Transition metal complexes of a super rigid anthyridineligand: structural, magnetic and DFT studies

Abstract

Transition metal complexes of iron(II), cobalt(II), nickel(II), copper(II) and zinc(II) with a plane, super rigid ligand, 1,13,14-triaza-dibenz[a,j]anthracene (L), [M₂L₄](ClO₄)₄ (M = Fe, Co, Ni, Cu, Zn), were synthesized and their magnetic properties were studied. All complexes are dinuclear, tetracationic complexes bridged by four tridentate ligands. In a complex each L coordinates to two metal atoms with two nitrogen atoms chelating to one metal and the third nitrogen atom mono-coordinating to another metal. Crystal structure analysis indicated that the molecular structures of the five complexes are essentially the same despite significant distortion from the Jahn–Teller effect of the copper complex. The Cu–Cu distance is 2.907(1) Å, and all other M–M distances are ca. 3.3 Å. Antiferromagnetic couplings were observed for the Fe, Co, Ni and Cu complexes. The exchange parameters were J = −6 and −129 cm⁻¹ for Ni and Cu complexes, respectively. The mechanism was discussed by spin-polarization, superexchange coupling and DFT calculations. The J value obtained from the density functional B3LYP calculations is in good agreement with the experimentally determined value.