Synthetic pathways to obtain phosphates and arsenates of Co (II) and Ni (II) related to minerals: magnetic properties

Abstract Different methods to prepare phosphates and arsenates of transition metals related to minerals are described. M 3 (XO 4 ) 2 ·8H 2 O (M=Co, Ni; X=P, As) vivianite-like compounds were prepared by solution chemistry procedures. (Ni, Mg) 3 (PO 4 ) 2 (related to sarcopside) solid solutions were obtained by thermal treatments of the octahydrated phases. Using hydrothermal conditions three new compounds were synthesized: Co 3 (HPO 4 ) 2 (OH) 2 (related to lazulite) and M 12+ x H 4−2 x (PO 4 ) 6 (HPO 4 ) 2 (OH) 6 (M=Co, Ni), dumortierite-like hexagonal phases. In every case, the magnetic properties are discussed with respect to the crystal structure and the nature of the transition-metal ion.