<p>Coordination materials are pivotal for advancing multidisciplinary science. Conventional synthetic methods, solid-, liquid-, and gas-phase, suffer from limited reactant scope and poor control over product formation, hindering fundamental research and applications. Here, we introduce a heterogeneous in situ approach using zero-valent metals as cation sources in water, combined with linker supersaturation. This enables universal, eco-friendly, and scalable synthesis of crystalline coordination materials. We demonstrate its power by solving the challenge of synthesizing titanium coordination compounds, previously inaccessible via conventional routes. The resulting titanium materials display diverse dimensionalities, structural variety, and broad functional-group tolerance, highlighting their promise for adsorptive separation. Notably, the method extends broadly across metals, including rare earths, transition and main-group metals. Thus, it establishes a general paradigm for heterogeneous in situ synthesis in coordination chemistry and enables energy-efficient production of advanced separation materials. Our work redefines coordination material synthesis and accelerates the development of inorganic–organic hybrid solids.</p>