The strongly hydrogen bonded species (CH3)2SO...H3O+ formed in concentrated hydrochloric acid displays a new low energy feature in its sulfur K-edge X-ray absorption near edge structure (XANES) spectrum. Density Functional Theory-Transition Potential (DFT-TP) calculations reveal that the strong hydrogen bonding decreases the energy of the transition S(1s) --> LUMO, which has antibonding sigma*(S-O) character, with about 0.8 eV. Normal coordinate force field analyses of the vibrational spectra show that the SO stretching force constant decreases from 4.72 N cm(-1) in neat liquid dimethyl sulfoxide to 3.73 N cm(-1) for the hydrogen bonded (CH3)2SO...H3O+ species. The effects of sulfur coordination on the ambidentate dimethyl sulfoxide molecule were investigated for the trans-Pd((CH3)2SO)2Cl2, trans-Pd((CD3)2SO)2Cl2 and cis-Pt((CH3)2SO)2Cl2 complexes with square planar coordination of the chlorine and sulfur atoms. The XANES spectra again showed shifts toward low energy for the transition S(1 s) --> LUMO, now with antibonding sigma*(M-Cl, M-S) character, with a larger shift for M = Pt than Pd. DFT-TP calculations indicated that the differences between the XANES spectra of the geometrical cis and trans isomers of the M((CH3)2SO)2Cl2 complexes are expected to be too small to allow experimental distinction. The vibrational spectra of the palladium(II) and platinum(II) complexes were recorded and complete assignments of the fundamentals were achieved. Even though the M-S bond distances are quite similar the high covalency especially of the Pt-S bonds induces significant increases in the S-O stretching force constants, 6.79 and 7.18 N cm(-1), respectively.

The protonated dimethyl sulfoxide cation (CH3)2SO-H+ formed in concentrated hydrochloric acid displays a new low energy feature in its sulfur K-edge X-ray absorption near edge structure (XANES) spe ...

The extent of metal-metal electronic coupling was quantified for a series of syn and anti stereoisomers of (FeCp)(2)-, (RhL(2))(2)- and (FeCp)(RhL(2))- (L(2)=1,5-cyclooctadiene (cod), L=CO) as-indacenediide mixed-valent ions by spectroelectrochemical and DFT studies. The effect of the syn/anti orientation of the metal units with respect to the planar aromatic ligand indicates that electron transfer occurs through the bridge rather than through space. The nature of the metal was found to be crucial: while homobimetallic diiron species are localised valence-trapped ions (Class II), the dirhodium analogues are almost delocalised mixed-valent ions (borderline and Class III). Finally, despite their redox asymmetry, even in the heterobimetallic iron-rhodium as-indacenediide complexes, strong metal-metal coupling is present. In fact, oxidation of the iron centre is accompanied by electron transfer from rhodium to iron and formation of a reactive 17-electron rhodium site. syn and anti Fe-Rh as-indacenediide complexes are rare examples of heterobimetallic systems which can be classified as borderline Class II/Class III species.

Complexes of the general formula [MoO(2)X(2)L(2)] (X=Cl, Br, Me; L(2)=bipy, bpym) have been prepared and fully characterized, including X-ray crystallographic investigations of all six compounds. Additionally, the highly soluble complex [MoO(2)Cl(2)(4,4'-bis(hexyl)-2,2'-bipyridine)] has been synthesized. The reaction of the complexes with tert-butyl hydroperoxide (TBHP) is an equilibrium reaction, and leads to MoV(I) eta(1)-alkylperoxo complexes that selectively catalyze the epoxidation of olefins. Neither the Mo-X bonds nor the Mo-N bonds are cleaved during this reaction. These experimental results are supported by theoretical calculations, which show that the attack of TBHP at the Mo center through the X-O-N face is energetically favored and the TBHP hydrogen atom is transferred to a terminal oxygen of the Mo=O moiety. After the attack of the olefin on the Mo-bound peroxo oxygen atom, epoxide and tert-butyl alcohol are formed. The latter compound acts as a competitive inhibitor for the TBHP attack, and leads to a significant reduction in the catalytic activity with increasing reaction time.

