Why NH2-NH2 in [co(Nh2-NH2)4Br2) is considered to be a single ligand, while as (en)2 in [co(en)2(h2o)(oNo)]^2+ is considered to be two?
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NH2-NH2 hydrazine behaves as a monodentate ligand with Co(III) and 4 hydrazine ligands are needed to form an octahedral complex
while ethylene diamine NH2−CH2−CH2−NH2 behaves a bidentate ligand and only 2 moles are needed to form a ring complex or chelate. octahedral complex.
Although hydrazine has 2 coordination sites with 2 nitrogen having lone pair but still it behaves as a monodentate ligand because both the N atoms are at a small distance apart and therefore the donation of lone pair is difficult because of the close proximity of the two lone pair there is repulsion and only one nitrogen forms a co-ordinate bond with the metal
In case of en the 2 co-ordination sites are separated by a carbon chain and so the molecule orients itself in such a way that both nitrogen are able to form a co-ordinate bond with Co ion. and thus only 2 molecules can form 4 bonds and the resulting structure is a chelate.
The structures of complex will help you understand better.
while ethylene diamine NH2−CH2−CH2−NH2 behaves a bidentate ligand and only 2 moles are needed to form a ring complex or chelate. octahedral complex.
Although hydrazine has 2 coordination sites with 2 nitrogen having lone pair but still it behaves as a monodentate ligand because both the N atoms are at a small distance apart and therefore the donation of lone pair is difficult because of the close proximity of the two lone pair there is repulsion and only one nitrogen forms a co-ordinate bond with the metal
In case of en the 2 co-ordination sites are separated by a carbon chain and so the molecule orients itself in such a way that both nitrogen are able to form a co-ordinate bond with Co ion. and thus only 2 molecules can form 4 bonds and the resulting structure is a chelate.
The structures of complex will help you understand better.
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