Imidazolate-bridged copper(II) complexes with infinite zigzag-chain and tetranuclear structures formed by deprotonation and self-assembly

Abstract

A method of molecular design of self-assembling metal complexes has been established. The copper(II) complex with a quadridentate ligand [Cu(HL²)]ClO₄ undergoes deprotonation of the imidazole proton under basic conditions to give an imidazolate-bridged polymeric compound [(CuL²)∞], where H₂L²=N-3-ethoxysalicylidene-N′-imidazol-4-ylmethylenecyclohexane-1,2-diamine. The latter compound crystallizes in the monoclinic space group P2₁/a with a= 15.515(5), b= 9.338(5), c= 12.660(2)Å, β= 95.33(2)°, and Z= 4, R= 0.078 for 1721 reflections. It has an infinite zigzag-chain structure and the variable-temperature magnetic data are well reproduced using the Ising model based on H=–2∑J_ijS_iS_j with a J value of –1.8 cm^–1. The complex [Cu(HL³)Cl]ClO₄ with a tridentate ligand gives an imidazolate-bridged tetranuclear complex [(CuL³)₄][Clo₄]₄ on deprotonation at the imidazole nitrogen, where HL³=N-imidazol-4-ylmethylene-N′,N′-dimethylpropane-1,3-diamine. The latter compound crystallizes in the triclinic space group P with a= 15.216(6), b= 15.592(5), c= 15.102(5)Å, α= 104.98(3)°, β= 108.44(3)°, γ= 61.12(2)°, Z= 2, and R= 0.096 for 6931 reflections. The structure consists of a cyclic tetranuclear molecule in which each imidazolate nitrogen atom co-ordinates axially to the copper(II) ion of the adjacent unit. Variable-temperature magnetic data are well reproduced using the Heisenberg model based on H=–2J(S₁·S₂+S₂·S₃+S₃·S₄+S₄·S₁) with J=–60.0 cm^–1.