Observation of 27Al n.m.r. paramagnetic shifts (large contact shift contributions) induced by lanthanoid shift-reagents in tris(acetylacetonato)aluminium(III)
Abstract
On the addition of tris(1,1,1,2,2,3,3-heptafluoro-7,7-dimethyloctane-4,6-dionato)LnIII[Ln(fod)3](Ln = La, Pr, Nd, Sm, and Eu) to a benzene solution of tris(acetylacetonato)AlIII[Al(acac)3], the 27Al resonance lines due to the free and the complexes Al(acac)3 have separately been observed at 25 °C; the chemical exchange is slow on the n.m.r. time scale and the separation of paramagnetic shifts into contact(cs) and pseudocontact(pcs) contributions implies a fairly large cs contribution and that the hyperfine splitting constant of the Al nucleus is positive.