Coordination Chemistry and Complexes

anap40

The Question
a)If manganese reacts with CO and PH3 ligands to form a stable, tricarbonyl 5 coordinate complex, what manganese oxidation state and charge for the complex can be expected? Why?

b)If the complex is diamagnetic how is manganese hybridized and what is the geometry of the complex?

c)The stability of this complex should increase if PH3 Ligands are replaced with PF3 ligands. Why?


What I know

For part a the complex should be called tricarbonyldiphosphinemanganese(II?)
It is a Mn surrounded by 3 CO and 2 PH3 and the C's and P's are bonded to the Mn.

For Part A)
I think the oxidation state should be 2 but only because that is what Mn normally is.


For Part B)
My guess is sp3d hybridized with a trigonal bipyramidal shape.
I only say this because that is the shape and hybridization of a molcule w/ 5 atoms bonded to it. Is there anything different that needs to be done when considering coordination complexes?

For Part C)
I really don't know why PF3 ligands would make it more stable, my only guess would be that F is much more electronegative so would stabilize the electron density better.

Thanks for any help.

anap40

bump

chemisttree

It does say diamagnetic. All electrons are paired. Are all the electrons paired in Mn+2? Start by writing the electronic configuration for [tex]Mn^0[/tex]

Why would the electronegativity of F 'stabilize the electron density better'?

anap40

Ok I figured out part c.
It has to do with the F being more electronegative than H so on PF3 the electron density around P is lower which allows more back bonding to occur.

I am still not sure how to do part a, examples in the book that asked for oxidation state give the charge of the complex. If I can get the oxidation state in part a, I should be able to do part b.

Thanks.

chemisttree

Write out the electron configuration of [tex]Mn^0[/tex] and all of the known ions of Mn. Then put 2 electrons in the empty orbitals (from the ligands) and see which ion gives a completely electron-paired result.

anap40

Ok, but should I assume that for part a it is diamagnetic, because it adds that in part b.
Does being diamagnetic have any effect on stability?


Correct me if I am wrong on the following:
For Mn^0, isn't the e config [Ar]3d^5 4s^2 with all 5 of the d electrons unpaired?

Then for Mn^2+, the e config is [Ar] 3d^5 because the 4s electrons will be lost since they are at a higher quantum level. Again, all the d electrons are unpaired.

Then for Mn^7+, the e config is [Ar], so there are 5 empty d orbitals which can bond w/ the 5 ligands.(Does it matter that the 4s orbital is empty? I'm guessing it doesn't)


I appreciate the help.

chemisttree

You're getting there. If it were not diamagnetic, where would the 5 pairs of electrons go? What energy levels (orbitals) would they occupy if it were paramagnetic?