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 103-104 L/mol cm. 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 104 to 105 L/mol cm. 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.