Synthesis and Characterization of Molybdenum Carbide Clusters Mo n C 4 n , ( n = 1 to 4)

Laser radiation (XeCl laser, 308-nanometer wavelength) focused into a cell containing Mo(CO) 6 vapor produced ultrafine particles in the extended waist of the laser beam. Negative ion mass spectrometry revealed molybdenum carbide cluster ions with a stoichiometry Mo n C 4 n ( n = 1 to 4). The Mo n C 4 n – ( n = 2 to 4) ions are completely unreactive with NH 3 , H 2 O, and O 2 , suggesting structures in which the molybdenum atoms are unavailable for coordination to additional ligands. Collision-induced dissociation studies of these anions show the loss of MoC 4 units as the main fragmentation pathway. This observation, together with the lack of addition reactions, provides a basis for structures in which a planar cluster of two, three, or four molybdenum atoms is surrounded by, and bonded to, carbon dimers.