Silver has two spin
I = 1/2 isotopes (
109Ag and
107Ag) with natural abundances of 48.18% and 51.82%, respectively. Although
109Ag has a lower natural abundance, it is the preferred isotope to observe as its gyromagnetic ratio is slightly higher than that of
107Ag. Direct observation of
109Ag is problematic in that the Larmor frequency is low, the NOE's to protons are negative and most importantly, the T
1's are very long (minutes to hours). In some silver phosphine complexes with
109Ag -
31P coupling, the problems of observing silver directly can be circumvented by using indirect detection via a
31P detected
31P -
109Ag HMQC. The advantages of using this approach are that the directly observed
31P frequency is 8.7 times higher than that of
109Ag and the relaxation delay in the experiment depends on the
31P T
1's which tend to be orders of magnitude shorter than those of
109Ag.
Below is an example of a
31P detected
31P -
109Ag HMQC for a silver phosphine complex. These data were acquired without
109Ag decoupling. In the
31P trace on the top of the spectrum one can see a single
31P resonance with coupling to both
109Ag and
107Ag. The
109Ag is indirectly observed in the F1 domain.
4 comments:
Glenn, do you have some more information on the Ag-P complex? Maybe a pointer to the crystal structure, or paper describing the compound?
Egon,
I ran this spectrum for a researcher here at the University of Ottawa. I left out any details of the specific complex from the BLOG entry as it is part of some work that is as yet unpublished. However, you can find more info about similar complexes from the following paper.
JACS Vol 124, pp 3946-3950 (2002).
cheers,
Glenn
Glenn, out of curiousity, what kind of probe did you use to acquire this spectrum?
Mike
Mike,
This spectrum was acquired on a 3 channel Bruker AVANCE 500 with a triple resonance 5 mm probe. The probe has one broadband channel, a fixed 31P channel and a proton channel. Although the very large 31P coil was meant for decoupling, it was used to observe 31P here.
cheers,
Glenn
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