New descriptors for an “unbiased” and chemically insightful comparison of ab-initio and X-ray derived charge densities
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Data di Pubblicazione:
2013
Citazione:
New descriptors for an “unbiased” and chemically insightful comparison of ab-initio and X-ray derived charge densities / C. Gatti, G. Saleh, L. Lo Presti. ((Intervento presentato al convegno Natta's Seeds Grow : from the crystallography and modeling of stereoregular polymers to the challenges of complex systems tenutosi a Milano nel 2013.
Abstract:
The results of modelling always need to be compared and validated against the experiment. To be meaningful, the comparison should be as much as possible unbiased, and, hopefully, should use tools also able to provide chemical insight. Being based on a quantum observable and measurable quantity, the Electron Density (ED) based descriptors enable a direct comparison of ab-initio and X-ray derived EDs. They also provide a description of chemical paradigms which is, in principle, freed at the outset from any model preconception or arbitrariness. Furthermore, as for their nature rooted in physics, they are ideally suited to validate or reject the interpretive models of chemistry based on useful, but arbitrary objects. In this lecture, we will discuss the capability of two of such descriptors, the Source Function (SF) [1] and the Reduced Density Gradient (RDG), to unveil electron delocalization effects and to detect non covalent interactions, respectively. The SF enables one to view chemical bonding and other chemical paradigms under a new perspective [1,2]. We recently addressed the question of whether the SF is also capable to reveal electron delocalization effects (EDEs) in a series of supposedly electron-conjugated compounds, investigated through ab-initio methods [2]. The study is here extended to various molecular crystals (benzene, naphtalene and a substituted binaphtyl-2-ol), whose ED and SF results were obtained from X-ray diffraction data. Regardless of the derivation of the ED, the answer to the question above is convincingly positive. The capability of the SF to reveal EDEs is independent from a / separation and EDEs may be recovered even when such separation is unfeasible or when symmetry reasons would preclude it. Use of the SF to test the concept of hypervalency in the K2SO4 crystal [4] will also be discussed. A novel non covalent interaction (NCI) descriptor, based on the RDG and enabling an easy-to-catch pictorial visualization of either the supposedly attractive (dispersive, hydrogen bonding) or allegedly repulsive (steric) intermolecular interactions, was recently developed [5]. We apply for the first time [6] this same tool to experimentally-derived ED’s of molecular solids (austdiol, benzene, famotidine) discussing its performance in synergy with Bader’s analysis and using our software code, NCI-Milano [7], purposedly developed for such an extension.
[1] R.F.W. Bader, C. Gatti Chem Phys. Lett. 1998, 287, 233-238.
[2] C. Gatti Struct. Bond. 2012, 147, 193-286.
[3] E. Monza, C. Gatti, L. Lo Presti, E. Ortoleva J. Phys. Chem. A 2011, 115, 12864-12878.
[4] M.S. Schmøkel, S. Cenedese, J. Overgaard, M.R.V. Jørgensen, Y-S Chen, C. Gatti, D. Stalke, B.B. Iversen Inorg. Chem. 2012, 51, 8607-8616.
[5] E.R. Johnson, S. Keinan, P. Mori-Sanchez, J. Contreras-Garcia, A.J. Cohen, W. Yang J. Am. Chem. Soc 2010, 132, 6498-6506.
[6] G. Saleh, C. Gatti, L. Lo Presti, J. Contreras-Garcia Chem. Eur. J. 2012,18,15523-15536.
[7] G. Saleh, L. Lo Presti, C. Gatti, D. Ceresoli J. Appl. Cryst. 2013, 46, 1513-1517.
Tipologia IRIS:
14 - Intervento a convegno non pubblicato
Keywords:
Quantum theory of atoms in molecules; non-covalent interactions; molecular recognition
Elenco autori:
C. Gatti, G. Saleh, L. Lo Presti
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