Ajit N. Gupta

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.

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.

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.

Polyoxomolybdate(VI) anion stabilized by ammonium cation via CS2 elimination from N-benzyl-N-methylferrocenyl dithiocarbamate

A new polyoxomolybdate [(FcCH2)NH2(CH2C6H5)]4[Mo8O26] has been obtained by the reaction of ammonium molybdate and potassium N-benzyl-N-methylferrocenyl dithiocarbamate in mild acidic condition. The resulting cluster has been characterized by microanalyses, electronic absorption, photoluminescence, IR, and 1H NMR spectroscopy, and its electrochemical properties. Quantum chemical calculations have been performed in order to explain the CS2 elimination from the dithiocarbamate moiety. Single-crystal X-ray analysis of this compound reveals that the ammonium cation generates an intricate 2-D supramolecular architecture.

Influence of ligand environment on the structure and properties of silver(I) dithiocarbamate cluster-based coordination polymers and dimers

Luminescent silver(I) homo- and heteroleptic pyridyl functionalised dithiocarbamate (dtc) complexes of the form, [{Ag(L)}4]∞ (L = N-benzyl-N-methylpyridyldtc (L1) 1, bis-(N-methylpyridyl)dtc (L2) 2) and [Ag(L)PPh3]2 (L = L1 (3), L2 (4)) have been synthesized and characterized by elemental analysis, TGA, spectroscopy (IR, 1H, 13C and 31P NMR and UV-Vis) and X-ray crystallography. Complexes 1 and 2 are isomorphous and have a tetranuclear cluster-based coordination polymeric structure. In these tetranuclear silver(I) cluster subunits the four Ag atoms form a distorted tetrahedron. Complexes 3 and 4 are also isostructural and have centrosymmetric structures in which each Ag atom forms a distorted tetrahedral coordination geometry. All complexes are weakly conducting and exhibit semiconductor behaviour. 1–4 are strongly luminescent in solid phase; a correlation between their structure and luminescent properties has been established.