Ab initio calculations on the ground states of dimethyl- and dichloro-bis(1,2-dimethylphosphinoethane)titanium, the structure and conformation of group V bent metallocenethiolates, and the interaction of bridging carbonyls with transition metal dimers /
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| Other Authors: | , , |
| Format: | Thesis Book |
| Language: | English |
| Published: |
1991.
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| Subjects: | |
| Online Access: | Link to OAKTrust copy |
| Abstract: | Experimentally, Ti(CH3)2(dmpe)2 has a diamagnetic singlet ground state while TiCl2(dmpe)2 has a paramagnetic triplet ground state. However, the stronger π donor, Cl, is expected to cause a larger splitting of the t[2g]-like orbitals. Hence, if the ground states are different one would expect TiCl2(dmpe)2 to be diamagnetic and Ti(CH3)2(dmpe)2 to be paramagnetic. In agreement with this simple reasoning, approximate molecular orbital calculations also predict a result contrary to experiment. Ab initio calculations with reasonable basis sets are required to produce qualitative agreement with the experimental results, while quantitative agreement requires significant correlation energy. Results reported here include single-determinant, generalized-valence-bond, complete-active-space, and direct configuration-interaction calculations in several basis sets on the compounds and several model compounds. The explanation of the differences in states lies in the electronegativity difference between Cl and CH3. The more electronegative Cl withdraws enough charge from the Ti to contract the d orbital sufficiently to cause the increased d-d electron repulsions in the Cl complex to outweigh the orbital splitting. Ab initio geometry optimizations are reported for several models of the bent metallocenethiolates (n^5 - C5H5)2M(SR)2. We have examined the simple rotation of the R group about the M-S bond in both mono- and di-thiolates. The S-M-S angle and R-S-M-S dihedral angel depend upon the metal d count, the nature of the Ma dn R group, and on each other in subtle ways. While in mod Nb d^1 complexes the SR groups reside in an exo conformation, the V d^1 complexes are all in an endo conformation. This unexpected difference is due to increased steric hindrance in the V complexes... |
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| Item Description: | Typescript (photocopy). Vita. "Major subject: Chemistry." |
| Physical Description: | xiv, 207 leaves : illustrations ; 29 cm |
| Bibliography: | Includes bibliographical references. |