monometallic

Monometallic refers to substances consisting of a single metallic element at the active site or as the sole metal in the structure. In coordination chemistry, a monometallic complex contains one metal atom coordinated to ligands. In materials science and catalysis, the term is used for monometallic catalysts and monometallic nanoparticles or single-atom catalysts, where all metal atoms are the same element.

Monometallic catalysts can be homogeneous (soluble molecular complexes) or heterogeneous (solid-supported metal species). Examples include many Rh, Pd, Ni, and Pt complexes used for hydrogenation, hydroformylation, and cross-coupling. Wilkinson's catalyst (RhCl(PPh3)3) is a classical monometallic homogeneous catalyst with a single Rh center. In heterogeneous catalysis, monometallic catalysts include metal nanoparticles of a single element on supports, or single-atom catalysts where isolated metal atoms are anchored on a substrate.

Advantages of monometallic systems include well-defined active sites, easier spectroscopic characterization, and predictable stoichiometry. Limitations can include a lack of synergistic effects seen in bimetallic or multimetallic systems, which can limit activity or selectivity in some reactions. They may also be more susceptible to poisoning or deactivation depending on the metal and support.

In practice, the term monometallic is used to distinguish single-metal-site systems from polynuclear, bimetallic, or multicentered catalysts. The concept spans both molecular chemistry and solid-state materials, reflecting structural simplicity alongside potential trade-offs in catalytic performance.