A new type of anionic framework in microporous potassium iron(II) phosphate K[Fe(PO4)]

A new iron(II) orthophosphate K[Fe(PO4)] has been obtained by hydrothermal synthesis and its crystal structure was determined by single-crystal X-ray diffraction: space group P2(1)/n, Z = 8, a = 9.6199(10), b = 8.6756(8), c = 10.8996(13) angstrom, beta = 115.577(8)degrees at 193 K, R = 0.023. Fe-II shows coordination numbers (CN) 4 (distorted tetrahedral) and CN 5 (distorted trigonal bipyramidal).The [FeO4] and [FeO5] units form together with the [PO4] tetrahedra a microporous 3D para-framework with open channels along the a and b directions. The potassium ions positioned in the channels show CN 7 and 8. The structural relations within the morphotropic row of non-isotypic K[M(PO4)] structures (M = Zn, Ni, Mn, Fe) are discussed on the basis of common basic structural units.