Two new heteroleptic cobalt(III)dialkyldithiophosphate complex cations with a 1,2-bis(diphenylphosphino)ethane (dppe) ancillary ligand having formula [Co{S₂P(OR)₂}₂(dppe)](B(C₆H₅)₄) (R = –C₂H₅ (Co–Et); –CH(CH₃)₂ (Co–Pr)) have been synthesized and characterized spectroscopically as well as via single crystal X-ray diffraction analysis. The single crystal X-ray diffraction analyses reveal that the immediate geometries around Co(III) in both complexes are distorted octahedral, which are satisfied by four sulfur atoms of two dialkyldithiophosphate ligands and two phosphorus centers of the dppe ligand. These complex cations are neutralized by tetraphenyl borate B(C₆H₅)₄ anions. The solid-state framework of both complexes are stabilized by C–H⋯π and C–H⋯C interactions. The nature of these interactions have been addressed with the help of Hirshfeld surface analysis, and percent contributions of pertinent interactions in the crystal structure of these complexes have been addressed using fingerprint plots. Both complexes have been used as heterogeneous electrocatalysts for the oxygen evolution reaction (OER). Results suggest that Co–Et is a better electrocatalyst for the OER, displaying an onset potential of 1.68 V and Tafel slope of 114 mV dec⁻¹. Furthermore, in the homogeneous electrocatalysis of the hydrogen evolution reaction (HER) using trifluoroacetic acid, the overpotential for Co–Et and Co–Pr have been 1.05 V and 0.92 V, respectively, with turnover frequencies of 1518 s⁻¹ and 287.5 s⁻¹, respectively. Overall, heterogeneous OER and homogenous HER results suggest that Co–Et can be used as an efficient molecular electrocatalyst for oxygen/hydrogen evolution reactions.

Coordination polymers (CPs) are an assorted class of coordination complexes that are gaining attention for the safe and sustainable removal of organic dyes from wastewater discharge by either adsorption or photocatalytic degradation. Herein, three different coordination polymers with compositions [Ni(HL)(H₂O)₂·1.9H₂O] (1), [Mn₃(HL)(L)(μ₃-OH)(H₂O)(phen)₂·2H₂O] (2), and [Cd(HL)₄(H₂O)]·H₂O (3) (H₃L = 2-(3,5-dicarboxyphenyl)-6-carboxybenzimidazole; phen = 1,10-phenanthroline) have been synthesized and characterized spectroscopically and by single crystal X-ray diffraction. Single crystal X-ray diffraction results indicated that 1 forms a 2D layer-like framework, while 2 exhibits a 3-connected net with the Schläfli symbol of (4⁴.6), and 3 displays a 3D supramolecular network in which two adjacent 2D layers are held by π···π interactions. All three compounds have been used as photocatalysts to catalyze the photodegradation of antibiotic dinitrozole (DTZ) and rhodamine B (RhB). The photocatalytic results suggested that the Mn-based CP 2 exhibited better photodecomposition of DTZ (91.1%) and RhB (95.0%) than the other two CPs in the time span of 45 min. The observed photocatalytic mechanisms have been addressed using Hirshfeld surface analyses.

Metal fabrication workshops (MFWs) are common businesses in Ugandan cities, and especially those producing metallic security gates, window and door frames (burglar-proof), and balcony and staircase rails. The objective of this study was to comparatively assess the pollution levels and potential health risks of manganese (Mn), chromium (Cr), cadmium (Cd), lead (Pd) and nickel (Ni) in pooled surface soil samples from four 5-, 7-, 8-, and 10-year-old MFWs (n = 28) and a control site (n = 8) in Mbarara City, Uganda. The concentration of the potentially toxic elements (PTEs) was determined using inductively coupled plasma–optical emission spectrometry. Contamination, ecological, and human health risk assessment indices and models were used to identify any risks that the PTEs could pose to the pristine environment and humans. Our results showed that PTE pollution of soils is occuring in the MFWs than at the control site. The mean concentrations of the PTEs (mg kg⁻¹) in the samples were: Mn (2012.75 ± 0.23–3377.14 ± 0.31), Cr (237.55 ± 0.29–424.93 ± 0.31), Cd (0.73 ± 0.13–1.29 ± 0.02), Pb (107.80 ± 0.23–262.01 ± 0.19), and Ni (74.85 ± 0.25–211.37 ± 0.14). These results indicate that the PTEs could plausibly derive from the fabrication activities in these workshops, which is supported by the high values of contamination factors, index of geoaccumulation, and the overall increase in pollution load indices with the number of years of operation of the MFWs. Human health risk assessment showed that there are non-carcinogenic health risks that could be experienced by children who ingest PTEs in the soils from the 7-, 8- and 10-year-old MFWs. The incremental life cancer risk assessment suggested that there are potential cancerous health effects of Cd and Ni that could be experienced in children (who ingest soils from all the four MFWs) and adults (ingesting soils from the 8- and 10-year-old MFWs). This study underscores the need to implement regulatory guidelines on the operation and location of MFWs in Uganda. Further research should be undertaken to investigate the emission of the PTEs during welding operations in the MFWs.

