Spectra-structure correlations in solid metal saccharinates. I. The carbonyl stretchings

Results from literature survey of the infrared carbonyl stretching bands of 73 solid saccharinates, saccharin and the saccharinato nitranion (the latter in diluted DMSO solution) are presented. The CO frequencies are correlated with the C-O and metal-saccharinato distances and the respective formal bond orders. The present survey reveals that occasionally some v(CO) frequencies in the spectra of saccharinates may be higher than that of saccharin (1725 cm^-1) indicating existence of molecular saccharin in the respective structures. Due to intra- and intermolecular reasons, often the numbers of v(CO) bands and structural types of CO groups do not coincide. Presumably due to both vibrational and structural factors, saccharinato v(CO) frequencies are not advantageous for very accurate prediction of the C-O and metal-saccharinato distances. Nevertheless, they can be used as a qualitative criterion for evaluation of the degree of covalency of metal-saccharinato bonding as well as for very approximate estimation of the C-O distances and metal-saccharinato bond orders.