Unveiling structural and electronic features of a thiocyanic-cobalt (II) complex through experimental and computational approaches

Thiocyanic-cobalt (II) complex has been synthesized via chemical reaction of the cationic compound propane-1,3-diamine, KSCN, with metallic salt CoCl 2 ·6H 2 O, then processed using room-temperature evaporation crystallization method. The synthesized complex has been fully investigated via single crystal X-ray diffraction analysis, UV-visible, FTIR spectroscopy, ATD-TG/DSC analysis, and theoretical studies. According to the single crystal structural study, the asymmetric unit is composed of four half cobalt bearing molecules and two non-coordinated thiocyanate molecules. Each cobalt center has a six-fold coordination completed via two N-bonded thiocyanate anions; two 1,3-Diaminopropanium co-ligands, establishing a slightly distorted octahedron geometry. The stabilization of the molecular organization is further explored via Hirshfeld surface analysis. Infrared spectroscopy was used to highlight the vibrational absorption bands. To highlight the optical characteristics, the title compound's solid-state UV-visible absorption spectra were acquired at T=25°C. The thermal behaviors were examined, and the complex's breakdown was demonstrated in the [28–700°C] range. The optimization of the Co-metal compound occurred using DFT calculations, which facilitated the calculation of the HOMO–LUMO energy gap. Reduced density gradient analysis provided insights into the non-covalent interactions. A molecular electrostatic potential map illustrated the reactive sites within the molecule. Theoretical analyses, including NBO and NLO studies, reveal significant ligand-to-metal charge transfer and a high first-order hyperpolarizability, suggesting that the synthesized Co(II) complex possesses promising nonlinear optical (NLO) characteristics for potential photonic and optoelectronic applications. The high crystal stability, approved by QTAIM/NCI-RDG analysis, guaranteed by the dominant hydrogen bonding network makes the complex reliable and durable, which is a key requirement for its integration into advanced solid-state NLO and optoelectronic devices.