Zeolitic and magnetic properties of a 24-membered ring porous nickel(II) phosphate, VSB-1

A large-pore, zeolitic nickel(II) phosphate, VSB-1, has been prepared under hydrothermal conditions. The unidimensional pore system is delineated by 24 NiO6 and PO4 polyhedra and has a free diameter of approximately 9 Angstrom. It becomes microporous on calcination in air at 623 K, yielding a BET surface area of 82 m(2).g(-1), and is stable in air to approximately 823 K. VSB-1 can be prepared in both ammonium and potassium forms, and exhibits ion-exchange properties that lead, for example, to the formation of the lithium and sodium derivatives. Other cations (e.g. Mn, Fe, Co, and Zn) can be substituted for Ni in VSB-1, up to a level as high as 30 atomic %. The parent compound exhibits canted antiferromagnetic order at T-N = 10.5 K with theta = -71 K; on doping with Fe, T-N increases to 20 K and theta decreases to -108 K. (C) 1999 Academie des sciences/Editions scientifiques et medicales Elsevier SAS.