Syntheses, Structures, and Properties of Trinuclear Complexes [M(bpca)₂{M‘(hfac)₂}₂], Constructed with the Complexed Bridging Ligand [M(bpca)₂] [M, M‘ = Ni(II), Mn(II); Cu(II), Mn(II); Fe(II), Mn(II); Ni(II), Fe(II); and Fe(II), Fe(II); Hbpca = Bis(2-pyridylcarbonyl)amine, Hhfac = Hexafluoroacetylacetone]

Five trinuclear complexes [M(bpca)2{M‘(hfac)2}2] (where MM‘2 = NiMn2, CuMn2, FeMn2, NiFe2, and FeFe2; Hbpca = bis(2-pyridylcarbonyl)amine; and Hhfac = hexafluoroacetylacetone) were synthesized almost quantitatively by the reaction of [M(bpca)2] and [M‘(hfac)2] in 1:2 molar ratio, and their structures and magnetic properties were investigated. Three complexes, with M‘ = Mn, crystallize in the same space group, Pna21, whereas two complexes, with M‘ = Fe, crystallize in P41, and complexes within each set are isostructural to one another. In all complexes, [M(bpca)2] acts as a bis-bidentate bridging ligand to form a linear trinuclear complex in which three metal ions are arranged in the manner M‘−M−M‘. The central metal ion is in a strong ligand field created by the N6 donor set, and hence the Fe(II) in the {Fe(bpca)2} moiety is in a low-spin state. The terminal metal ions (M‘) are surrounded by O6 donor sets with a moderate ligand field, which leads to the high-spin configuration of Fe(II). Three metal ions in all complexes are almost collinear, and metal−metal distances are ca. 5.5 Å. The magnetic behavior of NiMn2 and NiFe2 shows a weak ferromagnetic interaction between the central Ni(II) ion and the terminal Mn(II) or Fe(II) ions. In these complexes, σ-spin orbitals of the central Ni(II) ion and those of terminal metal ions have different symmetry about a 2-fold rotation axis through the Ni−Namide−M‘terminal atoms, and this results in orthogonality between the neighboring σ-spin orbitals and thus ferromagnetic interactions.