Search

This research study reports the synthesis, structural characterization and phenoxazinone synthase‐like activity of two structurally similar copper(II) complexes developed with a benzimidazole functionalized Schiff base (L). The ligand, L, was designed and synthesized in high yield by the reaction of p‐methoxy benzaldehyde with o‐phenylenediamine. The reaction of L with CuCl2 and Cu(NO3)2 leads to the formation of two isostructural complexes, [Cu(L)2Cl2]2 (1) and [Cu(L)2(NO3)2]2 (2). Single crystal X‐ray structural study reveals that both the Cu(II) centre in 1 and 2 adopts a square planar geometry. An attempt has also been made to understand the role of coordinated co‐ligands on the catalytic oxidation of 2‐aminophenol (2‐AP) to 2‐amino‐3H‐phenoxazine‐3‐one (2‐APX) in methanol. The presence of coordinated nitrate to Cu(II) ions imparts a more labile character to complex 2, and the catalytic efficiency (kcat/KM) for complex 2 (1.50 × 107) was determined almost double compared with that of complex 1 (8.78 × 106). Electro‐chemical and electrospray ionization mass spectrometry studies of 1 and 2 with 2‐AP suggests that the square planar geometries of the Cu(II) centres remain the driving force to develop enzyme‐substrate adducts and excellent catalytic performance of the complexes. Electrochemical and EPR spectral analysis of the reaction mixture confirm the presence of active 2‐AP−/2‐AP•− redox species in the course of catalytic oxidation and suggest the radical driven oxidative coupling of 2‐AP in an aerobic environment. Temperature‐dependent kinetic measurements were carried out to evaluate the activation parameters (Ea, ΔH‡, ΔS‡), which favours the higher rate of catalytic oxidation of 2‐AP for complex 2 than complex 1. [ABSTRACT FROM AUTHOR]

Two‐coordinate Cu(I) and Au(I) complexes supported by bicyclic (alkyl)(amino)carbene, [BICAAC‐CuCl] (1), [BICAAC‐CuI] (2), [(BICAAC)2Cu]+[PF6]– (3) and [(BICAAC)2Au]+[AuCl2]– (6) have been synthesized. The reaction of cyclic (alkyl)(amino)carbene, CAACcy with CuCl afforded [CAACcy‐CuCl] (4) and its further reaction with KPF6 gave [(CAACcy)2Cu]+[PF6]– (5). Complexes 1–6 have been characterized by multinuclear NMR, IR and UV‐Vis. spectroscopic method and high‐resolution mass spectrometry (HRMS). Single crystal X‐ray structure of heteroleptic complexes 1 and 4 and homoleptic complexes [(BICAAC)2Cu]+[CuI2]– (2'), 3 and 6 have also been determined. The crystal structure of these complexes confirmed linear two‐coordinate geometry around the metal centers. In the solid‐ state, complexes 1, 2', 4 and 6 displayed C−H⋯M (M=Cu, Au) and weak non‐covalent C−H⋯X (X=Cl, I) and C−H⋯H−C interactions. Computational calculations correlate well to the experimentally observed geometry and help elucidate the absorption characteristics type of transitions and the frontier orbitals involved in them. [ABSTRACT FROM AUTHOR]

Recently, an unprecedented observation of polar order, thermochromic behavior, and exotic mesophases in new chiral, bent‐shaped systems with a −CH3 moiety placed at the transverse position of the central core was reported. Herein, a homologous series of compounds with even‐numbered carbon chains from n=4 to 18 were synthesized, in which −Cl was substituted for −CH3 at the kink position and a drastic modification in the phase structure of the bent‐shaped molecule was observed. An unusual stabilization of the cubic blue phase (BP) over a wide range of 16.4 °C has been witnessed. Two homologues in this series (1‐12 and 1‐14) exhibit an interesting phase sequence consisting of BPI/II, chiral nematic, twist grain boundary, smectic A, and smectic X (SmX) phases. The higher homologues (1‐16 and 1‐18) stabilize the SmX phase enantiotropically over the entire temperature range. Crystal structure analysis confirmed the bent molecular architecture, with a bent angle of 148°, and revealed the presence of two different molecular conformations in an asymmetric unit of compound 1‐4. A DFT study corroborated that the −Cl moiety at the central core of the molecule led to an increase in the dipole moment along the transverse direction, which, in turn, facilitated the unusual stabilization of frustrated structures. Crystal polymorphism has been evidenced in three homologues (1‐10, 1‐12, and 1‐14) of the series. On the application of mechanical pressure through grinding, compound 1‐10 transformed from a bright yellow crystalline solid to a dark orange–green amorphous solid, which reversed upon dropwise addition of dichloromethane, indicating reversible mechanochromism in this class of compounds. In addition, excellent thermochromic behavior has been observed for compound 1‐10 with a controlled temperature–color combination. [ABSTRACT FROM AUTHOR]

