(NH4)(2)(C4O4), an anhydrous salt of acetylenedicarboxylic acid

摘要

Single crystals of anhydrous ammonium acetylenedicarboxylate ((NH4)(2)(C4O4), 1) were isolated from a precipitate crystallizing from an aqueous ammonia solution containing acetylenedicarboxylic acid. The crystal structure of 1 (C2/m, Z = 2) consists of ordered ammonium cations, which are connected via N-(HO)-O-... hydrogen bonds (N-O: 2.826 and 2.947 angstrom) to four oxygen atoms from four symmetry related acetylenedicarboxylates. The coordination by the bifunctional carboxylates leads to a three-dimensional framework structure. Coupled TGA/DTA/MS measurements show that 1 decomposes completely at about 450 K releasing NH3, CO2, and C2H2. No order-disorder transition Occurs in the temperature range between 20 K and the decomposition temperature. In contrast to Sr(C4O4), the other known anhydrous acetylenedicarboxylate, no negative thermal expansion is found below room temperature. (c) 2006 Elsevier SAS. All rights reserved.