M-S vibrational study in three-coordinate thiolato compounds (NEt4)2[M(SC6H4-p-X)3] and (NEt4)

By using p-substituted benzenethiolate ligands, the novel three-coordinate copper(I) and silver(I) thiolato complexes (NEt4)2[Cu(SC6H4-p-X)3] (X=Cl (1) and Br (2)), (NEt4)2[Ag(SC6H4-p-X)3] (X=Cl (3) and Br (4)) and novel clusters (NEt4)2[M4(mu-SC6H4-p-Cl)6] (M=Cu (5) and Ag(6)) have been prepared and structurally characterized by single crystal X-ray diffraction. All the complexes have three-coordinate sites having point-group D3h symmetry. The three-coordinate mononuclear silver(I) complexes 3 and 4 are the first examples. The M-S stretching bands were determined by far-IR and FT-Raman spectroscopies; nu(Cu-S) 363-372 cm(-1) and nu(Ag-S) 353-363 cm(-1). These results indicate that M-S stretching vibration energy in the three-coordinate metal(I) site of the mononuclear compounds or clusters is around 340-380 cm(-1), and it is a useful tool for determining their coordination modes.     

95Mo NMR studies of complexes containing the Mo2O52+ core and crystal structure of Mo2O5[SC6H4NHCH2C5H4N]2(C3H7NO)3

The crystal structure of Mo₂O₅[SC₆H₄NHCH₂C₅H₄N]₂(C₃N₇NO)₃ is reported and seen to consist of a single oxo-bridged species with each Mo atom bonded to cis dioxo groups and the nitrogen atoms and thiolate group of the tridentate ligand. ⁹⁵Mo NMR spectra of this and three related complexes are presented and attempts made to interpret them in terms of their crystal structures.     

The structure of a dinuclear silver(I) complex: Ag2[S2C2(CN)2] [P(C6H5)3]4

The crystal structure of the dimeric Ag maleonitriledithiolate complex, Ag₂[S₂C₂(CN)₂] [P(C₆- H₅)₃]₄ (1), has been performed. Complex 1 crystallizes in the space group P2₁/c with a = 12.2898(77), b = 23.8325(91), c = 23.1790(118) Å, β = 101.315(43)° and Z = 4. Refinement using 3253 reflections with F_o²>3σ(F_o²) yielded R = 0.0662, R_w= 0.0669. The most interesting aspect of the structure is the strong bridging interaction of the chelating maleonitriledithiolate ligand with the second Ag center, where a Ag-S distance of 2.478 Å is observed. The residual bonding capability of the sulfur atoms in the chelating anion [Ag(S₂C₂(CN)₂)(PPh₃)₂]⁻ for [Ag(PPh₃)₂]⁺ is demonstrated.     

Preparation,crystal structure and thermal behaviour of bischromatodihydroxobis-(pyridine)tricopper(II) [Cu3(CrO4)2(OH)2(C5H5N)2]

The title compound was prepared by slow crystallization from a hot aqueous solution of copper(II)- dichromate and pyridine. The structure determination was performed at room temperature on a single crystal in the triclinic space group P$\text{1}$, a = 5.378(1), b = 5.619(1), c = 13.569(2) Å, α = 93.32(1), β = 100.25(1), γ=98.45(1)°. Using 2026 reflections with F_o² > (F_o²) obtained on a CAD-4 single crystal diffractometer the structure was solved by conventional Patterson and Fourier methods and full matrix least-squares refinement to R = 0.047. The structure consists of complex chains built up from two different (4 + 2) distorted copper(II) octahedra sharing common edges. These chains are linked via OCrO bonds thus forming a two-dimensional infinite network. The pyridine rings extending into the space between these layers are disordered due to rotation around the CuN bond. In the course of the refinement two favoured positions with occupation probabilities 50:50 percent were found. During thermal decomposition the compound loses pyridine and water followed by a release of oxygen to yield poly- crystalline CuCr₂O₄ and CuO. An intermediate phase with empirical formula Cu₃O(CrO₄)₂ was detected by X-ray powder diffraction and its unit cell parameters were determined.     

