Stabilization techniques for low-valent organometallic species in acidic forms of large-pore zeolite Y are reported. The intrazeolite surface chemistry and thermal stability of Mesub 3SnCo(CO)sub 4 in HY zeolites (Hsub 45Nasub 10Alsub 55Sisub 137Osub 384 and Hsub 16Nasub 39Alsub 55Sisub 137Osub 384) were studied with X-ray absorption spectroscopy (Sn, Co edge EXAFS) and in-situ FTIR/TPD-MS techniques. The acidic zeolite Y host offers a chemically reactive surface that can interact with the Mesub 3Sn moiety of the bimetallic complex. FTIR and EXAFS data indicate attachment of the complex to the zeolite framework. The intrazeolite SnCo complex is accessible toward carbonyl substitution with PMesub 3. One observes growing attachment of the precursor (progressive substitution of methyl ligands at tin) to the zeolite with increasing temperature, while the Sn-Co bond and the Co-carbonyl moiety remain stable up to about 90degreeC. At higher temperatures the Sn-Co bond is cleaved, the carbonyl ligands are dissociated, and cobalt is oxidized in a reaction with the zeolite protons. 25 refs., 13 figs., 1 tab.