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 ΛL-[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, ΛL-[CdCl4{Co(l-Hcys-N,S)(en)2}] (1Cl), in which a cadmium(II) ion is weakly coordinated by a
thiolato group from a ΛL-[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, (ΛL)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, ΛL-[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 ΛL-[Co(l-Hcys-N,S)(en)2]2+ and ΛL-[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, ΛL-[Co(l-Hcys-N,S)(en)2][CdI4] (3). When ΛL-[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, (ΛL)n-[CdCl3{Co(l-cys-N,S)(en)2}]n (4Cl), in which
ΛL-[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, (ΛL)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.