Controlled binding of a L-cysteinato cobalt(III) octahedron to a cadmium(II) center

The binding ability of a chiral L-cysteinato cobalt(III) complex, [Co(L-cys-N,S)(en)2]+ (l-H2cys = L-cysteine, en = ethylenediamine), toward a cadmium(II) center, together with the construction of S-bridged CoIIICdII structures that are controlled by anions and pH, is reported. The reaction of Lambda(L)-[Co(L-Hcys-N,S)(en)2](ClO4)2 having a pendent COOH group with CdCl2 in a 1:1 ratio in water, followed by the addition of NaCl, gave an S-bridged CoIIICdII dinuclear complex, Lambda(L)-[CdCl4{Co(L-Hcys-N,S)(en)2}] (1Cl), in which a cadmium(II) ion is weakly coordinated by a thiolato group from a Lambda(L)-[Co(L-Hcys-N,S)(en)2]2+ unit, besides four Cl- anions. The corresponding 1:1 reaction with CdBr2 and NaBr yielded an S-bridged CoIIICdIICoIII trinuclear complex composed of an S-bridged CoIIICdIICoIII trinuclear cation and a [CdBr4]2- anion, (Lambda(L))2-[CdBr3{Co(L-Hcys-N,S)(en)2}{Co(L-cys-N,S)(en)2} ][CdBr4] (2), while a CoIIICdII dinuclear complex analogous to 1Cl, Lambda(L)-[CdBr4{Co(L-Hcys-N,S)(en)2}] (1Br), was obtained by the addition of HBr instead of NaBr. In the CoIIICdIICoIII cation of 2, a CdII center is very weakly coordinated by two thiolato groups from Lambda(L)-[Co(L-Hcys-N,S)(en)2]2+ and Lambda(L)-[Co(L-cys-N,S)(en)2]+ units, besides three Br- anions, with the trinuclear structure being sustained by an intramolecular COOH...OOC hydrogen bond. On the other hand, no S-bridged structure was obtained by the corresponding 1:1 reaction with CdI2 and NaI, giving only a mononuclear CoIII species with a [CdI4]2- counteranion, Lambda(L)-[Co(L-Hcys-N,S)(en)2][CdI4] (3). When Lambda(L)-[Co(L-cys-N,S)(en)2]ClO4 having a deprotonated pendent COO- group was reacted with CdCl2 in a 1:1 ratio in water, followed by the addition of NaCl, a one-dimensional (CoIIICdII)n polymeric complex, (Lambda(L))n-[CdCl3{Co(L-cys-N,S)(en)2}]n (4Cl), in which Lambda(L)-[Co(L-cys-N,S)(en)2]+ units are alternately linked by [CdCl3]- moieties through thiolato and carboxylate groups, was constructed. An analogous (CoIIICdII)n polymeric structure having [Cd(NCS-N)3]- moieties, (Lambda(L))n-[Cd(NCS-N)3{Co(L-cys-N,S)(en)2}]n (4NCS), was also produced by the use of Cd(ClO4)2 and NaSCN.