6.6. DFT Studies on Ruthenium and Rhodium Chain Complexes and a One-Dimensional Iodine Bridged Ruthenium Complex

Public examination of a doctoral dissertation in the field of chemistry

Doctoral candidate: M.Sc. Mika Niskanen 

Date and venue: 6.6.2011, at 12 noon, auditorium F100, Futura, Joensuu campus

 

ABSTRACT 

One-dimensional structures have long fascinated chemists and physicists with their unusual properties. Be the focus conductivity, optical or magnetic properties, or superconductivity, a great many scientific papers have been written on one-dimensional materials during the last century. Today these materials are of interest in the form of nanotubes, organic conductors, and chainlike structures of metal atoms. 

Metal–metal interactions and properties of various one-dimensional ruthenium and rhodium metal chains, and a one-dimensional chain of ruthenium complexes connected by iodine bridges were studied by density functional theory (DFT) methods and by quantum theory of atoms in molecules (QTAIM). 

Unsupported ruthenium carbonyl chains and similar chains with nitrogen ligands were investigated. QTAIM analysis revealed typical metal–metal bonding in the chains. The electronic absorption properties were studied as well, and a wide range of excitation wavelengths were obtained for the chains with polypyridine and 2,2’-biimidazole ligands. The wavelength range was further expanded by substitution of the nitrogen ligands. 

Compared with unsupported chains, in ligand-supported ruthenium extended metal atom chains (EMACs), the ruthenium–ruthenium interactions were stronger, bond lengths shorter, and the electron densities between metal atoms greater. Of the studied ruthenium EMACs with chains of 3,5,7, and 9 metal atoms, those with 7 and 9 atoms have not yet been synthesized. Comparing these with shorter EMACs, the calculations predicted noticeably lower HOMO-LUMO gaps for the hypothetical structures, and more evenly distributed electron density along the metal chain. 

M–M distances in the studied metal chain structures were longest for mononuclear and dinuclear rhodium 2,2’-biimidazole stacks. Electron absorption properties studied computationally were compared with experimentally noted color changes in crystals when the Rh-Rh distance decreased with lower temperature. An explanation for the shift was found in changes of the energy levels of the interacting Rh dz2 orbitals. 

Intriguing concerted halogen–hydrogen interaction was found between methanol and two I2 molecules in the crystal structure of iodine-bridged [RuI2(H2dcbpy)(CO)2]. The concerted halogen–hydrogen bond was studied by QTAIM and interaction energies were calculated. The hydrogen bonding appears to further stabilize the weak I2 ••• I2 halogen bond. 

The doctoral dissertation of Mika Niskanen entitled “DFT Studies on Ruthenium and Rhodium Chain Complexes and a One-Dimensional Iodine Bridged Ruthenium Complex” will be examined at the Faculty of Science and Forestry. The opponent in the public examination is Toomas Tamm from Tallinn University of Technology and the custos is Professor Tapani Pakkanen of the University of Eastern Finland. 

Photo available for download at http://www.uef.fi/vaitoskuvat

Contact: Mika Niskanen, tel.. +358 50 302 1419, mika.niskanen@uef.fi

Publishing year: 2011

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