Mao-Long Chen

Structures and thermal properties of strontium and barium 1,3-propanediaminetetraacetates

In neutral and acidic solution, homonuclear s-block metal complexes [Sr2(1,3-pdta)(H2O)3.5] n (1), {[Ba2(1,3-pdta)(H2O)6]·H2O} n (2), {[Sr(1,3-H2pdta)]·(H2O)} n (3), and [Ba(1,3-H2pdta)(H2O)3] n (4) {1,3-H4pdta=1,3-propanediamine-N,N,N′,N′-tetraacetic acid, CH2[CH2N(CH2CO2H)2]2} were isolated. In 1 and 2, hexadentate 1,3-pdta joins two metal ions via the diamine chain. In 3 and 4, the nitrogens of 1,3-H2pdta were protonated and show no coordination. There is no coordinated water in 3, unusual coordination for strontium. In 4, the coordination number is nine and there are three coordinated waters for each barium. One carboxy group of pdta is free without coordination. Thermal decomposition shows that temperatures of ligand elimination start at 408, 423, 298, and 250 °C for 1–4, respectively. Acidic condition is favorable for preparation of metal oxide at low temperature.

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.