Compositional space diagrams and crystallization sequences in M/Bpa/NaVO3 (M = Ni, Co) systems. Physical properties of [{Ni(H2O)(Bpa)}(VO3)2]·2H2O and {Co(Bpa)}(VO3)2 3D hybrid vanadates

Abstract

The 3D hybrid compounds {Co(Bpa)}(VO₃)₂ (1) and [{Ni(H₂O)(Bpa)}(VO₃)₂]·2H₂O (2), where Bpa is 1,2-di(4-pyridil)ethane, have been synthesized using mild hydrothermal conditions. The compositional diagrams for the Co(II)/Bpa/V_xO_y and Ni(II)/Bpa/V_xO_y systems have been constructed and qualitative crystallization sequences have been proposed. The 3D crystal structures of both compounds are closely related, and are constructed of inorganic layers pillared by the organic ligand. The UV-vis spectra for (1) shows the characteristic bands of the Co(II) d⁷high-spin cation in a slightly distorted trigonal bipyramid geometry. The thermal behaviour of (1) allows the determination of the expansion coefficients for the cell and angle parameters, which were closely related to the different types of bonds that exist in the crystal structure. The cobalt compound exhibits antiferromagnetic coupling of the cobalt centres within the inorganic layers, probably coupled in dimeric units, as is expected for the different magnetic exchange pathways. For (2), the diffuse scattering is probably related to the motion of the crystallization water molecules, which is observed in the (h0l), (h2l), (hk0) and (hk2) planes.