Carbonylates: structures, intermediates and reactivities

Homoleptic and heteroleptic carbonyl complexes can be easily reduced directly with alkali metals in liquid ammonia. This produces negatively charged complexes, so-called metal carbonylates. Ammonia crystals of the respective transition metal carbonylates are formed from the reaction solutions, which can be characterized using single crystal X-ray structure analysis. On the one hand, the alkali metals used are incorporated into the chelating agents used, such as crown ethers and cryptands.  On the other hand, the alkali metals together with the complex anions form dense networks in which the crystal packing is dominated by ion-dipole interactions. Carbonylates have been the subject of intensive research for a long time, but crystal structures are lacking, especially for the more highly charged species. A large number of carbonylates have been found, especially for groups 4 to 10. The oxidation states of these complexes range from moderate values of -1 to very strongly reduced examples with a formal oxidation state of -4. Various structural motifs have been observed for the mononuclear carbonylates: trigonal planar, tetrahedral, trigonal bipyramidal, square pyramidal and octahedral. This is where our research starts to isolate missing and new crystal structures of carbonylates and to characterize them using various methods.

This research project is part of the graduate college “Ion-Pairs in Re-Action” (GRK 2620) at the University of Regensburg. In cooperation with the working group of Prof. Patrick Nürnberger, the behavior of carbonylate solutions in liquid ammonia is investigated. To this end, a measurement setup is being developed to characterize possible transition states and products with the aid of vibrational spectroscopy. This should also make it possible to establish vibrational spectroscopy in liquid ammonia in general.