Control of molecular topology by stereochemical preferences of metal ions: double helical versus side-by-side structures in tetranuclear copper(ii) and nickel(ii) complexes

Abstract

The novel polydentate ligand N, -4H-pyrazole-3-carbonyl)-1,2-diaminoethane (L) was prepared in one-pot synthesis, employing Claisen condensation of 2-acetylpyridine and diethyl ethylene-1,2-bis(oxamate) followed by treatment with hydrazine hydrate. L possesses four bidentate chelating units and is expected to be able to bind metal ions in bis(binucleating) or tetradentate modes. Reaction of L with 1 equiv. of copper() or nickel() hydroxides in the presence of 2 equiv. KOH in DMSO affords mononuclear anionic complexes K 2) containing metal ions in square-planar environment of two pairs of deprotonated amide and pyrazolato nitrogens. Reaction of 1 with 2 equiv. of Cu(NO 3 ) 2 leads to complete rearrangement of the coordination sphere, yielding a tetranuclear product which was crystallised in the presence of picric acid in the form) was obtained as a result of spontaneous self-assembly from L and copper() nitrate in aqueous acetic acid. Reaction of 2 with 2 equiv. of Ni(NO 3 ) 2 yields a tetranuclear cationic complex 4) which contains four octahederal Ni ions coordinated in bis(binucleating) mode to two ligand threads disposed in side-by-side fashion and cis with respect to the Ni(1)-Ni(2) axis. In both 3a and 3b the ligand is coordinated in the same bis(binucleating) mode as in Ni complex 4, however, the Cu ions are squarepyramidal and the two ligand threads are disposed trans with respect to the Cu(1)-Cu(2) axis, thus giving rise to the double helical structures. 3a and 3b are the first examples of helicates comprising of bimetallic units. Formation of different topologies in 3a,b and 4 is elucidated in terms of different stereochemical preferences of these ions in mixed N,O-donor environments. All compounds were characterised by elemental analysis, ESI and MALDI mass spectrometry and UV-VIS spectroscopy, and complexes 3a, 3b and 4 by single crystal X-ray analysis. Magnetic susceptibility measurements (1.7-300 K) of powdered samples of tetranuclear complexes revealed strong (3b) or moderate (4) antiferromagnetic coupling within the dimeric units incorporating double pyrazolato bridges between paramagnetic centres. ExperimentalAll chemicals were commercial products of reagent grade and used without further purification. 1 H NMR spectra were recorded on Bruker AC-400 (400.13 MHz) and Bruker AC-500 DALTON

Checking the Route to Cluster Helicates

“…As a result, the Zn II complex is achiral and thus can be termed as a meso-helical, [27] box-like [28] or side-by-side [29] complex, as well as a mesocate. [30] This is one of the few crystallographically characterized examples of a double-stranded meso-helicate described in the literature. [28,29,31] The Zn···Zn distance is 7.16 Å, almost twice the intermetallic distance found in 1.…”

Coordination Versatility of Pyrazole‐Based Ligands towards High‐Nuclearity Transition‐Metal and Rare‐Earth Clusters

“…The ligand N,NЈ-bis (2-pyridylmethyl) [177] Magnetic susceptibility and EPR studies were performed only for the copper(II) compound. [179] Heterobimetallic compounds with the same ligand are also reported. Other examples of tetranuclear nickel(II) and copper(II) compounds have been reported with the ligand H 4 L6e.…”

“…[176] Pyrazole-3,5-dicarboxamides are often used as intermediates in the synthesis of pyrazoles with chelating amine side arms. [178,179] These compounds have different topology depending on the metal ion used: linear for nickel(II) ions and helical for copper(II) ions. The ligand N,NЈ-bis (2-pyridylmethyl) [177] Magnetic susceptibility and EPR studies were performed only for the copper(II) compound.…”

“…Therefore, the coordination ability of this type of ligands has also been studied, because when the amide is deprotonated, the metal ion can coordinate through the nitrogen atoms, whereas if it remains protonated, the coordination would be through the oxygen atom. [179] Weak and strong antiferromagnetic interactions have been found between the nickel(II) and copper(II) ions, respectively. [177] The nickel(II) compound is diamagnetic, whilst antiferromagnetic interactions between the copper(II) ions are mediated by the pyrazole bridges.…”

One-pot synthesis of nickel porphyrins with 2-pyridine-acetyl substituents: the unexpected Sonogashira cross-coupling products

“…2-Acetylpyridine is an important functional group found in many drugs [1], and it also has been widely used as the starting material for supramolecular systems [2], anti-tumor complexes [3], catalysis [4] and helicity study [5]. On the other hand, porphyrins have been extensively studied for multichromophore arrays, catalysis, photodynamic therapy and sensors because of their versatile electronic properties [6].…”