Spectroscopic evidence for characteristic hydrogen bonding pattern in a system with pseudo-Jahn-Teller effect: the chromium(II) saccharinate hexahydrate

Abstract

A detailed Fourier-transform infrared spectroscopic study of protiated and series of deuterated analogues of chromium(II) saccharinate hexahydrate has been carried out. The spectral appearances in the regions of O–H and O–D stretching modes (particularly those corresponding to the isotopically isolated, i.e. uncoupled oscillators) strongly imply that the hydrogen bonding network in the studied compound is similar to that in the case of copper(II) saccharinate hexahydrate, which is somewhat different from the other members of the isomorphous series of metal(II) saccharinates hexahydrates. Therefore, a reinvestigation of the hydrogen bonding network structure in the title system by neutron diffraction technique is proposed. The similarity of the hydrogen bonding network in the mentioned two compounds is due to the presence of a Jahn–Teller active ion in both of them, which, in a non-ideal octahedral immediate surrounding leads to a second-order (or pseudo-) Jahn–Teller effect. This is clearly seen e.g. from the bond length distortion indices which are an order of magnitude higher in the chromium and copper compounds as compared to the other members of the isomorphous series, that do not contain a Jahn-Teller active ion. A very good correlation between the crystallographically determined proton donor – proton acceptor O···O distances and the experimentally measured O–D stretching frequencies of the corresponding uncoupled oscillators has been found in the studied compound. The derived correlation equation has an excellent predictive value within a rather wide range of distances/frequencies.