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Dative bond confusion (or coordinate bond)

  • Thread starter dilan
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I am a little confused with this. I know what a dative bond is, but the problem is when it comes to complex ions I do not understand.

ok now for example

[tex]NH_3[/tex] + [tex]H^+[/tex] = [tex]NH_4^+[/tex]

So in this the lone pair of NH3 will fill the s- subshell of H and make it stable,

but say in [tex]Cu^2^+[/tex]
when this attracts six water molecules with six lone pairs, where do these lone pairs go? I mean what subshell does it fill?


I really appreciate if you can help me with this.
Thanks alot
 
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Answers and Replies

chemisttree
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they are dumped into the LUMO.
 
They go into a higher energy orbital.

Its more advanced than it seems though, The different shells actually sorta combine in a way called hybridisation, these shells form a difinitive shape. The lone pairs partially go into these hybridisation shells.

i think someone else could probably describe it more correctly. i'm not too confidant on the subject myself.
 
When cu2+ is hydrated, the lone pairs of electrons present on the oxygen atom of water are 'donated' to the d-orbital of the copper 2+ ion. This is why copper can form complexes (thats what the species is called).

This species has a certain structure which depends on the type of ligand attacking (in this case water), the number of bonds formed, and where the lone pairs go. Here, the orbitals undergo dsp^3 hybridisation (that basically means the number of lone pairs present in the respective orbital: in this case, 1 in 3d, 1 in 4s, and 3 in 4p) to give the species trigonal bipyramidal geometry (a triangle with two bonds perpendicular to the plane sticking out of the center).

Look up werner's theory/ability of d-block metals to form complexes if you want more detail.

Another example of a complex is Tollen's reagent [Ag(NH3)4]+ which gives your famous silver mirror test for aldehydes.
 
chemisttree
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If the copper is hydrated with 6 molecules of water, it cannot adopt a trigonal bipyramid structure. Only 5 ligands are required for a trigonalbipyramid...
 

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