REDOX-ACTIVE CROWN ETHERS - ELECTROCHEMICAL AND ELECTRON-PARAMAGNETIC RESONANCE STUDIES ON ALKALI-METAL COMPLEXES OF QUINONE CROWN ETHERS

Structural studies on [M(NCS).(5QC-HQDME)] (M = Li, Na) as well as free 6QC-HQDME and [M(NCS). (6QC-HQDME)] (M = Na, K) (where 5QC-HQDME is 15,17-dimethyl-16,18-dimethoxy-3,6,9,12-tetraoxabicyclo[12.3.1]octadeca(1,14,16)triene, and 6QC-HQDME is 15,17-dimethyl-16,18-dimethoxy-3,6,9,12,15-pentaoxabicyclo[15.3.1]heneico(1,14,16)triene) show that in all cases the metal ion binds to the anisole oxygen atom in the 1-position. Only in the case of [K(NCS).(6QC-HQDME)] do both benzylic O atoms bind to the metal ion; in the other complexes only one of these O atoms interacts with M+. In each complex all of the non-benzylic crown O atoms coordinate. These results indicate that the benzylic O atoms contribute suboptimally to complexation. Crystallographic data are as follows: [Li(NCS). (5QC-HQDME)], monoclinic, C19H28NO6SLi, space group P2(1)/n, a = 14.103 (4) angstrom, b = 8.493 (4) angstrom, c = 19.128 (8) angstrom, beta = 108.70 (9)-degrees, Z = 4; [Na(NCS).(5QC-HQDME)], monoclinic, C19H28NO6SNa, space group P2(1)/c, a = 10.182 (4) angstrom, b = 8.601 (1) angstrom, c = 25.631 (3) angstrom, beta = 97.29 (3)-degrees, Z = 4; 6QC-HQDME, orthohombic, C20H32O7, space group P2(1)2(1)2(1), a = 8.195 (1) angstrom, b = 11.541 (1) angstrom, c = 22.449 (3) angstrom, Z = 4; [Na(NCS).(6QC-HQDME)].MeCN, monoclinic, C23H35N2O7SNa, space group P2(1)/c, a = 11.308 (1) angstrom, b = 14.521 (2) angstrom, c = 16.440 (4) angstrom, beta = 91.56 (1)-degrees, Z = 4; [K(NCS).(6QC-HQDME)], monoclinic, C21H32NO7SK, space group P2(1)/c, a = 17.377 (3) angstrom, b = 10.600 (2) angstrom, c = 27.538 (7) angstrom, beta = 102.41 (3)-degrees, Z = 8. Electrochemical and EPR studies show that redox-active crown ethers incorporating quinone groups successfully couple ion binding by the crown ether to the redox state of the quinone group. Alkali metal ions cause potential shifts that establish-differential redox-induced complexation that qualitatively and quantitatively differs from ion-pairing effects. They also perturb the EPR hyperfine splittings in the semiquinone moieties in a characteristic fashion, as well as in one case giving rise to Na-23 superhyperfine splitting.