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

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 P1 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.