Heinrich Billetter

Noncentrosymmetric coordination networks based on nitrate and acetylenedicarboxylate anions

Abstract Single crystals of Ba2(ADC)(NO3)2 · 4 H2O (1), Ba7(ADC)6(NO3)2 · 14 H2O (2), and Ba3(ADC)2Cl(NO3) × 5 H2O (3) were prepared by crystallisation at the phase boundary of a two phase system (ADC = C2(COO)2). They crystallize in noncentrosymmetric space groups (1: C2221, Z = 4; 2: I2, Z = 2; 3: P2212, Z = 2). For 1 a SHG signal of approx. 0.29 KDP (1 KDP = SHG of KH2PO4) was determined. All hitherto known compounds of the almost linear dianion of acetylenedicarboxylic acid crystallize in centrosymmetric space groups, but by inserting trigonal planar nitrate anions into the crystal structure a symmetry breaking seems to occur, which leads to noncentrosymmetric crystal structures. Several examples from the literature show that this observation might be also valid for other compounds.

Über die Dialkaliacetylendicarboxylate Na2(C2(COO)2)(H2O)4 und K2(C2(COO)2)(H2O) / On Dialkali Acetylenedicarboxylates Na2(C2(COO)2)(H2O)4 and K2(C2(COO)2)(H2O)

Abstract From aqueous solutions containing acetylenedicarboxylic acid and Na2CO3 or KOH single crystals of Na2(C2(COO)2)(H2O)4 (P21/n, Z = 2) and K2(C2(COO)2)(H2O) (P1̅, Z = 2) were obtained by slow evaporation of the solvent. In Na2(C2(COO)2)(H2O)4 the sodium atom is co-ordinated almost octahedrally by three water molecules and three oxygen atoms of the carboxylate ligands. These octahedra are connected to layers, which are held together by hydrogen bonds. In K2(C2(COO)2)(H2O) two crystallographic distinct potassium ions exist both seven co-ordinate by oxygen atoms stemming from water molecules and carboxylate ligands. These KO7 polyhedra are linked to a threedimensional structure by the bifunctional carboxylate anions and the water molecules.

Ni(C2(COO)2)(H2O)4 · 2 H2O und Ni(C2(COO)2)(H2O)2: zwei Koordinationspolymere mit dem Acetylendicarboxylat-Dianion / Ni(C2(COO)2)(H2O)4 · 2 H2O and Ni(C2 (COO)2)(H2O)2: Two Co-ordination Polymers of the Acetylenedicarboxylate Dianion

From a solution of Ni(CH3COO)2 ∙ 4 H2O and acetylenedicarboxylic acid in deionized water single crystals of Ni(C2(COO)2)(H2O)4 ∙ 2 H2O(P21/a, Z = 2, isotypic to Co(C2(COO)2)(H2O)4 ∙ 2 H2O) were obtained by slow evaporation of the solvent. In the solid state structure nickel is octahedrally surrounded by four water molecules and two oxygen atoms of the carboxylate anions. These octahedra are connected to chains by the dicarboxylates. Heating the hexahydrate to 100 °C in a stream of argon leads to Ni(C2(COO)2)(H2O)2 (C2/c, Z = 4, isotypic to Mn[C2(COO)2] ∙ 2 H2O). Here, the NiO6 octahedron is built by two water molecules and four oxygen atoms of the dicarboxylate ligands, which connect the Ni octahedra to a three-dimensional network. Thermoanalytical investigations show another mass loss at about 200 °C, which leads to non-crystalline products. Finally, at about 400 °C NiO is formed. Measurements of the magnetic susceptibilities result in the expected behaviour for Ni2+ in an octahedral co-ordination (3A2 ground state). The effective magnetic moment at room temperature is μeff = 3.20 μB.