Synthesis, Characterization, and Chiral Properties of CoIII2AgI3 Pentanuclear, CoIII4ZnII4 Octanuclear, and CoIII Mononuclear Complexes with Aza-Capped Hexadentate-N3S3 Thiolate Ligands: Crystal Structures of [Ag3{Co(L)}2][PF6]3 and [Zn4O{Co(L)}4][PF6]6 (L = N(CH2NHCH2CH2S-)3)

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Abstract
The reaction of an S-bridged CoIII2AgI3 pentanuclear complex, [Ag3{Co(aet)3}2][BF4]3 (aet = NH2CH2CH2S-), with paraformaldehyde in basic acetonitrile, followed by adding aqueous ammonia, produced an aza-capped CoIII2AgI3 complex, [Ag3{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 I4̄2m with a = 13.012(1) Å, c = 24.707(2) Å, and Z = 4. In [1]3+ the two aza-capped [Co(L)] units are linked by three AgI atoms, such that the two CoIII atoms are encapsulated in a macrobicyclic metallocage, [AgI3(L)2]3-. [1]3+ was converted to an aza-capped CoIII4ZnII4 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]6·8H2O, empirical formula C36H100Co4F36N16O9P6S12Zn4, crystallizes in the monoclinic space group P21/n with a = 14.33(7) Å, b = 25.67(10) Å, c = 24.83(6) Å, β = 101.3(3)°, and Z = 4. In [2]6+ each of four [Co(L)] units is bound to each trigonal ZnII3 face of the tetrahedral [ZnII4O]6+ core, such that each CoIII atom is encapsulated in a macrobicyclic [ZnII4O(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 CoIII 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 (Δ or Λ) of the CoIII chiral centers; ΔΔ-[1]3+, ΔΔΔΔ-[2]6+, and Δ-[3] were derived from ΔΔ-[Ag3{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 CoIII chiral centers in [1]3+ and [2]6+, were estimated by comparing the CD spectra of ΔΔ-[1]3+, ΔΔΔΔ-[2]6+, and Δ-[3].

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