To determine which compound normally acts as a bidentate ligand in complexes with transition metal ions, we need to examine each of the options provided and understand what makes a ligand bidentate.
A bidentate ligand is one that can form two bonds with a metal ion. This typically means the ligand has two donor atoms that can each donate a lone pair of electrons to the metal ion.
Let's analyze each option:
A. Br
- Bromide ion (Br^-) is a monodentate ligand. It has only one lone pair on the single bromine atom to donate to a metal ion.
B. EDTA[tex]${ }^4$[/tex]
- EDTA (ethylenediaminetetraacetate) is a hexadentate ligand, not bidentate. It can form six bonds with a metal ion due to its multiple donor sites.
C. [tex]$C _2 O _4{ }^{2-}$[/tex]
- Oxalate ion (C2O4^2-) is a classic example of a bidentate ligand. It has two oxygen atoms that can each donate a pair of electrons, allowing it to form two bonds with a metal ion.
D. [tex]$NO _2{ }^{-}$[/tex]
- The nitrite ion (NO2^-) is generally a monodentate ligand. It can bind through one of its oxygen atoms or through the nitrogen, but it does not typically form two bonds simultaneously with a single metal ion.
E. Ethylene, [tex]$C _2 H _4$[/tex]
- Ethylene (C2H4) is not a ligand in the classical sense of coordinate bonding in coordination chemistry. It does not have lone pairs to donate but can interact with metal ions through π-complexes in organometallic chemistry. However, this is different from the typical coordination complexes discussed here.
Based on this analysis:
The correct answer is:
C. [tex]$C _2 O _4{ }^{2-}$[/tex]
Thus, oxalate ion (C2O4^2-) normally acts as a bidentate ligand in complexes with transition metal ions.
