An asymmetric homodinuclear complex containing the mu-x-oxobis(mu-x-carboxylato)diruthenium(III) core: X-ray structure of [Ru20(o2ec6H4-p-OMe)3(en) (PPh3)2] (C104)" 3CHC13

Asymmetric tri-bridged diruthenium(III) complexes, [Ru2O(O(2)CR)(3)(en) (PPh(3))(2)](ClO4) (R = C6H4-p-X: X = OMe (1a), Me (1b); en=1,2-diaminoethane), were prepared and structurally characterized. Complex 1a 3CHCl(3), crystallizes in the triclinic space group P (1) over bar with a = 14.029(5), b = 14.205(5), c = 20.610(6) Angstrom, alpha= 107.26(3), beta = 101.84(3), gamma= 97.57(3)degrees, V= 3756(2) Angstrom(3) and Z = 2. The complex has an {Ru-2(mu-O)(mu-O(2)CR)(2)(2+)} core and exhibits [O4PRu(mu-O)RuPO2N2](+) coordination environments for the metal centers. The novel structural feature is the asymmetric arrangement of ligands at the terminal sites of the core which shows an Ru... Ru separation of 3.226(3) Angstrom and an Ru-O-Ru angle of 119.2(5)degrees. An intense visible band observed near 570 nm is assigned to a charge transfer transition involving the d pi-Ru(III) and p pi-mu-O Orbitals. Cyclic voltammetry of the complexes displays a reversible Ru-2(III,III) reversible arrow Ru-2(III,IV) couple near 0.8 V (versus SCE) in MeCN-0.1 M TBAP.

Molecular mechanism for the specific inhibition of reverse transcriptase of rous sarcoma virus by the copper complexes of isonicotinic acid hydrazide

Isonicotinic acid hydrazide (isoniazid), one of the most potent antitubercular drugs, was recently shown, in our laboratory, to form two different complexes with copper, depending upon the oxidation state of the metal ion. Both the complexes have been shown to possess antiviral activity against Rous sarcoma virus, an RNA tumor virus. The antiviral activity of the complexes has been attributed to their ability to inhibit the endogenous reverse transcriptase activity of RSV. More recent studies in our laboratory indicate that both these complexes inhibit both endogenous and exogenous reactions. As low a final concentration as 50 μM of the cupric and the cuprous complexes inhibits the endogenous reaction to the extent of 93 and 75 per cent respectively. Inhibition of the exogenous reaction varies with the templates. The inhibition can be reversed by either β-mercaptoethanol or ethylene-diamine-tetra-acetic acid. The specificity of this inhibition has been ascertained by using a synthetic primer-template, −(dG)not, vert, similar15−(rCm)n, which is highly specific for reverse transcriptases. The inhibition is found to be template specific. The studies carried out, using various synthetic primer-templates, show the inhibition of both the steps of reverse transcription by the copper complexes of isoniazid.

A novel amino acid racemization in vitamin b6-amino acid schiff base copper complexes: crystal structures of aquo (5'-phosphopyridoxylidene-dl-tyrosinato) copper(II) 3.5H2O and aquo (5'-phosphopyridoxylidene-dl-phenylalaninato) copper(II) 2.5H2O

A novel racemization observed in the Vitamin B6-amino acid Schiff base complexes, aquo (5'-phosphopyridoxylidene-l-tyrosinato) copper(II) and aquo (5'-phosphopyridoxylidene-l-phenylalaninato) copper(II) is described. The racemization taking place in solution under mild acidic conditions (pH 5-6) was confirmed by CD studies and the products were characterized by single crystal X-ray diffraction. The structures of both complexes show almost parallel orientation of the aromatic side chain and the pyridoxal II-system. The activation of the αCsingle bondH group due to the intermolecular II- interaction is probably the reason for the unusual racemization observed.

