Simple linear asymmetrical complexes of silver(I): NC-Ag-NH3 and Br-Ag-NH3

The compounds Ag(CN)(NH3) and Ag(Br)(NH3) are remarkable in that they form solids containing the simple molecular units NC-Ag-NH3 and Br-Ag-NH3, rather than extended solids, and are the first examples of simple linear asymmetric complexes of silver(I).

The oxadiazolyldiazenido(1-) ligand: a remarkably versatile platform for the synthesis of heteropolynuclear transition metal complexes

Cyclo-condensation of aroyl hydrazides with the cationic tungsten-dichlorodiazomethane complex [BrW(dppe)(2)(N2CCI2)](+) affords neutral oxadiazolyldiazenido(1-) complexes which react readily with a wide range of transition and non-transition metal species to afford a novel series of crystallographically-characterised heteropolynuclear complexes containing bridging oxadiazolyldiazenido(1-) ligands.

Metal complexes of a dipyridine octaazamacrocycle: stability constants, structural and modelling studies

Two 28-membered octaazamacrocycles, [28]py(2)N(6) and Me-2[28]py(2)N(6), have been synthesized. The protonation constants of the N-methyl. derivative and the stability constants of its complexes with Ni2+, Cu2+, Zn2+, Cd2+, and Pb2+ were determined at 25degreesC in 0.10 mol dm(-3) KNO3. The high overall basicity of Me-2[28]py(2)N(6) is ascribed to the weaker repulsion between protonated contiguous charged ammonium sites separated by propyl chains. These studies together with NMR, UV-vis and EPR spectroscopies indicated the presence of mono- and di-nuclear species, The single crystal structure of the complex [Ni-2([28]py(2)N(6))(H2O)(4)]Cl-4.3H(2)O was determined, and showed each nickel centre in a distorted octahedral co-ordination environment. The nickel centres are held within the macrocycle at a large distance of 6.991(g) Angstrom from each other. The formation of mononuclear complexes was evaluated theoretically via molecular mechanics (MM) and molecular dynamics (MD) calculations and showed that these large macrocycles have sufficient flexibility to encapsulate metal ions with different stereo-electronic sizes. Structures for small and large metal ions are proposed.

Syntheses and spectroscopy of diamine complexes of Zn(II) and Cd(II) ethylxanthates and the molecular structures of [M(S2COEt)(2)TMEDA]: formation of US nanoparticles from [Cd(S2COEt)(2)] and [Cd(S2COEt)(2)TMEDA]

The zinc and cadmium ethylxanthate complexes of N,N,N',N'-tetramethylethylenediamine (TMEDA), [M(S2COEt)(2)TMEDA], were synthesized and characterized with infrared, H-1 and C-13 NMR spectroscopy, mass spectrometry and X-ray crystallography. Whereas the cadmium complex has a six-coordinate {CdS4N2} centre with bidentate xanthate ligands, the zinc complex contains four coordinate {ZnS2N2} zinc with two monodentate xanthate groups. The cadmium species [Cd(S2COEt)(2)(diamine)] (where diamine = N,N-dimethylethylenediamine or N,N'-diisopropylethylenediamine) were also synthesized. The surfactant-assisted formation of nanoparticles from [Cd(S2COEt)(2)] and [Cd(S2COEt)(2)TMEDA] was studied with TEM, XRD and XRF techniques. From [Cd(S2COEt)(2)], spherical nanoparticle aggregates 140-200 nm in diameter were obtained but from [Cd(S2COEt)(2)TMEDA], single nanoparticles were produced with estimated diameters in the range of 4-7 nm and almost no aggregation. (C) 2004 Elsevier Ltd. All rights reserved.

Trichloro-mono-beta-diketonato oxorhenium(V) complexes: synthesis, characterization and crystal structure

Oxorhenium(V) complexes of beta-diketonate systems have been synthesized and isolated in pure form. The red complexes n-Bu4N[ReO(R1COCHCOR2)Cl-3] (acac, R-1=R-2=CH3; bzac, R-1=CH3 and R-2=C6H5; bzbz, R-1=R-2=C6H5) have been characterized by elemental analyses, spectroscopic and other physico-chemical tools. One complex, n-Bu4N[ReO(bzbz)Cl-3] (1c) has been subjected to single-crystal X-ray analysis. In the structure of the anion, the metal has a six-coordinate octahedral environment in which the bidentate -diketone ligand is cis and trans to the terminal oxygen.

