Syntheses, crystal structures and magnetic properties of cyano- and phenoxide-bridged Fe(III)Mn(III) tetramers containing fac-Fe(III) tricyanides and Mn(III) Schiff bases

Three cyanide-linked Fe(III)Mn(III) bimetallic clusters, [(Tp)Fe(CN)(3)](2)[Mn(acphen)](2) [1; acphen = N,N'-ethylenebis(2-hydroxyacetophenylideneiminato) dianion], [(Tp) Fe(CN)(3)](2)[Mn(5-Bracphen)](2) [2; 5-Bracphen = N,N'-ethylenebis(5-bromo-2-hydroxyacetophenylideneiminato) dianion], and [(Tp)Fe(CN)(3)](2)[Mn(salen)](2)center dot 6H(2)O [3; salen = N,N'-ethylenebis(salicylidineiminato) dianion], were prepared by self-assembling a facial [(Tp)Fe(CN)(3)](-)[Tp = hydrotris(pyrazolyl) borate] precursor and respective Mn(III) Schiff bases. X-Ray crystal structure analyses revealed that each complex is composed of a central Mn(III) dimer doubly linked by phenoxides of the tetradentate N2O2 Schiff bases and the terminal [(Tp) Fe(CN)(3)](-) groups connecting to the center through cyanides. Using the spin Hamiltonian H = -2J(1)(S-Fe1 center dot S-Mn1 + S-Mn1 center dot S-Fe1a) - 2J(2)(S-Mn1 center dot S-Mn1a), where J(1) stands for the exchange coupling constant between Fe(III) (S-Fe = 1/2) and Mn(III) (S-Mn = 2) through cyanides and J(2) between Mn(III) ions via phenoxides, the best fits corresponded to J(1) = 2.61 cm(-1) and J(2) = 0.85 cm(-1) for 1, J(1) = 2.50 cm(-1) and J(2) = 1.30 cm(-1) for 2, and J(1) = -2.15 cm(-1) and J(2) = 0.55 cm(-1) for 3. The phenoxide routes transmit ferromagnetic interactions in all cases, while ferromagnetic or antiferromagnetic couplings occur through the cyanide linkage. Although the geometric parameters relevant to the magnetic Fe-C N-Mn pathways are analogous to each other their magnetic natures are varied across the compounds, which supports that a degree of orbital overlap is quite sensitive to a subtle structural change in the present system.