Ground State Geometry and Charge Transfe

Ground State Geometry and Charge Transfer Transition Energy of the Toluene-ICl Molecular Complex: An ab initio and TDDFT Methods : 

Ground State Geometry and Charge Transfer Transition Energy of the Toluene-ICl Molecular Complex: An ab initio and TDDFT Methods presented by Dr. Partha Sarathi Sengupta P.G. Department of Chemistry Vivekananda Mahavidyalaya, Burdwan Burdwan-713103, INDIA

Orientation of ICl with respect to the aromatic nucleus : 

Orientation of ICl with respect to the aromatic nucleus

Horizontal, parallel to the aromatic ring ? : 

Horizontal, parallel to the aromatic ring ? Not possible as π-electron cloud attracts the I(δ+) end and repels the Cl(δ-) end of ICl

Vertical, along the axis of the aromatic ring ? : 

Vertical, along the axis of the aromatic ring ? Not possible as the Cl δ- end should be repelled away from the π-electron cloud

Tilted at an angle w.r.t. the axis of the aromatic ring ? : 

Tilted at an angle w.r.t. the axis of the aromatic ring ? Tilted arrangement is more logical on electrostatic ground

Location of the I end of ICl : 

Location of the I end of ICl Located above a C atom of the aromatic ring ? Located above a C═C bond of the aromatic ring ? -Less likely because Me-group by its inductive effect increases the e-density at the C-atoms Located above the center of the aromatic ring ? -Not possible as the π-electron density is mainly concentrated at the periphery

Six possible conformations of the toluene-ICl complex : 

Six possible conformations of the toluene-ICl complex

Potential energy surface for DFT/ B3LYP method of the ortho-isomer of the Tol-ICl complex in the ground state in gas phase. SC1 means ortho C-I distance in Å and SC2 means orthoC-I-Cl angle in degree. : 

Potential energy surface for DFT/ B3LYP method of the ortho-isomer of the Tol-ICl complex in the ground state in gas phase. SC1 means ortho C-I distance in Å and SC2 means orthoC-I-Cl angle in degree.

Summary of PES results : 

Summary of PES results Each structure yielded a number of local minima The geometries at these minima were then used as initial guess for full optimization followed by frequency calculation to ascertain whether the optimized geometries were real minima or saddle points Structures (ii), (iv) and (vi) gave one imaginary frequency each, indicating that they were first order saddle points and not real structures Structure (iii) converged to structure (v) on full optimization

Slide 10: 

(a) (b) B3LYP-optimised geometries of (a) the ortho-isomer and (b) the para isomer of the Tol-ICl complex in the ground state in CCl4 medium These two structures were then subjected to counterpoise calculation in order to get the complexation energies after correction for basis set superposition error (BSSE).

Slide 11: 

Complexation Energies (∆Eb), BSSE, Counterpoise–Corrected Interaction Energy (∆EbCP) in kcal/mole, and number of Imaginary Frequencies (ni) for the Tol-ICl complex

: 

Complexation energy of the o-isomer > p-isomer according to DFT and this finding was substantiated by MP2 calculations For this reason we conclude that the o-isomer is the preferred structure of the Tol-ICl complex in its ground state, and this is in compliance with the fact that inductive effect of methyl group falls off with distance The sum of the charges on the Tol moiety and that on the ICl moiety of the complex in the ground state indicate that with respect to Tol the ICl moiety is negatively charged, and about 1.0 –1.4 % of the charge of an electron has been transferred from Tol to ICl in the ground state of the complex

TDDFT calculation for electronic spectra : 

TDDFT calculation for electronic spectra The Tol-ICl complex in the two isomeric forms (i) & (v), free ICl and free toluene were subjected to time dependent density functional theory (TDDFT) calculation for the excited states in CCl4 medium (dielectric constant 2.228) under the PCM formalism. The optimized ground state geometries in the CCl4 medium were used for such calculation

Slide 14: 

Toluene ICl Tol-ICl complex

Slide 15: 

UV-VIS spectra of the ortho isomer of toluene-ICl complex in CCl4 medium calculated by TDDFT/B3LYP/6-31++G(d,p). The CT absorption band appears at 365 nm A comparison of the TDDFT results reveals that the complex has an electronic transition different from those of the individual components and the ground-to-excited state transition electric dipole moment of the complex has a dominant component directed from Tol to ICl.

Conclusions : 

Conclusions Toluene and ICl form a charge transfer(CT) complex in CCl4 medium Thorough PES and geometry optimization reveal that in the ground state of the complex ICl stands slightly tilted at an angle of about 9º w.r.t. the vertical and the I atom faces the ortho C-atom of the aromatic nulcleus TDDFT/PCM calculations gives hνCT = 3.8 eV in CCl4 medium while the experimental values is 4.3 eV (somewhat underestimated*) However the TDDFT/PCM calculation separately on Tol, ICl and the complex (considered as a super molecule) clearly shows the appearance of a new absorption band ascribable to a CT process. *Tozer DJ, Handy NC, J Chem Phys 109:10180, 1998. *Tozer DJ, J Chem Phys 119:12697, 2003.

Acknowlegement : 

Acknowlegement Professor A.K. Mukherjee, whose constant inspiration and valuable advice is helping me to carry out my research work Amit S. Tiwary, my coauthor and one of my best friend.

Slide 18: 

Thanks to all