Structural features of two novel alluaudite-like arsenates Cd1.16Zn2.34(AsO4)(1.5)(HAsO4)(H2AsO4)(0.5) and Cd0.74Mg2.76(AsO4)(1.5)(HAsO4)(H2AsO4)(0.5)

Abstract

Two new compounds, Cd1.16Zn2.34(AsO4)(1.5)(HAsO4)(H2AsO4)(0.5) (1) and Cd0.74Mg2.76(AsO4)(1.5)-(HAsO4)(H2AsO4)(0.5) (2), have been prepared hydrothermally. Their crystal structures consist of chains of edge-sharing M1O(4)(OH0.5)(2), M1aO(4)(OH0.5)(2), M2O5(OH0.5), and M(2)aO(5)(OH0.5) octahedra (M1, M1a = Zn, Cd; M2, M2a = Zn for 1, and M1, M1a = Mg, Cd; M2, M2a = Mg for 2) that are stacked parallel to (1 0 1) and are connected by the [(AsO4)(0.5)(AsO3(OH))(0.5)](2.5-) and [(AsO4)(0.5)(AsO2(OH)(2))(0.5)](2-) tetrahedra. These chains produce two types of channels parallel to the c-axis. Cd atoms are located in channels 2, while in channels 1 are situated hydrogen atoms of O-H groups. The infrared spectra clearly show the presence of broad O-H stretching and bending vibrations centred at 3236, 2392 1575 and 1396 cm(-1) in (1), and 3210, 2379 1602 and 1310 cm(-1) in (2). The O-H stretching frequency is in good agreement with O center dot center dot center dot O distances. Furthermore, structural characteristics of compounds with similar alluaudite-like structures were discussed.