Intermolecular interactions involving organic fluorine have been the contemporary field of research in the area of organic solid state chemistry. While a group of researchers had refuted the importance of “organic fluorine” in guiding crystal structures, others have provided evidences for in favor of fluorine mediated interactions in the solid state. Many systematic studies have indicated that the “organic fluorine” is capable of offering weak hydrogen bonds through various supramolecular synthons, mostly in the absence of other stronger hydrogen bonds. Analysis of fluorine mediated interaction in the presence of strong hydrogen bonds has not been highlighted in detail. Hence a thorough structural investigation is needed to understand the role of “organic fluorine” in crystal engineering of small organic fluorinated molecules having the possibility of strong hydrogen bond formation in the solution and in the solid state. To fulfil this aim, we have synthesized a series of fluorinated amides using 3-methoxyphenylacetic acid and fluorinated anilines and studied their structural properties through single crystal and powder X-ray diffraction methods. Our results indicated that the “organic fluorine” plays a significant role in altering the packing characteristics of the molecule in building specific crystal lattices even in the presence of strong hydrogen bond. [ABSTRACT FROM AUTHOR]

Strong hydrogen bonds play a significant role in crystal packing. In particular, the involvement of interactions involving fluorine in controlling the crystal packing requires appropriate attention, especially in the presence of other strong hydrogen bonds. In the present study, a detailed quantitative assessment has been performed of the nature, energetics and topological properties derived from the electron density in model compounds based on fluorinated benzamides (a total of 46 fluorine-substituted benzamides containing multiple fluorine atoms) in the solid state. The primary motivation in the design of such molecules is to enhance the acidity of the interacting H atoms in the presence of an increasing number of F atoms on the molecular scaffold, resulting in increased propensity towards the formation of intermolecular interactions involving organic fluorine. This exercise has resulted in the identification of new and frequently occurring supramolecular synthons involving F atoms in the packing of molecules in the solid state. The energetics associated with short and directional intermolecular C sp2-H...F-C sp2 interactions with significantly high electrostatic contributions is noteworthy, and the topological analysis reveals the bonding character of these ubiquitous interactions in crystal packing in addition to the presence of C sp2-F...F-C sp2 contacts. [ABSTRACT FROM AUTHOR]

A new one-dimensional (1-D) Pb(II) coordination polymer, [Pb(2,2′-bpy)(NO3)2(H2O)]n(1) (2,2′-bpy = 2,2′-bipyridine), has been synthesized and characterized by different spectroscopic techniques and X-ray single-crystal analysis. From the X-ray crystal structure of1, the Pb2+can be best described as a highly distorted pentagonal bipyramid with O4 (water) and O6 (nitrate) at apical positions (O4–Pb–O6 of 143.7(1)°). Variability in bond distances reveals that Pb2+is unsymmetrically surrounded by two nitrates, one 2,2′-bpy and one water. Nitrates bridge between monomers. The molecule crystallizes in the monoclinicP21/n(14) space group. This is the first example of a 1-D Pb(II) polymer in which nitrates show three different coordination motifs (terminal, chelating, and bridging). Solid state as well as solution phase UV–vis spectral analysis and mass spectrometric studies clearly reveal instability with breakdown of Pb(II) polymer in aqueous solution. The arrangement of the 2,2′-bpy, water, and nitrates leaves a coordination gap at the Pb(II) occupied probably by a stereo-active lone pair of electrons. [ABSTRACT FROM AUTHOR]

Abstract: To investigate the interactions between hydrogen bond donor and acceptor giving rise to three dimensional networks, compounds [Ni(H2O)6](ClO4)2 ·2{(CH2)6N4}·2H2O (1), [Ni(H2O)6]Cl2 ·2{(CH2)6N4}·4H2O (2) and [Cd(H2O)4{(CH2)6N4}2](ClO4)2 ·2H2O (3) (where (CH2)6N4 =hexamethylenetetramine) have been prepared and their crystal structures were investigated. In all three complexes, the metal coordination is octahedral. The hexamine molecules are complexed in the cadmium compound, 3 but are free in the nickel salts, 1 and 2. The supramolecular structures of 1 and 2 show motif linking the cationic moieties with hexamine which are in turn interwoven with anionic moieties via water molecules. In contrast the supramolecular structure of 3 shows motif. [Copyright &y& Elsevier]

