A new class of cobalt cyclic trinuclear complexes with four fused aromatic rings, [Co3(η-C5H5)3(S6C6)] and [Co3(η-C5H4Me)3(S6C6)], was synthesized by a condensation reaction of [Co(η-C5H5)(S2C2H2)] and [Co(η-C5H4Me)(S2C2H2)], respectively, in aqueous halogenoacid solution. The complexes undergo reversible three-step 1eâ reductions in aprotic media forming two mixed-valence states, with overall charges 1â and 2â. The thermodynamic stability of the mixed-valence complexes estimated from the redox potential differences and the degree of internuclear electronic interaction evaluated from the intervalence-transfer bands depends markedly on the size of the electrolyte cation and the solvent polarity; larger cations and more polar solvents increase the stability and the electronic interaction. The EPR spectra of [Co3(η-C5H5)3(S6C6)] reduced by [Co(η-C5Me5)2] in propylene carbonate (pc) indicate that the 1â and 3â species are paramagnetic with S = ½, whereas the 3â species formed by reduction with Na in thf gives a spectrum of the quartet state (S = ) denoting ferromagnetic interaction. This difference is attributed to a weaker internuclear interaction caused by a stronger electrostatic effect of the smaller counter ion, Na+ in thf, compared to [Co(η-C5Me5)2]+ in pc.
在卤素酸
水溶液中,通过[Co(δ--
C5H5)(S2
C2H2)]和[Co(δ--C5H4Me)(S2 )]的缩合反应,合成了一类新的具有四个融合芳香环的
钴环三核配合物[Co3(δ-- )3(S6C6)]和[Co3(δ--C5H4Me)3(S6C6)]。这些配合物在非沸腾介质中经历了可逆的三步 1eâ 还原过程,形成两种混合价态,总电荷分别为 1â 和 2â。根据氧化还原电位差估算出的混合价态络合物的热力学稳定性以及根据核间电子相互作用带估算出的核间电子相互作用程度明显取决于电解质阳离子的大小和溶剂的极性;阳离子越大、溶剂的极性越强,稳定性和电子相互作用就越强。在
碳酸丙烯酯(pc)中被[Co(δ--C5Me5)2]还原的[Co3(δ-- )3(S6C6)]的 EPR 光谱表明,1â 和 3â 物种是顺磁性的,SÂ =Â ½ ,而在 thf 中与 Na 还原形成的 3â 物种的光谱为四元态(SÂ =Â ),表示
铁磁相互作用。与 pc 中的[Co(δ--C5Me5)2]+ 相比,thf 中较小的反离子 Na+ 的静电效应更强,从而导致核内相互作用更弱。