COBALT(III) COMPLEXES OF CROWN THIOETHERS - THE CRYSTAL-STRUCTURE OF (1,4,7,11,14,17-HEXATHIACYCLOEICOSANE)COBALT(III) TETRAFLUOROBORATE DIHYDRATE

The syntheses of several Co(III) complexes containing crown thioether ligands are reported. The complexes are characterized using UV-Vis abs orption spectroscopy, carbon-13 and cobalt-59 NMR spectroscopy, and cy clic voltammetry. The structure of the cobalt(III) complex of the 20-m embered macrocyclic hexathioether, 20S6, 1,4,7,11,14,17-hexathiacycloe icosane, has also been determined by single-crystal X-ray diffraction. The stereoisomer obtained is a racemic set in which the two trimethyl ene bridges are cis to each Ether and the two diethylene units lie in a facial relationship. Crystal data for [Co(20S6)](BF4)(3) . 2H(2)O: C 14H32B3CoF12O2S6; monoclinic, space group C2/c; a = 17.186(5), b = 16. 014(3), c = 10.283(2), beta = 98.57(2)degrees, V = 2798.45 Angstrom(3) , Z = 4. The crown thioethers discussed in this paper all function as strong field ligands towards Co(III), in contrast to their behavior to wards Cr(III) and V(III). Solution carbon-13 NMR studies show the pres ence of a single meso diastereomer for [Co(18S6)](3+) and a single dia stereomer for [Co(20S6)](3+). Chemical shifts for Co-59 NMR spectra co rrelate with the ligand field strengths and also show the presence of a single diastereomer for both hexathioether complexes. The electroche mical behavior of several hexakis(thioether) complexes of Co(III) is d escribed. The synthesis of the heteroleptic complex, [Co(9S3)Cl-3] is reported, and this complex can be used as an intermediate in the prepa ration of mixed crown hexakis( thioether) complexes such as [Co(9S3)(1 0S3)](3+). (C) 1998 Elsevier Science S.A. All rights reserved.