CuII Pyrazolyl-Benzimidazole Dinuclear Complexes with Remarkable Antioxidant Activity.

Three dinuclear coordination complexes generated from 1-n-butyl-2-((5-methyl-1H-pyrazole-3-yl)methyl)-1H-benzimidazole (L), have been synthesized and characterized spectroscopically and structurally by single crystal X-ray diffraction analysis. Reaction with iron(II) chloride and then copper(II) nitrate led to a co-crystal containing 78 % of [Cu(NO3 )(µ-Cl)(L')]2 (C1 ) and 22 % of [Cu(NO3 )(µ-NO3 )(L')]2 (C2 ), where L was oxidized to a new ligand L' . A mechanism is provided. Reaction with copper chloride led to the dinuclear complex [Cu(Cl)(µ-Cl)(L)]2 (C3 ). The presence of N-H⋅⋅⋅O and C-H⋅⋅⋅O intermolecular interactions in the crystal structure of C1 and C2 , and C-H⋅⋅⋅N and C-H⋅⋅⋅Cl hydrogen bonding in the crystal structure of C3 led to supramolecular structures that were confirmed by Hirshfeld surface analysis. The ligands and their complexes were tested for free radical scavenging activity and ferric reducing antioxidant power. The complex C1 /C2 shows remarkable antioxidant activities as compared to the ligand L and reference compounds.

Coordination complexes constructed from pyrazole-acetamide and pyrazole-quinoxaline: effect of hydrogen bonding on the self-assembly process and antibacterial activity.

Two mononuclear coordination complexes of N-(2-aminophenyl)-2-(5-methyl-1H-pyrazol-3-yl)acetamide (L1), namely [Cd(L1)2Cl2] (C1) and [Cu(L1)2(C2H5OH)2](NO3)2 (C2) and one mononuclear complex [Fe(L2)2(H2O)2](NO3)2·2H2O (C3), obtained after in situ oxidation of L1, have been synthesized and characterized spectroscopically. As revealed by single-crystal X-ray diffraction, each coordination sphere made of two heterocycles is completed either by two chloride anions (in C1), two ethanol molecules (in C2) or two water molecules (in C3). The crystal packing analysis of C1, C2 and C3, revealed 1D and 2D supramolecular architectures, respectively, via various hydrogen bonding interactions, which are discussed in detail. Furthermore, evaluation in vitro of the ligands and their metal complexes for their antibacterial activity against Escherichia coli (ATCC 4157), Pseudomonas aeruginosa (ATCC 27853), Staphylococcus aureus (ATCC 25923) and Streptococcus fasciens (ATCC 29212) strains of bacteria, revealed outstanding results compared to chloramphenicol, a well-known antibiotic, with a normalized minimum inhibitory concentration as low as 5 µg mL-1.

Solvent induced supramolecular polymorphism in Cu(II) coordination complex built from 1,2,4-triazolo[1,5-a]pyrimidine: Crystal structures and anti-oxidant activity.

Two Cu(II) coordination complexes, C1 and C2 of the formula [Cu(4)2(H2O)2], have been prepared by reaction between CuCl2·2H2O and 7-ethoxycarbonylmethyl-5-methyl-1,2,4[1,5-a]pyrimidine (L) in a 1:2 M:L molar ratio. The L molecule decomposes during the reaction process into 7-carboxy-5-methyl-[1,2,4]-triazolo[1,5-a]pyrimidine (4) through an intermediate, ethyl 2,2-dihydroxy-2-(5-methyl-[1,2,4]triazolo[1,5-a]pyrimidin-7-yl)acetate (5), which has been isolated and its crystal structure determined by X-ray diffraction. The X-ray analysis of the single crystals of [Cu(4)2(H2O)2] obtained from the slow evaporation of EtOH and MeOH, separately, revealed the formation of "solvent induced" polymorphs C1 and C2, respectively. The primary supramolecular synthon for C1 and C2 are six membered ring, and square shaped hydrogen bonded architecture, respectively. The self-assembly of such synthons resulted in a two dimensional hydrogen bonded sheet supported by OH⋯O interactions. In addition, the antioxidant properties of the ligands and its complexes were evaluated in vitro using 1,1-diphenyl-2-picrylhydrazyl acid, 2,2'-azino-bis (3-ethylbenzothiazoline-6 sulfonic acid radical scavenging methods and ferric reducing antioxidant power.

Novel Co(II) and Cu(II) coordination complexes constructed from pyrazole-acetamide: Effect of hydrogen bonding on the self assembly process and antioxidant activity.

