The crystal structure of gladiusite, (Fe2+, Mg)(4)Fe-2(3+)(PO4)(OH)(11)(H2O)

The crystal structure of gladiusite, (Fe2+,Mg)(4) Fe-2(3+) (PO4) (OH)(11) ( H2O), monoclinic, a 16.950 (2), b 11.650 (1), c 6.2660 (6) Angstrom, beta 9 0.000 (4)degrees, V 1237.3(4) Angstrom (3), space group p2(1)/n, Z = 2, D(c alc.) = 3.08 g cm(-3), was solved by direct methods for a twinned crystal a nd refined to an R-1 index of 5.4% based on 1214 observed [F-0 > 4 sigmaF] unique reflections measured with MoK alpha X-radiation on a CCD diffractome ter. There is one P site tetrahedrally coordinated by four O atoms. There a re six distinct octahedrally coordinated M sites containing Fe3+, Fe2+, Mg and Mn2+; the octahedra are coordinated by O atoms, OH and H2O groups. The (M phi (6)) (phi = unspecified anion) octahedra each share two trans edges to form a rutile-like [M phi (4)] chain along [001]. Pairs of chains, shift ed relative to each other by a half-octahedron, link together through commo n edges to form a ribbon extending along c; thus, each octahedron shares fo ur edges with other octahedra. These ribbons are connected through common v ertices of (M phi (6)) octahedra into a framework with channels along the c axis. The (PO4) tetrahedra share each of two vertices with three (M phi (6 )) octahedra, and the remaining two vertices are connected to octahedra thr ough hydrogen bonds. There is a system of hydrogen bonds in the crystal str ucture of gladiusite (D-A < 3.50 Angstrom), some of them bifurcated. The Mo ssbauer spectrum of gladiusite shows three doublets, two of which may be as signed to Fe2+ in octahedral coordination and one of which may be assigned to Fe3+ in octahedral coordination. The intensity ratios of the various dou blets indicate that Fe2+/(Fe2+ + Fe3+) = 0.49.