The pillared layered framework of Ba3(In1-xMx)2(HXO4)6 (0 ≤ x ≤ 1; M = Fe, Cr; X = P, As):: synthesis, crystal structure, thermal stability and Mossbauer spectroscopy

The hydrothermal synthesis, single crystal structure analysis, spectroscopic and thermal stability studies of the compounds Ba-3(In1-xMx)(2) (HXO4)(6) (0 less than or equal to x less than or equal to 1; M = Cr, Fe; X = P, As) are reported. The 3D framework of these new phosphates can be described as a pillared layered framework. The metal cations (In3+, Fe3+, and Cr3+) occupy two crystallographically independent octahedral sites, M(I) and M(2). The layers are formed of M(2)0, octahedra and (HPO4) tetrahedra sharing corners, with M(1)0, octahedra serving as pillars between adjacent layers. Single crystal study of Ba-3(In0.5Fe0.5)(HPO4)(6) shows that indium and iron segregate between the two metal sites with Fe occupying primarily the site M(1) and In located primarily in M(2) site. Interactions between the building units within the layers occur through hydrogen bonding. Barium cations are located between the pillars, in 8-membered ring tunnels and are coordinated by 12 oxides. The phases loose three water molecules through condensation of six HXO4 groups to form Ba2M2(X2O7)(3) at temperatures between 480 and 600 degreesC. Mossbauer spectroscopy shows the presence of high-spin Fe3+ in octahedral coordination. (C) 2001 Editions scientifiques et medicales Elsevier SAS. All rights reserved.