In the present study, two pyrazole-acetamide derivatives namely N­(2­aminophenyl)­2­(5­methyl­1H­pyrazol­3­yl) acetamide (L1) and (E)­N­(2­(1­(2­hydroxy­6­methyl­4­oxo­4H­pyran­3­yl)ethylideneamino)phenyl)­2­(5­methyl­1H­pyrazol­3­yl) acetamide (L2) have been synthesized and characterized by infrared spectrophotometry (IR), nuclear magnetic resonance spectroscopy (NMR) and electrospray ionization-mass spectrometry (ESI-MS). Two coordination complexes of L1 and L2, namely [Co(L1)2(EtOH)2]·Cl2 (1) and [Cu(L2)]·H2O (2), respectively have been synthesized and characterized by elemental analysis and spectroscopic studies. The solid state structure of these two complexes was established by single crystal X-ray crystallography. In complex 1, the amide O and pyrazole N atoms of two molecules of L1 take part in coordination with octahedral Co(II) ions, the remaining two coordination sites being occupied by two EtOH molecules leading to a N2O4 coordination environment. On the other hand, the imine N atoms, pyrazole N and O atoms of the 2­hydroxy­6­methyl­4H­pyran­4­one function present in L2 are involved in coordination with Cu(II) ions, resulting in a distorted square planar geometry displaying a N2O4 chromophore, in complex 2. The crystal packing analysis of 1 and 2, revealed 1D and 2D supramolecular architectures respectively, via various hydrogen bonding interactions, which are discussed in the present account. Furthermore, the antioxidant activity of the ligands and their complexes were determined in vitro by 1,1­diphenyl­2­picrylhydrazyl (DPPH), 2,2'­azino­bis(3­ethylbenzothiazoline­6­sulphonic acid (ABTS) and ferric reducing antioxidant power(FRAP), showing that the ligands L1 and L2 and complexes 1 and 2 present significant antioxidant activity.

Coordination polymers built from 1,4-bis(imidazol-1-ylmethyl)benzene: from crystalline to amorphous.

The supramolecular chemistry of the bis-imidazole ligand 1,4-bis(imidazol-1-ylmethyl)benzene, popularly known as bix, has been explored by various researchers in order to synthesize functional coordination polymers (CPs). The flexibility of the bix ligand, its unpredictable conformation and its coordination behaviour with transition metal ions have resulted in a huge number of structurally diverse and functionally intriguing CPs. In this perspective review we discuss the progress in CPs of bix between 1997 and today. More precisely, this review emphasizes the developments in functional supramolecular coordination polymers built from the bix ligand, from crystalline materials to amorphous nanomaterials.

Crystal engineering of Fe(II) spin crossover coordination polymers derived from triazole or tetrazole ligands.

The past decade has witnessed intense research activity in the area of Fe(II) spin crossover coordination polymers, which are structurally diverse and functionally intriguing materials. In this endeavor, a less exploited series of ligands have been selected among various N-donor triazole and tetrazole molecules. Developing conventions that allow the tailoring of such functional materials with predictable architecture and properties is an important objective and current interest in crystal engineering. However, detailed knowledge on the structure-property correlation is still scanty due to the small number of crystal structures of such compounds. The principal focus is to decipher the effect of various supramolecular factors such as intermolecular interactions, hydrogen bonding etc., on the resultant Fe(II) coordination polymers. This tutorial review aims at highlighting some of the developments of such structurally diverse and functionally intriguing 1D polymeric chains, 2D and 3D networks built from triazole or tetrazole ligands exhibiting fascinating spin crossover phenomena.

Coordination polymers: what has been achieved in going from innocent 4,4'-bipyridine to bis-pyridyl ligands having a non-innocent backbone?

The last two decades have witnessed the research activities in the area of coordination polymers (CPs), which are structurally diverse and functionally intriguing materials. In this endeavor, the most exploited ligand has been a structurally rigid N-donor compound having an innocent backbone (incapable of forming hydrogen bond) namely 4,4'-bipyridine. Much has been achieved by exploiting this wonder ligand in the area of CPs. However, the positional isomers such as 3,3'-bipyridine or 4,3'-bipyridine (which understandably induce diverse ligating topology as compared to their more symmetrical 4,4' counterpart) were not exploited in much detail presumably because of the difficulty in their synthetic accessibility. To get access to such N-donor ditopic ligands having diverse ligating topology, much efforts have been focused in the last decade or so to design such positional isomers of 4,4'-bipyridine having a non-innocent backbone (capable of forming hydrogen bond). The principal focus of such studies is to decipher the effect of diverse ligating topology and the non-innocent backbone of the ligands on the overall supramolecular structures and functions of the resultant CPs. This tutorial review aims at highlighting some of the developments of such structurally diverse and functionally intriguing CPs derived from N-donor ditopic ligands having a non-innocent backbone.

