Quantum chemical study of Pnicogen bond based on point-of charge and MEP Presented By: Hussein M. H. Ali
Pnicogen bond based on point-of-charge AGENDA Introduction INTRODUCTION Sigma-hole & Pnicogen Interaction AIMS & OBJECTIVES COMPUTATIONAL METHODS RESULTS & DISCUSSION Introduction CONCLUSION
Pnicogen bond based on point-of-charge introduction Sigma-hole & Pnicogen Interaction Pnicogens are the nitrogen family located in group 15 in Sigma-hole periodic table started with nitrogen and ended with bismuth each member of this family contains five valence electrons. Pnicogens form non-covalent interaction called pnicogen bond and it’s categorized as sigma-hole interaction. Sigma-hole is a region of positive electrostatic potential along the extension of covalent bond as a result of anisotropic distribution of electron density around the molecule. This deficiency of electron enabled the molecule to interact non- covalently . Sigma-hole interaction is very directional and the strength increases with the increase of sigma hole size. The positive character of sigma-hole in going from the lighter to heavier (more polarizable) in nitrogen group . The size of sigma hole is affected by the type of atom which is covalently bonded along the sigma hole axis
Pnicogen bond based on point-of-charge Aims & Objectives The characteristics of pnicogen bond is still under debate and need more investigation to gain more information about the interaction . Study the 2D potential surface of the pnicogen-base molecule. Study the effect of pnicogen … point-of-charge distance and angle on pnicogen bond strength. Study the effect of pnicogen-Lewis base distance and angle on pnicogen bond strength.
Pnicogen bond based on point-of-charge Computational Methodology Molecular Optimization Six molecule were studied (XH 3 , XH 2 F & XF 3 : X= N and P). All molecules were optimized at MP2 method with 6- 311++G** basis sets using Gaussian software G09. All calculations were performed on CompChem-HPC. Molecular Electrostatic Potential MEPs of the studied molecules were generated at B3PW91/6-311G** level of theory. 2d GRID SCANNING All molecules’ lone pair area were scanned in 2d surface scanning from -2.5 Å to +2.5 Å along Y and Z axis and energy have been calculated at MP2/aug-cc-pVTZ level of theory. The scan was performed using Point-of-Charge approach (PoC). CompChem-HPC High Performance Computer
Pnicogen bond based on point-of-charge Computational Methodology Pnicogen bond Strength The strength of pnicogen bond was investigated by using 1d scanning with increasing the PoC distance from 2.5 Å to 8.0 Å along the X axis of extended covalent bond. PoC approach means that replacing Lewis base with negative point of charge. Point-of-charge at different distances along pnicogen X axis Pnicogen bond Angle The pnicogen bond angle was studied using angle software on CompChem website. PoC was oriented at different angles started from 90 ˚ to 270 ˚ on the extension of covalent bond. The energy was calculated at the MP2 level of theory. CompChem-HPC High Performance Computer
Pnicogen bond based on point-of-charge Results & discussion Molecular Electrostatic Potential The molecular electrostatic potential surfaces showed that there is no sigma hole in NH 3 and PH 3 . In NF 3 and PF 3 there are three sigma holes along the covalent bond of fluorine atom . In NH 2 F and PH 2 F there is only one sigma hole. MEP surfaces of all investigated molecules
Pnicogen bond based on point-of-charge Results & discussion 2d scanning grid The result of 2d grid scanning on the lone pair area showed that the interaction is repulsive on PH 3 and NH 3 molecules. The NH 2 F and PH 2 F molecules shown both repulsion and attraction as showed in figure (V). The attraction interaction appears in NF 3 and PF 3 which is predictable from MEP maps. 2D scanning grid along lone pair axis
Pnicogen bond based on point-of-charge Results & discussion Pnicogen Bond Strength The results showed that if there is a sigma hole the stabilization energy increases when getting closer to sigma hole. The stabilization energy decreasing with decreasing the value of PoC. Effect of pnicogen-PoC distance on molecular stabilization energy
Pnicogen bond based on point-of-charge Results & discussion Pnicogen Bond Angle PoC was oriented at different angles started from 90 ˚ to 270 ˚ on the extension of covalent bond. The energy was calculated at the MP2 level of theory.
Pnicogen bond based on point-of-charge Results & discussion Pnicogen…Lewis Base Complex Pnicogen … F - ion interaction was calculated to reveal the accuracy of our proposed point-of- charge approach. Both angle and distance effects were considered.
Pnicogen bond based on point-of-charge Results & discussion Substituent effect The result showed the more electronegative the atom bonded covalently the more size of sigma hole along the extension of covalent bond. Increasing of sigma hole size increases the stabilization energy. Substituent effect on pnicogen…point -of-charge interaction energy
Pnicogen bond based on point-of-charge Conclusion The characteristics of pnicogen interaction were reveled. The effect of angle and substituents on pnicogen bond energy was investigated and the effect of substituents depend on the electro-negativity of the halogen atom . Our developed Point-of-Charge approach is a real example to simulate Lewis base and giving us indication of sigma hole existence. The directionality of sigma-hole was proved during study and sigma hole size in phosphorous is bigger than nitrogen.
Pnicogen bond based on point-of-charge Acknowledgment
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