Starkfältligander

Starkfältligander is a term used in coordination chemistry to describe ligands that produce large crystal field splitting in transition-metal complexes. The name appears in some Nordic and German-language literature; in many English texts the concept is referred to as strong-field ligands. Starkfältligander promote high ligand-field effects and can favor low-spin states in appropriate geometries.

In octahedral or related coordination environments, strong-field ligands increase the energy gap Δo between the t2g and eg sets of d orbitals. This larger splitting stabilizes paired electrons in the t2g set, often yielding low-spin configurations and altering the complex’s magnetic and spectroscopic properties. The increased splitting also shifts electronic transitions to higher energies, influencing color and UV-Vis spectra.

Common Starkfältligander include cyanide (CN-), carbon monoxide (CO), nitrosyl (NO+), and certain phosphines and chelating amines under suitable conditions. The precise ranking of ligand-field strength is captured by the spectrochemical series, with strong-field ligands occupying the high-energy end. Δo and related parameters are typically determined from UV-Vis spectroscopy and ligand-field theory or Tanabe-Sugano analyses.

Applications and significance: Starkfältligander allow fine control of spin state and reactivity in catalysis, electronic materials, and spin-crossover systems. They stabilize low-spin configurations, influence magnetic behavior, and enable selective transformations in transition-metal chemistry. Safety considerations include the toxicity of some ligands (for example cyanide) and hazards associated with carbon monoxide and certain nitrosyl species.