May 28, 2023, 12:29:04 PM
Forum Rules: Read This Before Posting

Topic: M(acac)n Coordination Chemistry  (Read 15064 times)

0 Members and 1 Guest are viewing this topic.

Offline zeoblade

  • Regular Member
  • ***
  • Posts: 88
  • Mole Snacks: +1/-0
M(acac)n Coordination Chemistry
« on: October 17, 2009, 05:10:57 AM »
I have Cu(NO3)2.2H2O and acetylacetone to get me Cu(acac)2.

To balance this reaction: Cu(NO3)2 aq + 2C5H8O2 --> Cu(C5H7O2)2 + 2HNO3 aq seems to be correct, but could someone verify for me, please? With Cu(NO3)2.2H2O, I can leave out the dihydrate, right?

In another reaction Fe(NO3)3.6H2O, acetylacetone, but with NaHCO3 giving Fe(acac)3.

To balance this reaction: Fe(NO3)3 + 3C5H8O2 + 3NaHCO3 --> Fe(C5H7O2)3 + 3HNO3 + 3NaHCO3.

I feel the NaHCO3 is just facilitating the dehydrogenation of acetylacetone and can be left out of the equation since it's equally present on both sides, right? Similarly, I can leave out the hexahydrate from the balanced equation, right?

Last reaction I have MnCl2.4H2O and acetylacetonate but CH3COONa and KMnO4 giving Mn(acac)3.

To balance this equation is slightly different because I feel KMnO4 is also a source of Mn to make Mn(acac)3 but I don't know which is the primary source and which is secondary. The CH3COONa is like the NaHCO3 in the 2nd reaction to facilitate dehydrogenation of acetylacetone, right? Leaving out the tetrahydrate of the MnCl2, would I be allowed to balance this reaction like below:

4MnCl2 aq + KMnO4 aq + 15C5H8O2 + CH3COONa --> 5Mn(C5H7O2)3 + 7HClaq + KClaq + 4H2O + CH3COONa

I hope the hours I've spent trying to figure this out have been worthwhile, please do critique.

I'm trying to figure out the 'mode of coordination' of acetylacetonate anion and the vital structural differences in bond length and angle. The acetylacetonate anion seems to exist in three forms with resonating charge over the two oxygens and central carbon. Therefore, can I say C1 and C5 are tetrahedral in geometry 109.5o C2 to C4 are planar trigonal 120o? Or when there is a charge on the central carbon, there is an octet of electrons which makes that tetrahedral in geometry? Similarly when the charge resonates between the oxygens and carbon, wherever the charge is, makes that atom tetrahedral and the other two are trigonal planar?

I'm also wondering about acetylacetone, I've seen this term called tautomerism where one of the hydrogens of the central atoms becomes bonded to both oxygens leaving a double bond between one of the oxygens and the central carbon. In this case C1 and C5 are still tetrahedral geometry, C2 to C4 and the carbonyl bonded to the hydrogen are trigonal planar geometry, but what about the other C-O? What angle would that be?

Also is there some website where you can model and figure out the bond lengths of acetylacetone and acetylacetonate anion? I've no idea what specific lengths they are and need to find out how these structural differences would be reflected in their IR spectra.

Cu(acac)2 I expect to be square planar in geometry and no chirality because its square planar bidentate ligand but for Fe(acac)3 and Mn(acac)3 I would expect delta and lambda chirality. So, in synthesizing Fe(acac)3 and Mn(acac)3, would I expect equimolar racemic mixture so that it would not rotate plane polarised light because delta and lambda would cancel each other out?

I really feel this is very interesting kind of chemistry

Offline zeoblade

  • Regular Member
  • ***
  • Posts: 88
  • Mole Snacks: +1/-0
Re: M(acac)n Coordination Chemistry
« Reply #1 on: October 17, 2009, 07:12:19 AM »
I noticed quite distinct colours for some of them; the Cu(acac)2 appeared a strong blue with a little violet, the Fe(acac)3 appeared strong red, Mn(acac)3 appeared very dark. Now looking at the UV spectrum of this I can see why Cu(acac)2 is blue-violet, Cu(acac)2 seems to have strongest transmittance from 430-510nm but slightly weaker transmittance (still strong) all the way up to 720nm. Due to the transmittance across the spectrum and peaking around 430-510nm, that is to say it is the reason for the blue-violet colour of Cu(acac)2, right? I would have thought it would be more purple because its about 80-80% transmittance around the red region.

Similarly, Fe(acac)3 shows strong transmittance from 550nm upwards and peak absorbance around 430nm so I'm quite clear about why Fe(acac)3 is strongly red.

But Mn(acac)3 I'm wondering if my guess is correct or not. From 400nm there is a steeper gradient that absorbs plateauxs as it approaches 700nm where there is minimal absorbance/maximum transmittance. Now the Mn(acac)3 appeared VERY dark violet, almost black. Can I say that because there is a broad region of transmittance. Now if there is a broad range of transmittance, why is the Mn(acac)3 appearing so dark? I thought the more black something is, the more wavelengths it is absorbing at?

Sponsored Links