Prof. Eluvathingal D. Jemmis Department of Inorganic and Physical Chemistry Indian Institute of Science, Bangalore Friday, August 18, 2017 - 11:15am Chemistry Building, Room 400 Physical Seminar We show that the continuum behavior in the variation of the X-H stretch from blue- to red- through zero- shifting observed in H-Bonds also holds good for X-Z stretch in X-Z---Y complexes where Z = a main group fragment. This has been studied by ab-initio electronic structure calculations using Z= Hydrogen, Halogens, Chalcogens and Pnicogens as prototypical examples. Our analysis revealed that, the competition between negative hyperconjugation within the donor (X-Z) molecule and Charge Transfer (CT) from the acceptor (Y) molecule is the primary reason for the X-Z bond length change. Proper tuning of X- and Y-group for a particular Z- can change the blue-shifting nature of X-Z bond to zero-shifting and further to red-shifting. In contrast to the weak intermolecular interactions in the main group compounds, electron-saturated (18-electron) transition metal complexes show reluctance towards weak metal-bond formation. We propose that the nature of valence electron density distribution in transition metal complexes is the primary reason for this reluctance. We propose that weak interactions form a part of the larger continuum of the nature of the chemical bond. The strong among the so-called weak interactions are stronger than the weak among regular X-Z bonds. We end with an unconventional use of halogen bond to strengthen the sextuple bond in Cr2. References: 1. J. Joseph, EDJ; Red- Blue- or No-Shift in Hydrogen Bonds: A Unified Explanation, J. Am. Chem. Soc., 129, 4620-4632 (2007). 2. J. Joy, J. Anex, EDJ; Continuum in the X-Z---Y Weak Bonds: Z= Main Group Element, Journal of Computational Chemistry (P.Schleyer Issue), 37, 270-279 (2016). 3. J. Joy, EDJ; Contrasting Behavior of the Z Bonds in X-Z..Y Weak Interactions: Z = Main Group Elements Vs Transition Metals, Inorg. Chem., 56, 1132−1143 (2017). 4. J. Joy, EDJ; A Halogen Bond Route to Shorten the Ultrashort Sextuple Bond in Cr2 and Mo2, Chem. Commun. 53, 8168-8171(2017).