K2NIWO2(PO4)(2) - A NEW STRUCTURE TYPE RELATED TO KTIOPO4 (KTP)

Substitution of the two symmetrically unrelated Ti4+ ions in the struc ture of the well known non-linear optical crystal KTiOPO4 (potassium t itanyl phosphate, KTP, space group Pna2(1)) by Ni2+ and W6+ (2Ti(4+) - -> Ni2+ + W6+) leads to the new compound K2NiWO2(PO4)(2) [dipotassium nickel bis(monophosphato)tungstate, KNiWP], which forms a new structur e type. The main structural characteristic of tetragonal KNiWP (space group P4(1,3)2(1)2))is helical chains of corner-linked alternate [WO6] and [NiO6] octahedra along [001] connected via phosphate groups. Stru ctural and metric relationships exist between the KNiWP and KTP struct ure types.