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 ——(2)Crystal Structure and Crystal Chemistry

Extensive studies have been devoted to the synthesis and characterization of V-P-O compounds because of not only their relevance to catalytic and adsorptive properties, but also their rich and complex structural chemistry. In order to elucidate the influence of chemical component on the framework stability of VPO system, the crystal structure of the allomer (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) of V_9P_8-en was characterized by X-ray single crystal diffraction method (R=(0.0540) for the data [I2sigma(I)]). Results show that V_9(P,B)_8-en crystallized in the monoclinic space group P2(1)/n with lattice parameters of a=1.43134(9)nm, b=1.01256(6)nm, c=1.83156(12)nm, β=90.280(2)°, V=2.6545(3)nm~3, Z=2. The structure consists of complex 3-dimensional intercrossing channels including a very large tunnel of 1.83nm in diameter, in which both protonated ethylenediamine and water species are occluded. It has been demonstrated that element B substitutes partially for P in tetrahedron (the atomic ratio of B:P is 0.1838:7.8162), and the substituted quantity of P in[HPO_4]is bigger than in[PO_4] by refining the site occupancy of V and P atoms. Compared with V_9P_8-en, the crystal parameters, contents in pores and charges between template and framework for V_9(P,B)_8-en change to some extent. The successful elucidation of these differences between the two compounds can be helpful for the investigation of the structural stability mechanism of open framework vanadium phosphates.