Impact of substituents on the crystal structures and anti-leishmanial activity of new homoleptic Bi(iii) dithiocarbamates

Six new functionalised homoleptic Bi(iii) dithiocarbamate complexes, [Bi(L1-L6)(3)] (L1 = (N-4-nitrobenzyl-N-furfuryl)dithiocarbamate 1, L2 = (N-4-chlorobenzyl-N-3-methylpyridyl)dithiocarbamate 2, L3 = (N-4-bromobenzyl-N-3-methylpyridyl)dithiocarbamate 3, L4 = (N-4-dimethylaminobenzyl-N-3-methylpyridyl)dithiocarbamate 4, L5 = (1-(2-pyridyl)piperazine)dithiocarbamate 5 and L6 = (N-4-methoxybenzyl-N-benzyl)dithiocarbamate 6), have been prepared and characterised by elemental analyses, powder X-ray diffraction (PXRD) and (IR, UV-Vis, H-1 and C-13{H-1} NMR) spectroscopy. The structures of the six complexes have been revealed in the solid state by X-ray crystallography and assessed by DFT calculations. Complexes 1 and (2, 5 and 6) are similarly dimeric in which the three dithiocarbamate ligands are bound to the seven and eight-coordinate Bi(iii) centre, respectively, in asymmetric S,S-bidentate and mu(2),kappa(2) S,S-chelating/chelating-bridging modes. By contrast, complex 4 is monomeric with a six-co-ordinate metal atom while complex 3 forms a polymeric structure with the metal in a seven-coordinate environment. The specific geometries of all compounds are distorted by the stereochemical lone pair. In these complexes, supramolecular structures have been sustained by non-covalent C-HMIDLINE HORIZONTAL ELLIPSISN, C-HMIDLINE HORIZONTAL ELLIPSISO, C-HMIDLINE HORIZONTAL ELLIPSISCl, C-HMIDLINE HORIZONTAL ELLIPSISBr, C-HMIDLINE HORIZONTAL ELLIPSIS pi, C-HMIDLINE HORIZONTAL ELLIPSIS pi (BiCS2, chelate) and HMIDLINE HORIZONTAL ELLIPSISH interactions. The anti-leishmanial activities of the complexes have been tested; 5 and 6 showed potential anti-promastigote activity with IC50 values of 7.16 and 7.44 mu M, and anti-amastigote activity with IC50 values of 8.40 and 9.70 mu M, respectively. Cytotoxicity assays for complexes 1-6 showed toxicity on promastigotes but lower toxicity against the RAW 264.7 cell line at different concentrations.