Complex(es in) Materials
Funding: DFG BR2010/8-1 and 10-1 (Normalverfahren)
Coordination polymers from metal complex fragments with meridional tridentate chelate ligands
The tripyrrin ligand is unique in its ability to stabilize one- and three-dimensional supramolecular constructs of pentacoordinate transition metal ions. This is achieved through an effective steric blocking of the sixth coordination site of the chelated ion. Linear coordination polymers were obtained with a variety of anionic bridging ligands such as trifluoroacetate, azide, thio- and selenocyanate, and with pseudohalides of higher order. The use of cyanometallates also allows the preparation of homo- and heterodimetallic species that have been structurally characterized in two cases. In addition to the coordinative bonds, different secondary interactions such as hydrogen bonding or π-stacking contacts were found to be stabilizing additive elements that allow a synthesis of materials with functionalized inner surfaces.
View along the polymeric chain of tripyrrincadmiumselenocyanate
One important aspect of this chemistry is the design of appropriate, functionally optimized ligands beyond the rather sensitive tripyrrine moiety. An interesting ligand class in this regard is that of the tridentate pincer ligands of the BAI (BisAryliminoIsoindolin)-type. Simple representatives have long been established in catalysis, while recently new derivatives occured in a large structural variety and were successfully introduced to the coordination of transition metal ions (especially for palladium(II)). In the Bröring Group, complexes of this ligand class are prepared, organized in one-dimensional coordination polymers, and examined for non-linear optical, semiconducting and magnetic properties.
Molecules on Surfaces
Metallocorroles can be deposited on metalic surfaces without decomposition using high vacuum vapor deposition techniques. STM allows the detection and manipulation of surface-bound corroles as single, individual molecules. On the surface, the saddle conformation typical for many metal corroles leads to a complete loss of symmetry and thus to the observation of multiple configurations of the same species. For example, 12 different configurations (6 rotational isomers as enantiomeric pairs) are observed for a simple iron triphenylcorrole on a Cu(111) surface, and STM provides for the opportunity to interconvert these states by manipulation with the STM tip. A racemization process could thus been visualized with molecular resolution for the first time. These and other features concerning e.g. the electronic interaction with the surface and the specific aggregation behavior of these and other coordination compounds are studied in collaboration with Dr. Germar Hoffmann.
Twelve configurations of iron triphenylcorrole on a Cu(111) surface
Further projects in molecular materials are concerned with charge transfer compounds, 1D-, 2D and 3D polymeric multiporphyrinoids, and highly porous networkstructures from molecular building blocks ("MOFs").