ELECTROSTATIC MODEL OF COOPERATIVE EFFECTS IN HYDROGEN-BONDED SYSTEMS- COOPERATIVE EFFECT OF BASE OF CATION ON THE A-H STRETCHING VIBRATIONAL FREQUENCY
Nd. Sokolov, ELECTROSTATIC MODEL OF COOPERATIVE EFFECTS IN HYDROGEN-BONDED SYSTEMS- COOPERATIVE EFFECT OF BASE OF CATION ON THE A-H STRETCHING VIBRATIONAL FREQUENCY, Journal of molecular structure, 437, 1997, pp. 201-211
Certain empirical regularities of cooperative effects in L...A-H...B c
lusters (where A-H...B is a hydrogen-bonded dimer and L is a metallic
cation) are interpreted in terms of a simple electrostatic model. The
potential energy surface (PES) of the intermolecular interaction is ap
proximated by the sum of the coulombic interaction energies of the ato
mic effective (residual) charges, allowing for the inductive action on
the neighbouring bonds and the exchange repulsion of nearest atoms. M
aking use of the given PES, the relative frequency shift (Delta nu/nu(
0)) of the stretching frequency nu(S)(AH) under the action of B and L
in the A-H...B dimer and L...A-H...B cluster is found. For a series of
compounds with a variable base B, the quantities (Delta nu/nu(0))(AHB
) and (Delta nu/nu(0))(LAHB) appear to be linearly related. This regul
arity, generated by the three-body interaction in the L...A-H...B clus
ter, has previously been established experimentally. A factor of the l
inear dependence of the above-mentioned quantities (the ''cooperativit
y factor'') is proportional to the electric field strength of the cati
on charge at the position of the A atom. This is in accord with the ex
perimental data for a range of cations. One fitting parameter was used
to estimate the proportionality factor. The possibility of describing
cooperative effects in terms of an electrostatic model shows that the
se effects are not stipulated by electron delocalization in the hydrog
en-bonded systems, as postulated in some investigations. (C) 1997 Else
vier Science B.V.