Prof Nik Kaltsoyannis
Research
Our research focuses on the computational investigation of the electronic and geometric structure and reactivity of molecules from all areas of the periodic table. We employ a variety of techniques, including density functional theory and multiconfigurational ab initio methods. We are particularly interested in linking our research with experimental projects in order to achieve a more complete understanding than is possible from either approach working in isolation.
Our main area of research is heavy element chemistry, especially f elements. We are part of the Theoretical User Laboratory of ACTINET-13 (http://www.actinet-i3.eu/index.php?option=com_content&view=article&id=23&Itemid=23) and the ESPRC funded DIAMOND nuclear waste consortium (http://www.diamondconsortium.org/index.htm).
We are interested in applying the Quantum
Theory of Atoms‑in‑Molecules (http://www.chemistry.mcmaster.ca/bader/)
to the bonding in heavy element molecules. Assessing the extent of
ionicity/covalency in f‑element bonding is not always straightforward, and the
QTAIM is a very useful tool to this end, as set out in two of our recent
papers: Dalton Transactions 39 (2010) 6719 and Dalton Transactions 40 (2011) 124. The image below is the molecular graph of [U(OPh)3]2(µ-η2:η2-N2),
featured in another of our recent papers: Journal of the American Chemical Society 133 (2011) 9036.
Another
area of interest is the electronic structure of the iconic organometallic
sandwich molecule cerocene (Ce(η8‑C8H8)2 below) and its actinide analogues. A
hotly contested debate as to the oxidation state of the Ce atom has played out
in the literature over the past two decades, with many experimental and
theoretical techniques being trained on this target. In the mid 1990s, we were
part of the experimental team that conducted X‑ray absorption spectroscopic
studies (J. Am. Chem. Soc. 118 (1996) 13115) of cerocene and, more
recently, conducted an EPSRC‑funded theoretical investigation of cerocene and
An(η8‑C8H8)2
(An = Th‑Cm), which employed state of the art multiconfigurational quantum
chemical techniques (J. Phys. Chem. A 113 (2009) 2896 and 8737). This
computational work has conclusively established that cerocene is a Ce(IV)
compound with a multiconfigurational ground state, has reconciled the
conflicting experimental and theoretical data, and shown that the
multiconfigurational character of the ground states of the actinide analogues
increases as the 5f series is crossed.
Hydrogen has been
suggested as a clean energy carrier to be used in combination with hydrogen
fuel cells in many forms of road vehicles from motor bikes to buses. However,
the implementation of hydrogen as a fuel has met with several practical difficulties,
and it has therefore been suggested to incorporate a material into the storage
tank that binds to the hydrogen and increases the hydrogen storage capacity of
the tank. A storage‑material–H2 binding enthalpy of between 20 and
40 kJmol-1 is ideal and, to achieve this, the incorporation of
transition metal fragments into storage materials is being explored, such that
the TM–H2 interaction occurs via
the Kubas interaction. This process involves σ-donation from the filled H‑H
σ-bonding orbital into an empty d orbital of a metal, and simultaneous
π-back-donation from a filled metal d orbital into the vacant σ* anti-bonding
orbital of the H2 molecule (similar to the synergic bonding
described by the Dewar-Chatt-Duncanson model for the interaction of, for
example, CO with transition metals). In collaboration with experimentalists at
the Sustainable Environment Research Centre at the University of Glamorgan, we
are probing the electronic structure of molecular models for the TM–H2
binding sites in potential hydrogen storage materials, and have established
that Kubas binding is indeed occurring in these systems. The images below show ball and stick representations of
the optimised geometries of H2‑free and H2‑bound
molecules representing the benzyl disiloxy Ti(III) and dibenzyl siloxy Ti(III)
binding sites in mesoporous amorphous silica based materials, as described in Journal of the American
Chemical Society 132 (2010) 17296.
