#metal complexes

Finally available in a bottle

Researchers succeed in gaining access to an important chemical compound

Since the discovery of the first homoleptic metal carbonyl complex Ni(CO)4 more than 130 years ago, scientists have been trying to obtain further such compounds formed from a carbon monoxide molecule and a metal -- compounds that are important for basic research as well as applications. The last new compound of this type to be bottled, the Co(CO)5 cation, was reported in 2003. However, extensive research in the gas phase has shown that far more metal carbonyl complexes than those known to date should exist, including the chromium hexacarbonyl cation.

A team led by the chemists Prof. Dr. Ingo Krossing from the University of Freiburg and Prof. Dr. Frank Breher from the Karlsruhe Institute of Technology were able to prepare this compound in common solvents and fill it into a bottle as a stable compound in crystalline form. They present their results in the journal Nature Communications.

Metal leads to the desired configuration

Scientists at the University of Basel have found a way to change the spatial arrangement of bipyridine molecules on a surface. These potential components of dye-sensitized solar cells form complexes with metals and thereby alter their chemical conformation. The results of this interdisciplinary collaboration between chemists and physicists from Basel were recently published in the scientific journal ACS Omega.

Dye-sensitized solar cells have been considered a sustainable alternative to conventional solar cells for many years, even if their energy yield is not yet fully satisfactory. The efficiency can be increased with the use of tandem solar cells, where the dye-sensitized solar cells are stacked on top of each other.

The way in which the dye, which absorbs sunlight, is anchored to the semiconductor plays a crucial role in the effectiveness of these solar cells. However, the anchoring of the dyes on nickel oxide surfaces -- which are particularly suitable for tandem dye-sensitized cells -- is not yet sufficiently understood.

Transition metal complexes: Mixed works better

Transition-metal complexes -- that is a cumbersome word for a class of molecules with important properties: An element from the group of transition metals sits in the centre. The outer electrons of the transition-metal atom are located in cloverleaf-like extended d-orbitals that can be easily influenced by external excitation. Some transition-metal complexes act as catalysts to accelerate certain chemical reactions, and others can even convert sunlight into electricity. The well-known dye solar cell developed by Michael Graetzel (EPFL) in the 1990s is based on a ruthenium complex.

Why not Iron?

However, it has not yet been possible to replace the rare and expensive transition metal ruthenium with a less expensive element, such as iron. This is astonishing, because the same number of electrons is found on extended outer d-orbitals of iron. However, excitation with light from the visible region does not release long-lived charge carriers in most of the iron complex compounds investigated so far.