Imidazole-imidazole stacking in some inorganic complexes

Reaction of CuCl2 center dot 2H(2)O with the 1:1 condensate (L) of 2-(2-aminoethyl) pyridine and 1-methyl-2-imidazolecarboxaldehyde in methanol yields monomeric CuLCl2 center dot H2O (1). Recrystallisation of 1 from aqueous methanol medium containing excess of PF6- affords the 1D coordination polymer [CuLCl](n)(PF6)(n) (2). A chloride bridge results in the coordination polymer. A face-to-face interaction is observed between the imidazole rings in 2. The interaction influences the structure and magnetic properties of 2 markedly. The complex 2 is ferromagnetic with a J value of 1.79 +/- 0.01 cm (1). The imidazole fragments in 2 are coordinated to the metal. In mononuclear [HgL2 ''](ClO4)(2), where L '' is the 1:2 condensate of ethylenediamine and 1-methyl-2-imidazolecarboxaldehyde, the imidazolyl moieties are not under the direct influence of the metal. Here the imidazole-imidazole interaction is angular and more distant. (C) 2009 Elsevier B.V. All rights reserved.

Uranyl(VI) and lanthanum(III) thio-diglycolamides complexes: synthesis and structural studies involving nitrate complexation

New tri-functional ligands of the type R2NCCCH2SCH2CCNR2 (where R = iso-propyl, n-butyl or iso-butyl) were prepared and characterized. The coordination chemistry of these ligands with uranyl and lanthanum(III) nitrates was studied by using the IR, (HNMR)-H-1 and elemental analysis methods. Structures for the compounds [UO2(NO3)(2)((Pr2NCOCH2SCH2CONPr2)-Pr-i-Pr-i)] [UO2(NO3)(2)((Bu2NCOCH2SCH2CONBu2)-Bu-i-Bu-i)(2)] [La(NO3)(3)((Pr2NCOCH2SCH2CONPr2)-Pr-i-Pr-i)(2)] and [La(NO3)(3)((Bu2NCOCH2SCH2CONBu2)-Bu-i-Bu-i)(2)] were determined by single crystal X-ray diffraction. These structures show that the ligand acts as a bidentate chelating ligand and bonds through both the carbamoyl groups to the uranyl and lanthanum(III) nitrate groups. Solvent extraction studies show that the ligand can extract the uranyl ion from the nitric acid medium but does not show any ability to extract the americium (III) ion. (C) 2009 Elsevier Ltd. All rights reserved.

Metal complexes of cyclen and cyclam derivatives useful for medical applications: a discussion based on thermodynamic stability constants and structural data

A series of the most common chelators used in magnetic resonance imaging ( MRI) and in radiopharmaceuticals for medical diagnosis and tumour therapy, H(4)dota, H(4)teta, H(8)dotp and H(8)tetp, is examined from a chemical point of view. Differences between 12- and 14-membered tetraazamacrocyclic derivatives with methylcarboxylate and methylphosphonate pendant arms and their chelates with divalent first-series transition metal and trivalent lanthanide ions are discussed on the basis of their thermodynamic stability constants, X- ray structures and theoretical studies.

Oxorhenium(V) complexes with tetradentate NSNO pyridylthioazophenolates: syntheses, spectral and electrochemical studies

A family of oxorhenium (V) complexes of newly designed pyridylthioazophenolate ligands has been synthesized and isolated in pure form. The solid state structure of an organic compound (HL1) has been established by X-ray crystallography. The molecular structure observed in the solid state is that the two molecules of the ligand (HL1) in the asymmetric unit have similar geometries, except for the orientation of the pyridine ring. This series of organic moieties acts as tetradentate monobasic NSNO donor chelators in oxorhenium(V) complexes which has been characterized by elemental analyses, IR, H-1-NMR, UV-Vis. The complexes are 1: 1 electrolytes in nature in MeOH solution, the counter anion being ClO4). The electrochemical studies of the [(ReO)-O-V(L)Cl]ClO4 complexes in MeCN using TBAP as supporting electrolyte exhibit quasi-reversible voltammogram showing one-electron couple for [(ReO)-O-VI(L)Cl](2+)-[(ReO)-O-V(L)Cl](+) in the 1.11-1.29 V vs SCE range.

Ruthenium (III) complexes of tetradentate NSNO pyridylthioazophenolates: Synthesis, spectral studies, crystal structure and redox properties

A family of ruthenium (III) complexes of tetradentate monobasic NSNO donor chelators (HL) have been synthesized and isolated in their pure form. On chromatographic separation, trans-dichloro and cis-dichloro ruthenium (111) complexes of pyridylthioazophenolates are eluted using 19:1 and 7:3 (v/v) DCM-MeOH mixtures, respectively. Both cis and trans isomers of the dark brown colored ruthenium (111) complexes, having the general formula of [Ru(L)Cl-2], have been characterized by elemental analyses, spectroscopic and other physico-chemical tools. The magnetic moments of both the cis- and trans-[Ru(L)Cl-2] complexes are in the range of 1.71-1.79 BM. One of the complexes, trans-[Ru(L1)Cl-2] (2a), has been subjected to single-crystal X-ray analysis which confirms that the chlorines are in mutually trans positions in the molecule. The EPR spectra of the cis-[Ru(L)Cl-2] complexes (1) in DMF are consistent with the fact that the complexes are low-spin octahedral with one unpaired electron having three different g values (g(x) not equal g(y) not equal g(z)) complexes are monomeric with an octahedral coordination sphere. The electrochemical studies of [Ru(L)Cl,] in DMF show a quasi-reversible voltammogram. The reduction potentials for the cis-isomers are comparatively lower than those of the corresponding trans isomers. On reaction with the bidentate bipyridyl ligand in the presence of AgNO3, the cis-[Ru(L)Cl-2] complexes (1) produce a series of complexes with the general formula [Ru(L)(bpy)(2)](PF6)(2) (3). which have also been characterized by elemental analyses, spectroscopic and other physico-chemical tools. (c) 2006 Elsevier Ltd. All rights reserved.

