| Abstract: | Co(C2(COO)2)(H2O)4 · 2 H2O and Co(C2(COO)2)(H2O)2: Two Co‐ordination Polymers of the Acetylenedicarboxylate Dianion By reaction of CoCO3 with an aqueous solution of acetylenedicarboxylic acid and subsequent crystallisation single‐crystals of Co(C2(COO)2)(H2O)4 · 2 H2O were obtained (P21/a, Z = 2). In the solid state structure cobalt is octahedrally surrounded by four water molecules and two oxygen atoms of the carboxylate anions. These octahedra are connected to chains by the dicarboxylates. Already at ambient conditions Co(C2(COO)2)(H2O)4 · 2 H2O looses four water molecules to give Co(C2(COO)2)(H2O)2 (isotypic to MnC2(COO)2] · 2 H2O, C2/c, Z = 4). The cobalt cation is now octahedrally co‐ordinated by two water molecules and four oxygen atoms of the dicarboxylate ligands, which connect the Co octahedra to a three dimensional network. Thermoanalytical investigations show another mass loss at about 200 °C, which leads to non‐crystalline products. Measurements of the magnetic susceptibilities result in the expected behaviour for Co2+ in an octahedral co‐ordination (high spin, 4T1 ground state). The effective magnetic moment at room temperature is neff = 5.51 μB. |
