Preparation and Properties of S-Bridged CoIIIAgI3CoIII Pentanuclear Complexes Having a Triple Helical Chirality. Crystal Structure of [Ag3{Co(aet)3}2](BF4)3 (aet = 2-Aminoethanethiolate)

Abstract

Abstract Novel S-bridged CoIIIAgI3CoIII pentanuclear complexes, [Ag3{Co(aet)3}2]3+ (1) and [Ag3{Co(l-cys-N,S)3}2]3− (2), were prepared by reacting fac(S)-[Co(aet)3] (aet = 2-aminoethanethiolate) or ΔLll-fac(S)-[Co(l-cys-N,S)3]3− (l-cys = l-cysteinate) with Ag+ in a ratio of 2 : 3. The crystal structure of 1(BF4)3 was determined by X-ray crystallography. 1(BF4)3·H2O, chemical formula C12H38B3N6OF12S6Co2Ag3, crystallizes in the orthorhombic space group Pnma with a = 16.397(2), b = 13.239(2), c = 15.803(4) Å, V = 3430.5(9) Å3, Z = 4, and R = 0.066. In 1 the two thiolato S atoms from two octahedral fac(S)-[Co(aet)3] units coordinate to each of three Ag atoms, such that the three S–Ag–S linkages form a triple helical structure. 1 gave only racemic isomer, ΔΔ and ΛΛ, which were optically resolved by cation-exchange column chromatography, while the ΔLllΔLll isomer was selectively formed for 2 with a retention of the absolute configuration of the starting ΔLll-fac(S)-[Co(l-cys-N,S)3]3−. 1 was converted to the S-bridged tricobalt(III) complex [Co{Co(aet)3}2]3+ by a reaction with I− in the presence of Co2+, accompanied by an intermolecular exchange and racemization of the Δ/Λ-fac(S)-[Co(aet)3] units. The electronic absorption and CD spectral properties of 1 and 2 are also reported.