The synthesis of intra-Na56Y zeolite anchoring of [Rh-6(CO)(12)(mu (3)-CO)(4)] involves the deposition of [Rh(CO)(2)Cl](2) vapor into the Na56Y cavities followed by reductive carbonylation under a mixed CO and H2O atmosphere. The physicochemical characterization was based on a multianalytical approach, including Fourier transform infrared and Na-23 double rotation (DOR) nuclear magnetic resonance (NMR) spectroscopies and CO gas chemisorption. The decarbonylated species of the intrazeolitic [Rh-6(CO)(12)(mu (3)-CO)(4)] is proposed to contain a Rh-4 cluster, which reacts with CO at low temperature, generating [Rh-4(CO)(9)(mu (2)-CO)(3)] clusters, and with CO and H2O at high temperature to form [Rh-6(CO)(12)(mu (3)-CO)(4)] clusters. Na-23 DOR NMR signal shifts of the site II Na+ cations in the Na56Y supercages and infrared band shifts of bridging CO Ligands in the [Rh-6(CO)(12)-(mu (3)-CO)(4)]-Na56Y provide complementary evidence for the anchoring of [Rh-6(CO)(12)(mu (3)-CO)(4)] inside the supercages. These patterns suggest that a strong interaction occurs between the oxygen end of face-bridging CO ligands and the site II Na+ supercage cations.