Tarlok S. Lobana

Synthesis of [2-(pyridin-2′-yl)phenyl]-mercury(II) arylthiosemicarbazonates: An unusual coordination mode of a deprotonated 2-formyl-(2-hydroxy-benzene)-thiosemicarbazone

Abstract The reactions of [2-(pyridin-2′-yl)phenyl]mercury(II) acetate with 2-formyl-benzene-(Hbtsc), 2-formyl-(2-hydroxybenzene)-(H2stsc) and 2-formyl-(4-methoxybenzene)-(Hmbtsc) thiosemicarbazones in ethanol in 1:1 ratio at room temperature formed [Hg(C6H4C5H4N)L] (L=btsc, 1; Hstsc, 2; mbtsc, 3). The derivative [Hg(C6H4C5H4N)L] 2 crystallises in the triclinic space group P1 (n. 2), Z=2, R=0.0353 and V=906.8(3)A3. Mercury is bonded strongly only to sulphur atom of thiosemicarbazonate anion [Hg–S, 2,357(2)A] and Hg...N(3) distance of 3.126(6)A, slightly less than the sum of the van der Waals radii (3.28 A) shows a weak interaction. The pyridyl nitrogen binds strongly to Hg [Hg–N(4), 2.575(6)A] with a short C(9)HgN(4) bite angle of 74.6(2)°, but Hg retains near linearity in CPhHgS bond angle [177.8(2)°]. 1H and 19;Hg NMR spectra in CDCl3 solution reveal two isomers (A and B) for each of 1–3 and probably also a third isomer (C) for 2. The similarity of 1H and 19;Hg data of B isomers (minor for 1 and 3; major for 2) clearly support that thiosemicarbazones are unidentate S-donors as established for crystallized B isomer of 2 (major) by X-ray study, with pyridyl nitrogen of 2-pyridylphenyl coordinating to Hg. The A isomers (major for 1 and 3; minor for 2) have presumably N3,S-coordinated thiosemicarbazonates with weak Hg–N(pyridyl) interaction and the Hg atom formally tetracoordinated.

Synthesis of CuII-RuII-CuII trinuclear complexes via redox reaction of copperI across thiosemicarbazones coordinated to rutheniumII.

Pyridine-2-carbaldehyde thiosemicarbazones [C5H4N1-C(H)N2-N3H-C(S)-N4HR, R = H, L1H2; CH3, L2H2-Me; CH2CH3, L3H2-Et] with Ru(PPh3)3Cl2 have formed mononuclear RuII precursors for the generation of trinuclear complexes. The reaction of 2 mol each of L1H2, L2H2-Me, or L3H2-Et with Ru(PPh3)3Cl2 in the presence of Et3N has yielded mononuclear complexes [Ru(N3,S-L1H)2(PPh3)2] (1), [Ru(N3,S-L2H-Me)2(PPh3)2] (2), and [Ru(N3,S-L3H)2(PPh3)2] (3). The addition of 2 equiv of copperI chloride solution to complex 1 in acetonitrile has formed a novel trinuclear complex, (Ph3P)2RuII(L1)2CuII2Cl2 (4), in which the pendant amino group (-N4H2) loses one hydrogen along with the oxidation of CuI to CuII. In this complex, RuII is bonded to two P, two S, and two N3 atoms, while each CuII is coordinated to N1, N2, N4, and Cl atoms. Reaction with copper(I) bromide yielded a similar trinuclear complex, (Ph3P)2Ru(L1)2CuII2Br2 (5). From precursors 2 and 3, analogous complexes (Ph3P)2RuII(L2-Me)2CuII2Cl2 (6), (Ph3P)2RuII(L2-Me)2CuII2Br2 (7), (Ph3P)2RuII(L3-Et)2CuII2Cl2 (8), and (Ph3P)2RuII(L3-Et)2CuII2Br2 (9) have been synthesized. These complexes have been characterized using analytical, spectroscopic, and electrochemical techniques. Single-crystal X-ray crystallography has been carried out for precursor 2 and all of the trinuclear complexes, 4-9. X-band electron spin resonance and UV-vis spectra have confirmed the presence of CuII. The cyclic voltammetry studies support the RuII/RuIII redox behavior of this metal in trinuclear complexes.

Symmetrisation, isomerism and structural studies on novel phenylmercury(II) thiosemicarbazonates: correlation of the energy barrier to rotation of the amino group with the bonding parameters of the thioamide group

