... DOI: 10.1039/B206782J (Paper) Dalton Trans., 2003, 153-159 Show Compounds ... 19,20,25,29 The pyridine compounds 5-Et and 5-Oct show ν PO bands at 1192 cm −1 and 1195 cm −1 and no adsorptions in the region 1250–1200 cm −1 . The 31 P{ 1 H} NMR spectra ...