Metalligand

Metalligand, also written metalloligand or metallo-ligand, is a ligand that contains a metal atom as an integral part of its structure and can coordinate to a metal center other than the one in its own moiety. This concept is used to build heterometallic complexes and supramolecular assemblies such as coordination polymers and metal-organic frameworks. Metalligands differ from conventional organic ligands because the embedded metal can participate in redox chemistry or influence the donor properties of the ligand.

Most metalligands are multidentate and designed to bridge two or more metal centers. They may coordinate through conventional donor atoms (N, O, S) on the ligand framework, or use the metal center itself as a coordination site. The choice of metals, oxidation states, and geometry governs assembly, electronic communication, and catalytic activity. Metalligands can be rigid to maintain predefined geometries or flexible to accommodate different metals.

Synthesis involves either functionalizing a preformed metal complex with additional chelating groups or coordinating a metal-containing fragment to a secondary binding site. In some strategies, two metalligand units self-assemble with other metal precursors to form discrete heterometallic complexes or extended networks.

Applications include heterometallic catalysis, cooperative redox processes, magnetic and luminescent materials, and porous solids such as MOFs and coordination polymers. The approach enables tuning of properties by combining different metal centers within a single framework or molecule.

Examples include metalloligands based on ruthenium, zinc, copper, or lanthanide centers bearing ancillary donor groups that bind to a second metal, or porphyrin- or terpyridine-based fragments designed to coordinate another metal ion.