Melonjosephite, Ca2[(Fe2+0.5FeO3+0.5)4(OH)2(PO4)4], Z = 2, orthorhombic, a = 9.542(1), b = 10.834(1), c = 6.374(1)Å, space group Pbam, has chains of edge-sharing Fe–O octahedra oriented parallel to the c axis. R(hkl) = 0.043 for 728 independent reflections. Dimers of edge-sharing Fe–O octahedra share vertices with octahedra of the chains to form sheets parallel to {010} with the formula [Fe2(OH)(Op)7]2. The (PO4) tetrahedra link within and between sheets to form a framework structure. The CaO7 polyhedron occurs in pockets between the sheets.

Although two independent Fe atom sites occur in the structure, the mixed valence pair (Fe2+, Fe3+) is evenly distributed between them. Average bond distances are Ca–0 = 2.47Å, Fe(1)–0 = 2.08Å, Fe(2)–O = 2.06Å, P(l)–O = 1.54Å, P(2)–O = 1.54Å.

Regions of the melonjosephite crystal structure can be directly related to the octahedral tetramer found in leucophosphite, K2[Fe3+4(OH)2(H2O)2(PO4)4].2H2O, and regions of the structure of olmsteadite, K2Fe2+2[Fe2+2Nb5+2O4(H2O)4(PO4)4] and related compounds.

This content is PDF only. Please click on the PDF icon to access.

First Page Preview

First page PDF preview
You do not currently have access to this article.