Nickel(II) complexes of tetradentate NSNO pyridylthioazophenol ligands: synthesis, characterization and crystal structure

Two sets of nickel(11) complexes of a series of tetradentate NSNO ligands were synthesized and isolated in their pure form. All these complexes, formulated as [Ni(L)Cl](2) and [Ni(L)(N-3)](2) [HL = pyridylthioazophenols], were characterized using physicochemical and spectroscopic tools. The solid-state structures of two complexes (1a and 2a) were established by X-ray crystallography. The geometry about the nickel ion of the complexes is octahedral and the complexes are dimeric in nature. In 1, two Ni(II) ions are bridged by two Cl- anions while in 2 they are bridged by two azide ions in a mu-1,1-bridging fashion. (C) 2008 Elsevier Ltd. All rights reserved.

Argon predissociation spectroscopy of the OH-center dot H2O and Cl-center dot H2O complexes in the 1000-1900 cm(-1) region: Intramolecular bending transitions and the search for the shared-proton fundamental in the hydroxide monohydrate

We present argon predissociation vibrational spectra of the OH-.H2O and Cl-.H2O complexes in the 1000-1900 cm(-1) energy range, far below the OH stretching region reported in previous studies. This extension allows us to explore the fundamental transitions of the intramolecular bending vibrations associated with the water molecule, as well as that of the shared proton inferred from previous assignments of overtones in the higher energy region. Although the water bending fundamental in the Cl-.H2O spectrum is in very good agreement with expectations, the OH-.H2O spectrum is quite different than anticipated, being dominated by a strong feature at 1090 cm(-1). New full-diniensionality calculations of the OH-.H2O vibrational level structure using diffusion Monte Carlo and the VSCF/CI methods indicate this band arises from excitation of the shared proton.

Oxo-rhenium(V) complexes with bidentate phosphine ligands: synthesis, crystal structure and catalytic potentiality in epoxidation of olefins using hydrogen peroxide activated bicarbonate as oxidant

Two oxorhenium(V) complexes with bidentate phosphine ligands were synthesized and isolated as [ReOCl3(dppm)] 1 and [ReOCl3(dppp)] 2 [where dppm = 1,1-bis(diphenylphosphino) methane and dppp = 1.3-bis(diphenylphosphino) propanel. Complex 2 was structurally characterized. Both the complexes were used as catalysts in the epoxidation of olefins using NaHCO3 as co-catalyst and H2O2 as terminal oxidant. (c) 2008 Elsevier B.V. All rights reserved.

Substituent effects in single helix-double helix interconversions in copper(I) complexes

The copper(I) complex of L, the 1:2 condensate of benzil dihydrazone and 2-formylpyridine, exists as single, helical [CuL](+) and double helical [Cu2L2](2+) in dichloromethane solution but crystallizes only as the double helicate [Cu2L2](ClO4)(2). In contrast, earlier [New J Chem, 27 (2003) 193] it has been found that with L', the 1:2 condensate of benzil dihydrazone and 2-acetylpyridine, only the single helical monomeric species [CuL'](+) is isolable as solid. This contrasting behaviour of the copper(I) complexes of L and L' are scrutinised here by density functional calculations.

Stereochemically non-rigid helical mercury(II) complexes

Reactions of the 1: 2 condensate (L) of benzil dihydrazone and 2-acetylpyridine with Hg(ClO4)(2) center dot xH(2)O and HgI2 yield yellow [HgL2](ClO4)(2) (1) and HgLI2 (2), respectively. Homoleptic 1 is a 8-coordinate double helical complex with a Hg(II)N-8 core crystallising in the space group Pbca with cell dimensions: a = 16.2250(3), b = 20.9563(7), c = 31.9886(11) angstrom. Complex 2 is a 4-coordinate single helical complex having a Hg(II)N2I2 core crystallising in the space group P2(1)/n with cell dimensions a = 9.8011(3), b = 17.6736(6), c = 16.7123(6) angstrom and b = 95.760(3). In complex 1, the N-donor ligand L uses all of its binding sites to act as tetradentate. On the other hand, it acts as a bidentate N-donor ligand in 2 giving rise to a dangling part. From variable temperature H-1 NMR studies both the complexes are found to be stereochemically non-rigid in solution. In the case of 2, the solution process involves wrapping up of the dangling part of L around the metal. (C) 2008 Elsevier B.V. All rights reserved.