The reaction of [Ni{Co(aet)(2)(pyt)}(2)](2+) (aet = 2-aminoethanethiolate, pyt = 2-pyridinethiolate) with [PtCl4](2-) gave an S-bridged (CoPtCoIII)-Pt-III-Co-II trinuclear complex composed of two [Co(aet)(2)(pyt)] units, [Pt{Co(aet)(2)(pyt)}(2)](2+) ([1](2+)). When a 1:1 mixture of [Ni{Co(aet)(2)(pyt)}(2)](2+) and [Ni{Co(aet)(2)(en)}(2)](4+) was reacted with [PtCl4](2-), a mixed-type S-bridged (CoPtCoIII)-Pt-III-Co-II complex composed of one [Co(aet)(2)(pyt)] and one [Co(aet)(2)(en)](+) units, [Pt{Co(aet)(2)(en)}-{Co(aet)(2)(pyt)}](3+) ([2](3+)), was produced, together with [1](2+) and [Pt{Co(aet)(2)(en)}(2)](4+). The corresponding (CoPtII)-Pt-III-Co-III trinuclear complexes containing pymt (2-pyrimidinethiolate), [Pt{Co(aet)(2)(pymt)}(2)](2+) ([3](2+)) and [Pt{Co(aet)(2)(en)}{Co(aet)(2)(pymt) (en)}{Co(aet)(2)(pymt)}](3+) were also obtained by similar reactions, using [Ni{Co(aet)(2)(pymt)}(2)](2+) instead of [Ni{Co(aet)(2)(pyt)}(2)](2+). While [Pt{Co(aet)(2)(en)}(2)](4+) formed both the DeltaLambda (meso) and DeltaDelta/LambdaLambda (racemic) forms in a ratio of ca. 1:1, the preferential formation of the DeltaDelta/LambdaLambda form was observed for [1](2+) (ca. DeltaLambda:DeltaDelta/LambdaLambda = 1:3) and [2](3+) (ca. Delta(en)Lambda(pyt)/Lambda(en)Delta(pyt):DeltaDelta/LambdaLambda = 1:2). Furthermore, [3](2+) and [4](3+) predominantly formed the DeltaDelta/LambdaLambda form. These results indicate that the homochiral selectivity for the S-bridged (CoPtCoIII)-Pt-III-Co-II trinuclear complexes composed of two octahedral [Co(aet)(2)(L)](0) or (+) units is enhanced in the order L = en < pyt < pymt. The isomers produced were separated and optically resolved, and the crystal structures of the meso-type DeltaLambda-[1]Cl(2)(.)4H(2)O and the spontaneously resolved DeltaDelta-[4](ClO4)(3)(H2O)-H-. were determined by X-ray analyses. In DeltaLambda-[1](2+), the Delta and Lambda configurational mer(S)(.)trans(N-aet)-[Co(aet)(2)(pyt)] units are linked by a square-planar Pt-II ion through four aet S atoms to form a linear-type S-bridged trinuclear structure. In DeltaDelta-[4](3+), a similar linear-type trinuclear structure is constructed from the Delta-mer(S)(.)trans(N-aet)-[Co(aet)(2)(pymt)] and Delta-C-2-cis(S)-[Co(aet)(2)(en)](+) units that are bound by a Pt-II ion with a slightly distorted square-planar geometry through four aet S atoms.