Cation···π interactions: QTAIM and NBO studies on the interaction of alkali metal cations with heteroaromatic rings

The cation···π interactions of alkali metal cations (Li⁺, Na⁺, and K⁺) with five-membered heteroaromatic rings [furan(C₄H₄O), thiophene(C₄H₄S), pyrrole(C₄H₅N)] were examined by high level ab initio calculations, to investigate the different roles of C₄H₄O, C₄H₄S, and C₄H₅N as the electron donor, the influential factors that affect these interactions, the nature of this kind of cation···π interaction, and to determine topological and energetical properties to characterize these interactions. The sulfur atom in C₄H₄S plays a certain role in the cation···π interactions except the C–C π bond, which is different from C₄H₄O and C₄H₅N. The size of cation and the character of heteroaromatic ring are two influential factors that affect the cation···π interactions. The studied cation···π interactions can be classified as “closed-shell” and noncovalent interactions. The electron density and its Laplacian at the bond critical points and ring critical points generated upon complexation are useful measurements for the strength of cation···π interactions.     

Physicochemical properties and catalytic activity of metal–carbon carrier composite materials

Composite metal–carbon materials are created on the basis of different kinds of carbon (multiwall carbon nanotubes, carbon black, Sibunit carbon–carbon material) and metals (Ag, Ni, Co), and their physicochemical and catalytic properties are investigated. It is shown that interaction between metals and carbon carriers proceeds not only with the functional groups on the surfaces of the carriers, but also through a system of–C–C–conjugated bonds. Silver deposited on the surface of a carbon carrier has a crystalline structure (d _cr = 10–15 nm), while nickel has an amorphous lamellar structure. Based on quantum-chemical calculations using the density functional theory, it is shown that cumene oxidation occurs via a homogeneous–heterogeneous mechanism.     

Polymer-supported 2,2′-dipyridylmethane: catalytic activity of transition metal complexes in hydrogenations and oligomerizations

The palladium(II) acetate complex of the chelating ligand 2,2′-dipyridylmethane supported on polystyrene-2% divinylbenzene is an efficient catalyst for hydrogenation of alkenes and alkynes. Cyclopentadiene can be reduced with high selectivity to cyclopentene, but no selectivity is observed for the non-conjugated diene 1,5-cyclooctadiene. In the hydrogenation of 3-methylcyclohex-2-en-1-ol only small amounts of ketone are formed as a by-product, in contrast to the reaction catalysed by palladium on charcoal. Nickel(II) complexes of the same ligand catalyze the trimerization of butadiene to 1,5,9-cyclododecatrienes.     

QTAIM and ETS-NOCV analyses of intramolecular CH···HC interactions in metal complexes

The topological analysis, based on the quantum theory of atoms in molecules (QTAIM) of Bader and the ETS-NOCV charge and energy decomposition method have been used to characterize coordination bonds, chelating rings, and additional intramolecular interactions in the ZnNTA and ZnNTPA complexes in solvent. The QTAIM and ETS-NOCV studies have conclusively demonstrated that the H-clashes (they are observed only in the ZnNTPA complex and classically are interpreted as steric hindrance destabilizing a complex) are characterized by (i) the electron flow channel between the H-atoms involved, as discovered by the ETS-NOCV analysis (on average, ΔE(orb) = -1.35 kcal mol(-1)) and (ii) QTAIM-defined a bond path that indicates the presence of a preferred quantum-mechanical exchange channel, hence, they should be seen as H-H intramolecular bonding interactions. The main reason for the formation of a weaker ZnNTPA complex was attributed to the strain energy (from both QTAIM and ETS-NOCV techniques) and the larger Pauli repulsion contribution found from the ETS-NOCV analysis. An excellent agreement between physical properties controlling the stability of the two complexes was found from the two techniques, QTAIM and ETS-NOCV.     

Naringenin Schiff base: antioxidant activity,acid–base profile,and interactions with DNA

A Schiff base derived from naringenin (NTSC) and its complex with Cu(II) ([Cu(H₃L)(OAc)]·H₂O, Cu(II)–NTSC) have been synthesized and characterized by physicochemical and spectroscopic methods. EPR studies confirmed that nitrogen, oxygen, and sulfur are the donor atoms bound to Cu(II) in the complex. The geometry of the complex has been modelled using DFT methods. Furthermore, naringenin and NTSC were used for the formation of Cu(II) complexes in solution, for comparison of biological activities. Antioxidant studies confirmed better radical scavenging activity of both NTSC and its Cu(II) complex compared to naringenin. The interaction of these compounds with calf thymus DNA was monitored by UV–Vis spectroscopy.     

