Crystal structures of the potassium and rubidium salts of (3,5-dichlorophenoxy)acetic acid: two isotypic coordination polymers

The two-dimensional coordination polymeric structures of the hydrated potassium and rubidium salts of (3,5-dichlorophenoxy)acetic acid (3,5-D), namely, poly[μ-aqua-bis[μ3-2-(3,5-dichlorophenoxy)acetato]dipotassium], [K2(C8H5Cl2O3)2(H2O)]n, and poly[μ-aqua-bis[μ3-2-(3,5-dichlorophenoxy)acetato]dirubidium], [Rb2(C8H5Cl2O3)2(H2O)]n, respectively, have been determined and are described. The two compounds are isotypic and the polymeric structure is based on centrosymmetric dinuclear bridged complex units. The irregular six-coordination about the alkali cations comprises a bridging water molecule lying on a twofold rotation axis, the phenoxy O-atom donor and a triple bridging carboxylate O atom of the oxoacetate side chain of the 3,5-D ligand, and the second carboxyate O-atom donor also bridging. The K—O and Rb—O bond-length ranges are 2.7238 (15)–2.9459 (14) and 2.832 (2)–3.050 (2) Å, respectively, and the K...K and Rb...Rb separations in the dinuclear units are 4.0214 (7) and 4.1289 (6) Å, respectively. Within the layers which lie parallel to (100), the coordinating water molecule forms an O—H...O hydrogen bond to the single bridging carboxylate O atom