Chelating and bridging diphosphinoamine (PPh2)(2)N(Pr-i) complexes of copper(I)

The ligand bis(diphenylphosphino) isopropylamine (dppipa) has been shown to be a versatile ligand sporting different coordination modes and geometries dictated by copper(I). Most of the molecular structures were confirmed by X-ray crystallography. It is found in a chelating mode, in a monomeric complex when the ligand to copper ratio is 2:1. A tetrameric complex is formed when low ratios of ligand to metal (1: 2) were used. But with increasing ratios of ligand to metal (1: 1 and 2: 1), a trimer or a dimer was obtained depending on the crystallization conditions. Variable temperature P-31{H-1} NMR spectra of these complexes in solution showed that the Cu-P bond was labile and the highly strained 4-membered structure chelate found in the solid state readily converted to a bridged structures. On the other hand, complexes with the ligand in a bridging mode in the solid state did not form chelated structures in solution. The effect of adding tetra-alkylammonium salts to solutions of various complexes of dppipa were probed by P-31{H-1} NMR and revealed the effect of counter ions on the stability of complexes in solution. (C) 2008 Elsevier B.V. All rights reserved.

Spectrophotometric and potentiometric investigations of copper (II)-ethanolamine complexes - Part II. Monoethanolamine (Analysis of mixed hydroxy complexes with polarographic evidence)

Potentiometric, spectrophotometric and polarographic evidence has been presented for the formation of mixed hydroxy complexes in coppermonoethanolamine system. A method has been developed for the analysis of Bjerrum formation curves taken in presence of 0·1, 0·2, 0·5 and 1·0 M monoethanolammonium ion with respect to hydroxy complexes. The formation of CuAOH+, CuA2OH+ and CuA3OH+ is shown and the corresponding stability constants are calculated at different concentrations of MEA ion. Curves showing the distribution of pure and hydroxy complexes at various pA values in solutions containing different concentrations of MEA ion have also been given.

Spectrophotometric and potentiometric investigations of copper (II)-ethanolamine complexes - Part I. Monoethanolamine

Spectrophotometric and potentiometric investigations have been carried out on copper-monoethanolamine complexes. Job plots at 920, 760 and 620 mµ have indicated the formation of CuA++, CuA2/++ and CuA3 ++. The$$\bar n - pA$$ curves have been obtained by a slight modification of the method of corresponding solutions and by pH measurements. The$$\bar n$$ vs. pA curves obtained at different metal concentrations coincide indicating the formation of mononuclear complexes. Experiments conducted with 0·1. 0·2, 0·5 and 1·0 M monoethanolammonium ion indicate the formation of mononuclear hydroxy complexes above pH 6. The nature of E m vs pA curves is closely analogous to that of$$\bar n$$ vs. pA curves. Absorption spectra taken at pH 9·8 with different amounts of monoethanolamine has given evidence for the formation of (CuA3OH·A)+.$$\bar n - pA$$ curves have been analyzed and the values ofβ 1, 1,β 1, 2 andβ 1, 3 have been obtained. Curves showing the distribution of complexes and the absorption curves of the individual complexes (CuA++, CuA2/++, and CuA3/++) have been calculated.

Nitrosation of N,N′-ethylenebis-(acetylacetoneimine) complexes of copper (II) and nickel(II) and characterization of the products

Isonitroso derivatives of copper(II) and nickel(II) complexes of N,N′-ethylenebis(acetylacetoneimine) have been prepared by nitrosation of the respective complexes using nitric oxide as well as nitrite ion. The condensation of isonitrosoacetylacetone in the presence and in the absence of nickel(II) has been investigated. The i.r. and electronic spectra and magnetic moment of the nickel(II) and copper(II) complexes have been studied. The nature of bonding of the ligand to the metal ion is discussed. The complexes have planar structures.

Spectrophotometric and potentiometric investigations of copper (II)-Ethanolamine complexes - Part III. diethanolamine (Gaussian analysis of electronic spectra in mono and diethanolamine systems)

Spectrophotometric and potentiometric investigations have been carried out on copper-diethanolamine system. Job plots at 900, 900 and 580 mμ have indicated the formation of CuD++, CuD2++ and CuD3++. The n- pA curves obtained indicate the formation of CuD++, CuD2++, CuD3++, CuDOH+, CuD2OH+ and CuD3OH+. The n- pA curves have been analyzed to obtain the stability constants of these complexes. Absorption curves of pure complexes have been computed by a graphical method. Gaussian analysis of the absorption curves of pure and hydroxy complexes show the presence of a second band, indicating that the structure is that of a distorted octahedron.

