Metal-ion Complexation of Noncyclic Poly(oxyethylene) Derivatives. Complexation in Aprotic Solvent and Isolation of Their Solid Complexes

The interaction of homogeneous polyethylene glycol(PEG) (EOn, n=1–8) with the alkali and magnesium metal cations and the ammonium cation was investigated on the basis of 1H NMR(PMR) downfield shifts in acetone-d6 or in acetonitrile-d3 The specific complexations of EO4 with Mg2+, EO6 with Na+ and Ca2+, and EO7 with K+ were demonstrated by PMR studies, and their solid complexes were isolated. No specific interaction was detected for Rb+ and Cs+ in PMR studies. The magnesium ion interacts strongly with 15-crown-5, 18-crown-6, and PEG in acetone, and the Mg(SCN)2-EO4 and the Mg(SCN)2-above crown ether complexes were isolated. The terminal hydroxyl groups of PEG play an important role in the complexation with Li+ and Mg2+ in acetone. The formation of the 1 : 1 complex with Ca(SCN)2 was observed both for EO6 and for EO7. Strontium and barium thiocyanates formed solid complexes with PEG(EOn, n=2–8) and with glymes(tri- to octaglyme). Some novel complexes of 12-crown-4 and 15-crown-5 with NaSCN and Ca(SCN)2 were also isolated . The mechanism of metal-ion complexation of poly(oxyethylene) derivatives is discussed in terms of the coordination geometry.