Salts of the cobalt(I) complexes [Co(CO)5]+ and [Co(CO)2(NO)(2)]+ and the Lewis acid-base adduct [Co2(CO)7CO--B(CF3)3].

The reaction of [Co(2)(CO)(8)] with (CF(3))(3)BCO in hexane leads to the Lewis acid-base adduct [Co(2)(CO)(7)CO--B(CF(3))(3)] in high yield. When the reaction is performed in anhydrous HF solution [Co(CO)(5)][(CF(3))(3)BF] is isolated. The product contains the first example of a homoleptic metal pentacarbonyl cation with 18 valence electrons and a trigonal-bipyramidal structure. Treatment of [Co(2)(CO)(8)] or [Co(CO)(3)NO] with NO(+) salts of weakly coordinating anions results in mixed crystals containing the [Co(CO)(5)](+)/[Co(CO)(2)(NO)(2)](+) ions or pure novel [Co(CO)(2)(NO)(2)](+) salts, respectively. This is a promising route to other new metal carbonyl nitrosyl cations or even homoleptic metal nitrosyl cations. All compounds were characterized by vibrational spectroscopy and by single-crystal X-ray diffraction.