Sextuple Bonds

[GreyDergal]

Well basicly i was on wikipedia and stumbled upon this http://en.wikipedia.org/wiki/Sextuple_bond .My only question is, are they real, and if so why do they work it sounds like way to many electrons to me.

[hypervalent_iodine]

Well I think the wiki article fairly much answered your question. Essentially, given enough electrons and low-lying (in terms of energy) orbitals, it is possible.

[mississippichem]

Well basicly i was on wikipedia and stumbled upon this http://en.wikipedia.org/wiki/Sextuple_bond .My only question is, are they real, and if so why do they work it sounds like way to many electrons to me.

 

It's just a rare case that a metal in at least a [imath]d^3[/imath] configuration has three non-bonding d-orbitals with the correct symmetry to get the multiple delta bonds. Usually, something called Jahn-Teller distortion prevents this from happening in already singly-bonded bimetallic species. These M-M multiple bonds are most common in second row d-block metals like Rhodium, ruthenium, osmium...you know, all the expensive ones.

 

You should have a look at "Wade's Rules" and the "isolobal principle" if you are really interested.

Edited February 19, 2011 by mississippichem

[John Cuthber]

What is the point of a vote?

They exist, or they don't. The vote will not change the fact, nor will it inform you of the bond order.

[Horza2002]

Well obviously yes they can exist...the Wiki article tells you that and give the references which describes the bonds. As it says in the article, these species are normaly observed at reduced temperature; they say dimolybdenum was observed at 7K (-264oC). They are just rare and difficult to observe is all. In chemistry, there are a lot of weird and wonderful molecules that only exist in extremly low temperatures or for the smallest amount of time.

 

Mississippichem, are they more common with the latter metals because the orbitals are bigger and just allow for a better overlap?

[mississippichem]

Mississippichem, are they more common with the latter metals because the orbitals are bigger and just allow for a better overlap?

Basically yes. The Jahn-Teller effect also becomes less pronounced as the ratio of metal ionic radius to dative bond length becomes smaller which kinetically speaking allows greater probability of a a gerad symmetric d-d overlap event [remember the analogous [imath]\pi[/imath] bonds have the opposite ungerad symmetry]. Breaking it down even further, the reduced Jahn-Teller effect ends up allowing a greater MO overlap integral.

 

These high order bond clusters are more thermodynamically stable than their observed temperature ranges would have one believe. The major "road-block" is in the kinetics of the formation of the bond.

 

Strongly [imath]\pi[/imath]-accepting ligands also serve to stabilize these species as the probability distribution of the electrons in the [imath]\delta[/imath]-orbitals becomes less concentrated and more "through-space" hyperconjugative geometry effects are allowed. This creates somewhat of a feedback loop that can serve to stabilize these high order bonds, albeit somewhat marginally.

[Horza2002]

Arr ok yes, that makes sence. It's been a while since I've thought about inorganic chemistry with MO theory (sorry Mississippichem I know its your baby!)