Nanhai Singh

Synthesis, structure and light-harvesting properties of some new transition-metal dithiocarbamates involving ferrocene.

Nine new transition-metal dithiocarbamates involving ferrocene (Fc), namely, [M(FcCH(2)Bzdtc)(2)] (M=Ni(II) (1), Cu(II) (2), Cd(II) (3), Hg(II) (4), Pd(II) (5), Pt(II) (6) and Pb(II) (7); Bzdtc=N-benzyl dithiocarbamate) and [M(FcCH(2)Bzdtc)(3)] (M=Co(II) (8) and UO(2) (VI) (9)), have been synthesised and characterised by micro analyses, IR spectroscopy, (1)H and (13)C NMR spectroscopy, and in three cases by single-crystal X-ray analysis. The peak broadening in the (1)H spectrum of the copper complex indicates the paramagnetic behaviour of this compound. A square-planar geometry around the nickel and copper complexes and distorted linear geometry around the mercury complex have been found. The latter geometry is attributed to the bulkiness of the methylferrocenyl and benzyl groups. The observed single quasi-reversible cyclic voltammograms for complexes 2, 8 and 9 indicate the stabilisation of a metal centre other than Fe in their characteristic oxidation state. These complexes have been used as a photosensitiser in dye-sensitised solar cells.

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

Intermolecular anagostic interactions in group 10 metal dithiocarbamates

New functionalized homoleptic xanthate and dithiocarbamates of the form [M(L)2] (M = Ni(II), L = L1 (4-methoxyphenethylxanthate) 1, L2 (4-ethoxycarbonylpiperidine-1-dithiocarbamate) 2, L3 (N,N′-difurfuryldithiocarbamate) 3; M = Pt(II), L3, 4, M = Pd(II), L4 (N-benzyl-N′-3-methylpyridyldithiocarbamate) 5) have been synthesized and characterized using microanalyses, and their structures have been investigated by X-ray crystallography. All five complexes are centrosymmetric with the central metal in a distorted square planar structure; the distortion varies in the order Pt > Pd > Ni. In 3, 4 and 5 the ligand framework and crystal packing effects force the methylene proton on the substituents into close proximity with the metal centers, forming intermolecular C–H⋯M (M = Ni, Pt and Pd) anagostic interactions and generating a 1-D polymeric chain; 4 and 5 are the first examples containing Pt and Pd that exhibit such interactions. Similar anagostic interactions are also observed in 2 but are rather weaker. These interactions have been supported by theoretical calculations. The xanthate complex 1 displays unique S⋯S intermolecular interactions leading to a 1-D polymeric chain, while no significant intermolecular interactions involving the metal centres have been found. The supramolecular structures are sustained by weaker O⋯H, S⋯H, C–H⋯π and C–H⋯π (chelate, CS2M) interactions. 1 is weakly conducting (σrt = 1.39 × 10−7 S cm−1) but shows semiconductor behaviour in the 303–363 K range. The platinum complex 4 shows luminescent properties in solution.

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.

Effect of pyridyl substituents leading to the formation of green luminescent mercury(II) coordination polymers, zinc(II) dimers and a monomer

Pyridine-2, -3 and -4 functionalized dithiocarbamate ligands yielded the coordination polymers with mercury, namely [{Hg(L)2}n] (L = L1, C5H4NCH2NCS2CH2C7H5O2 (1); L2, C5H4NCH2NCS2CH3 (2); L3, C5H4NCH2NCS2CH2C4H3O (3); and L4, C5H4NCH2NCS2CH2CH2C6H5 (4)), [PhHg(L3)] (5), and mononuclear [Hg(L5)2], L5 = C5H4NCH2NCS2CH2C6H5 (6). Unexpectedly, the pyridine-2-functionalized ligand, L6, C5H4NCH2NCS2CH2C6H5 gave a cyclized product, benzyl-2H-imidazo[1,5-a]pyridine-3-thione (7), C14H13N2S, instead of a mercury complex. Complexes with zinc were also characterized, namely dinuclear [Zn2(L5)4] (8) and [Zn2(L7)4], L7 = CH3CH2O2C5H9NCS2 (9) and a mononuclear complex [Zn(L8)2], L8 = C4H3NCH3CH2NCS2CH2C6H5 (10). These ten compounds have been characterized by microanalysis and X-ray crystallography. Complexes (1, 2) and 3 are 1-D and 2-D coordination polymers in which the ligands are uniquely bonded in the bridging-chelating mode in a μ2, κ3-N, S, S fashion establishing square pyramidal five-coordinate and octahedral six-coordinate geometries about the Hg atom respectively. The structure of 4 is also a 1-D coordination polymer formed via bridging sulphur bonds with a five-coordinate distorted geometry about the mercury atom. 6 is a mononuclear mercury(II) complex forming an interesting polymeric 1-D architecture through intermolecular Hg⋯S interactions. 8 is the first example of a homoleptic dinuclear zinc(II) dithiocarbamate complex bridged through ligand L5 in a μ2, κ3-N, S(11), S(13) bridging-chelating manner. L7 and L8 form a typical S, S-bridged dimer 9 and a mononuclear complex 10. The nature of the Hg–N and Zn–N bonds in the coordination polymers 1, 2 and 3 and in the dinuclear 8 has been assessed by DFT calculations. Complexes 1–9 are luminescent in both solution and solid phases; especially, significant red shifted green emission in the solid phase for the coordination polymers 1, 2 and 3 shows good structure–property correlations.

