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Spectroscopy and Structures of Metal-Cyclic Hydrocarbon Complexes

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Spectroscopy and Structures of Metal-Cyclic Hydrocarbon Complexes University of Kentucky UKnowledge University of Kentucky Doctoral Dissertations Graduate School 2010 SPECTROSCOPY AND STRUCTURES OF METAL-CYCLIC HYDROCARBON COMPLEXES Jung Sup Lee University of Kentucky, [email protected] Right click to open a feedback form in a new tab to let us know how this document benefits ou.y Recommended Citation Lee, Jung Sup, "SPECTROSCOPY AND STRUCTURES OF METAL-CYCLIC HYDROCARBON COMPLEXES" (2010). University of Kentucky Doctoral Dissertations. 39. https://uknowledge.uky.edu/gradschool_diss/39 This Dissertation is brought to you for free and open access by the Graduate School at UKnowledge. It has been accepted for inclusion in University of Kentucky Doctoral Dissertations by an authorized administrator of UKnowledge. For more information, please contact [email protected]. ABSTRACT OF DISSERTATION Jung Sup Lee The Graduate School University of Kentucky 2010 SPECTROSCOPY AND STRUCTURES OF METAL-CYCLIC HYDROCARBON COMPLEXES ABSTRACT OF DISSERTATION A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the College of Arts and Sciences at the University of Kentucky By Jung Sup Lee Lexington, Kentucky Director: Dr. Dong-Sheng Yang, Professor of Chemistry Lexington, Kentucky 2010 Copyright © Jung Sup Lee 2010 ABSTRACT OF DISSERTATION SPECTROSCOPY AND STRUCTURES OF METAL-CYCLIC HYDROCARBON COMPLEXES Metal-cyclic hydrocarbon complexes were prepared in a laser-vaporization molecular beam source and studied by single-photon zero electron kinetic energy (ZEKE) and IR-UV resonant two-photon ionization (R2PI) spectroscopy. The ionization energies and vibrational frequencies of the metal complexes were measured from the ZEKE spectra. Metal-ligand bonding and low-lying electronic states of the neutral and ionized complexes were analyzed by combining the ZEKE measurements with density functional theory (DFT) calculations. In addition, C-H stretching frequencies were measured from the R2PI spectra. In this dissertation, metal complexes of 1, 3, 5, 7-cyclo-octatetraene (COT), toluene, p-xylene, mesitylene, hexamethylbenzene, biphenyl, naphthalene, pyrene, perylene, and coronene were studied. For each metal-ligand complex, different effects from the metal coordination have been identified. Although free COT is a nonaromatic molecule with a tub-shaped structure, the group III transition metal atoms (Sc, Y, and La) donate two electrons to a partially filled π orbital of COT, making the ligand a dianion. As a result, metal coordination converts COT into a planar, aromatic structure and the resulting complex exhibits a half-sandwich structure. For the Sc(methylbenzene) complexes, the benzene rings of the ligands are bent and the π electrons are localized in a 1, 4-diene fashion due to differential Sc binding with the carbon atoms of the rings. Due to differential metal binding, the degenerate d orbitals split and the Sc-methylbenzene complexes prefer the low-spin ground electronic states. In addition, as the number of methyl group substituents in the ligand increases, the ionization energies (IEs) of the Sc- methylbenzene complexes decrease. However, Ti, V, or Co coordination does not disrupt the delocalized π electron network within the carbon skeleton in the high-spin ground states of the metal complexes. For group VI metal (Cr, Mo, and W)-bis(toluene) complexes, methyl substitution on the benzene ring yields complexes with four rotational conformers of 0°, 60°, 120°, and 180° conformation angles between two methyl groups. In addition, variable-temperature ZEKE spectroscopy using He, Ar, or their mixtures has determined the totally eclipsed 0° rotamer to be the most stable. When there are two equivalent benzene rings, the metal (Ti, Zr or Hf) binds to both the benzene rings of biphenyl, or the metal (Li) binds to one of the benzene rings of naphthalene. On the other hand, the metal (Li) favors the ring-over binding site of the benzene ring with a higher π electron content and aromaticity in pyrene, perylene, and coronene. KEYWORDS: PFI-ZEKE Spectroscopy, IR-UV R2PI Spectroscopy, metal-cyclic hydrocarbon complexes, Ionization Energy, Density Functional Theory Jung Sup Lee December 14, 2010 SPECTROSCOPY AND STRUCTURES OF METAL-CYCLIC HYDROCARBON COMPLEXES By Jung Sup Lee Dr. Dong-Sheng Yang Director of Dissertation Dr. John E. Anthony Director of Graduate Studies December 14, 2010 RULES FOR THE USE OF DISSERTATIONS Unpublished dissertations submitted for the Doctor’s degree and deposited in the University of Kentucky Library are as a rule open for inspection, but are to be used only with due regard to the rights of the authors. Bibliographical references may be noted, but quotations or summaries of parts may