Channel structure in the new BiCoPO5. Comparison with BiNiPO5. Crystal structure, lone pair localisation and infrared characterisation
1999; Elsevier BV; Volume: 1; Issue: 6 Linguagem: Inglês
10.1016/s1293-2558(00)80097-7
ISSN1873-3085
AutoresEl Mostafa Ketatni, F. Abraham, Olivier Mentré,
Tópico(s)Solid-state spectroscopy and crystallography
ResumoThe new compound BiCoPO5, monoclinic, P21/n, a = 7.2470(1) A, b = 11.2851(2) A, c = 5.2260(1) A and β = 107.843(1) °, Z = 4, was synthesised and structurally characterised by powder X- ray diffraction and infrared spectroscopy. It is isostructural with bismuth nickel oxyphosphate BiNiOPO4. The crystal structure is built from a complex tridimensional assembly of (Co/Ni)2O10 dimers linked by PO4 groups. This forms large tunnels running along c which host Bi3+ cations. Smaller tunnels running along a and crossing the latter were also evidenced. It is noteworthy that the original BiNiPO5 lattice is appreciably increased with Co2+ cations as the transition metal. This feature is essentially pointed out by the Co-O longer distances. The Bi3+ cation is surrounded by a strongly distorted oxygen octahedron. Reducing the BiO bonds to the three shortest, Bi environment can be considered as tetrahedral considering the BiO3Lp polyhedron, Lp = 6s2 lone pair (Lp). The lone pair localisation was performed from electrostatic interactions and revealed Lp - Bi distance of 0.68 A and 0.58 A, for Co2+ and Ni2+ compounds respectively. The infrared spectra of the two compounds are essentially the same and only show slight shifts of the significant bands.
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