SYNTHETIC PATHWAYS TO OBTAIN PHOSPHATES AND ARSENATES OF CO(II) AND NI(II) RELATED TO MINERALS - MAGNETIC-PROPERTIES

Different methods to prepare phosphates and arsenates of transition me tals related to minerals are described. M3(XO4)2.8H2O (M = Co, Ni; X = P, As) vivianite-like compounds were prepared by solution chemistry p rocedures. (Ni, Mg)3(PO4)2 (related to sarcopside) solid solutions wer e obtained by thermal treatments of the octahydrated phases. Using hyd rothermal conditions three new compounds were synthesized: Co3(HPO4)2( OH)2 (related to lazulite) and M12+xH4-2x(PO4)6(HPO4)2(OH)6 (M = Co, N i), dumortierite-like hexagonal phases. In every case, the magnetic pr operties are discussed with respect to the crystal structure and the n ature of the transition-metal ion.