Metal-metal bonding versus metal ligand bonding /
A fundamental and recurring question concerning the M-M distances in complexes of the type M[]L[]X[], where M is one of a number of transition metal atoms, L is a bridging bidentate ligand (e.g., RCO[]) and X is an axial ligand (of which there may be 0, 1 or 2), is the extent to which these distance...
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| Format: | Thesis Book |
| Language: | English |
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[Place of publication not identified] :
[publisher not identified] ;
2000.
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| Subjects: | |
| Online Access: | http://proxy.library.tamu.edu/login?url=http://proquest.umi.com/pqdweb?did=731981501&sid=1&Fmt=2&clientId=2945&RQT=309&VName=PQD |
| Summary: | A fundamental and recurring question concerning the M-M distances in complexes of the type M[]L[]X[], where M is one of a number of transition metal atoms, L is a bridging bidentate ligand (e.g., RCO[]) and X is an axial ligand (of which there may be 0, 1 or 2), is the extent to which these distances are influenced by the identity of M, the nature of L, and the presence of X. It is for compounds of chromium that this question arises in its most acute form, since Cr-Cr distances range from 1.83 [] to 2.69 [] depending on L, X and n, all within the common structural motif of the paddlewheel arrangement of the four L ligands. It was believed that when L is a divergent-bite ligand or a carboxylate ligand, the Cr-Cr distance will be well above 2.0 []. On the other hand, when L is a non-divergent-bite nitrogen-donor ligand, the Cr-Cr bond length will be less than 2.0 []. In this dissertation, molecular structures of two dichromium paddlewheel complexes, one with a dimetal unit supported by four carboxylate ligands, the other embraced by four divergent-bite ligands, both without axial coordination, have been determined for the first time. It has been concluded that when axial coordination is absent, no matter what type of bridging ligands is used, Cr-Cr distances around 2.0 [] be achieved. In addition, an elongation from 1.858(1) to 2.265(1) [] of a Cr-Cr bond supported by a non-divergent nitrogen-donor ligand has been observed for the first time. The bond length increase is achieved largely, if potentially, by injection of electron density into the [] orbitals of the Cr-Cr bond. Furthermore, an oxidative scission of a Mo-Mo quadruple bond has been found. It shows how the formation of four additional molybdenum-nitrogen bonds overwhelms the Mo-Mo bond. All the experimental facts lead to the conclusion that the M-M separation is largely determined by the relative strength of the M-M bonding and the axial metal-ligand bonding. |
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| Item Description: | Vita. "Major Subject: Chemistry". |
| Physical Description: | x, 131 leaves : illustrations ; 28 cm. Issued also on microfiche from University Microfilm Inc. |
| Bibliography: | Includes bibliographical references (leaves 103-107). |