Controlling nucleation and crystal growth of a distinct polyoxovanadate cluster: an in situ energy dispersive X-ray...

The formation of the antimonato polyoxovanadates [V(14)Sb(8)(C(6)H(15)N(3))(4)O(42)(H(2)O)]·4H(2)O (1), (C(6)H(17)N(3))(2)[V(15)Sb(6)(C(6)H(15)N(3))(2)O(42)(H(2)O)]·2.5H(2)O (2), {C(6)H(15)N(3)}(4)[V(16)Sb(4)O(42)]2H(2)O (3) (C(6)H(15)N(3)=1-(2-aminoethyl)piperazine, AEP) has been studied under solvothermal conditions by using in situ energy dispersive X-ray diffraction (EDRXD). The syntheses were performed with an identical ratio for Sb(2)O(3) and NH(4)VO(3). If the reactions slurries are not stirred during the solvothermal reaction and by applying 70-75% amine concentration, the products contain all three compounds, whereas 3 is observed at 80%. Under stirring conditions, variation of the concentration of AEP led to crystallization of the three different compounds at distinct concentrations, that is, 1 is formed at 75%, 1 and 2 between 75 and 80% and 3 at 80%. At an amine concentration of 77.5%, first reflections of 2 occurred and at later stages, compound 1 started to crystallize. The sample with the lowest number of V(IV) species was formed at the lowest amine concentration, whereas crystallization of 3 required the highest concentration. The formation of the compounds occurred without crystalline intermediates and/or precursors. With increasing reaction temperature, the incubation time was significantly reduced.