Prof Andrea Sella
Our work is in two main areas: a) early transition metal and lanthanide bonding and reactivity and b) synthesis of new nanostructured materials.
A. Lanthanide structure and bonding
For several years we have been preparing simple monomeric compounds to test out ideas about structure and bonding. For example, a few years ago we prepared a unique series of lanthanide chalcogenolates which differ only in the donor atom of the chalcogenolate and which show the striking differences between the different ligands. This work led to a collaboration with the computational chemistry group of Prof Nik Kaltsoyannis which suggests that electrostatic effects are significant contributors to the structures of lanthanide alkoxides – in particular repulsion between the cationic lanthanide centre and the carbon on the highly polar C-O bond of the alk/aryloxide results in significant linearization of the group.
We are also currently collaborating with Prof Kaltsoyannis and Prof. J. C. Green at Oxford to explore the electronic structure of [LnCp3] complexes by Variable Energy Photoelectron Spectroscopy (VEPES). Recent experiments have shown that the f1 complex [CeCp3] rather surprisingly gives two ionization states rather than one, suggesting that [CeCp3]+ is multiconfigurational. Further studies on [YbCp3] suggest that it is multiconfigurational in the ground state, as indicated by both the PES and magnetic studies.
Because VEPES studies of the classic three-coordinate amide complex [Ce(NR2)3] (R = SiMe3) also show behaviour similar to that of the cyclopentadienyls, we are currently measuring EPR spectra of this and its f13 analogue [Yb(NR2)3] in collaboration with Dr Chris Kay here at UCL.
Related to this, we are exploring the chemistry of cerium (IV). Several years ago we published a XANES study showing that, in line with theoretical predictions, the iconic molecule cerocene, [Ce(h-C8H8)2] was an unusual example of a trivalent complex in which there is very strong coupling between the cerium and the COT ligands. Because the result flies in the face of received wisdom we are currently preparing new examples of Ce(IV) coordination compounds and organometallics including the new family [CeCp3(OAr)] (Ar = substituted aromatic group) in order to broaden the scope of our earlier results as well as to gain a deeper understanding of the chemistry of these very reactive and often quite unstable species.
B. New approaches to amorphous and clathrate tetrel phases.
In collaboration with Prof Paul McMillan we are developing new methods for the synthesis of amorphous and clathrate phases of the silicon and germanium. The work involves combining classical solid state synthesis with "wet" organometallic chemistry using Schlenk lines. We have recently demonstrated the superconductivity of amorphous germanium under high pressure conditions and current work is focused on developing methods to prepare alloy materials of this type.