Structural chemistry of dicyclopentadienidehalides of lanthanides Part 4. Erbiumdicyclopentadienidechloride [Er(C5 H5)2Cl]2

The crystal structure of erbiumdicyclopentadienidechloride [Er(C₅H₅)₂Cl]₂ has been determined from X-ray diffraction data. The compound crystallizes in space group P2₁/c with a=11.056(3), b= 8.015(1), c=12.154(3) Å, β=110.28(2)°, V= 1010.2(7) ų, D_c=2.189 g cm⁻³ and Z=2 dimers. The structure has been refined by full-matrix least- squares techniques to a conventional R factor of 0.027 for 2042 reflections (with I > 2σ(I)). In the unit cell centrosymmetric dimers of orte type exist with bridging chlorine atoms and C₅H₅ groups bonded in η⁵-fashion to the metal (mean ErC 2.59 Å). The [Er(C₅H₅)₂Cl]₂-type is compared to the [Sc(C₅H₅)₂Cl]₂-type structure which is realized in several dicyclopentadienidebromides of the lanthanides.     

Synthesis, 95Mo NMR spectra and x-ray crystal structure of MoO2(C14H11N2O)2(C2H5H)1 and Mo2O5(C14H11N2O)2(C2H5OH)1(H2O)1

The crystal structures and ⁹⁵Mo NMR spectra of two complexes formed between 2-α-hydroxybenzyl- benzimidazole (C₆H₅·CHOH·C₇H₅N₂=HOBB), as its sodium salt, and MoO₂Cl₂ are reported. [MoO₂- (OBB)₂]·EtOH (OBB=deprotonated HOBB) crystallizes in space group P2₁/n, with a=12.8441(7), b=15.917(3), c=13.314(2) Å, β=97.163(8)° and Z =4. The structure was determined from 3096 observed reflections and refined to a final R value of 0.030. The complex is a six coordinate cis-dioxo species, the ⁹⁵Mo spectrum of which shows a single sharp peak at 56 ppm in dimethylformamide (DMF). The second complex, [Mo₂O₅(OBB)₂]·EtOH·H₂O, crystallizes in space group Pbca, with a=22.482(4), b=16.442(3), c=18.407(3) Å and Z=8. The structure was determined from 2936 observed reflections and refined to a final R value of 0.061. The complex is a binuclear doubly bridged species in which one metal atom is six coordinate while the other is five coordinate. Its ⁹⁵Mo NMR spectrum in DMF shows a sharp peak at 124 ppm and a second broader much weaker peak at 51 ppm.     

Structural and stereochemical studies on reactive iridium(III) dihydride complexes of the triphosphine ligand C6H5P[CH2CH2CH2P(C6H11)2]2

The iridium(III) dihydride complexes IrH₂X- (Cyttp) (X = Cl, I) possess a mer-octahedral structure in which the hydrides are cis to each other and the Cyttp ligand is chelated around an edge of the octahedron. The phenyl group on the central phosphorus atom is oriented away from the chloride ligand in the crystal structure, and Nuclear Overhauser Effect (NOE) measurements show that this anti coordination geometry is maintained in solution. Treatment of IrH₂Cl(Cyttp), 1a, with TIBF₄ and CH₃CN results in a mixture of anti and syn diastereomers, whereas CO gives only the syn diastereomer of the type [IrH₂(CH₃CN)(Cyttp)]⁺ and Tl⁺.     

Reaction mechanism of CH3M≡MCH3 (M=C, Si, Ge) with C2H4: [2+1] or [2+2] cycloaddition?

