Noncentrosymmetric coordination networks based on nitrate and acetylenedicarboxylate anions

Abstract

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.