Monoanionic molybdenum and tungsten tris(dithiolene) complexes: A multifrequency EPR study

Stephen Sproules, Priyabrata Banerjee, Thomas Weyhermüller, Yong Yan, James P. Donahue, Karl Wieghardt

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Abstract

Numerous Mo and W tris(dithiolene) complexes in varying redox states have been prepared and representative examples characterized crystallographically: [M(S 2C 2R 2) 3] z [M = Mo, R = Ph, z = 0 (1) or 1- (2); M = W, R = Ph, z = 0 (4) or 1- (5); R = CN, z = 2-, M = Mo (3) or W (6)]. Changes in dithiolene C-S and C-C bond lengths for 1 versus 2 and 4 versus 5 are indicative of ligand reduction. Trigonal twist angles (Θ) and dithiolene fold angles (α) increase and decrease, respectively, for 2 versus 1, 5 versus 4. Cyclic voltammetry reveals generally two reversible couples corresponding to 0/1- and 1-/2- reductions. The electronic structures of monoanionic molybdenum tris(dithiolene) complexes have been analyzed by multifrequency (S-, X-, Q-band) EPR spectroscopy. Spin-Hamiltonian parameters afforded by spectral simulation for each complex demonstrate the existence of two distinctive electronic structure types. The first is [Mo IV( AL 3 5-•)] 1- ( AL = olefinic dithiolene, type A), which has the unpaired electron restricted to the tris(dithiolene) unit and is characterized by isotropic g-values and small molybdenum superhyperfine coupling. The second is formulated as [Mo V( BL 3 6-)] 1- ( BL = aromatic dithiolene, type B) with spectra distinguished by a prominent g-anisotropy and hyperfine coupling consistent with the (dz 2) 1 paramagnet. The electronic structure disparity is also manifested in their electronic absorption spectra. The compound [W(bdt) 3] 1- exhibits spin-Hamiltonian parameters similar to those of [Mo(bdt) 3] 1- and thus is formulated as [W V( BL 3 6-)] 1-. The EPR spectra of [W( AL 3)] 1- display spin-Hamiltonian parameters that suggest their electronic structure is best represented by two resonance forms {[W IV( AL 3 5-•)] 1- ↔ [W V( AL 3 6-)] 1-}. The contrast with the corresponding [Mo IV( AL 3 5-•)] 1- complexes highlights tungsten's preference for higher oxidation states.

Original languageEnglish (US)
Pages (from-to)7106-7122
Number of pages17
JournalInorganic Chemistry
Volume50
Issue number15
DOIs
StatePublished - Aug 1 2011

All Science Journal Classification (ASJC) codes

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

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