Synthesis, crystal structure, redox property and theoretical studies of a pyrrole containing cobalt(III) Schiff base compound

A new mononuclear cobalt(III) complex with a pentadentate Schiff base ligand derived from the condensation of N-(3-aminopropyl)-propane-1,3-diamine with pyrrole-2-aldehyde has been synthesized and structurally characterized by X-ray crystallography. Structural analysis shows that the geometry of cobalt(III) ion is a distorted octahedron in which triamine part of the pentadentate ligand occupies the meridional positions, while two pyrrole nitrogen atoms are in cis disposition. Despite the potentially interesting similarities of pyrrole-based ligands to porphyrin systems, the present complex is inactive towards the oxidation of o-aminophenol, while analogous systems with pyridine containing ligands have proven to be efficient functional models for phenoxazinone synthase. Although the electrospray ionization mass spectral study clearly indicates the formation of a complex-substrate aggregate, the inability towards oxidation of o-aminophenol by the present complex can be explained electrochemically, where strong electron donating ability of the deprotonated pyrrole moiety reduces the possibility of reduction of cobalt(III) to cobalt(II).

Synthesis, structure and diverse coordination chemistry of cobalt(III) complexes derived from a Schiff base ligand and their biomimetic catalytic oxidation of o-aminophenols

This paper deals with the syntheses and structural characterizations of four new cobalt(III) compounds (1–4) derived from a N3O donor Schiff base ligand and their catalytic activity towards the aerobic oxidation of o-aminophenols. Both counter ions and solvents used for the synthesis have significant influence on structural diversity of the resulting complexes. X-ray crystallography reveals that although the geometry of cobalt(III) centres are octahedral in all the cases but the coordination environments are significantly different in them. All these complexes show diverse reactivity towards the catalytic oxidation of o-aminophenols in which availability of substitutionally labile sites at the metal centre for substrate o-aminophenols binding is the main reason for higher catalytic activity in 2 and 3 than others. Furthermore, we have examined the detailed kinetic studies of the aerobic oxidation of one substituted o-aminophenol, namely 2-amino-5-methylphenol, using 2 and 3 as catalysts in which facile oxidation of the substituted o-aminophenol was noticed. ESI mass spectral study has been carried out in order to get insight into mechanistic pathway of functioning such catalytic activity.publishe

Influence of bridging and chelating co-ligands on the distinct single-molecule magnetic behaviours in ZnDy complexes

Four new heterometallic ZnDy complexes, [ZnDy(L)(NO3) 3(py)] CH2 Cl2 (1) (py stands for pyridine), [ZnDy(L)(m-OAc)(OAc)2] 3H2 O (2), [ZnDy(L)(m-OAc)(OAc)(NO 3)] (3), and [ZnDy(L)(m-piv)(piv)2][ZnDy(L) (m-piv)(piv)(OAc)] 1.5H2O (4), have been synthesized from a methyl substituted o-vanillin based compartmental Schiff base ligand, N,N0-bis(3-methoxy-5-methylsalicylidene)-1,2-phenylenediamine (H2L), in association with various secondary co-ligands like acetate (OAc), nitrate and pivalate (piv), and magneto-structurally characterised. They possess a nearly identical [Zn(II)–Dy(III)] core, bridged by the phenoxo-O atoms of the compartmental Schiff base ligand. Magnetic studies revealed the distinct single- molecule magnetic (SMM) behaviours through single to multiple relaxation channels, in which 1, 2 and 4 can display slow relaxation of magnetisation at a zero dc field, the performance of which can be further improved by applying a magnetic field at the expense of the reduction of under barrier relaxation processes, while 3 shows only field-induced weaker slow magnetic relaxation behaviours. Ab initio calculations were performed for the in-depth understanding of the magnetic dynamics in these complexes. The difference in the magnetic behaviours of the four complexes can be ascribed to the effect of bridging/chelating co-ligands in these complexes. Therefore, the present report highlights that the magnetic anisotropy is sensitive to the bridging/chelating co-ligands used, leading to the distinct magnetic dynamics in these systems.publishe

The first example of a centro-symmetrical bis(imido)-bridged dinuclear cobalt(iii) complex: synthesis via oxidative dehydrogenation and phenoxazinone synthase activity

