The crystal structure of leightonite, K2Ca2Cu(SO4)4.2H2O, C2/c, a=11.654(2), b=7.497(1), c= 0.097(1)Å; beta=125.21(1)°, V= 720.8(2)Å3, Z=2 has been solved by means of direct methods and refined to R=3.90% for 1564 Fo>4s(Fo), using MoKa X-ray data from a crystal twinned on {20-1}. Structural sub-units [Ca(SO4)2]2- formed by one CaO8 polyhedron and two opposite-sided SO4 tetrahedra are linked by edge sharing. These sub-units are linked to each other by corner sharing to form a three-dimensional framework with channels, where the Cu atoms are present. The framework of CaO8 polyhedra and SO4 tetrahedra exhibits a perfect orthorhombic symmetry while the copper atoms located on two sites (Cu1 and Cu2) are not equivalent because of their different partial occupancy (0.37 and 0.13, respectively). Both Cu1 and Cu2 link 6 oxygen atoms according to two rhombically elongated octahedra (2+2+2 Jahn-Teller distortion). A partial occupancy was also found for K (50%) and Ow (50%), that are disordered on the same site. The crystal structure of leightonite closely resembles that of the triclinic polyhalite, K2Ca2Mg(SO4)4.2H2O, with the main difference being the different distribution of Cu in leightonite with respect to Mg in polyhalite.
Disordered distribution of Cu in the crystal structure of leightonite, K2Ca2Cu(SO4)4 . 2H2O.
2002
Abstract
The crystal structure of leightonite, K2Ca2Cu(SO4)4.2H2O, C2/c, a=11.654(2), b=7.497(1), c= 0.097(1)Å; beta=125.21(1)°, V= 720.8(2)Å3, Z=2 has been solved by means of direct methods and refined to R=3.90% for 1564 Fo>4s(Fo), using MoKa X-ray data from a crystal twinned on {20-1}. Structural sub-units [Ca(SO4)2]2- formed by one CaO8 polyhedron and two opposite-sided SO4 tetrahedra are linked by edge sharing. These sub-units are linked to each other by corner sharing to form a three-dimensional framework with channels, where the Cu atoms are present. The framework of CaO8 polyhedra and SO4 tetrahedra exhibits a perfect orthorhombic symmetry while the copper atoms located on two sites (Cu1 and Cu2) are not equivalent because of their different partial occupancy (0.37 and 0.13, respectively). Both Cu1 and Cu2 link 6 oxygen atoms according to two rhombically elongated octahedra (2+2+2 Jahn-Teller distortion). A partial occupancy was also found for K (50%) and Ow (50%), that are disordered on the same site. The crystal structure of leightonite closely resembles that of the triclinic polyhalite, K2Ca2Mg(SO4)4.2H2O, with the main difference being the different distribution of Cu in leightonite with respect to Mg in polyhalite.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
