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.

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High-resolution infrared absorption spectra of the H2CO···HF complex and its monomers are recorded in gas phase in C=O and C−H regions by means of Bruker HR 125 spectrometer recorded with a resolution of 0.05 cm−1. Upon the complexation in the HF stretching band of complex the asymmetrical shape was not observed due to weak interaction between C=O and C−H stretching of the H2CO···HF complex. Quantum-chemical calculations are performed in mp2//6-311++g(3df, 3pd) approximation and calculated geometrical, energetic, and spectral parameters of the complex.

The lone pair of the N atom is a common electron donor in noncovalent bonds. Quantum calculations examine how various aspects of the base on which the N is located affect the strength and other properties of complexes formed with Lewis acids FH, FBr, F2Se, and F3As that respectively encompass hydrogen, halogen, chalcogen, and pnicogen bonds. In most cases the halogen bond is the strongest, followed in order by chalcogen, hydrogen, and pnicogen. The noncovalent bond strength increases in the sp

The imidazolium cation has a number of different sites that can interact with a nucleophile. Adding a halogen atom (X) or a chalcogen (YH) group introduces the possibility of an NX···nuc halogen or NY···nuc chalcogen bond, which competes against the various H-bonds (NH and CH donors) as well as the lone pair···π interaction wherein the nucleophile lies above the plane of the cation. Substituted imidazoliums are paired with the NH3 base, and the various different complexes are evaluated by density functional theory (DFT) calculations. The strength of XB and YB increases quickly along with the size and polarizability of the X/Y atom, and this sort of bond is the strongest for the heavier Br, I, Se, and Te atoms, followed by the NH···N H-bond, but this order reverses for Cl and S. The various CH···N H-bonds are comparable to one another and to the lone pair···π bond, all with interaction energies of 10–13 kcal/mol, values which show very little dependence upon the substituent placed on the imidazolium.