Compositional Analysis of Metal(IV) Phosphate and Phosphonate Materials—Pitfalls and Best Practices

Metal(IV) phosphate and phosphonates materials have increasingly found their applications in water purification, heterogeneous catalysis, drug delivery, and proton-exchange membrane fuel cells. The strong linkage between tetravalent metal cations and phosphate/phosphonate groups offers a unique bottom-up design platform, resulting in chemically stable inorganics or hybrids. Task-specific physiochemical functionalities could be deposited by modifying the phosphate/phosphonate groups before the material synthesis. The high reactivity between the metal centre and the phosphorus-containing linker, on the other hand, often leads to obtaining unordered materials (amorphous solids or coordination polymers). The chemical composition of the prepared materials is a key parameter in guiding the synthetic approach and in governing their performances. This narrative review focuses on critically summarising the traditional and advanced analytical methods for probing the composition of these materials. The reader is introduced to and guided on the advances and restrictions of different analysis techniques when probing metal(IV) phosphates/phosphonates. Both solution-based and solid-state spectroscopic techniques are covered with a focus on understanding the quantity and the linkage status of the phosphorus-containing moieties. These techniques include atomic spectroscopy, mass spectroscopy, nuclear magnetic resonance spectroscopy, X-ray-based methods, and neutron activation analysis.