Folding and unfolding movements in a [2]pseudorotaxane.

A new dibenzo[24]crown-8 derivative (1) was synthesized and functionalized with aromatic moieties such as naphthalene and coumarin units. These two fluorophores are known to form an effective FRET (Forster resonance energy transfer) pair, and this formed the basis for the design of this host crown ether derivative. Results of the steady-state and time-resolved fluorescence studies confirmed the resonance energy transfer between the donor naphthalene moiety and acceptor coumarin fragment, while NMR spectra and computational studies support a folded conformation for the uncomplexed crown ether 1. This was found to form an inclusion complex, a [2]pseudorotaxane type with imidazolium ion derivatives as the guest molecules with varying alkyl chain lengths ([C(4)mim](+) or [C(10)mim](+)). The host crown ether (1) tends to adopt an open conformation on formation of the interwoven inclusion complex (1·[C(4)mim](+) or 1·[C(10)mim](+)). This change in conformation, from the folded to a open one, was predicted by computational as well as (1)H NMR studies and was confirmed by single crystal X-ray structure for one (1·[C(4)mim](+)) of the two inclusion complexes. The increase in the effective distance between the naphthalene and coumarin moieties in the open conformation of these inclusion complexes was also supported by the decrease in the effective FRET process that was operational between naphthalene and coumarin moieties in the free molecule (1). Importantly, this inclusion complex formation was found to be reversible, and in the presence of a stronger base/polar solvent, such as triethyl amine/DMSO, the deprotonation/effective solvation of the cationic imidizolium ions ([C(4)mim](+) or [C(10)mim](+)) resulted in decomplexation or dethreading with restoration of the original emission spectra for 1, which signifies the subsequent increase in the FRET process. Thus we could demonstrate that a molecular folding-unfolding type of movement in the crown ether derivative could be induced by chemical input as an imidazolium ion.

Chiral gels derived from secondary ammonium salts of (1R,3S)-(+)-camphoric acid.

In order to have access to chiral gels, a series of salts derived from (1R,3S)-(+)-camphoric acid and various secondary amines were prepared based on supramolecular synthon rationale. Out of seven salts prepared, two showed moderate gelation abilities. The gels were characterized by differential scanning calorimetry, table top rheology, scanning electron microscopy, single crystal and powder X-ray diffraction. Structure property correlation based on X-ray diffraction techniques remain inconclusive indicating that some of the integrated part associated with the gelation phenomena requires a better understanding.

A novel, air-stable phosphine ligand for the palladium-catalyzed Suzuki-Miyaura cross-coupling reaction of chloro arenes.

A novel, air-stable phosphine ligand, prepared from readily available 2-bromonitrobenzene and vinylmagnesium bromide, combines with Pd(CH(3)CN)(2)Cl(2) to afford an effective catalyst for Suzuki-Miyaura cross-coupling of aryl, heteroaryl, and allyl chlorides with phenylboronic acid.

3,3'-{Ethane-1,2-diylbis[carbonylbis(azanediyl)]}dipyridinium tetra-chloridoplatinate(II).

In the crystal structure of the title compound, (C(14)H(18)N(6)O(2))·[PtCl(4)], the cation and square-planar anion are located on special positions (on a twofold axis and an inversion centre, respectively). In the crystal structure, N-H⋯Cl hydrogen bonds lead to a staircase-like motif. The central ethane backbone of the cation is disordered over two positions of equal occupancy.

catena-Poly[[[triaqua-sulfatozinc(II)]-µ-3,3'-bis-(3-pyrid-yl)-1,1'-(m-phenyl-ene)diurea] methanol solvate monohydrate].

In the title coordination polymer, {[Zn(SO(4))(C(18)H(16)N(6)O(2))(H(2)O)(3)]·CH(3)OH·H(2)O}(n), the Zn(2+) ion adopts a slightly distorted cis-ZnN(2)O(4) octa-hedral geometry arising from three coordinated water mol-ecules, one sulfate ion and two bridging 3,3'-bis-(3-pyrid-yl)-1,1'-(m-phenyl-ene)diurea (bpmpbu) ligands. The dihedral angles between the central benzene ring and two terminal pyridine rings of the bpmbpu mol-ecule are 10.58 (17) and 34.63 (16)°. In the crystal, the ligands bridge the Zn(II) ions, thus generating a one-dimensional zigzag coordination polymer propagating in [010]. The crystal structure features extensive N-H⋯O and O-H⋯O hydrogen-bonding inter-actions.

