Natrophosphate, Arctic Mineral and Nuclear Waste Phase: Structure Refinements and Chemical Variability

The crystal structures of natural (Mt. Koashva, Khibiny alkaline massif, Kola Peninsula, Russian Arctic) and synthetic (obtained from an aqueous solution sodium phosphate fluoride (1:1) by evaporation at room temperature (RT)) natrophosphate, Na7(PO4)2F·19H2O, have been investigated using single-crystal X-ray diffraction analysis. Natrophosphate its analogue are cubic, Fd-3c, a = 27.6942(3) Å (natrophosphate RT), 27.6241(4) 100 K), 28.1150(12) (synthetic 27.9777(7) K). structure is based upon the super-octahedral [Na6(H2O)18F]5+ polycationic complexes consisting six edge-linked Na6(OH2)5F octahedra sharing one common fluorine vertex. A site statistically occupied Na H2O with prevalence refined occupancy factors O:Na equal to 0.53:0.47 for natrophosphate 0.75:0.25 analogue. coordination in enlarged compared sample, which agrees well higher molecules. general formula natrophosphates can be written as Na6+xHxF(PO4)2·(19 + x)H2O, where x 0–1. chemical variability allows explain discrepancies solubility reported different authors. information-based parameters structural complexity 3.713 bit/atom 2109.177 bit/cell that classify structurally very complex mineral.