Department of Chemistry, Indian Institute of Technology Delhi, New Delhi 110016, India;
Biographical Information
Sajesh P. Thomas is an Assistant Professor in the Department of Chemistry, Indian Institute of Technology Delhi, since 2021. He leads a research group, Materials and Quantum Crystallography Lab (MQCL), at IIT Delhi with a focus on X-ray quantum crystallography to explore chemical bonds and intermolecular interactions- towards deriving quantitative insights into crystal engineering of molecular materials such as flexible crystals, pharmaceutical solids and piezoelectrics. He completed his PhD at the Indian Institute of Science, Bangalore in 2014 under the supervision of T. N. Guru Row, where he worked on charge density analysis and crystal engineering studies of pharmaceutical solids. After his PhD, he worked with Mark A. Spackman at the University of Western Australia, Perth, as a postdoctoral fellow, and Bo B. Iversen at Aarhus University (Denmark) as a Marie-Curie fellow.
Lecture 42: Sajesh Thomas
Chemical Applications of X-ray Quantum Crystallography
Sajesh P. Thomas1*
1Department of Chemistry, Indian Institute of Technology Delhi, New Delhi 110016, India;
X-ray quantum crystallography (QCr) is rapidly expanding with the introduction of powerful techniques such as Hirshfeld Atom Refinement (HAR) and X-ray wavefunction refinement (XWR), in addition to the conventional multipole models. In this presentation, I will discuss some chemical applications of these tools, focusing on unusual chemical bonds and intermolecular interactions in crystals. Our recent QCr studies have concentrated on dynamic bonds, which are essential in dynamic covalent chemistry involving reversible bond formation and cleavage. Using high-resolution X-ray quantum crystallography and computational analyses, we explored the electronic properties of Se−N bonds in the organo-selenium antioxidant ebselen and its derivatives. The reconstructed X-ray wavefunctions reveal that the Se−N bonds display low electron density in the bonding region and a positive Laplacian value at the bond critical point. Further analyses, including bond orders, covalency, ionicity, and measures such as LOL (Localized Orbital Locator) and ELF (Electronic Localization Function), indicate that the Se−N bond exhibits unique closed-shell characteristics. These findings have significant implications for understanding charge-shift bonds in the thermochromic crystals of diphenyl diselenide (dpdSe) and diphenyl ditelluride (dpdTe). Further, some applications of QCr in crystal engineering will be discussed, focusing on mechanically flexible crystals and molecular piezoelectrics.
References:
[1] S. Grabowsky et al, Chemical Science, 2017, 8, 4159–4176.
[2] S. P. Thomas et al, Angew. Chem. Int. Ed. 2023, 62, e202311044.
[3] S. P. Thomas et al, Chem. Eur. J. 2024, 30, e202303384.
[4] A. Rahman, S. P. Thomas et al, Small, 2024, 20, 2402120.
[5] A. H. Dar, S. P. Thomas et al, Small, 2024, 2406184.
[6] A. Sudheendranath, S. P. Thomas et al, ChemRxiv, 2024, 10.26434/chemrxiv-2024-0b9dt