Electrophilic Substitution Reactions of Copper(II) Acetylacetoneimine Complexes with Arene Diazonium Ions

Copper(II) complexes of ethylene/propylene-bis(acetylacetoneimine), Cu(baen) or Cu(bapn), react quickly and quantitatively in aqueous methanol at the methine position with arene diazonium ions in a stepwise manner to yield mono- and di-substituted copper(II) complexes. All the complexes are paramagnetic with μeff∼1.88 B.M. In all the complexes the diazo substituted part of the ligand coordinates to the metal through the agr-nitrogen of the azo group and the imine nitrogen, forming glyoxaliminearylhydrazone type of ligand system. The complexes have been characterized by elemental analysis, electronic, esr, ir and mass spectroscopic methods.

Reactions of copper(I) aryloxides with phenyl isothiocyanate: steric and ligand control in the oligomerization of [N-phenylimino(aryloxy)methanethiolato]copper(I) complexes

The preparation of five different copper(I) complexes [CuSC(=NPh)(OAr)}L(n)]m (1-5) formed by the insertion of PhNCS into the Cu-OAr bond and the crystal structure analyses of three of them have been carried out. A monomeric species 1 (OAr = 2,6-dimethylphenoxide) is formed in the presence of excess PPh3 (n = 2, m = 1) and crystallizes as triclinic crystals with a = 12.419(4) angstrom, b = 13.298(7) angstrom, c = 15.936(3) angstrom, alpha = 67.09(3)-degrees, beta = 81.63(2)-degrees, gamma = 66.54(3)-degrees, V = 2224(2) angstrom3, and Z = 2. The structure was refined by the least-squares method to final R and R(w) values of 0.038 and 0.044, respectively, for 7186 unique reflections. Copper(I) 2,5-di-tert-butyl-4-methylphenoxide results in the formation of a dimeric species 2 in the presence of P(OMe)3 (n = 1, m = 2), where the coordination around Cu is trigonal. Crystals of 2 were found to be orthorhombic with a = 15.691(2) angstrom, b = 18.216(3) angstrom, c = 39.198(5) angstrom, v = 11204(3) angstrom3, and Z = 8. Least-squares refinement gave final residuals of R = 0.05 and R(w) = 0.057 with 6866 unique reflections. A tetrameric species 3 results when PPh3 is replaced by P(OMe)3 in the coordination sphere of copper(I) 2,6-dimethylphenoxide. It crystallizes in the space group P1BAR with a = 11.681 (1) angstrom, b = 13.373(2) angstrom, c = 20.127(1) angstrom, a = 88.55(l)-degrees, beta = 89.65(l)-degrees, gamma = 69.28(1)-degrees, V = 2940(l) angstrom3, and Z = 2. Least-squares refinement of the structure gave final values of 0.043 and 0.05 for R and R(w) respectively using 12214 unique reflections. In addition, a dimeric species 4 is formed when 1 equiv of PPh3 is added to the copper(I) 4-methylphenoxide, while with an excess of PPh3 a monomeric species 5 is isolated. Some interconversions among these complexes are also reported.

Structure, Spectra and Redox Behaviour of Copper(11) Complexes of Bis( benzimidazoly1)diamine Ligands

The linear quadridentate ligand N,N'-bis(benzimidazoI-2-ylethyl)ethane-l,2-diamine (L') and its 1 - methylbenzimidazole analogue (L2) and homologues form 1 : 1 complexes with Cu(CIO,),; L' also forms complexes of the types CuL'X, where X = NO,, PF,, Br or CI and CuL'(X)Y where X = CI or Br and Y = CIO, or Br. Deep blue CuL1Br,*2H20 crystallizes in the monoclinic space group C2/c with Z = 4, a = 9.91 9(2), b = 16.626(3), c = 14.1 02(3) le\ and p = 94.39(2)". The structure was solved by Patterson and Fourier difference methods and refined by the least-squares technique to R = 0.064 for 2195 independent reflections with / > 1.50(/). The molecule lies on a two-fold axis symmetrically around Cu". The co-ordination around Cu" is found to be square planar with two amino nitrogens and two benzimidazole nitrogens forming the equatorial plane [CU-N 1.983(3) and 2.037(4) A]. The bromides are at longer distances [3.349(1) A] in axial sites. Ligand field and EPR spectra indicate that one bromide or chloride ion is axially co-ordinated to Cu" in [CuL1l2+. This ion exhibits quasi-reversible redox behaviour. Electrochemical studies of the dihalides in methanol have established the presence of [CuL'X,], [CuL'(X)]+ and [CuL'I2+ in equilibrium. In complexes with 565 [CuL4I2+ [L4 = N,Nbis( benzimidazol-2-ylmethyl)ethane-l,2-diamine] and 555 [CuL3] [L3 = N,N'-bis(1 -methylbenzimidazol- 2-ylmethyl)propane-l,3-diamine] chelate rings, Cull does not seem to lie in the N, square plane, as revealed by their low A values and irreversible electrochemical behaviour. The Cu"-Cu' redox potentials in methanol are in the order [CuL1I2+ < [CuL3I2+ < [CuL4I2+; this illustrates that sixmembered chelate rings are suitable to stabilize Cu", when CU-N 0 interactions are favourable.

