Re: complex ammonia

[Paul Sears <psears at nrn1_NRCan.gc.ca>]

> From: "Adam Shaw" <adams1 at comcen_com.au>
> Subject: Re: Complex Ammonia
> 
> Regarding complex ammonia, Paul said:
> >Ammonia can certainly be complexed, but I don't see how ammonium (NH4+)
> >can be complexed any further than it is - the H+ is complexing the
> >ammonia, and it has no further way of hanging on to anything else.
> 
> Well N can form more than 4 bonds - as you may know, complex structures
> form from coordinate covalent bonding and actually it is not uncommon to
> see it forming five bonds.

	I'll have to disagree with that.  One may see structures _drawn_
that show five (HNO3, for instance), but in fact there are only four
available orbitals (the 2s and 3 2p's), so one can only get four real
bonds, and certainly the N would be very hard put to bond to five other
atoms - no usable orbitals.

HNO3 is better written as H-O-N+=0
                              |
                              O-

There is a + on the N and a - on an O.  The nitrogen has its maximum
four bonds.  When it forms four, one of those is what is sometimes called
"co-ordinate covalent", in that both electrons in it come from the nitrogen,
instead of one from each atom in the bond.

I would be very interested to hear of an example with five.


-- 
Paul Sears        Ottawa, Canada