Exploring the effects of halide anions and pressure on the structural and functional properties of helical coordination polymers: Cu(SCN2H4)3X (X = Cl, Br, I)

A combined experimental and computational study was conducted on the non-centrosymmetric Cu(I) coordination polymers [Cu(thiourea)₃]X (X = Cl (CTC), Br (CTB), I (CTI)) to investigate the relationships between their structural characteristics under varying external pressure and their mechanical, microstructural, thermophysical, optical and electronic properties. The crystal structure of the [Cu(thiourea)₃]Cl complex was redetermined with higher precision, providing more refined structural details. All three compounds crystallize in a tetragonal system with similar polymeric connectivity but differ in halide ion size, significantly impacting their functional properties. Morphological and microstructural analyses, using various models, revealed insights into crystallite size, lattice strain, and crystal growth mechanisms. The elastic parameters were calculated using the PBE functional (Perdew-Burke-Ernzerhof) with the Generalized Gradient Approximation (GGA) to evaluate the ductility, anisotropy, machinability, and mechanical stability of the three coordination polymers. The electronic properties, including band structure and density of states, were analyzed under pressure. The results reveal moderate band gap values ranging from 1.71 to 1.98 eV, positioning these materials as promising candidates for optoelectronic devices. This study underscores the pivotal influence of halide anion radius and external pressure in tuning the functional properties of these polymers, providing valuable insights for the design and advancement of cutting-edge material applications.