Molecular and Crystal Structures of New Binuclear Thiooxalate-Bridged Complexes: (.mu.-Trithiooxalato-S,S':S',S'')bis[bis(triphenylphosphine)silver(I)], the First Verified Simultaneously End-on/Side-on Coordinated Thiooxalate, and (.mu.-1,1-Dithiooxalato-S,O:S',O')bis[bis(triphenylphosphine)metal(I)] (Metal = Copper, Silver)

A study of asymmetrical mixed-valent Mo2-Mo2 complexes in the class III regime

Three novel asymmetrical dimolybdenum dimers, [Mo₂(DAniF)₃]₂(μ-OOCCOS) (DAniF = N,N'-di(p-anisyl)formamidinate) ([OO-OS]), [Mo₂(DAniF)₃]₂(μ-S₂CCO₂) ([SS-OO]), and [Mo₂(DAniF)₃]₂(μ-SSCCOS) ([SS-OS]), have been synthesized and characterized by either single-crystal X-ray crystallography or ¹H NMR spectroscopy. The structural asymmetry for these compounds gives rise to a redox asymmetry, which enlarges the potential separation (ΔE_1/2) between the two [Mo₂] units. The mixed-valance (MV) species [OO-OS]⁺, [SS-OO]⁺ and [SS-OS]⁺, prepared by one-electron chemical oxidation of the neutral precursors, exhibit an intense and symmetrical intervalence charge transfer (IVCT) absorption band in the near-IR region, along with the high energy metal (δ) to ligand (π*) (ML) and ligand (π) to metal (δ) charge transfer (LMCT) absorptions. The LMCT band, which is absent in the neutral precursors, is reflective of the cationic [Mo₂]⁺ unit in the MV species; therefore, it is evidenced that in the MV complexes optical electron transfer from the electron donor to acceptor occurs, while the thermal process is energetically unfavorable. The C(1)-C(2) bonds (1.44-1.48 Å) that connect the two [Mo₂] units are significantly shorter than a C-C single bond, showing that the two Mo₂ centers are strongly coupled. For the series, TD-DFT calculations show that the molecular orbitals have an unsymmetrical charge density distribution over the two dimolybdenum sites. For each of the complex systems, the calculated orbital energy gaps, SOMO(δ - δ)-LUMO(bridging ligand π*), HOMO-8(bridging ligand π)-SOMO(δ - δ) and SOMO(δ - δ)-HOMO-1(δ + δ), are in good agreement with the observed MLCT, LMCT and IVCT absorption band energies, respectively. The consistency in energy between the IVCT band and the SOMO(δ - δ)-HOMO-1(δ + δ) gap permits assignment of the MV complexes to Class III in the Robin-Day scheme.

Bonding preferences of C2X4-bridged bimetallic transition metal complexes of Ti, Cu, and Ag

The bonding preference of transition metal species of general formula [(PH3)2M]2(mu-C2X4), where M = Cu or Ag and X = O, S, Se, or Te, and (Cp2Ti)2(mu-C2X4), where X = S or Se, are explored using density functional theory. The relative energies of metal binding to the bridging ligand in a dithiolene-like vs dithiocarbamate-like manner are evaluated. In all cases, the most stable structure corresponds to dithiolene-like (or side-side) bonding, consistent with the vast majority of these compounds which have been experimentally characterized. However, for M = Ag and X = S, Se, or Te, the two isomers are nearly degenerate.