Remarkable low symmetry hydrogen bonding network in the structure of ReCl2(NCMe)(NO)(PMe3)2

The title compound 1 crystallizes in the space group P21/a with Z=44, being the largest Z value for a transition metal complex observed up to now. Responsible for the unusual high number of independent molecules in the asymmetric unit is a dense network of hydrogen bonds, which do not follow the general rule of lowest entropy in crystals. Methyl groups serve exclusively as H donor groups, leading to hydrogen bonds of the type CH⋯O and CH⋯Cl. The putative appearance of bond-stretch isomers within one single crystal could be traced to a hidden disorder phenomenon. Density functional calculations provided further evidence for this conclusion.