Transition metal complexes with macrocyclic oxathiaethers

Complexation studies with Ni(II), Co(III), Co(II), Cd(II), and Cu(II) for t he two mixed oxathia crown ligands 1-oxa-4,7-dithiacyclononane (9S(2)O) and 1,10-dioxa-4,7,13,16-tetrathiacyclooctadecane (18S(4)O(2)) are reported. T hese ten complexes have been characterized by a variety of means including electronic spectroscopy, cyclic voltammetry, and nuclear magnetic resonance spectroscopy. Furthermore, the complexes [Ni(18S(4)O(2)](BF4)(2), [Cu(9S(2 )O(2)])(BF4)(2) and [Ni(9S(2)O)(2)](ClO4)(2), have been characterized by si ngle crystal X-ray diffraction. For the complex [Ni(18S(4)O(2)](BF4)(2) the diastereoisomer obtained is the one which contains the two oxygen atoms tr ans to each other and a meridional positioning of the diethylene S-O-S moie ty. Selectivity for this particular stereoisomer is also supported by NMR d ata for the Cd(II) and Co(III) complexes, and this selectivity arises from the conformational preferences of the individual C-O and C-S bonds in the m acrocycle. Both the nickel-sulfur and nickel-oxygen bonds in the complex ar e highly compressed due to the rigid macrocyclic structure and are among th e shortest of these types of bonds found in any crown Ni(II) complex. The c opper(II) complex, [Cu(9S(2)O)(2)](BF4)(2), shows an interesting Jahn-Telle r distortion from an octahedral geometry resulting in coordinate bonds whic h are all remarkably similar in length (CuS(4) 2.3293(6); Cu-S(7) 2.3336(6) ; and Cu-O(1) 2.355(2) Angstrom). The oxygen atoms are found in a trans pos ition around the copper(II) center, and the axial Cu-O bonds are elongated due to the Jahn-Teller distortion. In all of these complexes, the two oxath iaether ligands function as much weaker field ligands than do their crown t hioether analogs. Also, cyclic voltammetric experiments reveal that the oxa thia crowns do not have the ability to stabilize less common metal oxidatio n states, a common property of many crown thioether ligands. (C) 2000 Elsev ier Science S.A. All rights reserved.