Transition metal complexes with macrocyclic oxathiaethers

Complexation studies with Ni(II), Co(III), Co(II), Cd(II), and Cu(II) for the two mixed oxathia crown ligands 1-oxa-4,7-dithiacyclononane (9S2O) and 1,10-dioxa-4,7,13,16-tetrathiacyclooctadecane (18S4O2) are reported. These ten complexes have been characterized by a variety of means including electronic spectroscopy, cyclic voltammetry, and nuclear magnetic resonance spectroscopy. Furthermore, the complexes [Ni(18S4O2](BF4)2, [Cu(9S2O)2](BF4)2 and [Ni(9S2O)2](ClO4)2, have been characterized by single crystal X-ray diffraction. For the complex [Ni(18S4O2](BF4)2 the diastereoisomer obtained is the one which contains the two oxygen atoms trans to each other and a meridional positioning of the diethylene SOS moiety. Selectivity for this particular stereoisomer is also supported by NMR data 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 macrocycle. Both the nickelsulfur and nickeloxygen bonds in the complex are highly compressed due to the rigid macrocyclic structure and are among the shortest of these types of bonds found in any crown Ni(II) complex. The copper(II) complex, [Cu(9S2O)2](BF4)2, shows an interesting Jahn–Teller distortion from an octahedral geometry resulting in coordinate bonds which are all remarkably similar in length (CuS(4) 2.3293(6); CuS(7) 2.3336(6); and CuO(1) 2.355(2) Å). The oxygen atoms are found in a trans position 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 oxathiaether ligands function as much weaker field ligands than do their crown thioether analogs. Also, cyclic voltammetric experiments reveal that the oxathia crowns do not have the ability to stabilize less common metal oxidation states, a common property of many crown thioether ligands.