Wide line N.M.R. study of the proton hydrates in crystallized salts : III- di-aquooxonium ion

Abstract Wide line N.M.R. spectra have been recorded from 90 °K to room temperature for the four H 7 O 3 + salts: H 7 O 3 + C 6 H 3 Cl 2 SO 3 − ; H 7 O 3 + C 6 H 5 SO 3 − . H 7 O 3 + NO 3 − and H 7 O 3 + ClO 4 − . O-H versus O…O distances are obtained for the rigid lattice by an homogeneous method involving the use of a limiting diagram in the space (d OH )= f(d OO ). This diagram is discussed. In the three cases ( C 6 H 3 Cl 2 SO 3 − ; NO 3 − and ClO 4 − ) external hydrogen bonds appear as bent. The “homogeneous” d OH = g(d OO ) correlation curves are respectively near the lower limiting curve, the Ichikawa curve and the upper curve. This can be correlated with the number of four coordinated oxygen atoms in the structures. The motions are interpreted via a general H 7 O 3 + model: terminal H 2 O motions are sufficient to break the nitrate and perchlorate lattices (fusion). On an other hand the motions in the dichlorobenzene sulfonate undergo probably from this initial reorientation to a quasi-isotropic one as temperature increases. Activation energies point out the lowering of the H 7 O 3 + rigidity in the order NO 3 − > ClO 4 − > C 6 H 3 Cl 2 SO 3 − > C 6 H 5 SO 3 − . They correlate well with the mean external hydrogen bonds distances. At the beginning some topological aspects of (H 7 O 3 + ) x are presented.