Design and Characterization of Mixed Ligand Mn(II) Complex with 4-Iodo Acid for Enhanced Nonlinear Optical Applications: A Theoretical and Experimental Approach

Abstract

Pyridine-2-carboxylic acid derivatives have emerged as promising candidates for nonlinear optical (NLO) applications due to their strong optical nonlinearity, thermal stability, and diverse coordination chemistry. In this study, we synthesized a novel manganese (II) complex with 4-iodo-pyridine-2-carboxylic acid (H4Ipca) and 5,5 '-dimethyl-2,2 '-bipyridine (5,5dmbpy) as ligands. An octahedral coordination geometry around the Mn (II) center was found by XRD method. Spectroscopic analyses, including FT-IR and UV-Vis, confirmed key bonding characteristics and electronic transitions, with a major absorption peak observed at 281 nm, attributed to pi -> pi* and n -> pi* transitions. Theoretical calculations using density functional theory (DFT) indicated a substantially reduced HOMO-LUMO energy gap of 2.15 eV in the Mn (II) complex, suggesting enhanced electronic transitions and polarizability. Notably, the complex exhibited an impressive increase in first-order hyperpolarizability (beta) to 85.018 x 10-30 esu, significantly higher than that of its individual ligands, underscoring its high NLO activity. Frequency-dependent hyperpolarizability values further reached 412.5 x 10-30 esu, indicating strong responsiveness under dynamic electric fields. These findings position this Mn (II) complex as a strong candidate for advanced NLO materials, paving the way for future applications in photonic and optoelectronic devices.