PdCl(NO) - an iconic compound with corrugated Pd4Cl4 octagons built up by Pd2Cl2(NO)(2) moieties

During outstanding research in the late 1950s in Munich, which led to the development of the Wacker process for converting ethene into acetaldehyde by catalysis of PdCl2, black insoluble nitrosyl-palladium chloride (PdCl(NO)) was obtained. More than sixty years after its first synthesis, its crystal structure was now determined by X-ray diffraction. PdCl(NO) (mP16, P2(1)/c, a=10.2684(5), b=4.0737(2), c=7.8456(4) angstrom, beta=111.125(1)degrees, wR2=0.0572) consists of distorted Pd4Cl4 octagons in chair arrangement to which four distorted Pd2Cl2 squares are annulated on every second edge. In this arrangement each of the two Pd atoms of the squares are connected to one N-O group, bonded alternatively up and down to the Pd atoms with a Pd-N-O angle of 129 degrees. Such a square has the composition of the dimer which was found in the mass spectrum at 343.6 m/e. The octagons with four squares are interconnected to corrugated layers in the b-c-plane as a two-dimensional polymer.