X-ray photoelectron and diffuse reflectance infrared spectroscopic studies of hydrogen bonding in substituted anilinium chloride and trichlorostannate (II) derivatives

Article abstract of DOI:10.1002/pssa.2211440202

It is reported how the N - H - Cl hydrogen bonding in anilinium chloride and trichlorostannate (II) derivatives is affected by methyl and methoxy substitutions in the phenyl ring of an aniline group. Such hydrogen bonding has been confirmed by close N - Cl contacts in an X-ray structure determination on 2-methylanilinium trichlorostannate (II). Crystals are orthorhombic: space group P2₁2₁; a = 0.7290(3) nm, b = 1.9096(7) nm, c = 0.8233(4) nm, α = β = γ = 90°; V = 1.1461(8) nm³, Z = 4. The degree of hydrogen bonding manifests itself in changes in the core electron binding energies of the N and Cl atoms as observed by X-ray photoelectron spectroscopy (XPS), and also by the characteristic shift in the N - H stretching frequency measured by diffuse reflectance infrared spectroscopy. Correlations are observed between changes in the anilinium v(N - H) force constants and changes in the corresponding N(1s) and Cl(2p) binding energies. The varying degrees of hydrogen bonding depend on the positions and types of substituents on the aniline aromatic ring and correlate with their dissociation constants, pK_a; but, theoretical analysis of one of the methylaniline hydrochlorides shows that the position of the H atom in the hydrogen bond, N - H - Cl, is a significantly stronger influence on the fractional charge on nitrogen, suggesting that overall crystal structure may be the determining factor on N charge.