CHEMISORPTION OF CARBON-MONOXIDE ON PLATINUM CLUSTER ANIONS

Reactions of platinum cluster anions with carbon monoxide are investig ated using a flow tube reactor (flowing afterglow) instrument. The pla tinum cluster anions are prepared with a cathodic discharge source. Th e cluster anions, Pt(n)-(n less-than-or-equal-to 7), react with carbon monoxide in a flowing helium/argon buffer gas at 0.5 Torr total press ure and at 3(K) K. Clusters with four or more platinum metal atoms rea ct by addition of CO with an effective bimolecular reaction rate of gr eater than 70% of the calculated collision rate, while for n = 3 the r eaction rate is 16% of the collision rate. At high CO concentrations, additional CO molecules attach to the clusters to form platinum carbon yl anion intermediates, with little loss of metal atoms. Saturation li mits were found, above which no further CO addition occurred. The satu rated cluster species are Pt3(CO)6-, Pt4(CO)8-, Pt5(CO)9-, and Pt6(CO) 10-. The application of simple geometry arguments and electron countin g rules to infer possible skeletal structures of the metal clusters is discussed.