be published only with the permission of the author, and with the usual scholarly acknowledgements. Extensive copying or publication of the dissertation in whole or in part also requires the consent of the Dean of the Graduate School of the University of Kentucky. A library that borrows this dissertation for use by its patrons is expected to secure the signature of each user. Name Date DISSERTATION Jung Sup Lee The Graduate School University of Kentucky 2010 SPECTROSCOPY AND STRUCTURES OF METAL-CYCLIC HYDROCARBON COMPLEXES DISSERTATION A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the College of Arts and Sciences at the University of Kentucky By Jung Sup Lee Lexington, Kentucky Director: Dr. Dong-Sheng Yang, Professor of Chemistry Lexington, Kentucky 2010 Copyright © Jung Sup Lee 2010 Dedicated to my mentor, family, and friends… ACKNOWLEDGEMENTS I have received so much help from many wonderful people during the completion of this work. I owe great dept to my mentor, advisory committee members, lab mates, and family for their aid. My advisor, Dr. Dong-Sheng Yang, has been a mentor and role model during my graduate studies. His friendliness, patience, and compassion have allowed me to proceed to reach my goal even in difficult times. His dedication, guidance, and support will always be remembered and continue to inspire me in my future career. I would also like to acknowledge the attention and care that my advisory committee members have given me. Dr. Dennis J. Clouthier has taught me the fundamental knowledge in spectroscopy and theoretical calculations. The insights he has provided have served me to proceed on my research. Dr. Carolyn P. Brock has broadened my perspectives and her vast knowledge has helped me for better understanding and analysis of the results. Dr. Chang-Guo Zhan has given me helpful opinions about the computations which were essential for my research. Over the past years, all of my committee members have shared their wisdom, and their supervision was essential for me to obtain the valuable data and their analysis. In addition, I had great opportunity to work with many diverse co-workers. My previous lab mates, Dr. Yuxiu Lei, Dr. Serge Krasnokutski, Dr. Xu Wang, and Dr. Bradford R. Sohnlein have taught me how to carry on the experiment and computational calculations. Without their instructions, I could not have completed this work. Current and some of the early members of our group, Dr. Shenggang Li, Dr. Mourad Roudjane, Dr. Changhua Zhang, Dr. Yang Liu, Ms. Sudesh Kumari, Mr. Lu Wu, and Ms. Dilrukshi Hewage, have shared their helpful discussions and friendship. They have encouraged me to resolve various experimental and computational problems. Working with all of my lab mates has been very pleasant and a great experience for me. I will always remember their assistance and value the experience of working with such considerate and supportive people. iii Moreover, my family has given me guidance and support to keep me straight to reach for my goal. They were always besides me whenever I needed them. I am very grateful for my grandfather who has always given me support and attention to be a better person. I would also like to thank my mother and father who have supported me all these years. Without their guidance, I could not be who I am today. Also they have given me opportunity and pressured me to study further in US. If they had not done so, I would not have accomplished such work, nor met my wonderful wife. My wife and her family have helped me when I had hard time while separated from my family in South Korea and also treated me such that I would feel right at home. With the presence of all my family members, my life has always been filled with energy and joy. I can not express my gratitude for their support, understanding, and patience. During my graduate studies, I have learned so much in various aspects that I have never had a chance to do before. With everyone’s help, I was able to accomplish what I never dreamed possible. Now, I feel like I can go over any obstacles that lie ahead of me. The experience that I had in University of Kentucky will never be forgotten. This work is dedicated to all of my teachers, friends, and family. Thank you! iv TABLE OF CONTENTS ACKNOWLEDGEMENTS ............................................................................................... iii LIST OF TABLES ........................................................................................................... viii LIST OF FIGURES .............................................................................................................x CHAPTER 1. INTRODUCTION ........................................................................................1 1.1. Spectroscopy .............................................................................................................2
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