Synthesis and various DFT calculations of new Cd(II) crystal as dual-tasking complex in NLO and α-glucosidase inhibitory activities

The structure of the newly synthesized Cd(II) complex of 6-chloropyridine-2-carboxylic acid (6-ClPCA) was determined by the XRD method. The molecular structure was confirmed via single-crystal X-ray diffraction, while vibrational and electronic properties were investigated through FT-IR, UV–Vis spectroscopy, and DFT-based quantum chemical calculations. Five different DFT functionals were employed to optimize the molecular geometry and predict vibrational spectra, with statistical fitting parameters (MAD, RMS, MPD%, R²) applied to evaluate consistency with experimental data. The nonlinear optical (NLO) behavior of the complex was assessed using the Z–scan technique, revealing promising second-order hyperpolarizability values. In addition, enzyme inhibition assays and molecular docking studies were conducted to explore the biological potential of the Cd(II) complex, with notable binding affinities observed toward target enzymes. This integrated approach addresses several gaps in the literature by combining structural elucidation, electronic property analysis, NLO performance, and bioactivity evaluation within a single framework. Furthermore, the linear optical (LO), χ⁽¹⁾/P⁽¹⁾, second‒, and third‒order NLO, χ⁽²⁾/P⁽²⁾ and χ⁽³⁾/P⁽³⁾, susceptibility tensors/polarization parameters for Cd(II) complex were obtained at DFT/CAM-B3LYP and DFT/HSEh1PBE levels. At the same DFT levels, the E, P, and D (external electric field, polarization, and electric displacement, respectively) values of the Cd(II) complex were also computed. In addition, the refractive index (n) and optical band gap were determined in the UV–Vis region. DFT/CAM-B3LYP and DFT/HSEh1PBE levels were applied to investigate static and frequency–dependent LO and NLO parameters for the Cd(II) complex. The E, P, and D parameters for Cd(II) complex were found to be 1.614/4.314 × 10⁹ V/m, 4.042/6.525 × 10^‒2 C/m², and 5.471/2.705 × 10^‒2 C/m², respectively. These results indicate that the Cd(II) complex has a strong electronic response. Based on the Z–scan results, third‒order NLO susceptibility (χ⁽³⁾) and second‒order molecular hyperpolarizability (γ) for the complex were obtained at 1876.62 × 10⁻⁴ and ‒4676.33 × 10⁻²⁸ esu, respectively. Moreover, using DFT/CAM-B3LYP level, the < γ(0;0,0,0) > / < γ(‒ω;ω,0,0) > and < γ(‒2ω;ω,ω,0) > in ethanol were calculated at 3407.19 × 10⁻³⁶, − 1,974,417.9 × 10⁻³⁶, and − 15182.76 × 10⁻³⁶ esu, respectively. The IC₅₀ value of the Cd(II) complex for α-glucosidase inhibition was determined at 383.71 ± 1.54 µM. While a low level of measurable result was obtained against α-glucosidase for the Cd(II) complex, the NLO parameter determined in the third order with the Z–scan technique, and the second‒ and third‒order calculated NLO results showed the potential of being a suitable material for NLO optical devices containing environmentally responsive phase-modulating sensors and intensity-dependent detectors, etc. The findings suggest that the title complex holds potential for both optoelectronic and biomedical applications.