[Blooberfish]

Hi!

I am going to have a reexam in a 3rd year inorganic chemistry course in a couple of days. The question i failed on was regarding the TPA (Tris(2-pyridylmethyl)amine) ligand and the crystals it forms in the lab when using chlorides of V, Mn, Ni and Cu (specifically MCl_x, x=1, 2 or 3.)
The "hypothetical" situation was that some people had created the crystals, but had forgotten which metal chlorides were used. So, based on the structures given, overall complex charges and metrics shown, we should assign a metal ion to the 6 given structures, based on trends across the first row d-block elements.
(the full text is at the bottom of this post)


http://imgur.com/fKtTRWb

Can someone explain to me what these trends are and how to analyze this? I figured that the first structure must be vanadium, but this is only because it turned out to make a double-bond with oxygen when making
crystals of acetylacetone in the formula VO(acac)_2.

Thanks!


The full text of the task:

Imagine the following scenario for the class:
I gave some very precious tpa to the students and told them to make complexes of tpa using chlorides of V, Mn, Ni and Cu as starting materials. MCl_x, x=1, 2, 3.

The atomic arrangements we determined are shown below along with a few metics. When the complexes are charged, the charge is shown (but the counter ion not drawn). Atoms are CPK color coded (grey=C, white=H, blue=N, red=O, green=Cl, black=Unknown metal ion).

Everthing was looking rosy, but then to my chagrin, I discovered that apparently no-one had recorded which metal chloride they had used!

X-ray diffraction cannot tell us what the elements are, especially when they are close to each other on the periodic table. Thus on the basis of the structures, overall complex charges and metrics show, assign a metal ion (with oxidation state) on the basis of trends across the first row d-block elements. Write a balanced equation for the formation of the solid compounds (Hints: Include any possible counter anion in the formulation. It is not necessary to draw the structures, just write formulas. E.g. MCl₃, M(Cl₂)(tpa) = structure C)

Describe any measurements you think you could use to help confirm your assignment (i.e. do not list techniques randomly - rather mention a specific feature that you think would distinguish the compounds from each when using a particular technique).