Crystallographic aspects of hydrated salts of 4,6-diaminopyrimidine with the first five dicarboxylic acids

Abstract

Abstract The preparation, X-ray single-crystal structure determination and vibrational spectroscopic characterisation of five novel salts, i.e. bis(4,6-diaminopyrimidinium(1+)) oxalate tetrahydrate; 4,6-diaminopyrimidinium(1+) hydrogen malonate monohydrate; bis(4,6-diaminopyrimidinium(1+)) succinate octahydrate; bis(4,6-diaminopyrimidinium(1+)) glutarate dihydrate and bis(4,6-diaminopyrimidinium (1+)) adipate octahydrate, are presented. It is the first crystallographic study with the title cation. All the structures are centrosymmetric. The oxalate, succinate and adipate anions are situated about inversion centres in their respective structures. The dependence on the parity of the number of carbon atoms in the anions is apparent in the interplanar angles of the carboxylate or carboxylic groups. In all of the structures, there are intermolecular N–H···N, N–H···Oacid, N–H···Owater, Owater–H···Oacid and Owater–H···Owater hydrogen-bonds of moderate strength. The most common graph set motif, R 2 2(8), describes the arrangement of the involved carboxylic as well as of the primary- and secondary-amine groups. There is a growing complexity of arrangement of water molecules in the structures with longer anionic molecules. In 4,6-diaminopyrimidinium(1+) hydrogen malonate monohydrate, there is an intramolecular Oacid–H···Oacid bond, and the conformation of the hydrogen malonate ions with non-parallel carboxylic and carboxylate groups is not often observed. The structural parameters of the carboxylic or carboxylate groups in the dicarboxylic acids or their derivatives found in the Cambridge Structural Database (CSD) are compared with the title structures.