f.7 chem d-block complex(10點)

1.
there're many factors, like affinity of copper(II) to different ligands.
but i think the major issue is that, the reaction is a step-wise reaction.
when a little ammonia is added, ammonia ionizes to give ammonium ion and hydroxide. though hydroxide may not be as conc. as ammonia, don't forget there's an equilibrium:
[Cu(OH2)6](2+) + 2OH(-) <====> Cu(OH)2 ↓ + 6H2O
[Cu(OH2)6](2+) + 4NH3 <====> [CuNH3)4](2+) + 6H2O

upper reaction removes copper(II) from solution. precipitation of copper(II) favors the upper reaction.

not until ammonia concentration rises, the Cu(OH)2 ppt. reacts with NH3 to give complex.
also, :NH3 has higher affinity toward Cu(2+)m compared to :OH2 , related to hard-soft acid-base principle.


2.
possible. if excess NH3 is added at once, intermediate step may be passes.


3.
one possibility is that Fe(II) has smaller affinity towards NH3 than Cu(II).
well, in my impression there's ion like [Fe(NH3)6](2+) & [Fe(NH3)6](3+) , but they're uncommon.


4.
one way is to look at the hybridization of empty orbitals.
if it's sp3, then it's tetrahedral;
if it's dsp2, then it's square planar.

how to look?
first, write the electronic configuration of the central atom - be aware of charge! look at the lowest vacant orbital.
like Cu(II), it's [Ar] 3d9 , so lowest vacant orbital is 4s. it'll undergo sp3-hybridization -- look at the Cu-complex above.
like Pt(II) in cisplatin, it's [Xe] 4f14 5d8 , so lowest is 5d. it'll undergo dsp2, yielding square planar structure.