Crystal structure of mahnertite

Mahnertite, (Na (sub 0.88) Ca (sub 0.12) )Cu (sub 2.75) [AsO (sub 4) ] (sub 2) Cl (sub 0.62) 3.63 H (sub 2) O, M = 565.17, is tetragonal, with space group /4/ mmm,a = 10.037(1),c = 23.739(1) A,V = 2391.5(4) A 3 ,Z = 8, (super rho ) o = 3.32, rho c = 3.14 g/cm (super 3) , mu = 9.78 mm (super -1) . The crystal structure of mahnertite was solved and refined against data collected at the Daresbury S ynchrotron Radiation Source, using a 20 X 20 X 2 mu m (super 3) single crystal, lambda = 0.6898 A, F (000) = 2150, R = 0.049 for 639 reflections with I > 2 sigma (I). The structure consists of sheets parallel to (001), which comprise two symmetrically independent distorted Cu 5-vertex square pyramids Cu phi 5 (phi = O, Cl or H (sub 2) O) as well as AsO (super 4) tetrahedra. Four Cu phi 5 pyramids located around the 4-fold axis share edges to form clusters linked by AsO (super 4) tetrahedra. The sheets are linked by the common apical vertex of the Cu(2) Phi < 5 polyhedra. as a result, a heterogeneous framework is formed. (na, ca) atoms, additional cu(3) cations and H (super 2) O molecules are located in the interlayers. The mineral is structurally related to zdenekite, NaPbCu < (sub 5) (AsO (sub 4) ) (sub 4) Cl . 5H (sub 2) O.