Uncovering the fascinating chemistry of anionic transition metals

The unique properties of bulk solids stem from the connection between the composition and structure. Accordingly, it is crucial to continually search for compositions that produce novel and peculiar structures. One area that has remained relatively unexplored involves transition metal ions that are anionic, rather than the typically observed cationic. Additionally, the potential for gold-containing compounds to be active as heterogeneous catalysts makes these compounds of great interest.

 

This fascinating chemistry is made possible for these heavy, late 5d transition metals due to relativistic effects. The 6s orbitals are significantly contracted resulting in unusually high (for a metal) electron affinities. In fact, the electron affinity for Pt is 2.13 eV and for Au is 2.30 eV, both of which are greater than many main group elements including sulfur (2.08 eV). When surrounded by more electropositive elements, Pt and Au will readily become negatively charged (i.e., for Pt2− and Au−), leading to exceptional crystal chemistry. Yet, the complexity of anionic transition metal chemistry systems makes it virtually impossible to deduce the structure-composition relationship empirically. Pairing experimental studies with computational models is a useful practice to rationalize the nature of chemical bonding, leading to a refined understanding of anionic transition metal chemistry

 

Research in the Brgoch group focuses on employing a variety of methods to explore the crystal chemistry of these compounds. A majority of the synthesis is carried out using high-temperature sealed tube reactions while characterization consists of powder and single crystal X-ray diffraction.