Syntheses, single-crystal structures, vibrational spectra and DSC/TG analyses of orthorhombic and trigonal Ag[N(CN)2

Abstract

Abstract Colorless powders of orthorhombic Ag[N(CN)2] were synthesized by blending aqueous solutions Ag[NO3] with stoichiometric amounts of Na[N(CN)2] equally dissolved in water. Single crystals of both modifications of Ag[N(CN)2] could be obtained by recrystallizing the powder with aqueous ammonia. Non-isothermal evaporation of the solvent at room temperature within a few hours yielded the orthorhombic modification as the main product crystallizing in the space group Pnma (no. 62) with the unit-cell parameters a = 1612.45(12), b = 361.58(3) and c = 599.02(4) pm (Z = 4). Upon evaporating the solvent much more slowly, isothermally within a few days, mainly thin hexagonal platelets of the trigonal modification of Ag[N(CN)2] were obtained, crystallizing in the space group P3121 (no. 152) with the lattice constants a = 359.86(3) and c = 2285.91(17) pm (Z = 3). Both results corroborate earlier structure determinations, but show higher precision. The vibrational spectra confirm the presence of the dicyanamide anion [N(CN)2]−, but exhibit slight differences to literature data. Differential scanning calorimetry/thermogravimetry (DSC/TG) analyses were performed to further characterize the two modifications.