Synthesis, Structure, and Properties of a Novel Heterooctametallic Complex Containing a Cyclic Ru4Ni4 Core

Abstract

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 (...

The Effect of C‐2 Substituents of Salicylaldehyde‐Based Thiosemicarbazones on the Synthesis, Spectroscopy, Structures, and Fluorescence of Nickel(II) Complexes

“…Type I was shown by one tetranuclear Cu complex and two hexanuclear Cu and Ag complexes with ferrocenyl‐ and salicylaldehyde‐based thiosemicarbazones 41. Type II is observed only in a mixed‐metallic Ru–Ni octanuclear complex,42 and Type III is shown by the pyridyl‐ and 2‐hydroxy‐based bis(thiocarbohydrazones) 43. Type IV has been observed in one dinuclear Cu II complex of salicylaldehyde‐ N ‐ethylthiosemicarbazone44 and in several Ni II complexes reported in this paper.…”

Synthesis, structure and biological evaluation of bis salicylaldehyde-4(N)-ethylthiosemicarbazone ruthenium(iii) triphenylphosphine

“…Another major problem is drug resistance of certain cancer to traditional chemotherapeutics, many of which target DNA. [10][11][12][13]19,[22][23][24][25][26][27][28][29][30][31][32][33][34] From the literature, it has been found that there are two factors which are probably responsible for the formation of unusual four member NS chelation of thiosemicarbazone in ruthenium complexes. A wide range of biological activities possessed by substituted thiosemicarbazones and their metal complexes include cytotoxic, antitumor and antileukemic properties.…”

“…This challenge calls for new strategies and drugs that take advantage of novel molecular targets that are key components of cellular metabolism and replication. [10][11][12][13]19 One is the intramolecular hydrogen bonding between the phenolic hydrogen and the imine nitrogen which reduces the availability of the lone pair on the imine nitrogen and thus prevents coordination from it. [1][2][3][4][5][6][7][8][9] Thiosemicarbazones are of interest not only because of their biological relevancies but also due to their structural consequences.…”

“…A wide range of biological activities possessed by substituted thiosemicarbazones and their metal complexes include cytotoxic, antitumor and antileukemic properties. [10][11][12][13][14] Though few reasons have been offered for the unusual coordination behaviour of thiosemicarbazones, no one has explained clearly about their bonding behaviour. Usually, they bind to the metal ions either in the neutral thione form or in the negative thiolate form as a bidentate N,S donor by forming either an unusual four member NS chelate ring or an expected five member ring by utilizing either the N2 or N1 hydrazinic nitrogen atom.…”

“…Usually, they bind to the metal ions either in the neutral thione form or in the negative thiolate form as a bidentate N,S donor by forming either an unusual four member NS chelate ring or an expected five member ring by utilizing either the N2 or N1 hydrazinic nitrogen atom. [10][11][12][13][14][15][16][17][18][19][20][21] The incorporation of a third potential donor atom to the thiosemicarbazone ligands should increase their versatility and flexibility in the coordination behavior. [10][11][12][13]19,[22][23][24][25][26][27][28][29][30][31][32][33][34] From the literature, it has been found that there are two factors which are probably responsible for the formation of unusual four member NS chelation of thiosemicarbazone in ruthenium complexes.…”