The mechanism of the cycloaddition reaction CH₃M≡MCH₃ (M=C, Si, Ge) with C₂H₄ has been studied at the CCSD(T)/6-311++G(d,p)//MP2/6-311++G(d,p) level. Vibrational analysis and intrinsic reaction coordinate (IRC), calculated at the same level, have been applied to validate the connection of the stationary points. The breakage and formation of the chemical bonds of the titled reactions are discussed by the topological analysis of electron density. The calculated results show that, of the three titled reactions, the CH₃Si≡SiCH₃+C₂H₄ reaction has the highest reaction activity because it has the lowest energy barriers and the products with the lowest energy. The CH₃C≡CCH₃+C₂H₄ reaction occurs only with difficulty since it has the highest energy barriers. The reaction mechanisms of the title reactions are similar. A three-membered-ring is initially formed, and then it changed to a four-membered-ring structure. This means that these reactions involve a [2+1] cycloaddition as the initial step, instead of a direct [2+2] cycloaddition.     

Structural models for the interaction of Cd(II) with DNA: trans-[Cd(9-RGH-N7)2(H2O)4]2+

Reactions of Cd(NO(3))(2) with the model nucleobases 9-alkylguanine in water at neutral pH, give the compounds trans-[Cd(9-RGH-N7)(2)(H(2)O)(4)](NO(3))(2)(R=Me, Et), with the 9-alkylguanine ligands bound to the metal cation at the N(7) position. The X-ray structures of both compounds are reported. The six-coordinate Cd(II) complexes consist of a highly regular octahedral geometry in which the two 9-alkylguanine ligands are in a trans position to each other and approximately collinear with the metal cation. In addition, the networks of both compounds show interesting features. Thus, intramolecular H-bonds between O(6) and a coordinated water molecule are present, and self-association of guanines via H-bonding of N(3)-H...N(2) take place, leading to a 1D supramolecular polymeric ribbon. Density functional theory calculations have been applied to both compounds in order to study the stability of N(7) metalated guanine-guanine associations by comparing experimental and theoretical results. The potential relevance with regard to possible Cd(II)-DNA cross-links is briefly discussed.     

Synthesis of [11-2H2], [8-2H2], [7-2H2], [6-2H2], [5-2H2], [4-2H2] and [3-2H2] cis-9-octadecenoates

Deuterated oleates have been synthesized by semihydrogenation of acetylenic intermediates. [11-²H₂]Oleate was prepared by two-carbon chain extension of the C₁₆ alcohol obtained from [1-²H₂]octyl bromide and 7-octyn-1-ol. [8-²H₂] and [7-²H₂]oleates were both prepared from dimethyl suberate, tetradeutero intermediate C₁₆ alcohols were synthesized from [1,8-²H₄] and [2,7-²H₄]octane diols by monobromination, conversion to deuterated 9-decyn-1-ols and reaction with octyl bromide. Oxidation gave [8-²H₂]-9-octadecynoate and [2,7-²H₂]-9-octadecynoate, after semihydrogenation of the latter, deuterons at C-2 were removed by exchange with aqueous alkali. [6-²H₂] and [5-²H₂]oleates were obtained from methyl 5-tetradecynoate, semihydrogenation, deuterium exchange at C-2 and two malonate extensions gave [6-²H₂]oleate; reduction with lithium aluminum deuteride, two malonate extensions and semihydrogenation gave the [5-²H₂] ester. [4-²H₂] and [3-²H₂]oleates were both obtained from methyl 7-cis-hexadecenoate, exchange of the α protons and chain extension gave the [4-²H₂] ester and reduction with lithium aluminum deuteride and chain extension gave the [3-²H₂] ester.     

Linkage isomerism in the metal complex hexa(thiocyanato)rhenate(IV): Synthesis and crystal structure of (NBu4)2[Re(NCS)6] and [Zn(NO3)(Me2phen)2]2[Re(NCS)5(SCN)]

The linkage isomers [Re(NCS)₆]^2? and [Re(NCS)₅(SCN)]^2? are obtained by the reaction of [ReBr₆]^2? with NCS^? in dimethylformamide. Some differences in the chemical behavior allowed their separation and structural characterization in the form of (NBu₄)₂[Re(NCS)₆] (1) and [Zn(NO₃)(Me₂phen)₂]₂[Re(NCS)₅(SCN)] (2), respectively (Bu = n-C₄H₉ and Me₂phen = 2,9-dimethyl-1,10-phenanthroline).     

