CROWN THIOETHER COMPLEXES OF IRON(II) - CRYSTAL-STRUCTURES OF MESO-BIS(1,4,7-TRITHIACYCLODECANE)IRON(II) PERCHLORATE AND (1,4,7,11,14,17-HEXATHIACYCLOEICOSANE)IRON(II) PERCHLORATE

The structure of the meso stereoisomer of bis(1,4,7-trithiacyclodecane )iron(II) perchlorate, [Fe(10S3)2](ClO4)2, has been determined by sing le-crystal X-ray diffraction. Crystal data for meso-[Fe(10S3)2](ClO4)2 : C14H28FeS6ClO8; monoclinic, space group P2(1)/c; a = 7.373(4) angstr om, b = 9.482(4) angstrom, c = 17.205(6) angstrom; beta = 97.81(4)-deg rees, V = 1191.66 angstrom3; Z = 2. Carbon-13 NMR spectroscopy reveals that the predominant stereoisomer in solution is the gauche stereoiso mer whose X-ray crystal structure was previously reported by us. These two stereoisomers are readily separated using fractional crystallizat ion from water. The structure of the iron(II) complex of the twenty-me mbered macrocyclic hexathioether, 20S6, 1,4,7,11,14,7-hexathiacycloeic osane, has also been determined by single-crystal X-ray diffraction. T his is the first reported X-ray structure of a homoleptic complex of t his ligand. The stereoisomer obtained in our case is a racemic one in which the two trimethylene bridges are cis to each other and the two d iethylene units lie in a facial relationship to each other. Crystal da ta for [Fe(2OS6)](ClO4)2: C14H28FeS6Cl2O8; orthorhombic, space group P na2(1); a = 13.200(3) angstrom, b = 16.653(3) angstrom, c = 11.128(1) angstrom; V = 2446.15 angstrom3; Z = 4. Ultraviolet-visible absorption spectroscopy, carbon-13 NMR spectroscopy, and magnetic studies of the [Fe(20S6)]2+ complex are presented. In addition, the synthesis and ch aracterization of a third iron(II)-crown thioether complex with the li gand 18S6(1,4,7,10,13,16-hexathiacyclooctadecane)are reported. Carbon- 13 NMR spectroscopy shows that the only observed stereoisomer is the m eso stereoisomer in which all carbons are equivalent. All of the iron( II)-crown thioether complexes are low-spin, and the electrochemical be havior of the three complexes is described.