basic MeOH followed by recrystallization from DMF. Alternatively, 2 can be prepared by air oxidation of Mn(salpn)(H2O) in pyridine, followed by crystallization from CH2Cl2/cyclohexane. Compound 2.2DMF crystallizes in the monoclinic space group P2(1)/c with a = 10.722 (2) angstrom, b = 10.163 (3) angstrom, c = 17.564 (4) angstrom, beta = 100.67 (2)-degrees, V = 1890 (1) angstrom 3, and Z = 2. Using an isotropic spin-exchange Hamiltonian H = -2JS1.S2, variable-temperature magnetic data for 2 were fit well with a J value of -82 cm-1. The magnitude of J is significantly less than that for several other species containing the {Mn2O2}4+ core yet comparable to the value obtained for [Mn2O2(pic)2] (pic = 2-pyridinecarboxylate) (Inorg. Chem. 1989, 28, 4037). The reduction potential for 2 in DMSO (-0.39 V vs SSCE) for the IV,IV/IV,III couple is the lowest determined for a bis(mu-oxo)dimanganese complex.