6213
J. Am. Chem. SOC.1987, 109, 6213-6215 Table I. 1:l Metal Complexation Constants (log K ) metal ion (ionic
diamtr. A) 2"vd 15-cr0wn-5~~~18-crown-6*f Mg2+(1.30) 3.3 3.1 noncomplxtn unreported 2.1 3.9 2.9 2.9 Ca2+(1.98) 2.6 >5.5 2.3 2.6 Sr2+(2.26) unreoorted 7.0 1.6 2.4 Ba2+ 12.70'1 , " K = [M2+-complex]/[M2+][H_lL] (M-I) in EtOH at 25 OC. Standard deviation is fO.l. b K = [M2+-L]/[M2+][L](M-l) in MeOH at 25 OC (Izatt, R. M.; Bradshaw, J. S.; Nielsen, S. A,; Lamb, J. D.; Christensen', J. J. Chem. Rev. 1985, 85, 271-339). cCavity size (1.4-2.0 A). dCavity size (1.8-2.2 A). eCavity size (1.7-2.2 A). fCavity size (2.6-3.2 A). ~
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trophotometrically),