The reactions of phenylmercury(II) acetate with a series of alkyl, aryl and heterocyclic thiosemicarbazones in ethanol formed novel phenylmercury(II) derivatives of stoichiometry [HgPhL] [HLxa0=xa0RN3N2HC1(S)N1H2xa0= cyclopentanone 1, cyclohexanone 2, benzaldehyde 3, 2-hydroxybenzaldehyde 4, 4-methoxybenzaldehyde 5, pyrrole-2-carbaldehyde 6, thiophene-2-carbaldehyde 7 or furan-2-carbaldehyde 8 thiosemicarbazone], characterised with the help of analytical data, physical properties, IR, far-IR, multinuclear NMR (1H, 13C, 199Hg) spectroscopy and X-ray crystallography of complexes 1, 5 and 6. The 1H and 13C NMR data suggest that the N2H group is deprotonated during reaction with phenylmercury(II) acetate and co-ordination occurs via the N3,S atoms in a chelating mode. The 199Hg NMR data suggest symmetrisation phenomenon for complexes 3 and 5, 2[HgPhL]xa0⇌xa0HgPh2xa0+xa0[HgL], which is supported also by 1H and 13C NMR data. The δ(Hg) values reveal that shielding of Hg with the change of organic group in the thiosemicarbazones decreases in the order: 2-hydroxybenzenexa0⋙xa0 furanxa0>xa0benzenexa0>xa04-methoxybenzenexa0xa0thiophenexa0≈xa0cyclohexanonexa0≈xa0cyclopentanonexa0> pyrrole and the Lewis basicity of the thiosemicarbazones varies in the opposite order. The 1H and 13C NMR data reveal that 7 and 8 show isomerism. There are two strong [Hg–C 2.063(7) 1, 2.069(10) 5, 2.049(11) 6; Hg–S 2.382(2) 1, 2.357(3) 5, 2.377(3) A 6] and one weak bond [Hg–N3 2.489(6) 1, 2.611(7) 5, 2.492(9) A 6], with CPh–Hg–S bond angles of 162.9(2), 174.2(3), 165.8(3)° respectively. The weak intermolecular interactions via Hgxa0·xa0·xa0·xa0N2 [3.001(6) A] in 1 and via Hgxa0·xa0·xa0·xa0S in 5 [3.518(3) A] and 6 [3.528(3) A] form centrosymmetric dimers and Hg formally acquires four-co-ordination with two strong (Hg–C, Hg–S), one weak (Hgxa0·xa0·xa0·xa0N3) and one secondary (Hgxa0·xa0·xa0·xa0N2 or S) bonds. The preferred dimer formation via N2 nitrogen in 1, rather than via sulfur atoms (5 and 6) despite Hgxa0·xa0·xa0·xa0S affinity represents an unusual bonding mode. From the low-temperature 1H NMR studies of some selected complexes, the energy barrier (ΔGTc*, Tc is coalescence temperature) to rotation of the amino group about the C1–N1 bond was calculated and correlated with bonding parameters of the thioamide group in the solid state.

Diphenylthallium(III) thiosemicarbazonates: flexibility of coordination in the solid state and polymorphism in chloroform solution

Abstract The reactions of diphenylthallium(III) hydroxide in water–ethanol at room temperature with thiosemicarbazones HL=R=N(3)–N(2)H–C(1)(S)–N(1)H2 (RO=cyclopentanone, benzaldehyde, 2-hydroxybenzaldehyde, 4-methoxybenzaldehyde, acetophenone, furan-2-carbaldehyde, pyridine-2-formaldehyde and pyridine-2-acetaldehyde) afforded novel diphenylthallium(III) thiosemicarbazonates of stoichiometry [TlPh2(L)] (compounds 1–8, respectively) that were characterised with the help of analytical data, physical properties, IR spectrometry, multinuclear (1H, 13C and 205Tl) NMR spectroscopy and X-ray studies of 1, 7 and 8. In crystals of 1 (and probably also in those of 2, 4, 5 and 6), Tl(III) is bound to two phenyl carbons and to the N(3) and S atoms of the monodeprotonated thiosemicarbazone in a distorted trigonal bipyramidal coordination polyhedron with one vacant site in the equatorial plane. In 3 the metal atom is S,N(3),O-coordinated. In 7 and 8 there are three independent molecules: all three have distorted trigonal bipyramidal coordination with Tl coordinated to two carbon atoms and to the N(Py), N(3) and S atoms of the deprotonated thiosemicarbazones, but they differ significantly in their bonding parameters. The 205Tl NMR spectra suggest that for 1–6 more than one coordination mode is present in solution in chloroform, whereas for 7 and 8 there is only one species. Low temperature proton NMR studies of 7 and 8 showed that the energy barrier to rotation of the amino groups about the C1–N1 bond correlated with the bonding parameters of the thioamide group in the solid state; in both cases the barrier is somewhat higher than in thiosemicarbazonates of PhHg(II).

The crystal and molecular structures of cyclohexanone thiosemicarbazone

AbstractCyclohexanone thiosemicarbazone (Hchtsc) crystallizes in the triclinic crystal system with space group Pn

THE CRYSTAL STRUCTURE OF PHENYL(THIOPHENE-2-CARBALDEHYDE THIOSEMICARBAZONATO-N,S)MERCURY(II), [HgPh(tftsc)]

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Crystal and molecular structure of a lattice adduct, HgPh2•2[Hg(SCN)2(PPh3)2]: an unusual case of two-and four-co-ordinate mercury in the same unit cell

n (No. 2) and the following unit cell parameters: a = 6.2989(2), b = 7.9730(3), and c = 9.4118(2) Å α = 79.607(3), β = 85.519(2), and γ = 73.50(2)° V = 445.60(2) Å3, Z = 2. The lengths of the bonds C(1)–S, C(1)–N(1), C(1)–N(2), and N(2)–N(3) suggest electron delocalization in all four. The S atom is trans to N(3), and this E configuration is stabilized by intramolecular hydrogen bonding between N(3) and the N(1)H2 group. Two intermolecular hydrogen bonds involving the S atom and the N(1)–H(1b) and N(2)–H(2) groups give rise to a polymeric chain of molecule pairs.

Synthesis and X-ray crystal structure of chloro[2(1H)-pyridinethione-S]-bis(triphenylphosphine)copper(I)

Abstract The reaction of phenylmercury(II) chloride with acetophenonethiosemicarbazone (Hatsc) in ethanol in 1:1 mole ratio undergoes symmetrisation forming the products, HgCl2(Hatse)2 and Ph2Hg instead of the anticipated compound PhHgCl(Hatse). The analytical data, some physical properties, IR and NMR (1H, 11C, 199Hg) spectroscopy all support the formation of HgCl2(Hatse)2, 199Hg NMR of the solid obtained from the filtrate of the reaction provides evidence for Ph2Hg. This reaction represents the first example of a symmetrisation phenomenon observed in organomercury (II)-thiosemicarbazone chemistry.