Mononuclear, polynuclear, and cluster complexes of molybdenum and their reactions as models of biochemical systems and processes

An XAS study of molybdenum speciation in hydrothermal chloride solutions from 25–385°C and 600bar

“…In the Na 2 MoO 4 solution and in slightly acidified solutions (0.03 m HCl) containing varying amounts of NaCl, all data at all temperatures (25-385°C) and salinity (0-5.8 m NaCl) point to the predominance of a tetrahedral species based around the Cruywagen, 1999 andDement'ev et al, 2007). No evidence of Mo-Mo bonding was observed in the EXAFS spectra of our sample solutions.…”

“…These similarities suggest that MoO 2 Cl 2 (H 2 O) 2(aq) is probably the major species at 166°C, however, mixed species with the same average number of O and Cl ligands cannot be ruled out. At 340°C, the number of oxygen ligands drops to 1.1(3) and the number of chloride ligands increases to 5.1 (5) Dement'ev et al (2007). This is because as the number of terminal oxygen atoms decreases from 4 to 1, the Mo@O double bond strength increases and the bond distance shortens (Dement'ev et al, 2007).…”

“…10, Sample S9b at 25°C). The Mo-O distance of 1.77 Å determined by Yokoi et al (1993) is also similar to the mean MoAO distance in the tetrahedral molybdate ion ([MoO 4 ] cluster), but is too long for a Mo@O bond in MoO 2 (H 2 O) 4 2+ in acidic solutions ($1.67 Å , Dement'ev et al, 2007). The latter is consistent with our fitted mean MoAO bond length for the S9b solution at room temperature, 1.698(3) Å (Table 4).…”

“…No evidence of Mo-Mo bonding was observed in the EXAFS spectra of our sample solutions. While mononuclear species should predominate in the highly acidic solutions (Dement'ev et al, 2007), dimeric and/or polymeric Mo ions may be present in the molybdate solution (S1) and slightly acidified solutions (S12) of this study, as suggested by Tytko et al (1985); however, they are considered to be minor species and make very limited contribution to the overall spectra of sample solutions. Hence, the discussion here focuses on the monomeric Mo(VI) species.…”

“…At 340°C, the number of oxygen ligands drops to 1.1(3) and the number of chloride ligands increases to 5.1 (5) Dement'ev et al (2007). This is because as the number of terminal oxygen atoms decreases from 4 to 1, the Mo@O double bond strength increases and the bond distance shortens (Dement'ev et al, 2007). It should be noted that single scattering fitting of the first shell of EXAFS data only accounts for the average ligand numbers, therefore it cannot distinguish between mixed ligand species and mixtures of different species with same average number of ligands (e.g., Liu et al, 2012).…”