Symmetric and asymmetric dinuclear manganese(IV) complexes possessing a [MnIV2(μ-O)2(μ-O2 CME)3+ core and terminal Cl- ligands

Abstract

The synthesis of new dinuclear manganese(IV) complexes possessing the [MnIV2(μ-O)2(μ-O2C Me)]3+ core and containing halide ions as terminal ligands is reported, [Mn2O2(O2CMe)Cl2 (bpy)2]2[MnCl4] (1

bpy = 2,2′-bipyridine) was prepared by sequential addition of [MnCl3(bpy)(H2O)] and (NBzEt3)2[MnCl4] to a CH2Cl2 solution of [Mn3O4- (O2CMe)4(bpy)2]. The complex MnIV2O2(O2CMe)Cl(bpy) 2(H2O)](NO3)2 (2) was obtained from a water/acetic acid solution of MnCl2·4H2O, bpy, and (NH4)2[Ce(NO3)6], whereas the MnIV2O2(O2CR)X(bpy) 2(H2O)](ClO4)2 [X = Cl- and R = Me (3), Et (5), or C2H4Cl (6)

and X = F-, R = Me (4)] were prepared by a slightly modified procedure that includes the addition of HClO4. For the preparation of 4, MnF2 was employed instead of MnCl2·4H2O. [Mn2O2(O2- CMe)Cl2(bpy)2]2[MnCl4]· 2CH2Cl2 (1·2CH2Cl2) crystallizes in the monoclinic space group C2/c with a = 21.756(2) Å, b = 12.0587(7) Å, c = 26.192(2) Å, α = 90°, β = 111.443(2)°, γ = 90°, V = 6395.8(6) Å3, and Z = 4. [Mn2O2(O2CMe)Cl(H2O) (bpy)2](NO3)2·H2O (2·H2O) crystallizes in the triclinic space group P1̄ with a = 11.907(2) Å, b = 12.376(2) Å, c = 10.986(2) Å, α = 108.24(1)°, β = 105.85(2)°, γ = 106.57(1)° V = 1351.98(2) Å3, and Z= 2, [Mn2O2(O2CMe)Cl(H2O) (bpy)2](ClO4)2·MeCN (3·MeCN) crystallizes in the triclinic space group P1̄ with a = 11.7817(7) Å, b = 12.2400(7) Å, c = 13.1672(7) Å, α = 65.537(2)°, β = 67.407(2)°, γ = 88.638(2)° V = 1574.9(2) Å3, and Z = 2. The cyclic voltammogram (CV) of 1 exhibits two processes, an irreversible oxidation of the [MnCl4]2- at E1/2 ∼ 0.69 V vs ferrocene and a reversible reduction at E1/2 = 0.30 V assigned to the [Mn2O2(O2CMe)Cl2 (bpy)2]+/0 couple (2MnIV to MnIVMnIII). In contrast, the CVs of 2 and 3 show only irreversible reduction features. Solid-state magnetic susceptibility ξM) data were collected for complexes 1·1.5H2O, 2·H2O, and 3·H2O in the temperature range 2.00-300 K. The resulting data were fit to the theoretical ξMT vs T expression for a MnIV2 complex derived by use of the isotropic Heisenberg spin Hamiltonian (ℋ = -2JŜ1Ŝ2) and the Van Vleck equation. The obtained fit parameters were (in the format J/g) -45.0(4) cm-1/2.00(2), -36.6(4) cm-1/1.97(1), and -39.3(4) cm-11.92(1), respectively, where J is the exchange interaction parameter between the two MnIV ions. Thus, all three complexes are antiferromagnetically coupled.