Hydrothermal Synthesis and Crystal Chemistry of a Vanadium Borophosphate (H_3NCH_2CH_2NH_3)_2(H_3NCH_2CH_2NH_2)[V~III(H_2O)_2(V~IVO)_8(OH)_4(H(P,B) O_4)_4(P,B)O_4)_4(H_2O)_2]·3H_2O with Three-dimensional Open Framework ——(1) Hydrothermal Synthes

For the purpose of probing into the influence of chemical component on the framework stability of VPO system, a synthetic strategy was presented and a series of hydrothermal synthesis experiments were designed rationally based on the valence-matching principle. One vanadium borophosphate,(H_3NCH_2CH_2NH_3)_2(H_3NCH_2CH_2NH_2)[V~Ⅲ(H_2O)_2(V~ⅣO)_8(OH)_4 (H(P,B)O_4)_4((P,B)O_4)_4(H_2O)_2]·3H_2O(V_9(P,B)_8-en for short), was synthesized hydrothermally by molecular self-assembly technique. The typical molar ratio of starting reagents was n(V_2O_5):n(H_3BO_3):n(H_3PO_4):n(en):n(H_2O)= 0.89:3.50:3.50:3.6:265, and the hydrothermal reaction was run in 50 mL Teflon-lined stainless-steel autoclave(filling volume of 45～50%) at 175℃ for 6.5 days under autogenous pressure. The starting and the final pH values were 6.5 and 5.9 respectively. By EPMA, FT-IR and XRD methods, the chemical component and crystal structure of the compound were determined. It was shown that the atomic ratio of P:B was variable from 0.1:7.9 to 2.54:5.46 in different crystals, but the atomic ratio of V:(P+B) was almost 9:8 constantly. This blue tabular compound V_9(P,B)_8-en was an allomer of V_9P_8-en. By refining the site occupancy of V and P atoms in the structure of one crystal investigated, it was demonstrated that element B substituted partially for P in tetrahedron, and the atomic ratio of B:P was 0.1838:7.8162. The successful syntheses of this compound should be helpful for the investigation of the structural stability mechanism of open framework vanadium phosphates.