NMR and fluorescence spectral studies on bisdithiocarbamates of divalent Zn, Cd and their nitrogenous adducts: Single crystal X-ray structure of (1,10-phenanthroline)bis(4-methylpiperazinecarbodithioato) zinc(II)

The current paper describes the synthesis and characterization of the following adducts: [Zn(4-mpzdtc)2(1,10-phen)] · H2O (1), [Zn(4-mpzdtc)2(2,2′-bipy)] (2), [Cd(4-mpzdtc)2(1,10-phen)] (3), [Cd(4-mpzdtc)2(2,2′-bipy)] (4), [Zn(padtc)2(1,10-phen)] (5) and [Cd(padtc)2(1,10-phen)] (6) (where, 4-mpzdtc = 4-methylpiperazinecarbodithioate anion, padtc = N,N′-(iminodiethylene)bisphthalimide dithiocarbamate anion, 1,10-phen = 1,10-phenanthroline and 2,2′-bipy = 2,2′-bipyridine). All the synthesized complexes were characterized by UV–Vis, IR, NMR, (1H and 13C) and fluorescence spectra. A single crystal X-ray structural analysis was carried out for complex 1. IR spectra of the complexes show the contribution of the thioureide form to the structures. The observed deshielding of the α-protons for 1–6 in the 1H NMR spectra is attributed to the drift of electrons from the nitrogen of the NR2 groups, forcing a high electron density towards sulfur via the thioureide π-system. In the 13C NMR spectra, the most important thioureide (N13CS2) carbon signals are observed in the region 206–208 ppm. Fluorescence spectra of complexes 5 and 6 show intense fluorescence due to the presence of rigid conjugated systems such as phthalimide and 1,10-phenanthroline. The observed fluorescence maxima for complexes with a MS4N2 chromophore in the visible region are assigned to the metal-to-ligand charge transfer (MLCT) processes. Single crystal X-ray structural analysis of 1 showed that the zinc atom is in a distorted octahedral environment with a MS4N2 chromophore. VBS equivalent to 1.81 supports the correctness of the determined structure. The piperazine ring in the dithiocarbamate fragment is in the normal chair conformation.

Graphical abstractSix complexes with the MS4N2 (M = Zn or Cd) chromophore have been synthesized. IR spectra of the complexes show the contribution of the thioureide form to the structures. NMR and fluorescence spectra of the complexes show interesting properties. Single crystal X-ray structural analysis of one of the complexes showed the zinc atom to be in a highly distorted octahedral environment with the MS4N2 chromophore.Figure optionsDownload full-size imageDownload as PowerPoint slide