| Abstract: | Crystals from commercial samples of sodium cacodylate trihydrate, NaO2As(CH3)2·3H2O, were analyzed by single‐crystal X‐ray diffraction and two phases were identified, viz. penta‐μ‐aqua‐disodium(I) bis(dimethylarsenate), {Na2(H2O)5](C2H6AsO2)2}n, (I), and di‐μ‐aqua‐bistriaquasodium(I)] bis(dimethylarsenate), Na2(H2O)8](C2H6AsO2)2, (II). Both (I) and (II) form layered structures in which hydrated Na+ ions form layers in the ab plane, the cacodylate ions being located in between the layers. In (I), the two non‐equivalent Na+ ions (located at twofold axes) and the three non‐equivalent aqua ligands (one of which also lies on a twofold axis) form infinite polymeric layers, but in (II), layers of discrete centrosymmetric Na2(H2O)8]2+ ions are present. One of the commercial samples analyzed contained almost exclusively crystals of the tetrahydrate (II), while another sample consisted of a mixture of the two phases. |
