Comparative studies on the electronic structures of tetraformatoditungsten and dimethyltetraformatoditungsten by the relativistic X.alpha.-SW method: a d3-d3 metal dimer with a quadruple metal-metal bond (original) (raw)
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Inorganic Chemistry, 2021
The difference in [3 + 2] cycloaddition reactivity between fac-[MO 3 (tacn)] + (M = Re, 99 Tc; tacn = 1,4,7-triazacyclononane) complexes has been reexamined with a selection of unsaturated substrates including sodium 4vinylbenzenesulfonate, norbornene, 2-butyne, and 2-methyl-3-butyn-2-ol (2MByOH). None of the substrates was found to react with the Re cation in water at room temperature, whereas the 99 Tc reagent cleanly yielded the [3 + 2] cycloadducts. Interestingly, a bis-adduct was obtained as the sole product for 2MByOH, reflecting the high reactivity of a 99 TcO-enediolato monoadduct. On the basis of scalar relativistic and nonrelativistic density functional theory calculations of the reaction pathways, the dramatic difference in reactivity between the two metals has now been substantially attributed to differences in relativistic effects, which are much larger for the 5d metal. Furthermore, scalar-relativistic ΔG values were found to decrease along the series propene > norbornene > 2-butyne > dimethylketene, indicating major variations in the thermodynamic driving force as a function of the unsaturated substrate. The suggestion is made that scalar-relativistic effects, consisting of greater destabilization of the valence electrons of the 5d elements compared with those of the 4d elements, be viewed as a new design principle for novel 99m Tc/Re radiopharmaceuticals, as well as more generally in heavyelement coordination chemistry.
Inorganic Chemistry, 1999
The known tetrathiometalates MoS 4 2-/3-, WS 4 2-/3-, ReS 4-/2-/3-, and the unknown species TcS 4-/2-, RuS 4 0/-, and OsS 4 0/-/2were calculated using ab initio and DFT methods. The one-electron reduced species with d 1 configuration were shown to exhibit a slight Jahn-Teller distortion (T d f D 2d); the largest corresponding stabilization energy was obtained for MoS 4 3with-4.17 kcal/mol. Trends in vacuum bonding energies involve a destabilization on going from 5d n to 4d n systems and on reduction from d 0 to d 1 species, with the exception of Ru and Os complexes where the d 1 configurations are more stable than the d 0 forms. The d 2 species ReS 4 3and OsS 4 2have vacuum bonding energies similar to those of d 1 analogues. The metal contribution to the lowest unoccupied MO (e) of d 0 forms is lowest for the neutral RuS 4 and OsS 4 and highest for the dianions MoS 4 2and WS 4 2-. The DFT approach supported by correlated ab initio calculations describes the main features of the electronic spectra of the d 0 complexes. For the experimentally best accessible ReS 4 nsystem the absorption energies and stretching frequencies were well reproduced, and the related but hitherto unknown OsS 4ion is predicted to be a fairly stable paramagnetic species. Tetrathiometalates MS 4 nof the transition elements 1,2 with metal d 0 configuration (M) V, Nb, Ta and n) 3; 3 M) Mo, W and n) 2; 4 M) Re and n) 1) 4,5 have received attention in synthetic bioinorganic chemistry (precursors for models of Mo-7 and W-containing enzymes 8,9) and from catalysis where they serve as starting point for models directed at the improvement of hydrodesulfurization (HDS) catalysts for crude oil. 1,2,10-13 Under inorganic 4,11,15-20 and organometallic 21-30 aspects tetra-thiometalates are interesting as potentially chelating, bridging, and cluster-forming components with relatively low-lying unoccupied d orbitals and high-lying sulfur-based molecular orbitals. Among the consequences of this situation are intense, low-energy ligand-to-metal charge transfer (LMCT) transitions; for the Mo VI , W VI , and Re VII species these lie in the visible region. 4 Despite the relatively small HOMO-LUMO gaps, the reversible electrochemical reduction to d 1 species generally † Academy of Sciences of the Czech Republic.
Journal of the American Chemical Society, 1991
A Comparative Theoretical Analysis of the Physicochemically Dissimilar Tetrathiolate-and Oxalate-Bridged Dititanium Series, [ ( C P~T~)~(~-C~X~) ]~ (Where X = S, n = 0, 1-, 2-; X = 0, n = 0, 2+): An Explanation of Electron Delocalization from the Metal Centers Upon Replacement of the Oxalate Ligand with the Tetrathiooxalate Ligand Abstract: Although electronically equivalent with the oxalate-bridge ( C P~T~)~( W -C~O~)
Organometallics, 2000
The structural model of the trimethyldioxorhenium molecule, Me 3 ReO 2 (1), has been revised on the basis of analysis of its 1 H, 13 C, and 17 O NMR and vibrational spectra and of its gas electron diffraction (GED) pattern. The results are consistent with the molecular symmetry C s ; in the new model both oxo ligands together with one methyl group are located in the equatorial plane of a distorted trigonal bipyramid. Structure optimization by density functional theory (DFT) calculations and least-squares refinement to the GED data yield the valence angles (calc/expt; eq ) equatorial; ax ) axial; av ) average) ∠C eq ReO ) 118.0/ 118.5(10)°and ∠C eq ReC ax ) 74.3/73.5(11)°. The pseudoaxial Re-C bond distance is found to be shorter than the equatorial one, viz., Re-C ax ) 2.130/2.122(6) Å versus Re-C eq ) 2.193/ 2.199(22) Å, and RedO av ) 1.739/1.703(3) Å. It is suggested that the distortion from trigonal bipyramidal to edge-bridged tetrahedral coordination geometry is driven by the need for the axial C atoms to achieve optimal overlap with both the d z 2 and d yz orbitals on the Re atom. The DFT calculations indicate that the axial methyl groups are tilted in such a manner that the ∠ReCH valence angles in the ReC 3 plane are reduced to 100.8°. It is suggested that this tilting is due in part to bent Re-C ax bonds and in part to weak C-H‚‚‚Re agostic interactions.
Crystal structure of Th2Al deuterides
Journal of Alloys and Compounds, 2000
Three Th Al deuterides with compositions Th AlD , x 5 3.9, 2.7 and 2.3, were studied by powder neutron diffraction (PND). The 2 2 x lower deuterides were obtained by desorption under dynamic vacuum at 338 and 443 K, respectively. Th AlD has been reported to 2 4v iolate the ''rule of 2 A'', however Rietveld refinement of high quality PND data for saturated Th AlD , a 5 7.6260(4) A, 2 3.9c 5 6.5150(5) A, gave an acceptable D-D separation of 1.97 A. Space group I4 /mcm of the intermetallic with Al Cu-type atomic 2 arrangement is preserved and deuterium occupies one interstice, 16l, almost completely. For an intermediate D content, Th AlD , the 2 2 . 7 5d euterium sublattice becomes highly ordered giving a supercell with triple c-axis, a 5 7.6796(3) A, c 5 19.073 A. This superstructurē is described in space group P42m. Deuterium is situated in nine interstices, i.e. eight 4n sites and one 1d site. On further deuteriumr emoval towards the composition Th AlD , a 5 7.7014(5) A, c 5 6.2816(5) A, the deuterium sublattice becomes disordered. The 2 2 . 3 structure is again described in space group I4 /mcm. Deuterium partly occupies two different interstices, 16l and 4b. For all compositions, solely Th tetrahedral interstices are occupied by deuterium.