[smurf88]

Hi.

I produced a nickel complex with a thiosemicarbazone ligand.
I wanted to use NMR for the analysis. But can we use NMR to characterize nickel complex?
Nickel is a d⁸

I heard that we can't do NMR for nickels. I read in journals that they do NMR for nickel complexes. I am confused.
Please help me.
Thanks in advance

[Grundalizer]

No idea, but I'd be interested.  I know NMR is good for organic compounds...but something like a metal complex would have "strange" (compared to C-H) bonding, so I don't know how well the NMR reading could be interpreted...but I'll be following this thread so I can figure it out.

[smurf88]

Hi 

For a nickel complex, I need to determine whether it's a paramagnetic or diamagnetic compound first before I can proceed to NMR.
In order to know,characterization using  magnetic susceptibility can determine whether it's diamagnetic or paramagnetic.
If the nickel compound is found to be paramagnetic,then we can't do NMR for the complex.
I'm not too sure actually .

 

[verpa]

Actually, it's quite possible to run NMR on paramagnetic compounds.  My grad project was making organometallic iron compounds....as you might guess, relatively few of them were diamagnetic.

(this mostly concerns 1H NMR)

Step 1.  Lower your expectations ... you most likely will not see splitting patterns, instead integration and a bit of educated guesswork will be your friends.  Understand the more unpaired elections, the worse your resolution.  You can still guess at basic symmetry: 'how many peaks do I have?' if not actual environment.

Step 2.  Expect a !large! ppm window.  Mine was usually -30 ppm - 80 ppm for all my peaks.  If you have NMR specialists running the machines, bring them a cup of a coffee and ask them nicely to help you find the right settings on your system to shim it properly with that large of a window.

Step 3.  Scan a book on NMR ... most graduate level ones will discuss the paramagnetic effect's influence on t1 and t2.  If you want I can dig out mine to recommend, but again, who's ever in charge of the NMR can help you out better.  Next, find and read about this topic:
Evans Method ( of determining magnetic susceptibility in liquids ) -
http://www.measurement.sk/2005/S3/DeBuysser.pdf - will get you started ( be sure to check out the JChemEd paper, dead simple example).  It's a large amount of high-school math, but once you get the hang of it, you can get your mu-b in a few minutes.

Happy to answer further questions, if I can remember the answers.

[ardbeg]

if your complex is square planar, then the d8 nickel will be low spin and diamagnetic (see crystal field theory).  if it is octahedral it will be high spin and paramagnetic, which will broaden your NMR and make it look like hell.  if there is any octahedral distortion of the square planar geometry it will start to look broad.  also, dont use a coordinating solvent like pyridine, dmf or dmso, which will coordinate to a square planar nickel centre and induce octahedral broadening.

[McCoy]

Actually, it's quite possible to run NMR on paramagnetic compounds.  My grad project was making organometallic iron compounds....as you might guess, relatively few of them were diamagnetic.

(this mostly concerns 1H NMR)

just for curiosity sake, how can one determine the nmr of a paramagnetic compound? I thought itt was impossible. I tried cu(II) aca and it didn't work;which is understandable.

[CuLater]

just for curiosity sake, how can one determine the nmr of a paramagnetic compound? I thought itt was impossible. I tried cu(II) aca and it didn't work;which is understandable.

It depend upon a few things.  The way I did paramagnetic NMR (on Mn and Cu complexes) worked well but you have to live with the limitations; you'll lose resolution and detail on your peaks.  Fortunately, you can take advantage of the paramagnetic properties as well, probably with the help of your local NMR guru.  The presence of a paramagnetic center will broaden your peaks, probably a LOT, but will also shorten your relaxation/recycle time in your experiment.  That means that you can set up your spectrometer for super-fast cycle times.  I would typically collect 10,000-100,000 scans in 5-10 minutes.  Someone else mentioned that you need to open your sweep window as well, something like +80ppm to -80ppm isn't unreasonable to start hunting for peaks, maybe even wider.  The peaks will be broad, so once you collect and process your data, expand the vertical scale until you see the noise in the baseline.  In the samples I ran, the few random peaks that were in the diamagnetic region were probably upwards of 100x the size of the paramagnetically shifted peaks.

Once you know how to set up your instrument, it's not that difficult to collect data.  Then you just have to interpret it.  Yikes.  Even if you don't record spectra of your samples, you can also use the Evans method to determine magnetic susceptibility with NMR.  That's a relatively easy and very interesting experiment.

Good luck and have fun.

[verpa]

Was just checking to see if you had any luck with your scans.

One other thing I don't think we mentioned above is that you probably need higher molarities than you are used in organic NMR.

Once in grad school I was talking to a theory guy and mentioned that I was waiting to collect data on my catalyst until I had made 4ish grams of it.  His response was "I didn't know we were doing industrial scale sythesis here!"

[guffer]

Sorry for digging up this old thread.  I'm trying to synthesize a nickel complex which is probably tetrahedral, but what if it's picking up 2 solvent molecules as ligands? Is there an easy way to tell if it's octahedral rather than tetrahedral?

if your complex is square planar, then the d8 nickel will be low spin and diamagnetic (see crystal field theory).  if it is octahedral it will be high spin and paramagnetic, which will broaden your NMR and make it look like hell.  if there is any octahedral distortion of the square planar geometry it will start to look broad.  also, dont use a coordinating solvent like pyridine, dmf or dmso, which will coordinate to a square planar nickel centre and induce octahedral broadening.