ABSTRACT
Tellurium oxide clusters (TeO2)6 were investigated through density functional theory to gain information on the structure of TeO2 glass. Among a large number of stable conformers studied, a cyclic, nonsymmetric structure was optimized without terminal TeâO double bonds. The dimer of this structure, (TeO2)12, gives calculated Raman and infrared spectra in very good agreement with the experimental ones, with its total pair distribution function being also in agreement with results of neutron and high-energy X-ray diffraction studies. The (TeO2)12 cluster consists mainly of TeO4 units connected by asymmetric and nearly symmetric Te-O-Te bridges as in γ-TeO2 and involves also edge-sharing through double-oxygen Te-O2-Te bridges as in the ß-TeO2 polymorph. The optimized cluster structure is slightly unstable compared to the calculated global minimum structure, suggesting a kinetically stable product similar to its corresponding experimental TeO2 glass.
ABSTRACT
The synthesis and characterization of the tetrathiomolybdatorhodium(I) monoanionic complexes [L2Rh(µ-S)2MoS2](-) (L = CO (3), P(OPh)3 (4), P(O-o-Tol)3 (P(o-CH3C6H4)3; 5), P(OMe)3 (6), P(OEt)3 (7), P(O-i-Pr)3 (8); L2 = COD (1,5-cyclooctadiene; 2), cis-dppen (cis-Ph2PCHâCHPPh2; 9), dppe (Ph2PCH2CH2PPh2; 10), dppb (Ph2P(CH2)4PPh2; 11)) is presented. The complex 2 (NEt4(+) salt) was characterized by X-ray diffraction analysis. A detailed DFT study of the electronic structures of 2-4 and 6-8 has revealed the existence of extended electron delocalization over the four-membered Rh(µ-S)2Mo ring and hence the possibility of electronic communication between the metal centers. The electronic spectra were studied with TDDFT calculations, and the main absorption band in the visible region was assigned to ν(RhâMo) electron transfer transition, which is actually a HOMO-LUMO transition. The ν(RhâMo) transition was found to correlate linearly both with Tolman's electronic parameter of the phosphite ligands and the calculated HOMO-LUMO gap of the complexes, rendering it a well-defined ligand electronic parameter, which describes the net donating ability of monodentate and bidentate ligands (CO, COD, phosphites, diphosphines). The study of the variation of Δδ((31)P) and (1)J(Rh-P) of the phosphite complexes with respect to the QALE model electronic parameters χd, πp, and Ear has succeeded in the assessment of the σ and π effects on these NMR spectral parameters.
ABSTRACT
The protonation reaction of the unbridged quadruple metal-metal bond of [Mo(2)Cl(8)](4-) anion producing the triply bonded hydride [Mo(2)(µ-H)(µ-Cl)(2)Cl(6)](3-) is studied by accurate Density Functional Theory computations. The reactant, product, stable intermediates, and transition states are located on the potential energy surface. The water solvent is explicitly included in the calculations. Full reaction profiles are calculated and compared to experimental data. The mechanism of the reaction is fully elucidated. This involves two steps. The first is a proton transfer from an oxonium ion to the quadruple bond, being rate determining. The second, involves the internal rearrangement of chlorine atoms and is much faster. Activation energies with a mean value of 19 kcal/mol are calculated, in excellent agreement with experimental values.
Subject(s)
Chlorine Compounds/chemistry , Molybdenum/chemistry , Protons , Anions/chemistry , Models, Chemical , Models, Molecular , Quantum TheoryABSTRACT
A detailed study of the stepwise substitution of the chloride ligands in the [Re3(mu-Cl)3Cl9](3-) (1) anion by water molecules is presented using theoretical methods. Ligand lability as well as the structure and relative stability of the various mono-[Re3(mu-Cl)3Cl8(H2O)](2-) (2a,b) and dihydro-[Re3(mu-Cl)3Cl7(H2O)2](-) (3a-f) conformers is examined. Clear preferences for the positions of the incoming water ligands are proposed based on calculated energy and vibrational data, which fully agree with the experimental results.
