Molecular Co-Ru bimetallic carbonyl clusters, [HCoRu3(CO)(13)]/NaY, were synthesized by reductive carbonylation of Ru-3(CO)(12)/NaY and Co-2(O)(8) under CO/H-2 atmosphere. The clusters and their reversible decarbonylation were characterized by infrared spectroscopy. The data confirm the presence of intermediates in the reversible formation of bimetallic carbonyl clusters. This provides further indication of the potential for zeolite cages as microreactors for chemical synthesis.