Notable lattice deformation in a solid copper(II) dicyanamide complex induced by temperature-dependent supramolecular conformation

Low-dimensional compounds containing cyanido groups. Part XXXV. Structure, spectral, thermal and magnetic properties of a binuclear CuII-biquinoline complex with bridging and terminal dicyanamide ligands

From the system CuCl₂-biq-NaN(CN)₂ (biq is 2,2'-biquinoline), the binuclear molecular complex bis(μ-dicyanamido-κ²N¹:N⁵)bis[(2,2'-biquinoline-κ²N,N')(dicyanamido-κN¹)copper(II)], [Cu₂(C₂N₃)₄(C₁₈H₁₂N₂)₂] or [Cu₂(biq)₂(dca)₂(μ_1,5-dca)₂] (1) [dca is dicyanamide, N(CN)₂^-] was isolated and characterized by crystal structure analysis, and spectral, thermal and magnetic measurements. IR spectroscopy confirmed the presence of the biq and dca ligands in 1. Its solid-state structure consists of discrete centrosymmetric binuclear copper(II) units with double end-to-end dca bridges. Each Cu^II atom is in a distorted square-pyramidal environment with the equatorial plane formed by two nitrile N atoms from bridging dca groups, one of the two N atoms of the chelate biq molecule and one nitrile N atom from a terminal dca ligand, whereas the second biq N atom occupies the axial position. Thermal decomposition of 1 in an air atmosphere proceeds gradually, with copper(I) cyanide being the final decomposition product. Magnetic measurements revealed the formation of alternating spin chains and a relatively strong exchange interaction within the binuclear units was also confirmed by Broken Symmetry DFT (density functional theory) calculations.