Synthesis, Magnetic Properties, and Incomplete Double-Cubane Structure of Manganese(III)-Metal(II) Complexes [Mn(MeOH)L(OH)M(bpy)]₂ (M = Zn, Cu, Ni, and Mn; H₄L = 1,2-Bis(2-hydroxybenzamido)benzene; bpy = 2,2′-Bipyridine)

The manganese(III) complex K[MnL(py)₂]·py (H₄L = 1,2-bis(2-hydroxybenzamido)benzene, py = pyridine) reacted as a ligand complex at the two phenoxo oxygen atoms with metal(II) ion and 2,2′-bipyridine to give a series of heterometal complexes [Mn(MeOH)L(OH)M(bpy)h (M(II) = Zn (1); Cu (2); Ni (3); Mn (4)). X-ray structures were determined 1, C₆₈H₇₄N₈O₁₈Mn₂Zn ₂: n= 12.367(3) Å, α= 12.844(2) Å. c = 12.262(2) Å, α = 106.58(1)°, β= 117.89(1)°, γ = 78.57(2)°, triclinic, P1̄. and Z = 1. 2, C₆₈H₇₄N₈O₁₈Mn₂Cu ₂: a = 13.447(1) Å. b = 12.670-(2) Å. c = 21.732(1) Å, β = 107.076(5)°. monoclinic, P2₁/n, and Z=2. 3, C₆₈H₇₄N₈O₁₈Mn₂Ni ₂: a_= 12.358(3) Å, b = 12.847(3) Å, c= 12.315(3) Å, α= 106.63(2)°. β = 118.71(1)°, γ = 78.32(2)°, triclinic. P1̄, and Z = 1. 4. C₆₆H₆₆N₈O₁₆Mn₄: a = 12.511(2) Å, b = 21.129(3) Å. c = 12.811(1) Å. β= 110.12(1)°, monoclinic. P2₁/n, and Z = 2. The X-ray analyses confirmed that each of the crystals consists of an incomplete double-cubane molecule with a [Mn₂M₂O₆] core, in which two M(II) ions are bridged by two hydroxo groups to form a planar dinuclear moiety bridged by di-μ-hydroxo groups [(bpy)M(OH)₂M(bpy)]²⁺ and the dinuclear moiety is sandwiched between two Mn(III) complexes [Mn(MeoH)L]^-. The Mn(III) ion and the dinuclear M(II) moiety are triply bridged by the one hydroxo oxygen of the dinuclear moiety and two phenoxo oxygen atoms of the Mn(III) ligand complex. The two phenoxo oxygen atoms of the Mn(III) ligand complex coordinate as an axial ligand to two independent metal(II) ions of the dinuclear moiety. The magnetic susceptibilities of 1-4 were measured in the temperature range of 2-300 K. All the Mn(III) ions in these complexes are in a high-spin state of S_Mn = 2 with a d⁴ electronic configuration, and the metal(II) ions are in the spin states of S_Zn = 0, S_Ca = 1/2. S_Ni = 1, and S_Mn(11) = 1/2 (low-spin). The magnetic susceptibility data are well reproduced by the following spin Hamiltonian based on the rhombus spin coupling model with spin (S₁, S₂, S₃, S₄) = (2, S_M, 2, S_M), including a zero-field splitting term for the Mn(III) centers: H = g_Mnβ(S₁ + S₃)·H + gMβ(S₂ + S₄)·H - 2J(S₁·S₂ -f S₂·S₃ + S₃-S₄ + S₄·S₁) - 2J'(S₂·S₄) + D_Mn[S_1z² + S_3z²], in which g_Mn and g_M are the g factors of the Mn(III) and M(II) ions, J and J' are the Mn(III)-M(II) and M(II)-M(II) Heisenberg coupling constants, and D is the zero-field splitting parameter of Mn(III). The calculated best-fit parameters are as follows: g_Mn = 1.91, g_Ca = 2.39. J = -4.5 cm^-1, J' = -8.1 cm^-1, and D_Mn = -4.9 cm^-1 for 2; g_Mn = 1.97, g_Ni = 2.23, J = -1.5 cm^-1, J' = -2.6 cm^-1, and D_Mn = -5.5 cm^-1 for 3; and g_Mn =1.95, g_Mn(II) = 2.29. J = -3.5 cm^-1, J' = -14.1 cm^-1, and D_Mn = -12.0 cm^-1 for 4. The spin frustration due to the incomplete double-cubane structure is discussed.