35Cl NMR of Metal-Organic Frameworks: What Can We Learn?

Metal-organic frameworks (MOFs) are a diverse class of hybrid organic-inorganic materials with a wide range of applications. Chlorine often plays a crucial role in MOF structures; the local environment about Cl significantly affects material properties and applications. It is shown that direct characterization of Cl local environments within MOFs using ³⁵Cl wideline solid-state NMR (SSNMR) provides unique insights into the local electronic and chemical structure, including the Cl bonding mode. ³⁵Cl SSNMR provides clear information regarding hydrogen bonding within MOFs and also yields direct evidence of phase transitions. There is a strong correlation linking ³⁵Cl quadrupolar interaction parameters to local bond lengths and angles. It is also shown that ³⁵Cl SSNMR of MOFs can be effective when paramagnetic centers are directly bound to Cl, greatly expanding the applicability of this approach. Density functional theory calculations of quadrupolar interaction parameters are in good agreement with experimental values, particularly when dispersion corrections are used for geometry optimization. This work highlights the broad potential of ³⁵Cl SSNMR for investigating MOFs and invites further applications in the field.