uni question - nickel complex

Hi, for a group lab exp we had to make nickel complexes and I had to make [NiCl2(dppe)] which I think in long terms is NiCl2(Ph2PCH2CH2PPH2)

The overall eqn is NICl2.6H2O + dppe => NICl2(dppe) + 6H2O

In the write up it says I should be able to discuss the shape of the molecule, and factors that influece molecular shape. Now, any ideas what on earth is the shape of this molecule? I don't really know how to draw it properly. Also what factors do influence molecular shape? Maybe the number of ligands that can be removed?

Also, it asks me to relate the colour of the complex (orange) to the value of "m" which they say has been given to us. For some of the other complexes its given, values such as "2.91-3.41" but for mine it just has "0,". What does "m" stand for? what is it measuring? I saw someone had used some equation on this part, their complex was yellow so it absorbs at 420nm and they substituated it into some equation.

That seems like a load of waffle lol. Thanks for any help

Reply 1

cust

I have just finneshed a simmilar prac to do with NiBr2(PPh3)2 and NiBr2(PCy3)2, and the way we are supposed to discuss the structure is using spectra we took, for example we used a magnetic moments balance and that showed that the tri phenol complex was para magnetice and the only way it could be so using MO diagrams is tetrahedral. as the cyclohexanol complex was diamagnetic it is square planner then we took UV and IR spec, these showed that the sanple was trans square planner due to the bands observed.

As to the second question to do with the value C i am unable to help you sorry.

Reply 2

Kyri

That complex has a Ni 2+ metal which is a d8 configuration. d8 transition metals are very commonly square planar, which is consistent with a magnetic moment of 0 (I assume m is magentic moment). The magnetic moment of 0 is due to there being no unpaired electrons, which is a requirement to observed a magnetic momement. For the MO diagram for a square planar complex, look towards the bottom of this page http://en.wikipedia.org/wiki/Crystal_field_theory in case you don't already know it. All the energy levels will be filled except the top-most one (dx2-y2). The energy gap between the dxy and dx2-y2 orbitals is fairly large so for an electronic transition, a fairly high energy visible light wave would be absorbed. You observe an orange colour, so the wavelength absorbed is that of its complimentary colour: blue. As you know, blue is towards the UV direction of the visible light spectrum so is relatively higher in energy that most other colours.

I don't know for sure if this is right and I'm not sure what equation someone could have put a wavelength into. An equation that is relevant here is m = √n(n+2) where n is the number of unpaired electron. That gives you the spin-only value for the magentic moment. I'm just thinking out loud :biggrin: