Synthesis, characterization, and chiral properties of CoIII2AgI3 pentanuclear, CoIII4ZnII4 octanuclear, and CoIII mononuclear complexes with aza-capped hexadentate-N3S3 thiolate ligands: crystal structures of

The reaction of an S-bridged Co2(III)Ag3(I) pentanuclear complex, Ag3Co(aet)3]2]BF4]3 (aet = NH2CH2CH2S-), with paraformaldehyde in basic acetonitrile, followed by adding aqueous ammonia, produced an aza-capped Co2(III)-Ag3(I) complex, Ag3Co(L)]2]3+ (1]3+) (L = N(CH2NHCH2CH2S-)3). The crystal structure of 1]3+ was determined by X-ray crystallography. 1]PF6]3 x H2O, empirical formula C18H44Ag3Co2F18N8OP3S6, crystallizes in the tetragonal space group 142m with a = 13.012(1) A, c = 24.707(2) A, and Z = 4. In 1]3+ the two aza-capped Co(L)] units are linked by three Ag(I) atoms, such that the two Co(III) atoms are encapsulated in a macrobicyclic metallocage, Ag3(I)(L)2]3-. 1]3+ was converted to an aza-capped Co4(III)Zn4(II) octanuclear complex, Zn4OCo(L)]4]6+ (2]6+), by reaction with I- in the presence of Zn2+ and ZnO in water. The crystal structure of 2]6+ was also determined by X-ray crystallography. 2]PF6]6 x 8H2O, empirical formula C36H100Co4F36N16O9P6S12Zn4, crystallizes in the monoclinic space group P2(1/n) with a = 14.33(7) A, b = 25.67(10) A, c = 24.83(6) A, beta = 101.3(3) degrees , and Z = 4. In 2]6+ each of four Co(L)] units is bound to each trigonal Zn3(II) face of the tetrahedral Zn4(II)O]6+ core, such that each Co(III) atom is encapsulated in a macrobicyclic Zn4(II)O(L)] fragment. Treatment of 2]6+ with a basic aqueous solution resulted in a cleavage of the Zn-S bonds to produce an aza-capped Co(III) mononuclear complex, Co(L)] (3]), from which 1]3+ is readily reproduced by the reaction with Ag+ in water. All the reactions were found to proceed with retention of the absolute configuration (delta or lambda) of the Co(III) chiral centers; deltadelta-1]3+, deltadeltadeltadelta-2]6+, and A-3] were derived from deltadelta-Ag3Co(aet)3]2]3+. The contributions to circular dichroism (CD) from the triple helicity in 1]3+, besides from the asymmetric N and S donor atoms and the Co(III) chiral centers in 1]3+ and 2]6+, were estimated by comparing the CD spectra of deltadelta-1]3+, deltadeltadeltadelta-2]6+, and delta-3].