A bis(imido)-bridged dinuclear cobalt(iii) complex, [Co(amp)(μ-imp)Cl]Cl*2HO () [amp = 2-aminomethylpyridine; imp = 2-iminomethylpyridine anion], was synthesized by the reaction of cobalt(ii) chloride with 2-aminomethylpyridine in the presence of alkaline hydrogen peroxide at room temperature. X-ray crystallography reveals that both the metal centres in the molecule are related to each other through an inversion centre, and the geometry of each of the Co ions is a distorted octahedral structure having a CoNCl coordination environment. The most important feature of the structure is the modification of half of the coordinated amines by the oxidative dehydrogenation process which involves double bridging in the complex cation. To the best of our knowledge, this is the first example of a bis(imido)-bridged dinuclear cobalt(iii) complex derived from metal-assisted oxidative dehydrogenation of the coordinated primary amine ligand. Complex was found to be an excellent functional model for the phenoxazinone synthase, catalyzing the oxidative coupling of 2-aminophenol to the corresponding 2-aminophenoxazinone chromophore in dioxygen saturated methanol. The detailed kinetic investigations reveal that the phenoxazinone chromophore is produced via a potential complex-substrate intermediate

Synthesis, crystal structure, redox property and theoretical studies of a pyrrole containing cobalt(III) Schiff base compound

137-144<span style="font-size:9.0pt;font-family: " times="" new="" roman","serif";mso-fareast-font-family:"times="" roman";mso-ansi-language:="" en-us;mso-fareast-language:en-us;mso-bidi-language:ar-sa;mso-bidi-font-weight:="" bold"="" lang="EN-US">A new mononuclear cobalt(III) complex with a pentadentate Schiff base ligand derived from the condensation of N-(3-aminopropyl)-propane-1,3-diamine with pyrrole-2-aldehyde has been synthesized and structurally characterized by X-ray crystallography. Structural analysis shows that the geometry of cobalt(III) ion is a distorted octahedron in which triamine part of the pentadentate ligand occupies the meridional positions, while two pyrrole nitrogen atoms are in cis disposition. <span style="font-size:9.0pt; font-family:" times="" new="" roman","serif";mso-fareast-font-family:timesnewromansf;="" mso-ansi-language:en-us;mso-fareast-language:en-us;mso-bidi-language:ar-sa"="" lang="EN-US">Despite the potentially interesting similarities of pyrrole-based ligands to porphyrin systems, the present complex is inactive towards the oxidation of o-aminophenol, while analogous systems with pyridine containing ligands have proven to be efficient functional models for phenoxazinone synthase. <span style="font-size:9.0pt; font-family:" times="" new="" roman","serif";mso-fareast-font-family:"times="" roman";="" mso-ansi-language:en-us;mso-fareast-language:en-us;mso-bidi-language:ar-sa;="" mso-bidi-font-weight:bold"="" lang="EN-US">Although the electrospray ionization mass spectral study clearly indicates the formation of a complex-substrate aggregate, the inability towards oxidation of o-aminophenol by the present complex can be explained electrochemically, where strong electron donating ability of the deprotonated pyrrole moiety reduces the possibility of reduction of cobalt(III) to cobalt(II).</span

Tuning the geometry and biomimetic catalytic activity of manganese(III)-tetrabromocatecholate based robust platforms by introducing substitution at pyridine

The present report describes synthesis, characterization, crystal structures and catecholase activity of a series of five new manganese(III) complexes (1-5) derived from redox-noninnocent tetrabromocatecholate ligand in combination with different substituted pyridines. X-ray crystallography reveals that the geometry of manganese(III) centers in 1 and 2 is square pyramidal and they are pseudo-dimeric in the solid state resulting from the weak bonding of manganese(III) with a catecholate oxygen atom from the adjacent manganese(III) unit together with other weak interactions like hydrogen bonding and pi center dot center dot center dot pi stacking interactions. On the other hand, complexes 3-5 are discrete octahedral structures. All the complexes exhibit strong catecholase activity and their diverse catalytic activity can nicely be explained by the nature of substitution at pyridine ring - better electron donor inhibits the reduction of the metal center thereby lowering catecholase activity and vice versa (1 and 2 vs. 3-5). Besides the donor property of ancillary ligands, the structural distortion has also significant role in the biomimetic catalytic activity (1 vs. 2). (C) 2016 Elsevier Inc. All rights reserved

Synthesis, structure and magnetic properties of dinuclear cobalt-tetraoxolene complexes with bidentate terminal ligands