Compounds obtained by a solid–gas phase reactions between copper(II) chloride and bromide and 2,4-, 2,6- 3,4- and 3,5-lutidines were studied using thermogravimetry, far-infrared, electronic spectroscopy and X-ray diffraction. The results were compared with the corresponding data for the similar compounds with methylpyridines and 2,4,6-collidine. A special attention was paid to the host-guest phenomenon, a new structural feature of transition-metal halide complexes.

High- and low-oxidation state CpML3-type (M=Mn, Re; L=O, CO) cyclopentadienyl complexes have been investigated by vibrational spectroscopy (FTIR, FT-FIR, FT-Raman) and normal coordinate calculations. The vibrational spectra of CpMn(CO)3, CpRe(CO)3 complexes were revised and reinterpreted. For the oxo-complexes and Cp*-carbonyl compounds, Cp*Mn(CO)3 and Cp*Re(CO)3, a complete spectral assignment is proposed. The results of the normal coordinate analysis are in good agreement with the spectral evidence. The vibrational spectroscopic findings help to explain earlier observations, e.g. the significantly lower stability of CpReO3 in comparison to Cp*ReO3. Characteristic force constants have been determined for Cp and Cp* ligands. A method is described for estimating an approximate force constant for the metal cyclopentadienyl (Cp) ligand bond stretch in half sandwich type of complexes, based on the use of an effective ‘spectroscopic’ mass of the Cp-ligand.

Ambient- and low-temperature IR. FIR and FT-Raman spectra of the complexes trans-[RuX(NH/D-3)(4)SO2]X (X = Cl (1/1D), Br (2/2D), I(3/3D)) were measured to provide the bases for normal coordinate analyses (NCA). Further, X-ray structure analyses of 1-3 yielded the required bonding parameters and justify the assumption of an idealized symmetry C-2v-mm2 for the cations. In accordance with the results of the structure determinations, the NCA calculations show an increasing irans-influence of the halogeno ligand on the Ru-S bond in the series Cl < Br < I. Formerly estimated force constants f(r)(RuN) are confirmed and neglect of cis-interactions is justified. Inspections of the eigenvalues and the potential energy distributions show an intense mixing of valence and deformation vibrations in symmetry species A(1). (C) 2001 Elsevier Science B.V. All rights reserved.

Mixed oxo/imido derivatives of methyltrioxorhenium(VII) form dimers in the solid state at ambient temperature. Density-functional calculations show that the dimerization is exothermic. The most stable derivatives were calculated to display a pseudo trigonal-bipyramidal coordination with two bridging oxygen centers and the methyl groups in a Irans arrangement. This configuration is energetically more favored than a cis arrangement of the methyl groups and a pseudo square-pyramidal structure at the metal centers. In the case of methyltrioxorhenium(VII), the dimerization is slightly endothermic, even for the optimal dimeric structure, so that dimers cannot be isolated. However, there is evidence for the transient existence of oxygen bridges between methyltrioxorhenium(VII) in solution. For mixed imido/oxo species, oxygen bridging is observed in all cases of dimerization; results of thermogravimetric/mass spectrometric studies demonstrate that these bridging dimers are weakly bound. From vibrational spectroscopic analysis, there is no evidence for nitrogen-bridged homologues. The density-functional calculations show that imido groups form bridges only in the case of sterically undemanding ligands. However, these complexes are too unstable to be isolated.

Structural, electronical and vibrational properties of Cp− and Cp*−, and of alkali metal cyclopentadienyl (CpM, M=Li, Na, K) and pentamethylcyclopentadienyl (Cp*M, M=Li, Na) complexes have been studied. The main goals of the study were to investigate the influence of the CH3 groups on the spectral features and on the MC force constants and the change of ionic character of the MC bond for different metals. FT-IR, FT-FIR and FT-Raman spectra of LiCp* and NaCp* compounds were recorded. Density functional theory calculations have been performed in order to obtain optimized geometries, vibrational frequencies and IR intensities. Calculated vibrational data were systematically compared to the experimental ones. Based on the calculations and experimental data, the vibrational spectra of Cp− and CpM were revised and reinterpreted, and a complete assignment of Cp*− and Cp*Li, Cp*Na vibrations was proposed. Correlations have been determined for the different metal atoms and the charge distribution, bond orders, bond energies and force constants.

