Optical spectra of anionic boron cluster compounds and their utilization for photometric detection.

The article presents first collection of UV-vis absorption spectra of purely synthetic boron cluster compounds. Single-cage compounds have at least 11 cluster atoms; cobaltadicarboranes consists of 2 substituted 11-vertex bis(dicarbollide) clusters sandwiching the central cobalt atom. Spectrum of any of 18 investigated compounds has absorption maximum between 200 and 210 nm; its molar extinction coefficient is of the order of 10(3)-10(4)L/molcm. Second maximum exists in a spectrum of a single-cage compound if its exo-skeletal substituent absorbs UV-light above 200 nm. Spectra of cobaltadicarbaboranes both bridged and unbridged have pronounced second maxima between 270 and 300 nm. Their molar extinction coefficients range from 10(4) to 10(5)L/molcm. First light absorption minimum is close to 254 nm in spectra with two and more absorption maxima. Several correlations are derived between structure of investigated compounds and their UV-vis absorption spectra.