High Pressure Studies on Group VI Metal Hexacarbonyl Molecular Solids
Document Type
Dissertation
Degree
Doctor of Philosophy (PhD)
Major/Program
Mechanical Engineering
First Advisor's Name
Surendra K. Saxena
First Advisor's Committee Title
Committee Chair
Second Advisor's Name
Gautam Sen
Third Advisor's Name
Jiuhua Chen
Fourth Advisor's Name
Arvid Agarwal
Date of Defense
3-31-2010
Abstract
Group VI metal hexacarbonyls, M(CO)6 (M = Cr, Mo and W), are of extreme importance as catalysts in industry and also of fundamental interest due to the established charge transfer mechanism between the carbon monoxide and the metal. They condense to molecular solids at ambient conditions retaining the octahedral (Oh) symmetry of gas phase and have been extensively investigated by previous workers to understand their fundamental chemical bonding and possible industrial applications. However little is known about their behavior at high pressures which is the focus of this dissertation. Metal hexacarbonyls were subjected to high pressures in Diamond-Anvil cells to understand the pressure effect on chemical bonding using Raman scattering in situ.
The high-pressure results on each of the three metal hexacarbonyls are presented and are followed by a critical analysis of the entire family. The Raman study was conducted at pressures up to 45 GPa and X-ray up to 58 GPa. This is followed by a discussion on infra red spectra in conjunction with Raman and X-ray analysis to provide a rationale for polymerization. Finally the probable synthesis of extremely reactive species under high-pressures and as identified via Raman is discussed.
The high-pressure Raman scattering, up to 30 GPa, demonstrated the absence of ri-backbonding. The disappearance of parental Raman spectra for (M = Cr, Mo and W) at 29.6, 23.3 and 22.2 GPa respectively was attributed to the total collapse of the Oh symmetry. This collapse under high-pressure lead to metal-mediated polymeric phase characterized by Raman active S(OCO) feature, originating from intermolecular vibrational coupling in the parent sample. Further increase in pressures up to 45 GPa, did not affect this feature. The pressure quenched Raman spectra, revealed various chemical groups non-characteristic of the parent sample and adsorption of CO in addition to the characteristic 8(OCO) feature. The thus recorded Raman, complemented with the far and mid-infrared pressure quenched spectra, reveal the formation of novel metal-mediated polymers. The X-ray diffraction on W(C0)6 up to 58 GPa revealed the generation of amorphous polymeric pattern which was retained back to ambient conditions.
Identifier
FI15101538
Recommended Citation
Garimella, Subrahmanyam Venkata, "High Pressure Studies on Group VI Metal Hexacarbonyl Molecular Solids" (2010). FIU Electronic Theses and Dissertations. 3844.
https://digitalcommons.fiu.edu/etd/3844
Rights Statement
In Copyright. URI: http://rightsstatements.org/vocab/InC/1.0/
This Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s).