[MII(ADC)2/2(DMF)2(H2O)2]∞1(MII = Mn, Co, Ni, Zn): Four new coordination polymers with acetylenedicarboxylate (ADC2−) as bridging ligand

Single crystals of [MII(ADC)2/2(DMF)2(H2O)2]∞1 (MII = Mn (1), Co (2), Zn (4)) precipitated from DMF solutions containing Mn(NO3)2 · 6H2O, CoCl2 · 6H2O or Zn(NO3)2 · 6H2O and acetylenedicarboxylic acid (H2ADC). Single crystals of [Ni(ADC)2/2(DMF)2(H2O)2]∞1 (3) formed at the phase boundary of an aqueous silica gel containing H2ADC and a DMF solution of NiCl2 · 6H2O. The crystal structures were solved and refined from X-ray single-crystal data. All compounds crystallize in space group C2/c with Z = 4. [MII(ADC)2/2(DMF)2(H2O)2]∞1 chains are the characteristic structural feature. Within these chains MIIO6 octahedra are formed, the oxygen atoms belong to two DMF, two water and two ADC2− ligands. The ADC2− ligands are trans coordinating in an unidentate way, thus connecting the octahedral units to chains. The DMF and water molecules are in a cis coordination to each other. Hydrogen bonds (O⋯O: 2.83–2.845 Å) connect two polymeric chains. These double chains are held together by van der Waals interactions to form a 3D structure. Coupled DTA–TG–MS measurements on 3 and 4 show that 3 decomposes at 146 °C and 4 at 114 °C releasing H2O, C2H2, CO, CO2, and DMF. But the proceeding decomposition reactions in both compounds are quite different, as the residue after heating at 500 °C in an argon atmosphere is elemental Ni and graphite for 3 and ZnO for 4 as proven by XRPD experiments. This is in agreement with a general trend found for the decomposition of metal acetylenedicarboxylates: with noble metals the elements are formed, whereas with less noble metals the respective oxides are found.

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