engleski

Coordinational stereoisomerism in sodium complexes of D- and L- amino acid calix[4]arene derivatives

Sodium complexes of chiral calix[4]arene derivatives with four O-(N-acetyl-D-phenylglycylOMe) (1) and with four O-(N-acetyl-L-PhenylglycylOMe) (2) side arms were prepared, and their molecular and crystal structures were determined. The molecular assemblies of 1 and 2 in crystals are isostructural [sp. group: P4212, a = 15.005(1), c = 20.156(2) &Aring ; ; ] and in both structures only the upper part of the calix[4]arene molecule reveals crystallographic four-fold symmetry, whereas the terminal parts of the amino acid subunits disobey the four-fold symmetry and reveal significant structural disorder. The sodium cation occupies the lower rim cavity (Wyckoff position 2c), being indeed encapsulated by the four ether and four carbonyl oxygen atoms at the distances of 2.50 (1) and 2.44 (1) &Aring ; ; , respectively. The coordination polyhedron around Na+ is the regular square antiprism, having, nevertheless, the opposite helicity in two analogues which leads to two coordinational stereoisomers, clockwised ( ) and anti-clockwised ( ). Perchlorate anion, that neutralises the positive charge of sodium ion, is located at the Wyckoff position 4d of P4212. The molecules in the crystal structures of both 1 and 2 are arranged in head-to-head zig-zag layers running along the b axis.

nije evidentirano

nije evidentirano