Checking the Route to Cluster Helicates

Abstract

The aim of the work described here was to test the general applicability of our recently reported route to cluster helicates and to carry out a systematic study to relate the structural and coordinative properties of the organic strands with the microarchitectures of the resulting cluster helicates. Nine new ZnII, CuI and AgI complexes were prepared from three Schiff base ligands [H2La: bis(4‐methyl‐3‐thiosemicarbazone)‐2,6‐diacetylpyridine; H2Lb: bis(4‐methyl‐3‐thiosemicarbazone)‐2,6‐diacetylbenzene; H2Lc: bis(4‐ethyl‐3‐thiosemicarbazone)‐2,6‐diacetylbenzene]. The experimental data confirm that AgI and CuI tetranuclear cluster helicates were obtained with a [M4(Lx)2] stoichiometry, and this finding demonstrates the general applicability of the synthetic route. The cluster helicates presented in this work were characterized for the first time in solution by NMR spectroscopy. In addition, six of the nine complexes were characterized by X‐ray diffraction studies, and three of them were found to be tetranuclear cluster helicates. A detailed study of these three crystal structures leads us to state that the changes introduced in the organic strands do not prevent the assembly of the tetranuclear cluster dihelicates, but they do affect the microarchitectures. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

The use of sacrificial anodes for the electrochemical synthesis of metallic complexes

“…With the aim of increasing the denticity of the ligands, bisthiosemicarbazones derived from 2,6-diacetyl pyridine were also synthesized and some metal complexes were electrochemically obtained. This is the case for the electrolysis of an acetonitrile solution of bis- [131]. As in the case of the Cu(I) complexes, no significant differences between the Ag(I) complexes with similar ligands (with phenyl or pyridine spacer)…”

“…When an acetonitrile solution of bis(N-ethylthiosemicarbazone)-1,3-diacetylbenzene (H 2 L44b) was electrolyzed with a silver anode, the complex [Ag 4 (L44b) 2 ] was obtained [131].…”

“…·DMSO[145] revealed that, in the Zn(II) complexes, the thiosemicarbazonato dianionic ligands act as bidentate species towards one zinc atom and as terdentate ones towards the second metal center. However, in [Cd 2 (L50b) 2 ]·DMSO[145] the ligands act as dianionic pentadentate species with one of the sulfur atoms each ligand acting as a bridge between the two metal centers.The electrolysis of an acetonitrile solution of H 2 L50a with a copper anode allowed the synthesis of a complex, [Cu 4 (L50a) 2 ]·2CH 3 CN[131]. Its structure shows the pyridine nitrogen atoms do not coordinate the metal centers; so the ligands exhibit a dianionic tetradentate…”

AgI‐Directed Triple‐Stranded Helicates with meta‐Ethynylpyridine Ligands

“…Other signals at m / z 790.24 and 1473.58 were observed with low intensity for two bimetallic complexes with two and four strands, respectively [( 2a 2 Ag 2 ) 2+ and ( 2a 4 Ag 2 ) 2+ , Figure S14]. These results revealed that the 3:2 binding stoichiometry for the complex formed by 2a and Ag I ions was also the dominant coordination mode in solution 18b. For the Ag I complex of 3 , no featured peaks were detected, presumably because of the poor solubility of the complex in polar solvents such as acetonitrile and methanol used in the ESI experiments.…”

New 2,6-bis-[uracil-imino] ethylpyridine complexes containing the CdN6 core: Synthesis, crystal structures, luminescent properties and antiproliferative activity against C6 glioma cells

“…Generally hydrazone Schiff bases behave as pentadentate ligands through pyridinic nitrogen, imine nitrogens and carbonylic oxygen atoms and their chelating properties have been investigated for a great number of transition metal ions [1][2][3][4][5][6] and in an important field like the construction of helical complexes with high nuclearity [6]. The Schiff bases derived from functionalized amines give as a result ''bibracchial" ligands with donor groups in two pendant arms which can lead to important changes in the complexation capability of the ligands and can enhance the stability of the metal complexes.…”