Synthesis and X-ray crystal structures of an imidazolate-bridged polynuclear copper(II) complex exhibiting a unique helicoid structure and its precursor mononuclear complex

Abstract

The mononuclear copper(II) complex with the unsymmetrical quadridentate ligand [(4-imidazolyl)methyliminopropylsalicylideneiminato]copper(II) tetraphenylborate, [Cu(HL)][BPh₄], has been prepared and characterized. The complex deprotonates the imidazole proton in the presence of triethylamine to produce the imidazolate-bridged polynuclear complex [(CuL)_n]. The structures of both complexes have been established by single-crystal X-ray diffraction analyses. The mononuclear complex crystallizes in the monoclinic space group P2₁/n with a= 20.822(4), b= 14.132(3), c= 10.698(2)Å, β= 98.63(2)°, and Z= 4. The copper atom assumes a square-planar co-ordination environment with a slight distortion toward tetrahedral, where the dihedral angle between the CuN₂ and CuON planes representing the degree of tetrahedral distortion is 10.9°. The polynuclear complex crystallizes in the triclinic space group P with a= 15.421(5), b= 16.594(4), c= 10.537(1)Å, α= 115.08(1), β= 103.21(2), γ= 57.48(2)°, and Z= 2. The complex has a unique helicoid linear-chain structure along the c axis formed by the imidazolate bridges, where the copper atom assumes a square-based pyramidal co-ordination environment with the imidazolate nitrogen of the neighbouring copper complex occupying the axial position. The magnetic properties of the complex are well represented by the lsing model on the basis of a linear-chain structure.