Anionic 3D coordination polymer with two motifs of dibromo-bridged copper(II) moieties: Structure, magnetic properties, and DFT calculations

A three-dimensional (3D) anionic dibromo-bridged copper(II) polymer containing 4-amino-1,2,4-triazole (L) as a linker and 4-amino-1,2,4-triazolium as a counterion (HL) was synthesized. High synthetic temperature (60 degrees C) leads to formation of single crystals of a minor polymorphic phase. Both compounds, {[HL](2)[(Cu2Br4)L-2(Cu2Br6)]}(n), crystallize in the monoclinic space groups P2(1)/c (1) and C2/c (2), respectively. The calculated thermodynamic potentials indicate that the Gibbs energy of 1 is lower than of 2, making it difficult to isolate sufficient quantities of the latter in pure form for investigation. The optical and magnetic properties of the isolated P2(1)/c phase were studied, revealing a small band gap value of similar to 1 eV. The magnetic susceptibility of the P2(1)/c polymorph is influenced by various ferromagnetic and antiferromagnetic interactions between copper(II) ions. Possible exchange pathways that can be realized in the structure were considered and analyzed. Quantum chemical calculations of the band structure and magnetic exchange interactions were performed for both polymorphs.