An overview about the recent key developments of borophosphate chemistry since 2007 is given. The structural chemistry (B:P ratio, fundamental building units (FBUs), dimensionality and metal coordination), possible physical, and optical and chemical properties are discussed in detail in terms of materials obtained by traditional solid-state reactions, flux methods, and hydrothermal and ionothermal reactions. Borophosphates (BPOs) exhibit a tremendous structural variety. Which structure is formed depends critically on the chosen starting materials and synthetic conditions. For example, for metalloborophosphates (MBPOs) changing the metal-precursor can result in the formation of a new BPO. MBPOs containing chains or extended networks of interconnected transition metal-oxide polyhedra exhibit remarkable magnetic coupling schemes and electronic behavior aside from interesting optical behavior and catalytic properties. The exploration of novel fundamental building units (FBUs), such as FBUs with P−O− P bonds and two-dimensional mixed-coordinated anionic partial structures, that have not been observed previously advocates the great potential in designing novel functional BPOs for advanced applications. While many BPOs initially obtained from conventional synthetic methods can be prepared by hydrothermal synthesis, it has recently been realized that BPOs obtained by ionothermal methods often could not be synthesized by conventional synthetic methods. Thus, novel synthetic approaches offer access to new materials.

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