The electronic, structural, and magnetic properties of the chromium dihalides - from the gas-phase to the solid-state : a thesis submitted in partial fulfillment of the requirements of the degree of Doctor of Philosophy in Theoretical Chemistry at Massey University, Albany, New Zealand
dc.contributor.author | Vest, Brian Michael | |
dc.date.accessioned | 2009-04-17T02:58:12Z | |
dc.date.available | NO_RESTRICTION | en_US |
dc.date.available | 2009-04-17T02:58:12Z | |
dc.date.issued | 2008 | |
dc.description.abstract | Unrestricted Kohn-Sham (broken symmetry) density functional calculations have been used to determine the low-energy geometries of the chromium dihalide molecules (CrX2) and their clusters, Cr2X4, Cr3X6, and Cr4X8. The monomers are also investigated at a higher level, including coupled-cluster and state-average CASSCF computations. Our calculations show that the monomers have a 5B2 ground state arising from the Renner-Teller distorted 5IIg transition state, leading to a bent geometry. The global minima of the gas-phase clusters of CrF2 and CrCl2 consist of two-dimensional, anti-ferromagnetically coupled chains of CrX2 units forming four-membered, doubly bridged Cr2X2 rings, closely resembling their solid-state structures. The global minima of the CrBr2 and CrI2 clusters consist of the same two-dimensional chain-like structures for their dimers, but their trimers and tetramers consist of three-dimensional ’triangular’ structures which contain two capping ligands bound to three chromium atoms along with a Cr-Cr bond. Each Cr atom within these clusters has spin quantum number S=2. There is approximately a constant change in energy, between 45-55 kcal/mol, with every new CrX2 unit during cluster formation. Information about the structure of the CrCl2 clusters is used in the reanalysis of high-temperature electron diffraction data. The vapor at 1170 K contains about 77% monomeric molecules, 19% dimers, and a small amount of trimers. Monomeric CrCl2 is found to be bent with a bond angle of 149(10)degrees, in good agreement with our computations. Solid-state DFT calculations are performed on alpha-CrCl2 to determine the lattice structure and spin-coupling constants for the Cr atoms within the crystals. The GGA (PW91) method produces a structure in good agreement with the literature. In the lowest energy structure, the spins of the Cr atoms within the chains along the crystallographic c-axis are anti-ferromagnetically coupled with four parallel spins situated almost exclusively in the d-bands of Cr along these chains. This anti-ferromagnetic coupling is also seen in the CrX2 clusters. | en_US |
dc.identifier.uri | http://hdl.handle.net/10179/744 | |
dc.language.iso | en | en_US |
dc.publisher | Massey University | en_US |
dc.rights | The Author | en_US |
dc.subject | Chromium dihalides | en_US |
dc.subject | Physical properties | en_US |
dc.subject.other | Fields of Research::250000 Chemical Sciences::250600 Theoretical and Computational Chemistry | en_US |
dc.title | The electronic, structural, and magnetic properties of the chromium dihalides - from the gas-phase to the solid-state : a thesis submitted in partial fulfillment of the requirements of the degree of Doctor of Philosophy in Theoretical Chemistry at Massey University, Albany, New Zealand | en_US |
dc.type | Thesis | en_US |
massey.contributor.author | Vest, Brian Michael | |
thesis.degree.discipline | Theoretical Chemistry | en_US |
thesis.degree.grantor | Massey University | en_US |
thesis.degree.level | Doctoral | en_US |
thesis.degree.level | Doctoral | en |
thesis.degree.name | Doctor of Philosophy (Ph.D.) | en_US |
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