Synthesis of potassium cyanamide, and crystal structure determination by pareto optimisation of the cost functions 'lattice energy' and 'powder intensities'

The synthesis of K2CN2 was carried out by reaction of potassium hydrogen cy anamide (KHCN2) with potassium amide (KNH2) in liquid ammonia. The crystal structure has been determined by global optimisation techniques using the l attice energy and the difference between observed and calculated X-ray inte nsities as cost functions, simultaneously. The structure refinement has bee n performed by conventional Rietveld profile fitting of X-ray powder data ( monoclinic, C 2/m, a = 5.7877(1), b = 5.7030(1), c = 5.7857(2) Angstrom; be ta = 109.016(1) degrees; Z = 2). The CN22 - units are linear exhibiting a C -N bond length of 1.234(2) Angstrom, while potassium is coordinated by five nitrogen atoms forming a square pyramid. The structural relationships to a ristotypic K2NiO2 are pointed out. (C) 2000 Editions scientifiques et medic ales Elsevier SAS. All rights reserved.