Dative bond confusion (or coordinate bond)

[dilan]

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

NH_3 + H^+ = NH_4^+

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

but say in Cu^2^+
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

 

[chemisttree]

they are dumped into the LUMO.

 

[Nightsinger]

They go into a higher energy orbital.

Its more advanced than it seems though, The different shells actually sort of 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.

 

[chaoseverlasting]

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]

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...