Three new tertiary phosphane-appended heteroleptic Ni(II)-dithiolates with the formula [Ni(CAM)(dppe)] (Ni-1), [Ni(CAM)(dppf)] (Ni-2) and [Ni(CAM)(PPh₃)₂] (Ni-3) (CAM = cyanoacetamide dithiolate; dppe = 1,2-bis-(diphenylphosphinoethane); dppf = 1,1′-bis-(diphenylphosphino)ferrocene and PPh₃ = triphenylphosphane) have been synthesized and characterized spectroscopically and using single crystal X-ray diffraction technique. The single crystal X-ray analysis of Ni-1, Ni-2 and Ni-3 reveal distorted square planar geometry around Ni(II), wherein Ni(II) is coordinated to the two sulfur centres of a CAM ligand in the bidentate chelating mode and two phosphorus centers of dppe, dppf and PPh₃ ligands. Solid-state frameworks in these complexes are stabilized by C–O⋯H, C–N⋯H, C–S⋯H and C–H⋯C non-covalent intermolecular interactions. Ni-2 exhibits intramolecular (Ar)C–H⋯Ni anagostic interaction, which is absent in Ni-1 and Ni-3. Ni-3 exhibits intramolecular π⋯π stacking between the phenyl rings. The nature of these interactions have been assessed using Hirshfeld surface analyses, density functional theory (DFT) and quantum theory of atoms-in-molecules (QTAIM) calculations. Furthermore, the complexes have been employed as a homogeneous electrocatalyst for electrochemical hydrogen evolution reactions (HERs) using trifluoroacetic acid (TFA) as the hydrogen source. Electrochemical studies reveal turnover frequency (TOF) values of 319, 341 and 543 s⁻¹ for Ni-1, Ni-2 and Ni-3, respectively, at 50 mM concentration of TFA. The plausible reason for the relatively better electrocatalytic activity of Ni-3 is ascribed to the coordination flexibility of the PPh₃ ligand and the relatively larger positive natural charge over the nickel center and smaller HOMO–LUMO energy gap.

Construction of highly efficient non-platinum complexes as catalysts for electrochemical water splitting is the need of time. Herein, three new Ni(II)-based dithiolates, with formulas of [(dpdt)Ni(dppe)] (Ni-dpe), [(dpdt)Ni(dppf)] (Ni-dpf) and [(dpdt)Ni(PPh₃)₂] (Ni-pph) (dpdt = 3,4-dimethoxyphenylacetonitriledithiolate, dppe = 1,2-bis(diphenylphosphino)ethane, dppf = 1,1′-bis(diphenylphosphino)ferrocene and PPh₃ = triphenylphosphane), were synthesized and characterized. Single-crystal X-ray diffraction analysis of Ni-dpe revealed a distorted square planar coordination environment around nickel(II) fulfilled by two S and two P of the dpdt²⁻ and dppe ligands, respectively. Various non-covalent interactions, such as C–H⋯C, C–H⋯S and C–H⋯O, stabilized the lattice of Ni-dpe, and their nature was investigated using Hirshfeld surface analysis. Furthermore, the activities of these complexes as homogeneous electrocatalysts for HERs using trifluoroacetic acid (TFA) as a proton source and heterogeneous electrocatalysts for OERs in an aqueous KOH solution were evaluated. For homogeneous electrocatalysis, turnover frequencies (TOFs) of 402, 655 and 1761 s⁻¹ for Ni-dpe, Ni-dpf and Ni-pph were observed, respectively, at 100 mM TFA. The better electrocatalytic activity of Ni-pph was ascribed to the spatial flexibility of the PPh₃ ligands, which facilitated attainment of a more stable transition state than those of other complexes. For heterogeneous OERs, the results suggested that Ni-dpf displayed the lowest Tafel slope of 64 mV dec⁻¹ and the highest current density of 53.47 mA cm⁻², thereby exhibiting the best electrocatalytic activity.