Deamination and reductive deamination of (2-amino-5, 6-dimethylbenzimidazolyl)cobamide. Preparation of (2-hydroxy-5, 6-dimethylbenzimidazolyl)cobamide and (5, 6-dimethyl-[2(-14)C]-benzimidazolyl)cobamide

(2-Amino-5, 6-dimethylbenzimidazolyl)-cobamide (III) is transformed to (2-hydroxy-5, 6-dimethylbenzimidazolyl) cobamide (IV) by nitrous acid. Exchange of the NH2-group by hydrogen with nitrous acid/hypophosphorous acid yields vitamin B12 (I). This reaction completes a cycle vitamin B12 (I)----[carboxy(2-cyanoamino-4,5-dimethylphenyl)amino]cobamide+ ++ (II)----(2-amino-5,6-dimethylbenzimidazolyl)cobamide (III)----vitamin B12 (I), which allows chemical 14C-labelling of vitamin B12. In this procedure cyanogen bromide, which is necessary for the first step, was labelled with [14C] cyanide. By the following reactions a vitamin B12 was formed in which C-2 of the 5, 6-dimethylbenzimidazole moiety is labelled.     

An experimental and theoretical study of the electronic spectra of tetraethylammonium [bis(1,3-dithiole-2-thione-4,5-dithiolato)zincate(II)], [NEt4]2[Zn(dmit)2], and tetraethylammonium [bis(1,3-dithiole-2-one-4,5-dithiolato)zincate(II)], [NEt4]2[Zn(dmio)2]

Metal-dmit complexes and related compounds have been the object of intense study in the last decade. Despite such efforts on the study of its structural properties, very few attempts have been made to the spectroscopic study of these metal complexes. Experimental reports of its infrared, Raman and UV–Vis spectra present the main spectroscopic features, however, many details of the electronic structure have still to be fully investigated and inconsistent assignments are found in the literature. This work presents a detailed analysis of the UV–Vis spectra of the zinc-dmit, [Zn(dmit)₂]⁻², and the zinc-dmio complex, [Zn(dmio)₂]⁻². The experimental spectrum was deconvoluted and analysed with several theoretical methodologies including ab initio CI calculations, ab initio TD and zindo semi-empirical methods. The results confirm the multi-configuration nature of several excited states and the calculated results were concordant for several transitions. The results lead to a new assignment of the 457 nm band in the [Zn(dmit)₂]⁻² as π(pS_m) → π*CS band. In the metal-dmio, the sulfur substitution by oxygen results in a larger HOMO–LUMO gap and a change in the nature of the frontier orbitals. As the first transition we found, for the dmit compound, a high-intensity π → π*CS while for the zinc-dmio, a low-intensity π → σ*C–S transition.     

Genotoxic effects of the chlorinated hydroxyfuranones 3-chloro-4-(dichloromethyl)-5-hydroxy-2[5H]-furanone and 3,4-dichloro-5-hydroxy-2[5H]-furanone in Tradescantia micronucleus assays

This is the first report of clastogenic effects of chlorinated hydroxyfuranones (CHFs) in plants. Two byproducts of water chlorination, 3-chloro-4-(dichloromethyl)-5-hydroxy-2[5H]-furanone (MX) and 3,4-dichloro 5-hydroxy-2[5H]-furanone (MA) induced a dose dependent increase of micronuclei (MN) in pollen mother cells of Tradescantia when doses up to 100 μg MX and 500 μg MA were applied directly to the inflorescences. In contrast, exposure of the stems in aqueous solutions containing up to 1 mg/I MX and 10 mg/I MA did not cause a positive response.     