Abstract A non-heme tetra-iron cluster, [Fe 4 III(μ- O) 2 (μ- OAc) 6 (2,2′-bpy) 2 (H 2 O) 2 ](NO 3 −)(OH−) (1), [OAc = acetate; 2,2′-bpy = 2,2′-bipyridine] containing oxido- and acetato-bridges was synthesized and structurally characterized by different spectroscopic methods including single crystal X-ray diffraction studies. X-ray crystal structure analysis of 1 revealed that tetra-iron complex was crystallized in monoclinic system with C 2/ c space group. Each of the Fe centres in 1 was found to exist in octahedral geometry and interconnected by oxido- and acetato-bridges. Bond valence sum (BVS) calculation recommended the existence of iron centres in +3 oxidation state. Variable temperature magnetic measurement authenticated the dominating antiferromagnetic ordering among the iron centres in the solid state of 1. This tetra-iron cluster was also evaluated as an efficient catalytic system towards the oxidation of both linear & cyclic alkanes without production of primary C H bond oxidation products. Oxidation of secondary C H bonds attested the formation of both the corresponding alcohols & ketones in 27–900 TONs. The tetra-iron catalytic system with Alcohol/Ketone values 0.2–1.7 indicated the involvement of freely diffusing carbon-centered radicals rather than metal based oxidant. Graphical abstract This paper represents synthesis of a new oxido-acetato-bridged tetra-iron(III) complex, [Fe 4 III(μ- O) 2 (μ- OAc) 6 (2,2′-bpy) 2 (H 2 O) 2 ](NO 3 −)(OH−) which displays excellent catalytic activity towards C H activation property based on carbon centered radical in solution. Image 1 Highlights • Synthesis and characterization of an oxido-acetato-bridged tetrairon(III)-bipyridine complex. • The iron(III) complex displays antiferromagnetic ordering of iron centres in the solid state. • The iron complex efficiently activate C H bond of both linear & cyclic alkanes. • Probably generation of freely diffusing carbon-centered radical account for such activity. [ABSTRACT FROM AUTHOR]

A mononuclear nickel(II) complex, [Ni(bpy) 2 (OH 2 )(NO 3 )](NO 3 ) ( 1 ) [bpy = 2,2′-bipyridine], has been synthesised and structurally characterised by routine analytical techniques including a single crystal X-ray diffraction study. X-ray crystal structure analysis shows that 1 crystallises in the triclinic system with the P 1 ¯ space group and adopts an octahedral geometry. The nickel(II) complex has been evaluated as a functional model for phosphatase and catechol dioxygenase enzymes by using 4-nitrophenylphosphate (PNPP) and 3,5-di- tert -butylcatechol (DTBC) as model substrates in aqueous-DMF and acetonitrile media respectively. This mononuclear nickel complex exhibits good hydrolytic phosphoester cleavage efficiency, viz. a k cat value of 8.42 × 10 3 h −1 , and produces mostly benzoquinone ( k obs = 2.3 × 10 −3 min −1 ) and intradiol cleavage products during an investigation of catechol dioxygenase activity. [ABSTRACT FROM AUTHOR]

A mononuclear copper(II) complex [Cu(phen)(OH 2 ) 2 (NO 3 )](NO 3 ) ( 1 ) [phen = 1,10-phenanthroline] has been synthesized and structurally characterized by different spectroscopic characterization methods including single crystal X-ray diffraction study. X-ray crystal structure analysis shows that 1 adopts square pyramidal geometry with CuN 2 O 3 chromophore and the molecule crystallises in P 2 1 / n space group. 1 has been evaluated as model system for the catechol oxidase enzyme by using 3,5 -di -tert-butylcatechol (DTBC) as the substrate in methanol medium, revealing that 1 exhibits greater catalytic activity with K cat value 3.91 × 10 3 h −1 compared to a few copper(II) complexes of the same class. Electrochemical analysis suggests that the mononuclar Cu(II) complex mimics the catechol oxidase enzyme in methanolic medium through radical pathway. The complex cleaves the double strand of pBR 322 plasmid DNA in a concentration-dependent manner so as for the DNA to change from super coiled form to both nicked circular and linear forms. The complex is cytotoxic to the human hepatocarcinoma cell HepG2, as revealed in MTT assay. AO/EB and Hoechst 33528 fluorescent staining techniques were used to find the mode of cell death. Interestingly, AO/EB and Hoechst stained cells observed at IC 50 concentration shows that 1 brings about conformational change on DNA to induce apoptosis which would be the basis underlying its cytotoxic property. [ABSTRACT FROM AUTHOR]

