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D. Allen Clabo , Jr. Department of Chemistry Francis Marion University

Ab initio computational studies of the structures and energies of Li 2 MX 4 (M=Be, Mg, B + , Al + , X=halogen) isomers. D. Allen Clabo , Jr. Department of Chemistry Francis Marion University Southeast Regional Meeting of the American Chemical Society October 27, 2011, Richmond, VA.

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D. Allen Clabo , Jr. Department of Chemistry Francis Marion University

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  1. Ab initio computational studies of the structures and energies of Li2MX4 (M=Be, Mg, B+, Al+, X=halogen) isomers D. Allen Clabo, Jr. Department of Chemistry Francis Marion University Southeast Regional Meeting of the American Chemical Society October 27, 2011, Richmond, VA

  2. Abstract These inorganic molecules are significant by their unique atomic arrangements and easy rearrangements. This project extends our work with Li2MH4 isomers to include the halogenated analogues Li2MX4. We have located at HF/6-31G* and B3LYP/6-311+G* levels of theory the energy minima and the transition states for the isomerizations that demonstrate almost continuous transformation of the central MX3 and MX4 fragments. The preferred minima and the numbers of stationary points vary from one central metal to another and differ from the hydrides.

  3. Background • Experimental observations (ca. 1988) • Matrix isolation: Li2BeF4, etc. • Molten salts: Li2AlF5, Na2BeF4, Li2BF4+, etc. • Continuing theoretical studies • manuscripts in preparation (Li2MH4 and Li2MF4)

  4. Possible Structural Motifs C2v D2d C2v (cyclic) Cs C3v

  5. Computational Chemistry • Confirm experimental data • Predict unknown structures, rearrangement pathways • Explain structural preferences, bonding, stability trends, etc.

  6. Computational Methods • GAUSSIAN03 and 09 • Full optimization and frequency calculations • HF/6-31G* (“HF”) • B3LYP/6-311+G* (“DFT”) • Single-point energies • MP4SDTQ/6-31G*//HF/6-31G* (“MP4”) • CCSD(T)/6-311+G*//B3LYP/6-311+G* (“CC”)

  7. Li2BeX4 – Relative E (kJ/mol)

  8. Li2MgX4 – Relative E (kJ/mol)

  9. Li2BX4+ – Relative E (kJ/mol)

  10. Li2AlX4+ – Relative E (kJ/mol)

  11. Metal Hybridization • Natural population analysis • Hybridization as ratio of s:p:d orbital populations

  12. s:p population ratios in bond orbitals (hybridization)

  13. s:p population ratios in bond orbitals (hybridization)

  14. Conclusions • Preferred isomer is the cyclic C2v isomer only for Li2BeX4 • All other metals prefer (expected?) D2d geometry • All structures have orbital populations to suggest primarily covalent M-X bonding • C2v isomers have significant population distortion of one pair of M-X bonds, suggesting a non-covalent interaction

  15. Acknowledgements • D.A.C. acknowledges a valuable collaboration with Profs. P. v. R. Schleyer (U. of Ga.) and O. P. Charkin (Chernogolovka, Russia) • D.A.C. acknowledges the FMU Professional Development Committee for a sabbatical leave to complete some of this work and for financial support to attend SERMACS

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