Combined Theoretical and Experimental Analysis of the Bonding in the Heterobimetallic Cubane-Type Mo₃NiS₄and Mo₃CuS₄Core Clusters

Abstract

X-ray structural data for the cubane-type clusters [Mo3CuS4(dmpe)3Cl4](+) and Mo3NiS4(dmpe)3Cl4 (dmpe = 1,2-bis(dimethylphosphino)ethane) with 16 metal electrons have been compared with optimized structural parameters calculated using "ab initio" methodologies. Compound Mo3NiS4(dmpe)3Cl4 crystallizes in the cubic noncentrosymmetric space group P213 with a Mo-Ni distance of 2.647 Angstrom, that is 0.2 Angstrom shorter than the Mo-Cu bond length in the isoelectronic copper cluster. The best agreement between theory and experiments has been obtained using the B3P86 method. In order to validate the B3P86 results, accurate infrared and Raman spectra have been acquired and the vibrational modes associated to the cubane-type Mo3M'S4 (M' = Cu or Ni) unit have been assigned theoretically. The electronic changes taking place when incorporating the M' into the Mo3S4 unit have been analyzed from a theoretical and experimental perspective. The bond dissociation energies between M'-Cl and Mo3S4 fragments show that formation of [Mo3CuS4(dmpe)3Cl4](+) is 135 kcal/mol energetically less favorable than the Ni incorporation. The more robust nature of the Mo3NiS4 fragment has been confirmed by mass spectrometry. The X-ray photoelectron spectroscopy (XPS) spectra of the trimetallic and tetrametallic complexes have been measured and the obtained binding energies compared with the computed electronic populations based on topological approaches of the electron localization function (ELF). The energies and shapes of the Cu 2p and Ni 2p lines indicate formal oxidation states of Cu(I) and Ni(II). However, the reductive addition of nickel into [Mo3S4(dmpe)3Cl3](+) causes a small decrease in the Mo 3d binding energies. This fact prevents an unambiguous assignment of an oxidation state in a conventional way, a circumstance that has been analyzed through the covariance of the electronic populations associated to the C(M') core and V(Mo3Ni) and V(S(2)') valence basins where Mo3NiS4 is a particularly electronically delocalized chemical entity.

Influence of the Diphosphine Coordinated to Molybdenum and Tungsten Triangular M3S4 Cluster Hydrides in the Catalytic Hydrodefluorination of Pentafluoropyridine

“…Incidentally, the hydrido cluster [Mo3S4H3(dppe)3]PF6 does it in a noncentrosymmetric Cc space group from a racemic mixture in dichloromethane. The preferential crystallization of one of the enantiomers from racemic mixtures has been previously described for the closely related heterobimetallic cubane-type Mo3NiS4(dmpe)3Cl4 neutral compound [31]. A list of relevant bond distances and angles is given in Table 1.…”

Topological analysis of the metal-metal bond: A tutorial review

“…Bond strength from Raman M-M force constants, from δ → δ * electronic transitions or from X-ray photoelectron spectroscopy XPS (δ bond only [17]); 5. Oxidation state from NMR and XPS [18,19] or from electrochemical measurements; 6. Enhanced photoluminescence because of LMMCT excited states (electronic spectroscopy).…”

Efficient and Selective N‐Methylation of Nitroarenes under Mild Reaction Conditions

“…Upon Pt insertion, the electron precise Mo 3 S 4 4+ unit with six metal‐cluster skeletal electrons (CSE) to form three metal–metal bonds becomes a Mo 3 PtS 4 4+ cluster‐containing sixteen CSE, and so some changes in its redox properties are expected. The electronic delocalization in the resulting heterobimetallic system makes all schemes directed towards the metal oxidation states assignment inconclusive . Electrochemical properties of the incomplete 1 + and cubane‐type 3 + complexes have been investigated by cyclic voltammetry (see Table and Figure SI4 in the Supporting Information).…”