A quantum chemical study of host-guest systems with dimethylene-bridged clips and tetramethylene-bridged tweezers as host molecules and six different aliphatic and aromatic substrates as guests is presented. The geometries and binding energies of the complexes are investigated using the recently developed density functional theory with empirical corrections for dispersion interactions (DFT-D) in combination with the BLYP functional and basis sets of TZVP quality. It is found that the DFT-D method provides accurate geometries for the host-guest complexes that compare very favorably to experimental X-ray data. Without the dispersion correction, all host-guest complexes are unbound at the pure DFT level. Calculations of the clip complexes show that the DFT-D binding energies of the guests agree well with those from a more sophisticated SCS-MP2/aug-cc-pVTZ treatment. By a partitioning of the host into molecular fragments it is shown that the binding energy is clearly dominated by the aromatic units of the clip. An energy decomposition analysis of the interaction energies of some tweezer complexes revealed the decisive role of the electrostatic and dispersion contributions for relative stabilities. The calculations on the tweezer complexes show that the benzene spaced tweezer is a better receptor for aliphatic substrates than its naphthalene analogue that has a better topology for the binding of aromatic substrates. The tweezer with a OAc substituent in the central spacer unit is found to favor complex formation with both aliphatic and aromatic substrates. The theoretical results are qualitatively in very good agreement with previous experimental findings although direct comparison with experimental binding energies which include solvent effects is not possible. The good results obtained with the DFT-D-BLYP method suggest this approach as a standard tool in supramolecular chemistry and as the method of choice for theoretical structure determinations of large complexes where both electrostatic and dispersive interactions are crucial.
Articles you may be interested inAccurate ab initio ro-vibronic spectroscopy of the X ̃ 2 Π CCN radical using explicitly correlated methods An ab initio study of the vibronic, spin-orbit, and magnetic hyperfine structure in the X Π 2 electronic state of NCO An ab initio study of the hyperfine structure in the X 2 Π electronic state of CCCH Ab initio study of the vibronic and spin-orbit structure in the X 2 Π electronic state of CCCH Ab initio investigation of the vibronic spectrum involving the two lowest-lying electronic states of HCCO Potential energy surfaces for the electronic states of the HCCS radical correlating at linear nuclear arrangement with the X 2 ⌸ state are calculated by means of an extensive ab initio approach. Particular attention is paid to calculating accurate three-dimensional potential surfaces involving variations of two bending and torsional coordinates, which play the central role in vibronic interactions ͑Renner-Teller effect͒, determining the structure of spectra of this radical. In the second part of this paper we use these potential surfaces and the ab initio computed spin-orbit coupling constant to calculate vibronic spectra of HCCS and DCCS in the framework of a theoretical model developed in our laboratory. The results of the present study are in excellent agreement with those derived by Tang and Saito ͓J. Chem. Phys. 105, 8020 ͑1996͔͒ and thus strongly support the interpretation of their experimental findings.
Results of an ab initio investigation of the vibronic structure of the X 2Πu electronic state of C2H+2 are presented. Calculations are performed using a variational approach for handling the Renner–Teller effect in tetra-atomic molecules [Perić et al., Mol. Phys. 55, 1129 (1985)]. In these computations both the ab initio potential surfaces and those derived on the basis of experimental findings are employed. The results of the calculations strongly support the recent analysis of the C2H+2 spectrum [Pratt et al., J. Chem. Phys. 99, 6233 (1933)] and predict a number of yet unobserved features in the energy range between 0 and 3000 cm−1.
A variational approach for treating the Renner–Teller effect in tetra-atomic molecules [Perić et al., Mol. Phys. 55, 1159 (1985)] is extended to account for the effect of spin–orbit coupling. The approach is applied to compute the spin–orbit splittings of the vibronic levels in the X 2Πu state of C2H+2. The bending potential curves employed in a previous study [Perić and Peyerimhoff, J. Chem. Phys. (in press)] are improved by carrying out ab initio calculations at a higher level of sophistication. The results of the computations enable a reliable interpretation of recent experimental findings [Pratt et al., J. Chem. Phys., 99, 66 (1993)].
A model for the ab initio treatment of the Renner–Teller effect in tetra-atomic molecules is elaborated. It is based on the approach developed by Petelin and Kiselev [Int. J. Quantum Chem. 6, 701 (1972)]. Particular attention is paid to Π electronic states. Perturbative formulas are derived for several coupling cases. The model is checked by means of ab initio calculations at various levels of sophistication. Results of computations of various quantities related to the model are presented for the X 2Πu states of B2H+2 and C2H+2. The reliability of the basis assumptions is demonstrated by comparing the results obtained in the framework of the model considered with those of independent ab initio calculations.
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