Differences in the conversion of the polyunsaturated fatty acids [1-(14)C]22:4(n-6) and [1-(14)C]22:5(n-3) to [(14)C]22:5(n-6) and [(14)C]22:6(n-3) in isolated rat hepatocytes

The reasons why most cellular lipids preferentially accumulate 22:6(n-3) rather than 22:5(n-6) are poorly understood. In the present work the metabolisms of the precursor fatty acids, [1-(14)C]20:4(n-6), [1-(14)C]22:4(n-6) versus [1-(14)C]20:5(n-3), [1-(14)C]22:5(n-3) in isolated rat hepatocytes were compared. The addition of lactate and L-decanoylcarnitine increased the formation of [(14)C]24 fatty acid intermediates and the final products, [(14)C]22:5(n-6) and [(14)C]22:6(n-3). In the absence of lactate and L-decanoylcarnitine, no [(14)C]24 fatty acids and [(14)C]22:5(n-6) were detected when [1-(14)C]22:4(n-6) was the substrate, whereas small amounts of the added [1-(14)C]22:5(n-3) was converted to [(14)C]22:6(n-3). Lactate reduced the oxidation of [1-(14)C]22:4(n-6) and [1-(14)C]22:5(n-3) while L-decanoylcarnitine did not. No significant differences between the total oxidation or esterification of the two substrates were observed. By fasting and fructose refeeding the amounts of [(14)C]24:4(n-6) and [(14)C]24:5(n-3) were increased by 2.5- and 4-fold, respectively. However, the levels of [(14)C]22:5(n-6) and [(14)C]22:6(n-3) were similar in hepatocytes from fasted and refed versus fed rats. With hepatocytes from rats fed a fat free diet the levels of [(14)C]24 fatty acid intermediates were low while the further conversion of the n-6 and n-3 substrates was high and more equal, approx. 33% of [1-(14)C]22:4(n-6) was converted to [(14)C]22:5(n-6) and 43% of [1-(14)C]22:5(n-3) was converted to [(14)C]22:6(n-3). The moderate differences found in the conversion of [1-(14)C]22:4(n-6) versus [1-(14)C]22:5(n-3) to [(14)C]22:5(n-6) and [(14)C]22:6(n-3), respectively, and the equal rates of oxidation of the two substrates could thus not explain the abundance of 22:6(n-3) versus the near absence of 22:5(n-6) in cellular membranes.     

Investigations of the {ReO} core: A '2+2' complex from bidentate and potentially trident ligands: [ReO(η-HOC(6)H(4)-2-CH(2)NC(6)H(4)S)(η-SC(5)H(4)N)(PPh(3))

The reaction of [ReOCl(3)(PPh(3))(2)] with N-(2-hydroxybenzyl)-2-mercaptoaniline (H(3)hbma) (2) and 2-mercaptopyridine in hot CHCl yields [ReO(η(2)-HOC(6)H(4)-2-CH(2)NC(6)H(4)S)(η(2)-SC(5)H(4)N)(PPh(3))] (3). The structure of 3 consists of distorted octahedral Re(V) monomers. The coordination geometry at the rhenium is defined by a terminal oxo-group, the nitrogen and sulfur donors of the chelating mercaptopyridine, the nitrogen and sulfur donors of a bidentate (Hhbma)(2-) ligand, and the phosphorus of the PPh(3) group. The -C(6)H(4)OH arm of (Hhbma)(2-) is pendant, and the coordinated nitrogen of this ligand is present as a deprotonated amido nitrogen.     

Dithiocarbamates in heavy metal poisoning: complexes of N,N-di(2-hidroxyethyl)dithiocarbamate with Zn(II), Cd(II), Hg(II), CH3Hg(II), and C6H5Hg(II)

The complexes M(DHDC)2, CH3Hg(DHDC), and C6H5Hg(DHDC) (M = Zn, Cd, Hg; DHDC = N,N-di(2-hydroxyethyl)dithiocarbamate) were prepared and investigated in solution and in the solid state by using 1H and 13C NMR, ir, and Raman spectroscopy. The dithiocarbamate group is anisobidentate and the complexes are associated in solution and the solid state via hydrogen bonding. The possible relation of these structural properties to the behavior of DHDC in the treatment of cadmium poisoning is discussed.