Quantification of the trans influence in d⁸ square planar and d⁶ octahedral complexes: a database study

Abstract

A systematic search of the Cambridge structural database was undertaken to quantify the trans influence in square planar and octahedral transition metal compounds. For square planar geometry, d⁸ metal centers were studied, while octahedral searches focused on low-spin d⁶ complexes. Two probe ligands (PL) were used to measure the effect of the trans ligand (TL), chloride, and triphenylphosphine (PPh₃). For the TLs O=CX₂, NR₃, pyridine, and Cl⁻ (X = any non-metal, R = H or hydrocarbon), the effects on the metal–probe ligand (M–PL) distance were statistically equal and were taken as essentially no trans influence. The other ligands studied showed significant decrease in the mean M–PL bond order, relative to the above ligands: SR₂ = 0.941; S=CX₂ = 0.887; PPh₃ = 0.825; phenyl = 0.743; CR₃ = 0.719; hydride = 0.685. Some variation in the trans influence is observed, based on the geometry of the metal center and the PL. In general, electron-donating, σ-bonding ligands lead to a larger trans influence, but π-bonding effects can also be important, particularly when the probe ligand also has π-bonding properties.

Keywords:

• Trans effects
• Octahedral transition metal complexes
• Square planar transition metal complexes

Acknowledgments

The authors wish to thank Dr Carl LeBlond (Indiana University of PA) for supplying the initial idea for this project, and the University Senate Research Committee of Indiana University of PA, for financial support.