Hierarchical Hybrid Assembly: Programming Structural Complexity in Crystalline Materials

The design of crystalline materials has evolved from the construction of periodic frameworks toward increasingly complex architectures featuring ordered heterogeneity and emergent functions. Despite substantial progress in hybrid crystalline materials, a general framework for understanding hybrid assembly across different levels of structural organization is still lacking. Here, we introduce hierarchical hybrid assembly (HHA) as a strategy for integrating chemically distinct interactions or components while preserving long-range crystallographic order. At the interaction level, HHA integrates multiple interactions cooperatively within a single crystallographically ordered framework, whereas at the component level, HHA organizes chemically or structurally distinct components in a deterministic manner within a coherent crystalline architecture. Representative examples show how these two modes generate ordered structural complexity beyond statistical compositional mixing or weak interfacial coupling. We further identify interaction compatibility, crystallographic organization, and assembly pathway control as design principles for crystallographically defined complexity. Finally, we discuss the key challenges and future directions for advancing HHA toward broader structural diversity and complexity, predictive synthesis, and function-oriented materials design.