Transformations and reductions of γ-octamolybdates with their monomeric and dimeric amino polycarboxylates

Abstract

Investigations on aminopolycarboxylato molybdates resulted in the isolation of two interesting decameric species of iminodiacetato γ-octamolybdates (NH₄)₈{γ-Mo₈O₂₆[MoO₃(ida)]₂}·6H₂O (1) (H₂ida = iminodiacetic acid) and its partially reduced form, K₈{γ-Mo₈^VI/VO₂₆[Mo^VO₂(ida)]₂}·12H₂O (2). 1 is comparable with its formal polymeric coupling form of polyaminopolycarboxylato molybdate (NH₄)_8n{γ-Mo₈O₂₆[Mo₂O₆(1,3-pdta)]}_n·30nH₂O (3) from 1,3-propanediaminetetraacetate (H₄pdta = 1,3-propanediaminetetraacetic acid). The basic construction unit of the iminodiacetato γ-octamolybdates was isolated as a monomeric complex (NH₄)₄[MoO₃(ida)]₂·3H₂O (4). While those for propanediaminetetraacetato γ-octamolybdate are a dimeric species of (NH₄)₅[Mo₂O₆(1,3-pdta)]Cl·2H₂O (5) and K₄[Mo₂O₆(1,3-pdta)]·3H₂O (6) respectively. Moreover, polymeric octamolybdates with ammonium cations (NH₄)_6n(Mo₈O₂₇)_n·4nH₂O (7) and (NH₄)_4n(Mo₈O₂₆)_n (8) were obtained under heating and hydrothermal conditions, respectively. Monomeric iminodiacetato molybdate 4 can be transformed to its decanuclear species 1 with [Mo₈O₂₆]⁴⁻ anion. Mixed-valence complex 2 processes a unique deca-molybdenum core with a metallic Mo(V)–Mo(V) bond [2.573(2) Å]. The complexes have been characterized by elemental analyses, spectral, X-ray structural analyses and bond valence calculations. Complexes 1–6, except for 3, showed an obvious decomposition in solution, based on solution ¹³C NMR observations. NMR analyses revealed that the γ-Mo₈O₂₆ units in 1 and 2 show an effect on the carbon signals. This is attributed to the Mo–O–Mo bond between the Mo₈O₂₆ and MoO₃ida units. The dimeric species 5 and 6 dissociated to free ligands in ∼5% and ∼27%, respectively, based on ¹H NMR spectra.