The chemical composition of the synthesized CoMo6S24@NU1K was further interrogated via X-ray photoelectron spectroscopy (XPS). The Mo 3d spectrum consists of peaks located at approximately 228.7 and 231.8 eV, which correspond to the 3d5/2 and 3d3/2 components, respectively, of Mo 4+ in CoMo6S24@NU1K (Figure ). A broad S 2s feature was observed near the Mo 3d5/2 peak, which indicates multiple chemical states of sulfur. For further analysis, we examined the S 2p region, which was fitted with two distinct doublets (2p3/2, 2p1/2) (Figure ): (1) one doublet at (162.3 eV, 163.5 eV), which arises from terminal SH -and S2 2-ligands, (2) one doublet at (163.6 eV, 164.8 eV), which reflects the presence of bridging S2 2-and apical S 2-ligands. The convolution of Co 2p XPS spectra features is displayed in Figure . A prominent pair of peaks at around 779.78 and 795.00 eV can be attributed to Co(II) 2p3/2 and 2p1/2 , respectively. Satellite shake-up peaks at 782.27 eV and 798.13 eV in the spectrum of the as-prepared catalyst confirm the presence of cobalt in oxidation state II. Synchrotron-based X-ray absorption spectroscopy (XAS) was used to characterize the local structure of CoMo6S24@NU1K. FT curves at the Mo K-edge (Figure ) are characterized by two main peaks at 2.42 Å and 2.76 Å, corresponding to the nearest Mo-S and Mo-Mo bonds. Quantitative FEFF fitting establishes the similarity of Mo local structure in CoMo6S24@NU1K to that found in 1T'-MoS2. Indeed, within the uncertainties of published crystal structures of 1T'-MoS2, XAS-derived bond lengths for the MOF-enshrouded PTM cluster agree with the former (Supplementary Table ). To assess the local chemical environment of the lone cobalt center, the XAS spectrum at the Co K-edge was measured. Quantitative fitting of the EXAFS spectrum (Figure ) reveals that the local structure of Co is similar to that of Mo, with a fitted Mo-S bond length of 2.42 Å in the Mo K-edge and Co-S bond length of 2.33 Å in the Co K-edge and, fitted Mo-S and Co-S coordination numbers of 6. These results together point to retention of Co, and little structural disruption in the molybdenum-rich host cluster following sulfidation (trans-chalcogenation). The corresponding FT curves are fitted via the ARTEMIS model to obtain the quantitative parameters of the local structure near the element Mo and Co. Fitting results are summarized in Supplementary Table . The pair distribution function (PDF) provides a histogram of all atom-atom distances within the material, weighted by their scattering power. The differential PDF (dPDF) obtained by subtracting the PDF for NU1K from that obtained of CoMo6O24@NU1K and CoMo6S24@NU1K, isolates the contribution from the guest cluster and its interaction with the MOF. The dPDF of CoMo6O24@NU1K is well fit by a structural model derived from the CoMo6O24 structure (Figure ). The a, b and c in the Figure correspond to the different Mo … Co/Mo distances of 3.3 Å, 5.7 Å and 6.6 Å of Figure . Table shows the one-to-one correspondence between the atomic pairs assigned to all peak positions in the PDF and that of the crystal structure. There is a slight shift of peaks in the experimental dPDF compared to the simulated model, which could potentially be associated with a distortion or relaxation of the cluster when confined in the c-pore. By comparison, the CoMo6S24 cluster is more disordered, with only a few well-defined peaks discernable at low r. From Figure , peaks at 2.42 Å, 2.75 Å and 3.36 Å are attributed to the nearest Co/Mo-S, the nearest Mo-Mo, and Mo--Mo pairs, respectively. Among these, the nearest Co/Mo-S, the nearest Mo-Mo bond lengths match well with above EXAFS fitting results.