Phosphorus-31 chemical shifts temperature effect

Solvent and temperature effects have been especially studied in simple compounds—white phosphorus,(1969 180) PH3, (1967>43> PFS, (1968,51) phosphorus acid, phosphines, phosphonium compounds etc. (1965> 39 1967,169 1968,155 1969,53) phosphorus chemical shifts or line-widths,... 

TCP, Ca3(PC>4)2, exists in two crystal forms, viz. a-TCP and p-TCP. Both forms can only be prepared by calcination at high temperature (>800 °C).70 a-TCP is meta stable at room temperature and is more soluble than p-TCP in water. The crystal structure of a-TCP shows that there are 16 inequivalent phosphorus sites.110 Its 31P MAS spectrum contains only 14 peaks, where the chemical shifts range from —3 to 5 ppm.111 Although there are only three crystallographically inequivalent phosphorus sites for (3-TCP,112,113 there are as many as 16 resolved peaks in the 31P MAS spectrum because of the presence of some calcium vacancies.114 The 31P chemical shifts of (S-TCP are in the same range as reported for a-TCP, but the overall patterns of their 31P MAS spectra are quite different. In addition, it has also been found that even a minor substitution of Ca2+ by Na+, Mg21 or Zn2+ ions will perturb the 31P MAS spectrum, revealing the substantial effect of the counter ions near the phosphorus sites.114,115... 

The cluster containing arsenic is more fluxional than the phosphorus one. At high temperature, the ° Rh NMR spectrum of [RhioAs(CO)22] displays a simple resonance at 5( Rh) = —972 ppm which corresponds to the mean value of the chemical shifts of the rigid structure corrected to account for a temperature effect of +0.6ppm/°C. 

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