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

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-Mo8VI/VO26[MoVO2(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) A]. 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.