Magnetic Interactions through Imidazolate‐Bridges: Synthesis,Spectroscopy, Crystal Structure and Magnetic Properties of μ‐Imidazolato‐Bridged Copper(II) Complexes

The synthesis, characterization and crystal structures of substituted imidazolate bridged binuclear copper(II) complexes, Cu₂(dien)₂(L)](ClO₄)₃, where dien = diethylenetriamine, L = imidazolate (im^—) ( 1 ), 2‐methylimidazolate (mim^—) ( 2 ) and benzimidazolate (bim^—) ( 3 ), are reported. The copper(II) ions of 1 — 3 posses a square planar coordination environment with dien coordinating as a tridentate ligand and the fourth position being occupied by a nitrogen atom of the bridging μ‐imidazolato group. In all three compounds the tendency to form additional long apical bonds at the copper(II) ions to the oxygen atoms of the perchlorate anions is observed. Temperature depended susceptibility data of polycrystalline samples reveal an antiferromagnetic coupling of the copper(II) atoms in 1 — 3 with J = —63.8, —75.4 and —36.8 cm^—1, respectively. Significant changes for these coupling constants could not be observed for measurements on frozen aqueous solutions. ESR spectra for solids and frozen solutions are consistent with intramolecular antiferromagnetic exchange interaction between the metal ions. From the data reported it can be concluded that the predominate mechanism for transmitting exchange coupling through the imidazolate bridge is due to a σ exchange pathways.