The design of molecule-based systems with tuneable optical and/or magnetic properties has attracted considerable attention because of their potential applications in high-performance molecule-based electronic devices, switches, sensors and displays. In this regard, a large number of valence tautomeric tetraoxolene-bridged dinuclear cobalt complexes with tetradentate ancillary ligands have been reported, but none of these complexes contained a bidentate terminal ligand. In order to increase the scope in this field, the present report describes the synthesis, structures, electrochemical and magnetic studies of two dinuclear cobalt-tetraoxolene complexes, [Co2(dhbq)(bpy)4](PF6)3 (1(PF6)3) and [Co2(dhbq)(bpa)4](PF6)3·6H2O (2(PF6)3·6H2O), where H2dhbq is 2,5-dihydroxy-1,4-benzoquinone, with the bidentate terminal ligands 2,2′-bipyridine (bpy) and 2,2′-bipyridyl amine (bpa), respectively. An X-ray diffraction study reveals that the dianionic form of the redox active tetraoxolene ligand bridges the metal centers in these complexes, and one metal center is in the high spin cobalt(II) state while the other one is in the low spin cobalt(III) state. The present report will increase knowledge on the synthesis of such systems using bidentate terminal ligands. Variable temperature magnetic susceptibility measurements show no indication for valence tautomerism (VT) in either complex. Further attempts could be made to synthesize similar complexes from different solvents and/or using different counter ions to check whether such variations can bring VT in these systems

Solvent-Triggered Cis/Trans Isomerism in Cobalt Dioxolene Chemistry: Distinguishing Effects of Packing on Valence Tautomerism.

In this article, the synthesis and X-ray crystal structures of two cis/trans isomers of valence tautomeric (VT) cobalt dioxolene compounds are reported. The cis isomer (1) was isolated from the polar protic methanol solvent as a kinetic product, whereas the less polar nonprotic solvent acetone yielded the trans isomer (2). It should be noted that, although some coordination polymers involving cobalt bis(dioxolene) with the cis disposition are known for bridging ancillary ligands, such an arrangement is unprecedented for mononuclear compounds. A careful study of intermocular interactions revealed that the methanol solvent does not have much influence on the crystal growth in 1, whereas acetone forms strong halogen-bonding interactions that are crucial in the solid-state architecture of 2. This behavior can likely be used in crystal engineering to design new organic-inorganic hybrid materials. The energy difference between the two isomers was examined using DFT calculations, confirming that the trans form is in the thermodynamic state whereas the cis isomer is a kinetic product that can be converted into the trans isomer with time. Finally, both isomers exhibit solvent loss at elevated temperatures that is accompanied by a change in magnetic properties, associated with an irreversible valence tautomerism. Our results highlight the crucial role of the solvents for the isolation of cis/trans isomers in cobalt dioxolene chemistry, as well as the distinguishing effects of intermolecular forces and the solid-state packing on VT behavior

Impact of Positional Isomers on the Selective Isolation of cis-trans Isomers in Cobaltdioxolene Chemistry and Solvation Effects on the Valence Tautomerism in the Solid State

Three new mononuclear cobalt compounds, trans-[Co(3,5-dbcat)(3,5-dbsq)(4-Etpy) 2 ]•CH 3 CN (1), cis-[Co(3,5-dbcat)(3,5-dbsq)(3-NH 2 py) 2 ]•DMF (2) and trans-[Co(3,5dbcat)(3,5-dbsq)(4-NH 2 py) 2 ]•2DMF (3) (3,5-dbcat 2and 3,5-dbsq •− stand for 3,5-di-tertbutyl-catacholate and 3,5-di-tert-butyl-semiquinonate, respectively), derived from a redoxactive o-dioxolene ligand in presence of 4-ethylpyridine (4-Etpy), 3-aminopyridine (3-NH 2 py), and 4-aminopyridine (4-NH 2 py), respectively, have been synthesized and investigated with a view to examine possible influence of pyridine derivatives and solvation on the valence tautomeric (VT) process. Single crystal X-ray diffraction data for all compounds at room temperature suggest Co(III)(3,5-dbcat)(3,5-dbsq) charge distribution in these complexes. Further insight into the crystal structures discloses the diverse noncovalent interactions offered by the isomers of aminopyridine in 2 and 3, leading to the first example 2 of selective isolation of cis and trans isomers in cobalt-dioxolene chemistry induced by the positional isomers of the ancillary ligands. Variable temperature magnetic susceptibility data for all compounds between 2 and 300 K are consistent with the structural studies. At elevated temperatures, complex 1 exhibits a VT interconversion from low spin Co(III)-(3,5-dbcat)(3,5dbsq) to high spin Co(II)-(3,5-dbsq)(3,5-dbsq), triggered by the loss of lattice solvent molecules, while a partial interconversion is observed for complex 3 even heating up to 430 K. The present report overall highlights the impact of positional isomers on the selective isolation of cis-trans isomers in cobalt-dioxolene chemistry and solvation effects on the valence tautomerism in the solid state