Chelating and bridging bis(diphenylphosphino)aniline complexes of copper(I)

The ligand bis(diphenylphosphino)aniline (dppan) has been shown to be a versatile ligand sporting different coordination modes and geometries as dictated by copper(I) and the counter ion. The molecular structures of its Cu(I) complexes were characterized by X-ray crystallography. The ligand was found in a chelating mode and monomeric complexes were formed when the ligand to copper ratio was 2: 1 and the anion was non-coordinating. However, with thiocyanate as the counter anion, the ligand was found to adopt two different modes, with one ligand chelating and the other acting as a monodentate ligand. With CuX (X = Cl, Br), dppan formed a tetrameric complex when the ligand and metal were reacted in the ratio of 1:1. But reactions containing ligand and metal in the ratios of 1: 2 or 2: 1, resulted in the formation of a mixture of species in solution. Crystallization however, led to the isolation of the tetrameric complex. Variable temperature P-31{H-1} NMR spectra of the isolated tetramers did not show the presence of chelated structures in solution. Tetra-alkylammonium salts were added to solutions of various complexes of dppan and studied by P-31{H-1} NMR to probe the effect of anions on the stability of complexes in solution. The Cu-dppan complexes were robust and did not interconvert with other structures in solution unlike the bis(diphenylphosphino) isopropylamine complexes. (C) 2011 Elsevier B.V. All rights reserved.

Probing the limits of steric constraints in the oligomerization of copper(I) complexes: structures of two sterically congested oligomers

Oligomeric copper(I) clusters are formed by the insertion reaction of copper(I) aryloxides into heterocumulenes. The effect of varying the steric demands of the heterocumulene and the aryloxy group on the nuclearity of the oligomers formed has been probed. Reactions with copper(I)2-methoxyphenoxide and copper(I)2-methylphenoxide with PhNCS result in the formation of hexameric complexes hexakis[N-phenylimino(aryloxy)methanethiolato copper(I)] 3 and 4 respectively. Single crystal X-ray data confirmed the structure of 3. Similar insertion reactions of CS2 with the copper(I) aryloxides formed by 2,6-di-tert-butyl-4-methylphenol and 2,6-dimethylphenol result in oligomeric copper(I) complexes 7 and 8 having the (aryloxy)thioxanthate ligand. Complex 7 was confirmed to be a tetramer from single crystal X-ray crystallography. Reactions carried out with 2-mercaptopyrimidine, which has ligating properties similar to N-alkylimino(aryloxy)methanethiolate, result in the formation of an insoluble polymeric complex 11. The fluorescence spectra of oligomeric complexes are helpful in determining their nuclearity. Ir has been shown that a decrease in the steric requirements of either the heterocumulene or aryloxy parts of the ligand can compensate for steric constraints acid facilitate oligomerization. (C) 1999 Elsevier Science Ltd. All rights reserved.

Thermal analysis of metalorganic complexes of copper for evaluation as CVD precursors

Metalorganic complexes of copper have been synthesized by modifying the ligand in the beta-diketonate class of compounds. Detailed thermal analysis of several beta-diketonate complexes of copper has been carried out to evaluate their suitability as precursors for chemical vapor deposition (CVD). A comparison of their relative volatilities has been made by determining their sublimation rates at different temperatures. Thermal analyses of these complexes reveal significant differences among their volatilities and decomposition patterns.