X-RAY PHOTOELECTRON AND DIFFUSE-REFLECTANCE INFRARED SPECTROSCOPIC STUDIES OF HYDROGEN-BONDING IN SUBSTITUTED ANILINIUM CHLORIDE AND TRICHLOROSTANNATE(II) DERIVATIVES

It is reported how the N-H-Cl hydrogen bonding in anilinium chloride a nd trichlorostannate (II) derivatives is affected by methyl and methox y substitutions in the phenyl ring of an aniline group. Such hydrogen bonding has been confirmed by close N - Cl contacts in an X-ray struct ure determination on 2-methylanilinium trichlorostannate (II). Crystal s are orthorhombic: space group P2(1)2(1); a = 0.7290(3) nm, b = 1.909 6(7) nm, c = 0.8233(4) nm, alpha = beta = gamma = 90 degrees; V = 1.14 61(8) nm(3), Z = 4. The degree of hydrogen bonding manifests itself in changes in the core electron binding energies of the N and Cl atoms a s observed by X-ray photoelectron spectroscopy (XPS), and also by the characteristic shift in the N - H stretching frequency measured by dif fuse reflectance infrared spectroscopy. Correlations are observed betw een changes in the anilinium nu(N - H) force constants and changes in the corresponding N(1s) and Cl(2p) binding energies. The varying degre es of hydrogen bonding depend on the positions and types of substituen ts on the aniline aromatic ring and correlate with their dissociation constants, pK(a); but, theoretical analysis of one of the methylanilin e 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.