Nitrilotriacetic acid

NTA, commonly known as nitrilotriacetic acid, is a complexing agent of the same general type as EDTA but possesses an insufficient number of coordinating groups to form all the bonds necessary to chelate transition metals such as Fe and Zn with a single molecule. Therefore, either more than a single NTA molecule is required to form the metal complex or the metal may form additional bonds with either water or hydroxide, both of which increase the tendency to permit formation of metal hydroxides as precipitates instead of metal complexes.


Highlighting Features

Show central Fe and its nearest neighbors: 2 amino N and 5 carboxylate O

This model shows the coordination of the central Fe atom with five carboxylate oxygens and two amino nitrogens as the apices of a pentagonal bipyramid, and one carboxylate group uncoordinated with Fe. Fe-O bond lengths range between 1.94 and 2.05Å and the Fe-N bond lengths vary between 2.32 and 2.42Å. The symmetry of the central Fe atom with its nearest neighbors is a key factors in stability. In spacefilling mode, this model show that the central Fe atom is nearly completely concealed by coordinating oxygens and nitrogens. No coordination by additional water (H2O) or hydroxide (OH-) is permitted in this structure, a situation which adds to the stability of this complex.

Amine groups [x2](N-R3)
Acetic acid [x6] (CH2COOH).

This model is based upon the xyz coordinates of non-hydrogen atoms in crystals of Na3[Fe(NTA)2]·5H2O determined by x-ray diffraction.

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W Clegg, AK Powell, and MJ Ware. 1984. Structure of trisodium bis(nitrilotriacetato)ferrate(III) pentahydrate, Na3[Fe{N(CH2CO2)3}2]*5H2O. Acta Cryst. C40:1822-1824.