Effect of functionalities on the crystal structures of new zinc(ii) dithiocarbamates: a combined anti-leishmanial and thermal decomposition study

Abstract

New homoleptic zinc(II) dithiocarbamates, [Zn(L)₂] (L = N-ferrocenyl-N-methyl dithiocarbamate (L1) 1, (N-(benzo[d][1,3]dioxol-5-ylmethyl)-N-furfuryl) dithiocarbamate (L2) 2, N-(benzo[d][1,3]dioxol-5-ylmethyl)-(N-benzyl) dithiocarbamate (L3) 3, N-(benzo[d][1,3]dioxol-5-ylmethyl)-(N-methyl) dithiocarbamate (L4) 4, N-ethylmorpholine-(N-4-methoxyphenylmethyl) dithiocarbamate (L5) 5 and N-(benzo[d][1,4]dioxol-6-ylmethyl)-(N-benzylmethyl) dithiocarbamate (L6) 6, have been synthesized and characterized by elemental analyses and spectroscopy (IR, UV-vis, ¹H and ¹³C{¹H} NMR). X-ray crystallography revealed different dimeric structures for (1 and 2) and (3, 4, and 5) adopting distorted tetrahedral and TBP/SP coordination geometries, respectively, in which the dithiocarbamate ligands are bonded to the metal centers both in terminal S,S-chelating and μ₂,κ²S,S-bridging and μ₂,κ²-S,S-chelating–bridging arrangements. 6 is a mononuclear complex showing a distorted tetrahedral geometry. The supramolecular frameworks in these complexes have been sustained by C–H⋯S, C–H⋯O, C–H⋯π, π⋯π, C–H⋯π (ZnCS₂, chelate) and H⋯H interactions. The anti-leishmanial activities of the complexes have been screened; 4 and 6 showed potential anti-promastigote and anti-amastigote activities with IC₅₀ values of 0.66 ± 0.22, 1.48 ± 0.10 μg mL⁻¹ and IC₅₀ 2.98 ± 0.30, 2.51 ± 0.10 μg mL⁻¹, respectively. Cytotoxicity assays on both complexes showed toxicity on promastigotes but lower toxicity against the RAW 264.7 cell line at different concentrations. All the complexes show luminescence characteristics in CH₂Cl₂ solution at room temperature arising from the metal perturbed intra-ligand charge transfer (ILCT) states. Their TG analyses show single step decomposition with formation of binary ZnS and ternary FeZn₂S₃ materials which have been examined by PXRD, SEM and EDAX.