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 [{Ru I I (L)(cymene)} 4 ] 4 + [Cp* = η 5 -C 5 Me 5 , cymene = η 6 -p-MeC 6 H 4 Pr ι ; M = Rh I I I and Ir I I I ; HL = 6-purinethione (H 2 put) and 2-amino-6-purinethione(H 2 aput)] 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*)(H 0 . 5 put)} 4 ](CF 3 SO 3 ) 2 and [{Ir(Cp*)-(Haput)} 4 ](CF 3 SO 3 ) 4 revealed that they have similar S 4 structures with an alternate chirality array of CACA, and all ligands adopt a μ-1κΝ 9 :2κ 2 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) A] at both sides of the cavity. In the two Rh I I I - and Ru I I -H 2 aput systems, it turned out that the dimeric species are dominantly formed in the reaction solutions but finally convert into the tetrameric species.