Can proton-shared or ion-pair N-H-N hydrogen bonds be produced in uncharged complexes? A systematic ab initio study of the structures and selected NMR and IR properties of complexes with N-H-N hydrogen bonds
Jss. Toh et al., Can proton-shared or ion-pair N-H-N hydrogen bonds be produced in uncharged complexes? A systematic ab initio study of the structures and selected NMR and IR properties of complexes with N-H-N hydrogen bonds, J PHYS CH A, 105(48), 2001, pp. 10906-10914
Ab initio calculations are carried out to investigate the effects of extern
al electric Fields and chemical substitution on the properties of complexes
stabilized by N-H-N hydrogen bonds. Two-dimensional MP2/aug'-cc-pVTZ poten
tial energy surfaces in the N-a-H and N-b-H coordinates are generated for C
NaH:NbCH in the presence of external electric fields, and equilibrium dista
nces and two-dimensional anharmonic dimer- and proton-stretching frequencie
s are obtained. The N-N spin-spin coupling constant across the N-H-N hydrog
en bond, and the chemical shift of the hydrogen-bonded proton are computed
for the equilibrium structure at each field strength. Substitutent effects
on the properties of complexes stabilized by N-H-N hydrogen bonds are also
examined in complexes with pyrrole and di-substituted pyrroles as proton do
nors and seven nitrogen bases as proton acceptors. Equilibrium structures,
binding energies, and harmonic frequencies and intensities for the proton-s
tretching vibration are computed at MP2/6-31+G(d,p), Examination of both fi
eld and substituent effects allows correlations to be established between s
tructures, hydrogen bond type, and proton-stretching frequencies. In the ca
se of CNaH:NbCH these correlations extend to the NMR properties of the hydr
ogen bond. Both approaches suggest that proton-shared and ion-pair N-H-N hy
drogen bonds are unlikely to form in neutral complexes.