METAL-BONDING VS HYDROGEN-BONDING COMPLEXATION IN ZINC-COMPLEXES OF 18-CROWN-6

Interdiffusion of solutions of zinc chloride in diethyl ether and 18-crown-6 in 1,2-dichloroethane affords a crystalline complex, [18-crown-6.ZnCl.H2O]+2[Zn2Cl6]2-. Single-crystal X-ray diffraction analysis(C24H52Cl8O14Zn4; triclinic; P1BAR; a = 7.659(3) angstrom, b = 11.696(6) angstrom, c = 13.190(4) angstrom, alpha = 105.23(3)degrees, beta = 106.52(3)degrees, gamma = 91.07(3)degrees; Z = 1) reveals the ZnCl(H2O)+ cation to be coordinated to three crown ether oxygens, providing a five-coordinate distorted trigonal bipyramidal zinc. The crown ether displays a near-D3d symmetric conformation in this complex. Recrystallization from carbon tetrachloride/acetone affords an extensively hydrolyzed product, [Zn(H2O)6]2+-[ZnCl3(H2O)]-2.2(18-crown-6).(CH3)2C=O, in which both the octahedral [Zn(H2O)6]2+ cation and the tetrahedral [ZnCl3(H2O)]- anion are bound to the 18-crown-6 through an extensive three-dimensional network of hydrogen bonds. The crown ether in this complex (C27H70Cl6O21Zn3; orthorhombic; P2(1)2(1)2; a = 14.735(7) angstrom, b = 16.800(3) angstrom, c = 10.194(2) angstrom; Z = 2) displays a severely distorted, asymmetric conformation, giving rise to solid-state chirality.