Hi All,
I would need to analyse some complexes containing Co(II), Zn(II) and Ni(II) but I have been told that Cu source diffractometers would struggle to give meaningful information on these types of materials as they would not diffract very well. Do you confirm that? And, if you do, is there anything I could do to overcome this issue (other than changing the PXRD radiation source)?
Many thanks,
Antonio
Dear Henrik,
Many thanks for your reply.
Which energy levels would you use within the detector in order to eliminate/reduce the fluoresence?
Best regards,
Antonio
Hi Antonio,
as Henrik already mentioned the main issue with especially Fe/Co/Ni containing compounds measured by a Cu source is X-ray fluorescence which will cause a noisy pattern. Nevertheless, the amount of emitted radiation depends on the amount of TM atoms in your compound. For coordination compounds you usually have a lot of organic ligands surrounding some TM centers. Therefore, the fluorescence is less pronounced compared to e.g. pristine TM metal or oxides. Another approach to reduce the fluorescence is to use a thin PVC foil as a filter just placed in front of your detector (e.g. with scotch tape). The polymer contains Cl atoms which absorb most of the softer radiation coming from fluorescence while not affecting your Cu primary radiation too much.
I hope this will help a bit.
Best,
Simon
Henrik Lund , am using Bruker D2 with a Lynxeye detector.
Simon Welzmiller , thanks a lot for your exhaustive and helpful reply.
Hello Antonio,
Your advice as to the difficulties of using a copper tube are highly exaggerated. You can readily assess by calculating the mass attenuation coefficients (MACs) of the compounds of interest for Cu-Ka radiation and Co Ka-radiation.
For a copper tube, the Co complex will have an elevated MAC and therefore an enhanced background compared with the Ni complex. But the you will still get well defined XRD patterns for both complexes. Changing to a cobalt tube will reduce the background for the Co complex.
Overall then I would opt for a cobalt tube if there is a choice, but you can reasonably use a copper tube if that is used routinely in your lab.
Good luck.
Brian O'Connor
Unfortunately there is no simple band pass filter available in the x-ray regime in order to let only pass the Cu k-alpha radiation onto the XRD detector.
But there is a combination of filters, the so-called balanced filters or Ross-filter for setting up an effective bandpass filter via subtraction of filtered spectra or even filtered XRD pattern.
The application of a balanced filter set for the reduction of Fe, Co and Ni k-alpha radiation in XRD data is described in my answers of an RG question from some time ago:
https://www.researchgate.net/post/how_to_make_a_measurement_XRD_in_samples_containing_iron
Due to the non-perfect match of the filter transmission curves a complete cancellation of the unwanted fluorescent contributions is not possible, but you will get a very strong reduction.
You should try the 5,5µm Co and 5µmNi filter set.
Good luck
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