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I have run a 1H-103Rh HMQC on [Rh(acac)(cod)] and found the chemical shift of the 103Rh to be -7023 ppm. The frequency of the 103Rh was first obtained by running a paropt on the "decp90" pulse program and changing O2 in order to decouple the 103Rh. When I found the frequency at which the 103Rh decouple, I used that value for O2 in the 2D 1H-103Rh HMQC. However, I am sure that this value of -7203 ppm is incorrect, since all the literature references to 103Rh NMR states that the chemical shift range for 103Rh is between -2000 and 10000 ppm. Also, [Rh(acac)(cod)] is given in literature as having a chemical shift of +1287 ppm. I know that the peak is not folded, since I acquired a spectrum with the exactly the same parameters, but with O2p at 1000 ppm, but then I don't see any 1H-103Rh correlation. I am obviously doing something wrong, but can't figure out what. Have anyone encountered this with any X nuclei? The data were acquired on our 600 MHz Bruker Avance II, using a 5 mm TBI 1H/31P/BB inverse probe. Any advice on the matter will be appreciated. |
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It could be a referencing issue. What is your SFO1 and SF (or SR) values that you areusing for 103Rh, and what is the exact frequency of 0 PPM (e.g. TMS) for proton on your system (should be something like 600.13 MHz, look at the SF value on a proton spectrum) -Kirk - Kirk Marat (Aug 01 '13 at 09:34)
Just checked my Avance III system. The reference point in the Bruker nucleus table for 103 Rh is Rh(AcAc)3 (The IUPAC reference). Some literature has 103Rh referenced to Rh metal at a "chi" value of 3.16 MHz. The scales differe by about 8000 ppm. - Kirk Marat (Aug 02 '13 at 14:55)
Thanks for the answer. The SFO1 values are 600.2827 (1H) and 18.9936 (103Rh) and the SF values are 600.2800 (1H) and 19.1276 (103Rh). If I want to reference to Rh metal, should I then change SF (103Rh) to (600.2800 * 3.16)/100 = 18.9688? - Linette Bennie (Aug 13 '13 at 05:29)