Again, a simple Czjzek line could, in principle, be utilized to approximate reproduce the spectral shapes (Figure ). However, since the Czjzek distribution is a model of maximum entropy, it does not allow for a refinement of structural parameters of the material. In order to correlate spectral lineshape and structural parameters, an extended Czjzek model which considers local, well-defined EFG parameters and a long-range Czjzek-type noise, has to be utilized. However, to build such a model, educated guesses of the EFG parameters for the local structures are required (vide infra).To supplement structural analysis by NMR, XANES was used to gain insights into the local structure of Ga@SiO2. The edge energy of around 10372 eV in the XANES spectrum is characteristic of tetracoordinate Ga species (see SI S8), while comparison of the corresponding molecular analogs shows in general, [4]-Ga sites generally possess very similar white line profiles (SI S8). Notably there is no evidence in XANES for [6]-Ga species that would be expected for domains of GaOx. Notably, there are no features observed at 10367 eV (characteristic of tri-coordinate Ga) for Ga@SiO2, indicating that tri-coordinate species are not present in appreciable concentrations in this material at room temperature. 13,17,18 In order to further probe experimentally how the interaction of probe molecules affect the spectroscopic signature of Ga sites in gallosilicate species, we next looked into a series of molecular analogs for surface sites. Well-defined molecular Ga siloxides coordinated with probe molecule were prepared from Ga(OSi(OtBu)3)3(THF) (1-THF, THF = tetrahydrofuran). Leveraging the weak interaction of Ga III and THF in 1-THF, it was possible to stoichiometrically exchange THF with TPPO or py, to generate the corresponding well-defined, crystalline molecular species that possess structures tangible with probe molecule adducts of Lewis acidic Ga-surface species (Figure ).Treatment of 1-THF with py (3.8 equiv.) results in the displacement of 1 equivalent of THF (Figure ). The product, Ga(OSi(OtBu)3)3(py) (1-py), was isolated in 71% yield.