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

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dc.contributor.authorVest, Brian Michael
dc.date.accessioned2009-04-17T02:58:12Z
dc.date.availableNO_RESTRICTIONen_US
dc.date.available2009-04-17T02:58:12Z
dc.date.issued2008
dc.description.abstractUnrestricted 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.urihttp://hdl.handle.net/10179/744
dc.language.isoenen_US
dc.publisherMassey Universityen_US
dc.rightsThe Authoren_US
dc.subjectChromium dihalidesen_US
dc.subjectPhysical propertiesen_US
dc.subject.otherFields of Research::250000 Chemical Sciences::250600 Theoretical and Computational Chemistryen_US
dc.titleThe 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 Zealanden_US
dc.typeThesisen_US
massey.contributor.authorVest, Brian Michael
thesis.degree.disciplineTheoretical Chemistryen_US
thesis.degree.grantorMassey Universityen_US
thesis.degree.levelDoctoralen_US
thesis.degree.levelDoctoralen
thesis.degree.nameDoctor of Philosophy (Ph.D.)en_US
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