Chromium Environment within Cr-Doped Silico-Aluminophosphate Molecular Sieves from Spin Density Studies

X-/Q-band electron paramagnetic resonance (EPR) and hyperfine sublevel correlation (HYSCORE) spectroscopies have been employed, in conjunction with density functional theory (DFT) modeling, to determine the location of Cr⁵⁺ions in SAPO-5 zeotype materials. The interaction of the unpaired electron of the paramagnetic Cr⁵⁺ species with ²⁷Al could be resolved, allowing for the first detailed structural analysis of Cr⁵⁺ paramagnetic ions in SAPO materials. The interpretation of the experimental results is corroborated by DFT modeling, which affords a microscopic description of the system investigated. The EPR-active species is found to be consistent with isolated Cr⁵⁺ species isomorphously substituted in the framework at P⁵⁺ sites.