Preparation of high densitivity and resolution solid state NMR probe for transition metal nuclei

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There are many useful nuclei in low resonance frequency region. However, few studies of their solid state NMR spectra have been reported because of their low sensitivity. In order to overcome the difficulties in measurements of high resolution solid state MAS NMR spectra, We have prepared a high sensitive probe for nuclei having low resonance frequency (low-gamma) and half-integer spin. Especially, Ag-109 NMR probe is useful for material science of silver compounds. The important points to prepare the probe are as follows. (1) According to Hartman-Hahn condition, the CP time is much longer than that in usual C-13 experiments, 50-100 ms. In addition to this, the applied field is much stronger than that of C-13 case. Thus, the probe should work against high power for long time. (2) To fill larger amount of sample in a bullet sample tube, the coil diameter is enlarged. (3) The probe circuits are improved in response to the above conditions. On these basis we have prepared a probe and succeeded in measuring Ag-109 spectra of various silver compounds with high sensitivity. The CPMAS conditions was checked by using [Ag(2,9-phenanthroline)2]PF6. The plots of signal intensity vs. contact time were obtained for practical use. The maximum intensity was obtained at a contact time, t=50 ms.The spectra were measured for various Ag compounds from mononuclear to coordination polymers. We found that[Ag(dihydroxybenzoquinone dianion)]n is the best compound to obtain a strong signal within a short time due to its shortest distance of 109Ag...1H.In addition to the know-how for the measurements we have completed chemical shifts scheme depending on donor atoms of ligands. The shift ranges from 0 ppm to 1000 ppm. the origin of the chemical shift was also discussed by using linear type silver compounds of pyridine derivatives. The shift trend shows that sigma-andpi-mechanism are competing.