A New Class of S-Bridged CoIIIMCoIII (M = NiII, PdII) Trinuclear Complexes with Mixed Aliphatic and Aromatic Thiolate Ligands: Synthesis, Characterization, and Stereochemistry

Treatments of a mixture of CoCl2·6H2O, HL (Hpyt = 2-pyridinethiol, Hpymt = 2-pyrimidinethiol), and triethylamine with [Ni(aet)2] (aet = 2-aminoethanethiolate) in methanol led to the isolation of novel S-bridged CoIIINiIICoIII trinuclear complexes, [Ni{Co(aet)2(pyt)}2]^2+ ([1]^2+) and [Ni{Co(aet)2(pymt)}2]^2+ ([2]^2+), in which a NiII ion is coordinated by four aet S atoms from two tris(thiolato)-type [Co(aet)2(pyt or pymt)] units. The NiII ion in both [1]2+ and [2]2+ was replaced by a PdII ion through the reaction with Na2[PdCl4] in water, giving the corresponding CoIIIPdIICoIII trinuclear complexes, [Pd{Co(aet)2(pyt)}2]^2+ ([3]^2+) and [Pd{Co(aet)2 (pymt)}2]^2+ ([4]^2+). The related CoIIIPdIICoIII trinuclear complexes composed of one [Co(aet)2(pyt or pymt)] and one [Co(aet)2(en)]+ units, [Pd{Co(aet)2(pyt)}{Co (aet)2(en)}]^3+ ([5]^3+) and [Pd{Co(aet)2(pymt)}{Co(aet)2(en)}]^3+ ([6]^3+), were also prepared by the reactions of a 1:1 mixture of [Ni{Co(aet)2(pyt or pymt)}2]2+ and [Ni{Co(aet)2(en)}2]^4+ with Na2[PdCl4] in water, followed by the column chromatographic separation. The electronic absorption, CD, and NMR spectroscopies indicated that these CoIIIMCoIII trinuclear complexes produce only the racemic ((delta)(delta)/(lambda)(lambda)) isomer, in which each [Co(aet)2(pyt or pymt)] unit adopts a mer(S) configuration with two aet N atoms at the apical positions. For [1]^2+, [2]^2+, [3]^2+, and [4]^2+, another geometrical isomerism of syn–anti, which arises from the arrangement of the two terminal pyt or pymt S atoms, was identified.