The v(OH/OD) band shape of strong hydrogen bonded dimers of phosphinic acids.: Phenomenology and formation models

The infrared spectra of phosphinic acid R(2)POOH dimers (R = CH(3), CH(2)Cl, C(6)H(5)) have been studied in CCl(4) and CH(2)Cl(2) solutions (T = 300 K). The infrared spectra of deuterated R(2)POOD dimers (R = CH(3), CH(2)Cl) were also studied in the gas phase (T = 400-550 K) and solid state (T = 100-300 K). They are compared with previously studied spectra of the light (non-deuterated) dimers in the gas phase, in the solid state and in low-temperature argon matrices (T = 12-30 K) in the 4000-400 cm(-1) spectral region. It is found that the strong and broad v(OH) dimer bands have similar shapes, nearly equal values of bandwidth and low-frequency shift, and possess the Hadzi ABC structure irrespective of the type of acid, significant differences of dimerization enthalpies, influence of solvent, the type of H-bonded complexes (cyclic dimers in the gas phase, in solutions, and in inert matrices, and infinite chains in the solid state), and temperature in the range 12-600 K. Isotopic ratio of the first moments of light and deuterated acid bands has been measured. Analysis of the v(OH/OD) band of hydrogen bonded dimers of phosphinic acids shows that the interaction between the two intermolecular bonds O-H(...)O=P in a cyclic complex plays virtually no role in the mechanism of the P(OH/OD) band formation; the shape of v(OH/OD)) band is controlled mainly by the POOH(D)(...)O = fragment; and the band shape of strong hydrogen bonded complexes is formed by a number of vibrational transitions from the ground state to different combination levels in the region 35001500 cm(-1). (c) 2006 Elsevier B.V. All rights reserved.