Methyltrioxorhenium(VII) (MTO) forms octahedral adducts with bidentate Lewis bases. These complexes were isolated and fully characterized, including X-ray crystallography. The compounds display distorted octahedral geometry in the solid state with a tendency of disorder concerning the Re central atom. At elevated temperatures, they undergo rapid ligand-exchange reactions in solution. The ease of this ligand exchange depends mainly on the Lewis basicity of the ligand. The more Lewis basic the ligand is, the stronger the metal-ligand interaction is, as can be shown by NMR spectroscopy. All examined complexes are temperature stable but quite sensitive to light and moisture. In the presence of H(2)O(2), the complexes form very active and highly selective epoxidation catalysts. Peroxo complexes are generated, and at least one of the Re-N interactions is cleaved during this process. Total ligand dissociation only occurs in the case of very weakly coordinating bidentate ligands. The peroxo complexes of the MTO Lewis base adducts are, in general, more sensitive to water than MTO itself.

Combined Mössbauer and vibrational spectroscopic investigations revealed the presence of three structural units in the bis-terpyridine-iridium(III) complex in the solid state. A similar investigation of mixed o-phenanthroline halide complexes of iridium(III) indicated that the procedures elaborated to synthesize the cis and trans isomers of these complexes in fact led to the same product, the cisisomer.

Vibrational spectra of CH3Mn(CO)5 and CH3Re(CO)5 have been reinvestigated in particular in the far-IR (500–50 cm−1) region. Raman (3500–50 cm−1) solid phase (at ambient and liquid nitrogen temperature) and solution (in CH2Cl2) polarization data for the Re compound are presented. Based on the available and the present experimental data and the results of the normal coordinate calculations, the assignment of the frequencies has been reviewed and some modifications in the low frequency region have been suggested. Force-field calculations have been performed on the basis of vibrational data of the –CH3, –CD3, and –13CH3 species of gaseous, dissolved, and solid samples. Density functional theory calculations show that the rotational barrier of the methyl group is less than 0.5 kcal mol−1. The study of pressure effect on CO and M–CH3 stretching force constants proved that the stronger CO bonds have a relatively smaller pressure effect than the much weaker M–CH3 bonds. As a characteristic of pressure sensitivity ‘bond compressibility’ has been introduced.

FTIR and FT-Raman spectra of [PdCl3(C2H4)](-) and [PdCl3(C2D4)](-) anions have been recorded at greater sensitivity than hitherto and assigned on the basis of the well-studied Zeise's salt. Density functional theory (DFT) calculations were performed in order to obtain the optimised geometry, the vibrational frequencies and IR intensities of the Pd-complex. The comparison of the theoretical infrared spectra, the H/D isotopic shifts and the shifts in the CC stretching and CH scissoring frequencies upon coordination with those from experimental study show a remarkable agreement for the [PdCl3(C2H4)](-) and [PdCl3(C2D4)](-) species. The optimised PdC bond distance is 2.197 Angstrom, indicating that the metal ligand bond is weaker in [PdCl3(C2H4)](-) than in Zeise's salt but C2H4 seems to be more distorted in the Pd-analogue. The calculated force constants also confirm the lower stability of the Pd-complex. (C) 1999 Published by Elsevier Science S.A. All rights reserved.

The structural characteristics and thermal behaviour of the copper(II)-chloride and bromide complexes of 3-methylpyridine synthesised by a solid–gas phase technique are described. Far-IR spectra and results of the X-ray studies of the parent compounds and the intermediates indicate a host–guest phenomenon, a new structural feature of transition-metal halide complexes.