Gunjan Rajput

The interplay of secondary Hg⋯S, Hg⋯N and Hg⋯π bonding interactions in supramolecular structures of phenylmercury(II) dithiocarbamates

Three new phenylmercury(II) and one mercury(II) dithiocarbamate complexes viz.PhHg S2CN(PyCH2)Bz (1), PhHg S2CN(PyCH2)CH3 (2), PhHg S2CN(Bz)CH3 (3), and [Hg (NCS2(PyCH2)Bz)2] (4) (Py = pyridine; Bz = benzyl) have been synthesized and characterized by elemental analyses, IR, electronic absorption, 1H and 13C NMR spectroscopy. The crystal structures of 1, 2 and 3 showed a linear S–Hg–C core at the centre of the molecule, in which the metal atom is bound to the sulfur atom of the dithiocarbamate ligand and a carbon atom of the aromatic ring. In contrast the crystal structure of 4 showed a linear S–Hg–S core at the Hg(II) centre of the molecule. Weak intermolecular Hg⋯N (Py) interactions link molecules into a linear chain in the case of 1, whereas chains of dimers are formed in 2 through intermolecular Hg⋯N (Py) and Hg⋯S interactions. 3 forms a conventional face-to-edge dimeric structure through intermolecular Hg⋯S secondary bonding and 4 forms a linear chain of dimers through face-to-face Hg⋯S secondary bonding. In order to elucidate the nature of these secondary bonding interactions and the electronic absorption spectra of the complexes, ab initio quantum chemical calculations at the MP2 level and density functional theory calculations were carried out for 1–3. Complexes 1 and 2 exhibited photoluminescent properties in the solid state as well as in the solution phase. Studies indicate that Hg⋯S interactions decrease and Hg⋯N interactions increase the chances of photoluminescence in the solid phase

Unusual C–H⋯Ni anagostic interactions in new homoleptic Ni(II) dithio complexes

Six new homoleptic complexes of the general form [Ni(L2)] [L = L1 (9-fluorenylmethyl)xanthate (1); L2 (cyclobutylmethyl)xanthate (2); L3 (1-benzyl-4-hydroxypiperidine)xanthate (3); L4 (N-benzyl-N-methylpyridyl)dithiocarbamate (4); L5 (N-methylfuryl-N-methylpyridyl)dithiocarbamate (5); L6 (N-benzyl-N-methylfuryl)dithiocarbamate (6)] have been prepared and characterized by microanalysis, spectroscopy (IR, 1H and 13C NMR, UV-Vis) and their structures have been elucidated by X-ray crystallography. In all complexes the metals are four coordinate with square planar coordination geometries although in the crystal structures of 2 and 4 significant C–H⋯Ni anagostic intermolecular interactions in axial positions are found which involve the metal atom in chain motifs. As far as we are aware 2 and 4 are unique examples of homoleptic metal dithio complexes exhibiting such type of anagostic interactions. In the remaining complexes (1, 3, 5 and 6) supramolecular frameworks are stabilised by S⋯S, C–H⋯S, C–H⋯π and π⋯π non-covalent interactions. All six complexes are weakly conducting (σrt = 10−11–10−8 S cm−1; Ea = 0.37–1.40 eV) and show semiconductor behaviour in the 303–393 K temperature range.

Rare intermolecular M⋯H–C anagostic interactions in homoleptic Ni(II)–Pd(II) dithiocarbamate complexes

New functionalized homoleptic dithiocarbamates of the form [M(L)2] (M = Ni(II), L = L1, N-(3-methoxybenzyl)-N-(methylbenzyl)dithiocarbamate (1), L3, N-(3,4,5-trimethoxybenzyl)-N-(3-methylpyridyl)dithiocarbamate (3), L4, N-(4-methoxybenzyl)-N-benzyldithiocarbamate (4); Pd(II), L2, N-(N′-methyl-2-pyrrole)-N-benzyldithiocarbamate (2)) have been synthesized and characterized by microanalysis and their structures have been investigated using X-ray crystallography. All the four structures are centrosymmetric with the metal located in a square plane with minor distortions, Pd(II) greater than Ni(II). The crystal structures of 1 and 2 revealed the existence of unique intermolecular C–H⋯M (Ni, Pd) anagostic interactions between the methylene hydrogen atom on the ligand substituents and the metal centres and these enable the formation of 1-D polymeric chains. Particularly, geometric parameters (Pd⋯H–C = 2.61 A; ∠Pd⋯H–C = 173°) for the C–H⋯Pd interactions in 2 are at the border of anagostic and hydrogen bonding. By contrast, 4 shows interactions between the methylene hydrogen atom and the CS2Ni ring rather than the metal alone, while the interaction in 3 is intermediate between the two aforementioned types. These interactions are not shown in solution as revealed by their 1H NMR studies. DFT calculations have been performed to analyse these rare interactions. 1, 3 and 4 are weakly conducting, σrt = 10−10–10−12 S cm−1, and show semiconductor behaviour in the 313–373 K range.

