Synthesis, Characterization And Chiral Properties Of (Co2ag3i)-Ag-Iii Pentanuclear, (Co4zn4ii)-Zn-Iii Octanuclear, And Co-Iii Mononuclear Complexes With Aza-Capped Hexadentate-N3s3 Thiolate Ligands: Crystal Structures Of [Ag-3{Co(L)}(2)][Pf6](3) And [Zn4o{Co(L)}(4)][Pf6](6) (L = N(Ch2nhch2ch2s-)(3))

The reaction of an S-bridged (Co2Ag3I)-Ag-III pentanuclear complex, [Ag-3{Co(aet)(3)}(2)] [BF4](3) (aet = NH2CH2CH2S-) with paraformaldehyde in basic acetonitrile, followed by adding aqueous ammonia, produced an aza-capped (Co2Ag3I)-Ag-III complex, [Ag-3{Co(L)}(2)](3+) ([1](3+)) (L = N(CH2NHCH2CH2S-)(3)). The crystal structure of [1](3+) was determined by X-ray crystallography, [1][PF6](3). H2O, empirical formula C18H44Ag3Co2F18N8OP3S6, crystallizes in the tetragonal space group I(4) over bar 2 m with a = 13.012(1) Angstrom, c = 24.707(2) Angstrom, 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, [Ag-3(I)(L)(2)](3-). [1](3+) was converted to an aza-capped (Co4Zn4II)-Zn-III octanuclear complex, [Zn4O{Co(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). 8H(2)O, empirical formula C36H100Co4F36N16O9S12Zn4, crystallizes in the monoclinic space group P2(1)/n with a = 14.33(7) Angstrom, b = 25.67(10) Angstrom, c = 24.83(6) Angstrom, beta = 101.3(3)degrees, and Z = 4. In [2](6+) each of four [Co(L)] units is bound to each trigonal Zn-3(II) face of the tetrahedral [(Zn4O)-O-II](6+) core, such that each Co-III atom is encapsulated in a macrobicyclic [(Zn4O)-O-II(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; Delta Delta-[1](3+) Delta Delta Delta Delta-[2](6+), and Delta-[3] were derived from Delta Delta-[Ag-3{Co(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 Delta Delta-[1](3+), Delta Delta Delta Delta-[2](6+), and Delta-[3].