Structural features of two novel alluaudite-like arsenates Cd(1.16)Zn(2.34)(AsO(4))(1.5)(HAsO(4))(H(2)AsO(4))(0.5) and Cd(0.74)Mg(2.76)(AsO(4))(1.5)(HAsO(4))(H(2)AsO(4))(0.5)

Two new compounds, Cd(1.16)Zn(2.34)(AsO(4))(1.5)(HAsO(4))(H(2)AsO(4))(0.5) (1) and Cd(0.74)Mg(2.76)(AsO(4))(1.5)(HAsO(4))(H(2)AsO(4))(0.5) (2), have been prepared hydrothermally. Their crystal structures consist of chains of edge-sharing M1O(4)(OH(0.5))(2), M1aO(4)(OH(0.5))(2), M2O(5)(OH(0.5)), and M2aO(5)(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 [(AsO(4))(0.5)(AsO(3)(OH))(0.5)](2.5−) and [(AsO(4))(0.5)(AsO(2)(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.