Local structure and stacking disorder of chloro(phthalocyaninato)aluminium.

Chloro(phthalocyaninato)aluminium [(CHN)AlCl, Pigment Blue 79] is a molecular compound which crystallizes in a layer structure with stacking disorder. Order-disorder theory was applied to analyse and explain the stacking disorder and to determine the symmetry operations, which generate subsequent layers from a given one. Corresponding ordered structural models were constructed and optimized by force field and dispersion-corrected density functional theory methods. The superposition of the four lowest-energy stackings lead to a structure in which every second double layer looks to be ordered; in the other double layers the molecules occupy one of two lateral positions. This calculated superposition structure agrees excellently with an (incomplete) experimental structure determined from single-crystal data. From the optimized ordered models, the stacking probabilities and the preferred local arrangements were derived. Packing effects such as the distortion of the molecules depending on the arrangement of neighbouring molecules could also be determined.