Designing Solid Materials from Their Solute State: A Shift in Paradigms toward a Holistic Approach in Functional Materials Chemistry

Non-classical notions consider formation pathways of crystalline materials where larger species than monomeric chemical constituents, i.e., ions or single molecules, play crucial roles, which are not covered by the classical theories dating back to the 1870s and 1920s. Providing an outline of non-classical nucleation, we demonstrate that prenucleation clusters (PNCs) can lie on alternative pathways to phase separation, where the very event of demixing is primarily based on not the sizes of the species forming, as in the classical view, but their dynamics. Rationalizing, on the other hand, that precursors that can be analytically detected in prenucleation stages and that play a role in phase separation must be considered PNCs and cannot be explained by classical notions, we outline a variety of systems where PNCs are important. Indeed, in recent years, with the advent of non-classical theories, a primary focus of research concentrated on the fundamental understanding of oligomeric/polymeric and particulate species involved in nucleation and crystallization processes, respectively. At the same time, the near-to unfathomable potential of non-classical routes for the synthesis of inorganic functional materials slowly unfolds. An overview of recent developments in the fundamental and mechanistic understanding of non-classical nucleation and crystallization in this Perspective then allows us to map out the potential of cluster/particle-driven mineralization pathways to intrinsically tailor the properties of inorganic functional (hybrid) materials via structuration from the nano-to the mesoscale. This is of utter importance for the functionality and performance of materials, as it may even confer emergent properties such as self-healing. Biominerals-often formed via particle accretion mechanisms-demonstrate this impressively and thus can serve as a further source of inspiration how to exploit nonclassical crystallization routes for syntheses of structured and functional materials. These new avenues to synthetic approaches may finally provide a holistic material concept, in which fundamental chemistry and materials science synergistically alloy.