Three-dimensional 3d-4f hetero-bimetallic coordination polymers through hydrogen bonds: Synthesis, structures and Mössbauer spectrum analysis

Four cyano-bridged 3d-4f hetero-bimetallic Ln(III)-Fe(III) assemblies, {[Ln(DMF)₄(H₂O)₃(μ-CN)Fe(CN)₅] · H₂O)_n (Ln = Ce (1), Nd (2), Sm (3) and Gd (4); DMF = N,N-dimethylformamide), have been synthesized. X-ray crystallographic analysis of both 3 and 4 reveals three-dimensional network structures resulting from hydrogen bonds in the crystals. With respect to the coordination number on Sm(III) atoms, 3 is different from previously reported structures. Structural comparison indicates that the differences in magnetic properties between 3 and 4 do not derive from structural factors. Mössbauer spectra at both 298 and 10 K reveal that the characteristic quadrupole splitting for low-spin Fe(III) ions (S = 1/2) remains unchanged, indicating that the spin state of Fe(III) ions in 1-4 is not affected by temperature. The magnetic anisotropy derived from the ground states of Ln(III) ions with odd 4fⁿ electrons (n = 1, 3, 5 and 7), ²F_5/2, ⁴I_9/2, ⁶H_5/2 and ⁸S_7/2 for Ce(III), Nd(III), Sm(III) and Gd(III), respectively, dominates the exchange interaction in the Ln(III)-NC-Fe(III) systems.