Negative-ion mass spectrometry of closo-carboranes

The negative-ion mass spectra of the small closo-carboranes, 1,5-C2B3H5, 1,2-C2B4H6, 1,6-C2B4H6, and 2,4-C2B5H7 exhibit much more intense P– 1 ions than parent ions, indicating the ease with which conjugate base anions of these cage compounds are formed. Ionization efficiency diagrams were gathered for the parent regions as well as for important fragments. These suggest that negative ions of closo-carboranes are formed with somewhat more difficulty than those of nido-carboranes which appears to reflect the lack of bridging hydrogen atoms in the former. Percentage compositions of carborane mixtures have been determined by use of a combination of mass-spectral patterns and energy-dependency information.