A study of H2CO•••HF Complex by Advanced Quantum Mechanical Methods

Our research is focused on the ab initio calculations of the equilibrium structures, binding energies, harmonic and anharmonic vibrational frequencies of a hydrogen-bonded complex, which is formed between formaldehyde H2CO and hydrogen fluoride HF, using the Gaussian 09 package of programs with full 6311++G(3df, 3pd) basis sets in the MP2 second-order perturbation theory and CCSD(T) methods. Harmonic and anharmonic vibrational frequencies and intensities of the H2CO···HF complex were calculated by the Gaussian 16 package programs within the same approximation. Geometric changes and frequency shifts at the complex formation were evaluated. The H2CO···HF complex formation energy and the dipole moment were calculated in the CCSD(T)6311++G(3df, 3pd) approximation to be equal, respectively, to 7.78 kcal/mol and 4.2 D. Changes of the geometric, spectral, and energetic parameters of the complex proved the existence of a stable hydrogen bond F–H···O=CH2 between the components.

A Theoretical Study on Negative Solvation by Means of Quantum Chemical Calculations on the I(H2O)--Complex

By means of an “ab initio” all electron treatment of the I-/H2O complex in various geometrical arrangements, it has been attempted to derive some arguments for the general discussion about the phenomenon of negative solvation, based on the background of quantum chemistry. The most stable conformation of the complex is indicated to have C2v symmetry. Rotating of this conformation by 180° leads to an arrangement whose destabilization energy has about the same value as the complex formation energy, which, on the other hand, is only slightly higher than the hydrogen bond energy between two water molecules. These results contradict the formation of an almost rigid first hydration sphere and allow, further, the interpretation of the negative solvation by means of a “cooperative effect” between ion-solvent complex and other solvent molecules, in full agreement with the work of Engel and Hertz.