Reactions of di- and polynuclear complexes. 6. Reaction of [(.eta.5-C5H5)(CO)Fe{.mu.-C(CF3)=C(CF3)SMe}2Fe(CO)(.eta.5-C5H5)] with [Fe3(CO)12]. Ligand exchange between metals: synthesis and characterization of di- and trinuclear iron-alkyne complexes. Crystal structure of [{Fe(CO)3}2{.mu.-(CF3)CCC[Fe(.eta.5-C5H5)(CO)2]}]