New planar trans-copper(II) β-dithioester chelate complexes: synthesis, characterization, anticancer activity and DNA-binding/cleavage studies

Abstract New planar trans-copper(II) β-dithioester complexes, [Cu(L)2] (L = methyl-3-hydroxy-(3-pyridyl)-2-propenedithioate (L1 in 1), methyl-3-hydroxy-(2-naphthyl)-2-propenedithioate (L2 in 2), methyl-3-hydroxy-3-(p-methoxyphenyl)-2-propenedithioate (L3 in 3), methyl-3-hydroxy-3-(p-fluorophenyl)-2-propenedithioate (L4 in 4), and methyl-3-hydroxy-3-(p-bromophenyl)-2-propenedithioate (L5 in 5)), have been synthesized and characterized by elemental (C, H, N and S) analysis, ESI-MS, IR, and UV-vis spectra. The structures of HL3 and its corresponding complex 3 have been determined by X-ray crystallography. Electrochemical behavior of all complexes has been studied by cyclic voltammetry. All five planar complexes show efficient DNA-binding and DNA (PBR322)-cleavage in a concentration-dependent manner (1 > 3 > 5 > 2 > 4). Cleavage efficiency is enhanced in the presence of H2O2 as well as ascorbic acid. However, the order of increased efficiency of Cu(II) chelates differs in the presence of H2O2 as 4 > 1 > 2 > 3 > 5. Among these complexes, the pyridyl- and methoxy-functionalized 1 and 3 have shown higher self-activating capability in DNA-cleavage. All complexes show significant variation in IC50 on MCF-7 cell line. Additionally, treatment with the complexes gradually increases apoptotic cell death in dose-dependent manner in RAW 264.7 cell line. These findings highlight potential cancer protective nature of these complexes.

Anti-leishmanial activity of Ni(II), Pd(II) and Pt(II) β-oxodithioester complexes

New functionalized planar β-oxodithioester cis-chelate complexes, [M(L)2] (L = L1, methyl-3-hydroxy-3-(p-bromophenyl)-2-propenedithioate, M = Ni 1, Pd 5, Pt 9; L2, methyl-3-hydroxy-3-(p-fluorophenyl)-2-propenedithioate, Ni 2, Pd 6, Pt 10; L3, methyl-3-hydroxy-3-(naphthyl)-2-propenedithioate, Ni 3, Pd 7, Pt 11; methyl-3-hydroxy-3-(p-methoxyphenyl)-2-propenedithioate, Ni 4, Pd 8, Pt 12), have been synthesized and characterized by elemental analysis, IR, UV-Vis, 1H and 13C NMR spectroscopy; the structures of 2–4, 8 and 11 have been elucidated by X-ray crystallography. In all crystal structures, the metal has four-coordinate slightly distorted square planar geometry with a cis-configuration of the ligands. These complexes have been assessed for their use as anti-leishmanial agents; 7 and 9 showed impressive anti-promastigote and anti-amastigote efficacy with IC50 values of 0.59 ± 0.10 μg mL−1, 0.56 ± 0.10 μg mL−1 and IC50 0.85 ± 0.27, 1.99 ± 0.08 μg mL−1, respectively. Cytotoxicity assays on both compounds displayed toxicity on the promastigotes but less toxicity against RAW 264.7 cell lines at different concentrations. The Pd and Pt complexes exhibit luminescent characteristics in solution, originating from the intraligand charge transfer state.

Investigation of crystal structure, vibrational characteristics and molecular conductivity of 2,3-dichloro-5,6-dicyno-p-benzoquinone.

Molecular geometries and vibrational spectra for the ground state of 2,3-dichloro-5,6-dicyno-p-benzoquinone (DDQ) and its anion (DDQ(-)) were computed using DFT method at the B3LYP level employing 6-311++G(d,p) basis set whereas for the first excited state (DDQ(∗)), these were calculated using TD-DFT at the B3LYP level employing the 6-311++G(d,p) basis set available with the Gaussian 09 package. The spectra have been experimentally investigated and the observed IR and Raman bands have been assigned to different normal modes on the basis of the calculated potential energy distributions (PEDs). XRD of single crystal has been investigated to determine molecular and crystal structures of DDQ. In order to elucidate the transfer of electrons, electronic structure and electronic absorption have been calculated with the TD-DFT method. Vibronic interaction and its role in the appearance of superconductivity in the DDQ, DDQ(-) and DDQ(∗) molecules have been investigated. The present XRD, molecular, electronic and vibronic studies indicate that mainly the ag C=O stretching and ring stretching modes participate in the charge transfer process.

Synthesis, characterization, DNA binding and cleavage activity of homoleptic zinc(II) β-oxodithioester chelate complexes

Abstract New homoleptic zinc(II) complexes, [Zn(L)2], where L = methyl-3-hydroxy-(3-pyridyl)-2-propenedithioate L1 1, and methyl-3-hydroxy-(4-pyridyl)-2-propenedithioate L2 2, have been synthesized and characterized by elemental (C, H, and N) analysis, ESI-MS, and (IR, UV–vis, NMR) spectroscopy; the structure of 1 has been deduced by X-ray crystallography. The DNA binding and cleavage activity of the complexes have been studied. The cleavage potential of pBR322 DNA by 1 and 2 has been checked. Complex 1, which contains nitrogen of the pyridine group in the 3-position enhances DNA cleavage potential in the presence of ascorbic acid; however, the complex is protective against DNA cleavage in the presence of DMSO or H2O2. Also, 1 causes cytotoxicity against the MCF-7 breast cancer cell line. The efficient cytotoxic activity and DNA cleavage ability of 1 in the presence of ascorbic acid shows its potential anticancer properties and the need for further investigations of its potential as an anticancer drug.