Synthesis, structural elucidation, vibrational analysis, and optoelectronic properties of a new tetrabromocobaltate(II) complex with 4-dimethylaminopyridine ligand

Abstract

Despite the growing interest in cobalt-based hybrid complexes, the optical and electronic properties of DMAP-stabilized cobalt halides remain largely unexplored. In this study, we report the synthesis and comprehensive characterization of a novel cobalt(II) complex, DMAPCoBr₄ (DMAP = 4-dimethylaminopyridine). The compound was characterized by single-crystal X-ray diffraction, FTIR, Raman, UV–Visible spectroscopy, and photoluminescence studies. It crystallizes in the monoclinic system with space group C2/c and exhibits a distorted tetrahedral coordination geometry around Co(II). The experimental bond distances and angles were in excellent agreement with density functional theory (DFT) optimizations at the B3LYP/LanL2DZ level. Spectral data were corroborated with theoretical simulations, showing good concordance in vibrational modes and optical absorption. Electrostatic potential mapping, Mulliken charge analysis, and frontier molecular orbitals revealed electron-rich regions suitable for electrophilic interactions. The Tauc plot suggested a direct band gap of 2.13 eV, while the density of states (DOS) and photophysical data confirmed semiconducting behavior with potential optoelectronic applications. The compound also exhibits bright blue-violet fluorescence at 403 nm and a high second-order hyperpolarizability, suggesting its promise for nonlinear optical (NLO) devices. These results highlight the novelty of employing DMAP as a stabilizing ligand for cobalt tetrahalides, providing a multifunctional hybrid material with potential applications in optoelectronics, photonics, and nonlinear optics.