Synthesis, Spectroscopic Characterization, and DFT Insights into a Ni(II) Dithiocarbamate and Its Mixed-Ligand Derivative, with Conversion of the Parent Complex to Nanocrystalline Nickel Sulfide Exhibiting Enhanced Visible-Light Photocatalytic Activity

Abstract

This study reports the synthesis, spectroscopic characterization, and functional evaluation of a novel nickel(II) dithiocarbamate complex derived from 4-piperidinopiperidine and its corresponding mixed-ligand Ni(II) complex formed with 1,2-bis(diphenylphosphino)ethane (dppe). Elements (CHNS and Ni gravimetry), FT-IR, UV-Vis, and NMR spectroscopy were used to characterise the two complexes, which were produced in good yields through salt-metathesis and ligand exchange processes. Spectral data suggest a primarily square-planar coordination environment and validate the effective chelation of phosphine and dithiocarbamate ligands to the Ni(II) core. Density Functional Theory (DFT) investigation of a model Ni(II) dithiocarbamate species gave information about electronic structure, frontier orbital distribution, and chemical reactivity indices in addition to revealing a distorted square-planar geometry. Nanocrystalline nickel sulphide (NiS) was produced by thermally breaking down the dithiocarbamate precursor. PXRD, SEM/EDS, and UV–DRS analyses revealed phase-pure β-NiS with a band gap of about 3.08 eV. NiS has the potential to be an efficient photocatalyst for the removal of organic pollutants, as evidenced by photocatalytic studies that showed significant visible-light induced degradation of model organic dyes (Methylene Blue = 85% and Rhodamine-6G ≈ 70% after 180 min). For Ni(II) dithiocarbamate complexes and their generated nanomaterials, this work offers synthesis methods, thorough characterisation, and application insight.