Chemophiliac - 3-6-2007 at 16:14
does anyone have any info about the complexing of group 4 and group 5 elements? All I know is that Ti has a coordination number of 6. What are the
most common coordination numbers of these elements? I assume V is also most commonly 6?
Additionally, I'm just curious as well about the complexing of W and Mo, I know that Cr has coordination number 6 so I assume both are similar but I
know that Mo and W can both have more bonds.
12AX7 - 3-6-2007 at 16:38
I do know that Ti forms a strong, stable peroxo- complex. Dissolve titanium metal in sulfuric acid, giving a purple solution (Ti(3+) hydrato-, if I'm
not mistaken), then add peroxide, giving a bright red solution. Alternately, dissolve metal in hydrochloric (slow, if at all), giving a light purple
solution, and add peroxide.
Most form the usual complexes with lone pairs, like nitrogens, but getting them there may not be as easy. Titanium is oxygen-hungry. I do recall
tungsten makes an interesting "paddlewheel" complex, with four bipyridine units, a metal-metal quadruple bond, and two extra bonds allowing for redox
(sticking on chloride, say). It's got the lowest work function of anything, apparently...
Edit: hpp.
http://en.wikipedia.org/wiki/Di-tungsten_tetra%28hpp%29
Tim
[Edited on 6-3-2007 by 12AX7]
Pyridinium - 3-6-2007 at 20:16
Zr, Nb, and Ta form some complex anions with coordination number of 7, and also Ta forms one with coord. no. of 8. These are complexes with F, as far
as I know.
woelen - 3-6-2007 at 22:45
The second and third row elements have a much more limited aqueous chemistry in low oxidation states and their coordination chemistry is more
complicated. They hardly form simply aqua ions. They do form oxo-anions at high oxidation states (niobates, tungstates, molybdates) and at lower
oxidation states, polynuclear complexes can be formed with direct metal-metal links, but making such complexes usually requires rather special
conditions, such as special non-aqueous solvents, inert atmosphere and whatever other special things, which are not easily done at a simple (home)lab.
Pyridinium - 4-6-2007 at 12:19
The fluoro complexes of Ta, Nb, etc. require dissolving the oxides in concentrated HF, then adding extra NaF or KF, so they are definitely not a good
home chemistry project.
Dr. Beaker - 4-6-2007 at 13:17
This is such a wide subject...
Ti (IV) for example can be tetra coordinative (TiCl4, TiOMe4, TiCPCl2 and so on) and have a tetrahedral shape, it can also be pentacoordinative (like
in the anion TiCl5-) and offcourse octahedral.
The tri coordinative cation TiCp2Me+ is the active species in the homogenous ziegler nata olefin polymerization.
Chemophiliac - 5-6-2007 at 19:11
Hmm... very interesting. It sounds like the cordination chemistry of these elements can be quite complex, hence my confusion regarding which is the
most common coordination numbers of these elements. Where an element like Zinc, having a tetrahedral shaped 4-ccordinate system that dominates over
all other coordination numbers and complex shapes (4 coordinate tetrahedral is all I know of that Zinc has). So in this case, the nature of the
ligands and their ability to split the crystal field of the metal is extremely effective at changing the coordination numbers of these elements.