Abstract
The study presents the successful synthesis and crystallization of a square pyramidal copper(II) complex coordinated with glycine in its zwitterionic form \([\hbox {CuS}_{2}(\hbox {C}_{4}\hbox {H}_{10}\hbox {N}_{2}\hbox {O}_{4})]_{2}(\hbox {C}_{2}\hbox {H}_{5}\hbox {NO}_{2})_2\) (1), as confirmed by single crystal XRD study. The complex crystallizes in an orthorhombic system with space group \(Pna2_1\) , exhibiting a tetracoordinated copper center bound to oxygen and sulfur atoms in a cis-square planar geometry. The crystal structure is stabilized by a comprehensive grid of hydrogen bonds involving N–H \(\cdots\) O and N–H \(\cdots\) S interactions, which form characteristic graph-set motifs and contribute to a three-dimensional \(zig-zag\) molecular packing. FTIR confirmed glycine coordination and Cu–N/Cu–S bonding. Thermogravimetric analysis reveals that the title compound is thermally stable up to \(86\,^{\circ }\hbox {C}\) , adequate for room-temperature lasing applications, and its subsequent decomposition further supports the elemental composition of the material. UV–Visible spectra showed a strong peak at 208 nm, an absorption edge at 237 nm, and a wide band gap of 5.55 eV, indicating high electronic stability. Photoluminescence revealed broad emission from 370 to 532 nm, deconvoluted into ligand-centered, ligand-to-metal, and metal-centered transitions, demonstrating efficient energy redistribution within the complex. Glycine, in its zwitterionic form, acts as a bidentate ligand coordinating with transition metals to form complexes exhibiting nonlinear optical behavior, including nonlinear absorption, refraction, and excited-state transitions through metal-ligand charge transfer. The nonlinear optical studies by Z-scan revealed self-defocusing behavior and efficient optical limiting. The measured nonlinear refractive index \(n_2\) was \(2.786\times 10^{-8}\,\hbox {cm}^{2}\,\hbox {W}^{-1}\) , and the nonlinear absorption coefficient \(\beta\) was \(0.92\times 10^{-4}\,\hbox {cm}\,\hbox {W}^{-1}\) . The third-order nonlinear optical susceptibility \(\chi ^{(3)}\) was found to be \(2.46\times 10^{-6}\) esu, demonstrating significant third-order nonlinear response. Optical limiting measurements showed an onset threshold of \(1.545\times 10^{3}\,\hbox {W}\,\hbox {cm}^{-2}\) proving the material’s ability to shield optical devices from high-intensity light.
Graphic Abstract