Copper(II) and nickel(II) complexes of beta-aminoketoxime ligand: syntheses, crystal structures, magnetism, and nickel(II) templated coupling of oxime with nitrile.

The syntheses, molecular structures, and magnetic properties of a dicopper(II) complex, [Cu(2)(HL(1))(2)](ClO(4))(2) (1), and its nickel(II) analog, [Ni(2)(HL(1))(2)](ClO(4))(2) (2), of a beta-amino ketoxime ligand (H(2)L(1) = 4,4,9,9-tetramethyl-5,8-diazadodecane-2,11-dione dioxime) are discussed. The metal centers in out-of-plane oximate bridged dinuclear complexes (1 and 2) display distorted trigonal bipyramidal geometry and form a six-membered M(2)(NO)(2) ring oriented in a boat conformation. The two copper(II) centers in 1 interact ferromagnetically giving rise to a triplet-spin ground state whereas the two nickel(II) centers in 2 interact antiferromagnetically to stabilize a singlet-spin state. Variable temperature magnetic susceptibility measurements establish the presence of a weak ferromagnetic coupling (J = 13 cm(-1)) in 1 and a weak anitiferromagnetic coupling (J = -12 cm(-1)) in 2. The exchange coupling constant derived from B3LYP computations in conjunction with broken symmetry spin-projection techniques for the oximate bridged dinuclear copper(II) complex shows excellent agreement with the corresponding experimental value. A square-planar mononuclear nickel(II) complex of the dioxime ligand, [Ni(H(2)L(1))](ClO(4))(2) (3), is reported along with its crystal structure, which reacts with acetonitrile to produce a six-coordinate mononuclear complex, [Ni(L(2))](ClO(4))(2) (4). The ligand (L(2)) in complex 4 is the iminoacyl derivative of oxime, where the coupling of oxime and acetonitrile takes place via a proton-assisted pathway. The iminoacylation of H(2)L(1) works with other nitriles like butyronitrile and benzonitrile. Computational studies support a proton-assisted coupling of oxime with nitrile. The critical transition states have been located for the iminoacylation reaction. Complex 4 can be converted back to complex 3 by reacting with sodium acetate in methanol.

Supramolecular synthons in noncovalent synthesis of a class of gelators derived from simple organic salts: instant gelation of organic fluids at room temperature via in situ synthesis of the gelators.

The supramolecular synthon approach has been employed to synthesize noncovalently a series of low molecular mass organic gelators (LMOGs) derived from benzylammonium salts of variously substituted benzoic acids. The majority of the salts (75%) prepared showed interesting gelation properties. Instant gelation of an organic fluid, namely methyl salicylate, was achieved at room temperature by using most of the gelator salts by in situ synthesis of the gelators. Table top rheology and scanning electron microscopy (SEM) were used to characterize the gels. Single crystal X-ray diffraction studies revealed the presence of both 1D and 2D supramolecular synthons. X-ray powder diffraction (XRPD) studies indicated the presence of various crystalline phases in the fibers of the xerogels. By using these data, a structure-property correlation has been attempted and the working hypothesis for designing the gelator has been reinforced.

Combinatorial library of primaryalkylammonium dicarboxylate gelators: a supramolecular synthon approach.

Following the supramolecular synthon approach, a combinatorial library comprising 35 organic salts derived from 7 dicarboxylic acids (malonic-, succinic-, adipic-, L-tartaric-, maleic-, phthalic-, and isophthalicacid) and 5 primaryalkyl amines Me-(CH2)n-NH2 (n = 11-15) was prepared and scanned for gelation. About 66% of the salts in the combinatorial library were found to show moderate to good gelling ability in various polar and nonpolar solvents including commercial fuels such as petrol. The majority of the salts having a rigid, unsaturated anionic backbone (maleate, phthalate, and isophthalate) did not show gelation; only the corresponding hexadecylammonium salts showed gelation. Some of the representative gels were characterized by rheology, small-angle neutron scattering (SANS), optical microscopy (OM), and scanning electron microscopy (SEM). Single-crystal structures of two gelator and two nongelator salts were also discussed in the context of supramolecular synthon and structure-property correlation.