Interactions involving fluorine is an area of contemporary research. To unravel the importance of weak C–H⋯F hydrogen bonds and C–H⋯π interactions in organic compounds in the presence of strong hydrogen bond, a series of N -benzylideneanilines with simultaneously hydroxyl (–OH) and fluorine substitutions were synthesized for structural analysis. These compounds have been studied through experimental single crystal X-ray diffraction analysis and computational methods (Gaussian09 and AIM2000). The hydroxyl group present in all the molecules were found to form strong O–H⋯N hydrogen bond, but the spatial arrangement of the molecules connected by this hydrogen bond have been found to be controlled by the weak C–H⋯F and C–H⋯O hydrogen bonds, weak C–H⋯π and π⋯π interactions. This manuscript illustrates the importance of several weaker interactions in altering the packing modes in the presence of strong hydrogen bonds. [ABSTRACT FROM AUTHOR]

• Synthesis and characterization of a copper(II) complex. • Solvent induced distortion to the coordination environment of Cu(II) centre. • Bio-mimics of catecholase activity with high turnover number, 4.75 × 102 h–1. • Exploitation of fungicidal and anti-proliferative property. This research work reports the synthesis, single crystal X-ray structure, catechol oxidation, fungicidal and antiproliferative activity of a newly synthesized copper(II) complex, [Cu(L) 2 ]H 2 O . CH 3 OH (1) containing an azo-functionalized Schiff base, H L = 2-methoxy-6-((Z)-((4-((E)-phenyldiazenyl)phenyl)imino)methyl)phenol. The crystal structure analysis reveals that the Cu(II) centre exists in a highly distorted square planar geometry. The crystallize water and methanol form a strong intermolecular association through H-bonding. More importantly, the H atoms of the lattice water interact with the O atoms of ligand units leading to 5- and 6-membered cycles through the H-bonding network and distort the square planar geometry. The copper(II) complex has emerged as a bioinspired catalyst in the oxidative transformation of 3,5-di- tert -butylcatechol (DTBC) to o-benzoquinone in methanol with a high turnover number, 4.75 × 102 h–1. Electrochemical analysis of the copper(II) complex in presence of DTBC recommends the generation of catechol/o-benzosemiquinone redox couple in the course of oxidation. The EPR spectral analysis of 1 in presence of DTBC was found silent and suggested the antiferromagnetic interaction between copper centre and benzosemiquinone species. The copper(II) complex turns out to be a potential fungicidal agent against clinical candida albicans and scanning electron microscope studies confirm the destruction of the fungal cell membrane with the deposition of copper. The IC 50 value of the copper complex was determined as 15 µg/mL which suggests the excellent antiproliferative potency of the synthetic compound against the breast cancer cell lines, MCF-7. [Display omitted] [ABSTRACT FROM AUTHOR]

Synthesis and structural characterization of a linkage isomer, bis(2,2′-dipyridylamine)dithiocyanato(k -S)nickel(II), [Ni(dpa) 2 (k -SCN) 2 (1) of a previously reported Ni(II) complex, [Ni(dpa) 2 (k -NCS) 2 (dpa = 2,2′-dipyridylamine; SCN = thiocyanate) has been reported herein. X-ray structural analysis of 1 reveals that Ni(II) complex crystallizes in monoclinic system with P 2 1 / c space group and exists in trans configuration. The coordination geometry for 1 adopts a tetragonal structure. Supramolecular aspects of the Ni(II) complex indicate that N atom of SCN behaves as a donor and H atom of dpa ligand acts as a receptor in growing 1D crystalline structure along b axis in solid state. The aromatic rings in 1 prefer to exist in face-centred stacking with interplanar distance of 3.426 Å and supports strongly to form self-assembled 3D crystalline architecture. Hirshfeld surface analysis further recommends this crystalline assembly in solid state. 1 exhibits promising phosphatase activity towards disodium(4-nitrophenyl)phosphate (PNPP) in aqueous-methanolic medium. The hydrolytic phosphatase efficiency for 1 is determined in terms of turnover number (k cat) as 3.38 × 104 h−1. Moreover, density functional theoretical computations closely replicate the structural parameters and spectroscopic behaviour of 1. Image 1 • Synthesis and X-ray structure of a linkage isomer, bis(2,2′-dipyridylamine)dithiocyanato(k-S)nickel(II), [Ni(dpa)2(k-SCN)2]. • The nickel(II) complex efficiently cleave PNPP with TON, 3.38 × 104 h−1. • The theoretical findings employing DFT have been well corroborated with the experimental results. [ABSTRACT FROM AUTHOR]