SYNTHESIS AND STRUCTURAL STUDIES OF SOME FIRST ROW TRANSITION METAL COMPLEXES OF SALICYLALDEHYDE HYDRAZONE

Durch Mischen einer methanolisch-ethanolischen Losung des Hydrazons mit den entsprechenden Metallsalzen im Verhaltnis 2:1 wurden die Komplexe (I) bzw. (III) dargestellt.

Self assembly of homoleptic Ni(II) dithiocarbamates and dithiocarbimates via Ni⋯H–C anagostic and C–H⋯π (chelate) interactions

New homoleptic complexes of the form [Ni(L)2] (L = L1 (dibenzyl dithiocarbamate) 1, L2 (N-benzyl-N,N-dimethyl ethylene dithiocarbamate) 2, and (R)2[Ni(L3)2)] (L3 = p-chlorobenzene sulfonyl dithiocarbimate; R = (C2H5)4N+3, (C3H7)4N+4, (C6H13)4N+5) have been prepared and characterized by elemental analyses, IR, 1H and 13C NMR and UV-visible absorption spectra. In addition, their structures have been elucidated by X-ray crystallography. The crystal structure of 1 reveals unusual C–H⋯Ni intermolecular anagostic interactions in axial positions resulting in 1D supramolecular chains, whereas complex salts 3 and 5 display unique C–H⋯Ni anagostic interactions due to the close proximity of one or two methylene protons in the cationic moieties to the Ni(II) center of the [Ni(L3)2]2− complex anion, providing pseudo-square pyramidal and octahedral coordination environments respectively about the metal centers. To the best of our knowledge, 3 and 5 are the first examples of inter-ionic anagostic interactions within dithio complexes. Theoretical calculations have been performed for 3 and 5. The energy of interaction for 3 and 5 was found to be more than the previously reported neutral complexes. The supramolecular networks in all the complexes are sustained by non-conventional C–H⋯O, C–H⋯N and C–H⋯π (chelate, NiS2C) bonding interactions. All complexes are weakly conducting with σrt ∼10−6 S cm−1.

Influence of ligand environments on the structures and luminescence properties of homoleptic cadmium(II) pyridyl functionalized dithiocarbamates

Novel homoleptic pyridyl-3(N) functionalised dithiocarbamate complexes having polymeric, [Cd(L)2] (L = L1, C5H4NCH2NCS2CH2C6H5 (1), L2, (C5H4NCH2)2NCS2 (2), L3, C5H4NCH2NCS2CH2C4H3O (3) and L4, C5H4NCH2NCS2CH2C4H3S (4)); dinuclear, [Cd(L)2]2 (L = L5, (C8H6NCH2NCS2CH2NC5H4) (5)) and trinuclear, [Cd(L6)2]3 (L6 = CH3C6H4CH2NCS2CH2C4H3O) (6)) structures have been synthesised and characterized by elemental analysis, IR, UV-vis, and 1H and 13C NMR spectroscopy and their structures have been elucidated by X-ray crystallography. In 1–4, the cadmium(II) ions are six-co-ordinate with two bidentate dithiocarbamate ligands (L1–L4) in an equatorial plane and axially bonded by Py(N) of the dithiocarbamate ligands on adjacent molecules, thus adopting a distorted octahedral geometry (CdS4N2) in 2-D polymeric structures. Complexes 1 and 2 are isomorphous and have similar structures to those of 3 and 4, although they differ significantly in architecture and topology. In 3 and 4, the metal atoms occupy centrosymmetric sites. In marked contrast to these polymeric structures, complex 5 derived from ligand L5 containing a bulky indolyl substituent proved to be a dinuclear complex. In 5, the metal atom has a square pyramidal geometry. As in 1–4, the dithiocarbamate ligand in 5 is uniquely bonded to the metal centres in a μ2,κ3-N,S,S bridging-chelating fashion. Ligand L6 containing furfuryl and tolulyl substituents yielded a spectacular centrosymmetric trinuclear complex 6 with the central metal atom in an octahedral environment and the two outer metal atoms in square pyramidal environments in which the dithiocarbamate ligands are bonded in a μ2,κ2-S,S chelating-bridging and S,S chelating manner within the same molecule. To the best of our knowledge, 1–4 and 5 and 6 are the first examples of 2-D coordination polymeric, dinuclear and trinuclear cadmium dithiocarbamates. All the complexes show bright luminescence emission in the solid state; the coordination polymers 1 and 2 are strongly luminescent.

Preparation, spectroscopic investigation and antibacterial activity of some organomercury(II) and organotin(IV) dithio complexes

Phenylmercuric acetate, triphenyltin chloride and dibutyltin chloride react with alkali-metal or ammonium salts of some 1,1- and 1,2-dithio ligands in appropriate molar ratios to yield a series of organometallic dithio complexes of the type [PhHgX] (X = butylxanthate (Buxant−), cyclohexylxanthate (Cyxant−), benzylxanthate (Bzxant−) or pyrrolidin-1-yldithiocarbamate (Pdtc−); [(PhHg)2X] (X = isomaleonitriledithiolate (i-MNT2−) or 1-ethoxycarbonyl-1-cyanoethylene-2,2-dithiolate (ecda2−); Ph3SnX (X = Buxant− or Pdtc−); [(Ph3Sn)2(i-MNT)] and [Bu2SnMNT] (MNT2− = maleonitriledithiolate). These complexes have been characterized by elemental analysis, molar conductance measurements, IR, FT-Raman, 1H and 13C NMR and fast atom bombardment (FAB) mass spectra. Cyclic dimeric structures for phenylmercuryxanthates and monomeric structures for the remaining complexes are suggested. Antibacterial activities of the complexes and parent ligands have been screened against some well-known pathogenic bacteria. Organomercury dithiolates have been found to be more potential antibacterial than organotin complexes. Copyright