A STRUCTURAL STUDY OF (DIBENZYLDIAZA-18-CROWN-6) LANTHANUM(III) THIOCYANATE

The structure of the complex La(NCS)(3)C26H38N2O4 (1) was determined b y single-crystal X-ray diffraction and the structure of the coordinati ng ligand, C26H38N2O4 (2), was studied by the semi-empirical PM3 metho d. The bonding around La consists of a primary coordination of three t hiocyanate N atoms and a secondary coordination of two N atoms and fou r O atoms of the macrocycle. The primary coordination about La gives a n almost planar trigonal configuration that bisects the plane of the m acrocycle with La lying in the centre of the macrocycle cavity. The be nzyl groups that are attached to the macrocycle are in syn conformatio n with respect to the macrocycle plane with one of the La-NCS bonds po inting above the plane and the other two La-NCS bonds pointing below t he plane in the direction of the benzyl groups. The PM3 calculation sh ows that the optimised diazacrown has an open structure of a pseudo D- 2d symmetry with the two benzyl side-arms positioned away from the cav ity. (C) 1997 Elsevier Science B.V.