Cyclic Tetramers Composed of Rhodium(III), Iridium(III), or Ruthenium(II) Half-Sandwich and 6-Purinethiones

Six new cyclic tetranuclear complexes [{M(Cp*)(L)}4]4+ and [{RuII(L)(cymene)}4]4+ [Cp* = η5-C5Me5, cymene = η6-p-MeC6H4Pr i ; M = RhIII and IrIII; HL = 6-purinethione (H2put) and 2-amino-6-purinethione (H2aput)] were prepared in a self-assembly manner and characterized by NMR spectroscopy, electrospray ionization mass spectrometry, and X-ray crystal structure analysis. The two crystal structures of [{Rh(Cp*)(H0.5put)}4](CF3SO3)2 and [{Ir(Cp*)(Haput)}4](CF3SO3)4 revealed that they have similar S 4 structures with an alternate chirality array of CACA, and all ligands adopt a μ-1κN 9:2κ2 S 6,N 7 coordination mode. The orientations of the four bridging ligands are alternately up and down, and they form a central square cavity. Interestingly, the cationic tetramers of the former are stacked up along the c axis, resulting in an infinite channel-like cavity. The driving force of this stacking is due to intermolecular double hydrogen bonds [N(1)−H···N(21) = 2.752(4) Å] at both sides of the cavity. In the two RhIII- and RuII-H2aput systems, it turned out that the dimeric species are dominantly formed in the reaction solutions but finally convert into the tetrameric species.