<span lang="EN-CA">Reversible Chromotropic Activities of a Mixed-Chelate Nickel (II) Complex: Solvatochromism, Thermochromism and Computational Study

A new mixed-chelate nickel(II) complex, (N,N-Diethyl-N'-benzylethane-۱,۲-diamine)(acetylacetonato)nickel(II) tetraphenylborate, [Ni(acac)(diamine)]BPh۴, where the diamine is N,N-diethyl-N′-benzylethylenediamine and acac is the acetylacetonate anion, has been synthesized and characterized using elemental analysis, FT-IR, UV–Vis spectroscopy, molar conductance, thermal analysis, magnetic measurements, and DFT calculations at the B۳LYP/def۲-TZVP level. The complex exhibits pronounced chromotropic behavior, including solvatochromism and thermochromism, arising from an equilibrium between a four-coordinate square-planar species in non-coordinating solvents and a six-coordinate octahedral species upon axial coordination by polar solvents. In nonpolar solvents, the complex appears red with an absorption maximum around ۴۹۰ nm, while in coordinating polar solvents such as DMF, DMSO, and methanol, it shifts to green with absorption near ۶۱۰ nm, indicating octahedral geometry. Acetone solutions show coexistence of both species, revealing a reversible equilibrium influenced by solvent coordination. Temperature-dependent studies demonstrate thermochromic behavior in acetone, where the green octahedral form converts to the red square-planar form upon heating and reversibly returns upon cooling. Computational studies confirm the square-planar geometry of the isolated cation and support the experimental vibrational and electronic spectral data. These results highlight the role of ligand environment and solvent interactions in modulating the structural and chromic properties of nickel (II) complexes, offering potential applications in sensing, smart materials, and educational demonstrations.

کلیدواژه ها:

Nickel (II) ، mixed-chelate complex ، Solvatochromism ، Thermochromism ، square-planar ، octahedral ، DFT