Strucural Conversion of Sulfur-Bridged Polynuclear Complexes by Metal Replacement Reaction

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The aggregation of octaetal complexes with two or three thiolate ligands assisted by metal ions has been shown to form a variety of S-bridged polynuclear complexes containing several chiral centers. It has been noted that the structures of these polynuclear complexes are highly dependent on the coordination geometry of metal ions incorporated with the octahedral complexes. In order to better understand the properties characteristic of the S-bridged structure of this type, it is necessary to investigate analogous S-bridged polynuclear complexes composed of (tris)- or (bis)thiolato complex-units.In this study, we have found that the novel S-bridged Co^<III>Ag^I_3Co^<III> pentanuclear complexes, [Ag_3{Co(aet) _3}_2] ^<3+> and [Ag_3{Co(L-cys-N,S) _3}_2, ] ^<3->, were prepared by reacting fac(S)-[Co(aet or L-cys-N,S) _3] ^<0or3-> with linear Ag^+. In the Co^<III>Ag^I_3Co^<III>structure, the two thiolato S atoms from two fac(S)-[Co(aet or L-cys-N,S) _3] ^<0or3-> units coordinate to each of three Ag atoms, such that the three S-Ag-S linkages form a triple helical structure, On the other hand, the reaction of an S-bridged Co^<III>Ni^<II>Co^<III> trinuclear complex, [Ni{Co(aet) _2 (en)}_2]Cl_4, with Na_2 [PdCI_4 ] in a ratio of 1 : 1 gave an S-bridged Co^<III>Pd^<II>Co^<III> trinuclear complex, [Pd{Co(aet) _2 (en)}_2]Cl_4, while the corresponding 1 : 2 reaction produced an S-bridged Co^<III>Pd^<II> dinuclear complex, [PdCl_2{Co(aet) _2 (en)}]CI.In the Co^<III>Pd^<II>Co^<III> structure the Pd^<II> atom is coordinated by four S atoms from two cis(S)-[Co(aet) _2 (en)] ^+ units, while the Pd_<II> atom in the Co_<III>Pd_<II> structure is coordinated by two Cl atoms besides two S atoms from one octahedral unit.