Hapticity

In coordination chemistry, the hapticity of a ligand is understood to mean the number of ligand atoms (usually unsaturated carbon atoms) that are directly bound to the central atom of a complex . The indication of the hapticity provides information about the different binding states of a ligand when several atoms are available for binding.

Ligands that can contribute different numbers of atoms to the bond are, for example, unsaturated organic molecules such as allyl (C ₃ H ₅ ^- ), benzene (C ₆ H ₆ ) or cyclopentadienyl systems (C ₅ H ₅ ^- ).

The name is given by the letter η ⁿ (Greek eta ), which is placed in front of the name of the complex. The superscript n indicates the number of bound atoms. One reads η ⁿ as n-hapto (η ³ = trihapto , η ⁴ = tetrahapto , η ⁵ = pentahapto etc.).

The hapticity using the example of ferrocene :
[Fe (η ⁵ -C ₅ H ₅ ) ₂ ]
( bis (η ⁵ -cyclopentadienyl) iron )

The hapticity of ligands often changes with substitution or redox reactions :

Individual evidence

1. ↑ Gottfried Huttner: Molecular Structure of Bis (Hexamethylbenzene) -Ruthenium (0) . In: Angewandte Chemie, International Edition in English . 10, No. 8, 1971, pp. 556-557. doi : 10.1002 / anie.197105561 .