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

摘要

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 M1O₄(OH_0.5)₂, M1aO₄(OH_0.5)₂, M2O₅(OH_0.5), and M2aO₅(OH_0.5) 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 OH 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⋯O distances. Furthermore, structural characteristics of compounds with similar alluaudite-like structures were discussed.