There is considerable current interest in the chemistry of polynuclear complexes, largely because of their fascinating properties. [1] Mononuclear transition metal complexes of multidentate ligands in which some of the donor sites are unoccupied often serve as efficient building blocks for the construction of polynuclear assemblies. [2] In our attempts to generate new heteropolynuclear systems, we planned a stepwise synthetic strategy, and salicylaldehyde thiosemicarbazone (H 3 saltsc, 1) was chosen as the multidentate ligand for this study. This ligand has five potential donor sites: three N, one O, and one S atom. However, in its reaction with ruthenium and osmium, we observed an apparently unusual coordination mode in which the H 2 saltsc ligand utilizes only one N and one S donor site and forms a four-membered chelate ring (2). [3] Further studies showed that this type of coordination mode is in fact quite normal not only for H 2 saltsc but also for benzaldehyde thiosemicarbazones. [4] The three unused donor sites in 2 and their relative dispositions in space suggested that complexes containing this moiety should be able to bind to a second metal ion as a tridentate N,N,O donor ligand, and such a possibility is explored in the present study.The mononuclear mixed-ligand ruthenium(ii) complex [Ru(bpy) 2 (H 2 saltsc)] (bpy 2,2'-bipyridine) was prepared first. 2,2'-Bipyridine was chosen as the coligand because it is a recognized stabilizer of bivalent ruthenium, and complexes containing the Ru(bpy) 2 chromophore exhibit interesting luminescence properties, [5] so that a polynuclear complex constructed from [Ru(bpy) 2 (H 2 saltsc)] building blocks may also be expected to display such behavior. [Ru(bpy) 2 -(H 2 saltsc)]ClO 4 was obtained from the reaction of H 3 saltsc with [Ru(bpy) 2 (EtOH) 2 ] 2 , formed in situ from [Ru(bpy) 2 Cl 2 ] and AgNO 3 in warm ethanol in the presence of a base [Eq. (1)]. The crystal structure of [Ru(bpy) 2 (H 2 saltsc)]ClO 4 is [Ru(bpy) 2 Cl 2 ] À3 AgNO3 EtOH [Ru(bpy) 2 (EtOH) 2 ] 2 À3 H3 saltsc NEt3 [Ru(bpy) 2 (H 2 saltsc)] À3 NaClO4 [Ru(bpy) 2 (H 2 saltsc)]ClO 4(1) displayed in Figure 1. [6] The H 2 saltsc ligand is coordinated to ruthenium as a bidentate N,S donor in a four-membered chelate ring. The N 5 S coordination sphere around ruthenium Figure 1. ORTEP plot of the structure of [Ru(bpy) 2 (H 2 saltsc)] . Selected bond lengths [] and angles [8]: ).is distorted from ideal octahedral geometry. The phenolic oxygen atom O1, the imine nitrogen atom N5, and the amine nitrogen atom N7 of the H 2 saltsc ligand remained uncoordinated, and the Ru(H 2 saltsc) fragment is almost planar. The [Ru(bpy) 2 (H 2 saltsc)] complex cation thus appears to be a suitable building block for the construction of polynuclear complexes, and to test this hypothesis, [Ru(bpy) 2 (H 2 saltsc)]-ClO 4 was treated with one equivalent of Ni(ClO 4 ) 2´6 H 2 O in warm acetonitrile/ethanol. This reaction indeed afforded a polynuclear complex, namely [{Ru(bpy) 2 (saltsc)} 4 Ni 4 ](ClO 4 ) 4 [Eq. (2)]. 4 [Ru(bpy) 2 (...
