Recent studies in the coordination chemistry of heterocyclic thiones and thionates

Hydroxyl radical generated from the reaction of Cu(+) with hydrogen peroxide results in oxidative DNA damage, and this damage is implicated in aging, cancer, and many other diseases. Selenium- and sulfur-containing compounds can act as antioxidants, and coordination of selenium and sulfur to copper is one explanation for this antioxidant activity. To determine how copper coordination results in antioxidant activity, biologically relevant tris(pyrazolyl)methane and borate Cu(+) complexes of the formulas Tp*Cu(L) and [Tpm(R)Cu(L)](+), where (L = N, N'-dimethylimidazole selone, dmise; N, N'-dimethylimidazole thione, dmit; Tp* = hydrotris(3,5-dimethylpyrazolyl)borate; Tpm(R) = tris(pyrazolyl)methane, R = H; Tpm, R = Me; Tpm*, R = iPr; Tpm(iPr)), have been synthesized and characterized. The structures of complexes Tp*Cu(Dmit), Tp*Cu(dmise), [Tpm(R)Cu(dmise)][BF(4)], and [Tpm(R)Cu(Dmit)][BF(4)] (where R = H; Tpm, R = Me; Tpm*, R = iPr; Tpm(iPr)) were determined by X-ray crystallography. All the Cu(+) centers adopt distorted tetrahedral coordination geometry, and Cu-Se and Cu-S distances for all the complexes are approximately 2.30 A, and 2.20 A, respectively. The effects of counterion and steric bulk at the 3 and 5 positions of the pyrazolyl ring on the structural and spectroscopic properties are discussed. Selone or thione coordination to copper significantly alters the Cu(+/2+) redox potential: Cu-selone complexes have Cu(2+/+) potentials from -283 to -390 mV, whereas those of Cu-thione complexes range from 70 to -232 mV versus NHE. The Cu-selone complexes have Cu(2+/+) potentials near or below that of the cellular reductant NADH (-324 mV). Thus, selenium and sulfur coordination to copper in biological systems may prevent the Cu(2+) reduction by NADH required for the catalytic formation of damaging hydroxyl radical.

Probing the antioxidant action of selenium and sulfur using Cu(I)-chalcogenone tris(pyrazolyl)methane and -borate complexes.

Coordination of Cu(I) halides with N,N′-dimethylimidazole selone (dmise) and thione (dmit) ligands was examined by treating CuX (X = Cl, Br, I) with one or two equivalents of dmise or dmit. The reaction of CuI and CuBr with one molar equivalent of dmise results in unusual selenium-bridged tetrameric Cu4(μ-dmise)4(μ-X)2X2copper complexes with average Cu–Se bond lengths of 2.42 A and a Cu2(μ-X)2 core (X = I (1) or Br (6)) that’s in a rhomboidal structure. The reaction of CuX (X = Cl, Br, and I) with two equivalents of dmit or dmise results in trigonal planar Cu(I) complexes of two different conformations with the formula Cu(dmit)2X (3a, 3b, 4, and 7) or Cu(dmise)2X (2, 5, and 8) with average Cu–S and Cu–Se bond lengths of 2.23 A and 2.34 A, respectively. The coordination geometry around the copper center in complexes 1 to 8 is determined by the type of halide and chalcogenone ligand used, intramolecular π–π interactions, and short contact interactions between X–H (X = I, Br, Cl, Se or S). The theoretical DFT calculations are in good agreement with experimental X-ray structural data and indicate that dmise ligands are required for formation of the tetrameric complexes 1 and 6. Electrochemical studies show that the trigonal copper selone complexes have more negative potentials relative to analogous copper thione complexes by an average of 108 mV.

Synthesis, characterization, and DFT studies of thione and selone Cu(I) complexes with variable coordination geometries†

Synthesis, X-ray and spectroscopic characterization of obtained throught the one-step reaction of mbit·2I2 with tin metal powder (mbit = 1,1′-bis(3-methyl-4-imidazoline-2-thione)methane)

The reactions of I2 with 1,1′-methylene- and 1,1′-ethylene-bis(3-methyl-4-imidazoline-2-thione)(mbit and ebit) have been investigated in CHCl3 solution at different temperatures by spectrophotometry. The experimental data have been processed using two different procedures of computer analysis: SUPERSPEC based on the conventional Gauss–Newton–Marquardt least-squares method; and POWELSPEC, based on Powell's direct search method for the refinement of ΔH° and ΔS°. The ability of the two methods to identify the involved equilibria correctly was compared. Evidence for the stepwise formation of the 1 : 1 and 1 : 2 adducts has been obtained by the two methods for the mbit case, while POWELSPEC only was able to solve the ebit case satisfactorily. The crystal structures of the adducts mbit·2I2 and ebit·2I2 have been determined. They show that the thionic sulfur atoms co-ordinate two diiodine molecules, with S–I 2.683(2)(mbit·2I2) and 2.642(3)(ebit·2I2)A and with I–I 2.897(1) and 2.903(2)A respectively, the two S–I–I groups beings related by a two-fold axis. The structural features of the S–I–I linear group are in accordance with Fourier-transform IR and Raman spectral data and can be taken into account with a three-centre two-electron axial orbitally deficient bonding scheme.

Evaluation of thermodynamic parameters for highly correlated chemical systems: a spectrophotometric study of the 1 : 1 and 2 : 1 equilibria between I2 and 1,1′-methylenebis(3-methyl-4-imidazoline-2-thione)(mbit) and 1,1′-ethylenebis(3-methyl-4-imidazoline-2-thione)(ebit). Crystal and molecular structures of mbit·2I2 and ebit·2I2

Main Group Metal Halide Complexes with Sterically Hindered Thioureas XIV. A Reinvestigation of Coordination Sensitive Modes in the Solid State Vibrational Spectrum of 1,3-Dimethyl-2(3H)-imidazolethione and Related Compounds

The crystal structure of the title compound, [ZnCl2(C7H10N2S)2], shows a discrete molecular structure with tetrahedral geometry around the zinc ion. The mean Zn—Cl and Zn—S distances are 2.259 (4) and 2.372 (4) A, respectively. Bond angles around the zinc ion range from 102.8 (1) to 113.7 (1)°. Ring distances and angles in the ligand compare favorably with literature values of analogous compounds, and the mean C—S bond distance of 1.71 (1) A is close to the average distance of 1.72 A observed for several dialkylimidazolethione complexes of main group and transition metal halides.

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Jeffrey W. Mudge

Papers

Main Group Metal Halide Complexes with Sterically Hindered Thioureas XIV. A Reinvestigation of Coordination Sensitive Modes in the Solid State Vibrational Spectrum of 1,3-Dimethyl-2(3H)-imidazolethione and Related Compounds

Dichlorobis[1-methyl-3-(prop-2-enyl)imidazole-2(3H)-thione-S]zinc(II)