Crystal structure and Hirshfeld surface analysis of 1-(di-methyl-amino-meth-yl)-2-(pyrrolidin-1-ylmeth-yl)ferrocene complexes with zinc(II) bromide and cadmium(II) bromide.

Two transition-metal complexes, rac-di-bromido-[1-(di-methyl-amino-meth-yl)-2-(pyrrolidin-1-ylmeth-yl)ferrocene]zinc(II), [FeZnBr2(C5H5)(C13H22N2)] (rac-1), and rac-di-bromido-[1-(di-methyl-amino-meth-yl)-2-(pyrrolidin-1-ylmeth-yl)ferrocene]cadmium(II), [FeCdBr2(C5H5)(C13H22N2)] (rac-2), crystallize in the form of yellow blocks and were characterized by single-crystal X-ray diffraction. They were synthesized using rac-1-(di-methyl-amino-meth-yl)-2-(pyrrolidin-1-ylmeth-yl)ferrocene (rac-3) as starting material, which is characterized here for the first time. Both, the zinc center in complex rac-1 and the cadmium center in complex rac-2 exhibit a tetra-hedral coordination geometry. Nevertheless, there are some differences in terms of the bond lengths as well as the bond angles. Furthermore, not only the space groups, P21/n for rac-1 and P212121 for rac-2, but also the crystal packings differ from each other, which can be seen in different configurations of the pyrrolidine substituents. To investigate the inter-molecular inter-actions leading to these structural differences, Hirshfeld surface analyses were performed. They showed that H⋯H inter-actions make the largest contribution to the crystal packing in both structures, with 69.0% and 66.6% for rac-1 and rac-2, respectively.