Syntheses,structures and catalytic activities of low-coordinated rare-earth metal complexes containing 2,2′-pyridylpyrrolides

Reactions of the ligand precursors 2-(2′-pyridyl)-3,5-Me₂-pyrrole ( L ¹ H) and 2-(2-pyridyl)-3,4,5-Me₃-pyrrole ( L ² H) with [(Me₃Si)₂N]₃RE(μ-Cl)Li(THF)₃ in toluene afforded a series of low-coordinated rare-earth metal bis-amido complexes L ¹ RE[N(SiMe₃)₂]₂ [RE = Y ( 1a ), Dy ( 1b ), Er ( 1c ), Yb ( 1d )] and L ² RE[N(SiMe₃)₂]₂ [RE = Y ( 2a ), Dy ( 2b ), Er ( 2c ), Yb ( 2d )]. With the ionic radius of rare-earth metal increasing, the reaction of L ¹ H and [(Me₃Si)₂N]₃RE(μ-Cl)Li(THF)₃ gave dinuclear complexes ( L ¹ )₂RE(μ-Cl)(μ-η⁵:η¹:η¹- L ¹ )RE( L ¹ )[N(SiMe₃)₂]₂ [RE = Sm ( 1e ), Pr ( 1f )]; however, the reaction of L ² H and [(Me₃Si)₂N]₃Sm(μ-Cl)Li(THF)₃ afforded ( L ² )₂Sm[N(SiMe₃)₂]₂ ( 2e ). Results indicated that the ionic radius of rare-earth metal and subtle change in the ligands have substantial effects on the structure and bonding mode of complexes. The complexes showed a high catalytic activity for the ring-opening reaction of cyclohexene oxide with amines to afford various β-aminoalcohols under mild solvent-free conditions.     

Molybdenum(VI)–oxodiperoxo complex containing an oxazine ligand: synthesis,X-ray studies,and catalytic activity

A new mononuclear molybdenum(VI)–oxodiperoxo complex [MoO(O₂)₂(phox)] with a simple bidentate ligand, 2-(2′-hydroxyphenyl)-5,6-dihydro-1,3-oxazine (Hphox), has been synthesized and characterized by X-ray structure analysis, elemental analysis, infrared, and ¹H NMR spectroscopy. A triclinic space group P-1 was determined by X-ray crystallography from single-crystal data of this complex. The resulting complex functioned as a facile sulfide oxidation catalyst with urea hydrogen peroxide as terminal oxidant at room temperature. The catalyst showed efficient reactivity in oxidation of sulfides giving high yield and selectivity.     

Hydrodesulfurization catalysts P-Mo-W/γ-Al2O3: Characterization and catalytic activity

P-Mo-W/γ-Al₂O₃ catalysts with various Mo and W contents have been synthesized. The parameters of the porous structure of their sulfide and oxide forms have been determined. The geometric parameters of the active phase of the sulfide catalysts have been calculated using high-resolution transmission electron microscopy data. The catalytic activity has been estimated in dibenzothiophene (DBT) hydrodesulfurization (HDS). The reaction under the conditions examined proceeds mainly as direct hydrodesulfurization. The catalytic activity has been correlated with the Mo/W molar ratio and with the proportions of edge and corner sites.     

Transition metal complexes constructed by pyridine–amino acid: fluorescence sensing and catalytic properties

Transition Metal Chemistry - Four amino acid Schiff base complexes—one with a 3D network structure ({[Cd2(PYSA)2(H2O)]·3H2O}n (1)) and the other three with a supramolecular network...     

Design and development of several polymeric metal–organic frameworks,spectral characterization,and their antimicrobial activity

Coordination polymers were obtained by the reaction of metal acetates, M(CH₃COO)₂·xH₂O {where M = Mn(II), Co(II), Ni(II) and Cu(II)} with AFP ligand (AFP = 5,5'-(piperazine-1,4-diylbis(methylene))bis(2-aminobenzoic acid). The AFP ligand was prepared by the one-pot, two-step reaction of formaldehyde, 2-aminobenzoic acid, and piperazine. Structural and spectroscopic properties have been studied by elemental, spectral (FT-IR, ¹H NMR, ¹³C NMR, and UV–vis), and thermogravimetric analysis. UV–vis spectra and magnetic moment values indicate that Mn(II), Co(II), and Ni(II) polymer–metal complexes are octahedral, while Cu(II) and Zn(II) polymer–metal complexes are distorted octahedral and tetrahedral, respectively. The analytical data confirmed that the coordination polymers of Mn(II), Co(II), Ni(II), and Cu(II) are coordinated with two water molecules, which are further supported by infrared spectra and thermogravimetric analysis data. The prepared polymer–metal complexes showed good antibacterial activities against all tested microorganisms; however, the AFP ligand was also found to be effective, but relatively less than their polymer–metal complexes. Along with antibacterial activity, all the polymer–metal complexes exhibit significant antifungal activity against most of the tested fungal strains. The results of antimicrobial activity reveals that the AFP–Cu(II) showed the highest antibacterial and antifungal activity than other polymer–metal complexes.     

Binding site residues in β-lactamases: role in non-classical interactions and metal binding

Proteins bind with one or more metal ions in their native state to facilitate the biological function of the protein. The study of critical interactions between the biological molecules and metals is an important field of study. In this work, we focus on the functional specificity of residues coordinating with the metals commonly found in β-lactamases, Zn, Mg, Na, Cu, Mn, Ni, Fe, K, and Cd through non-classical interactions. All the residues located in the metal-binding site of β-lactamases are involved in non-classical interactions. The data obtained from this study will be useful to understand the functional role of metal-coordinating residues in the specificity of β-lactamases, thus offering promising strategy to design effective β-lactamase inhibitors.     

Characteristics of X-H···π interactions: ab initio and QTAIM studies

The MP2/6-311++G(d,p) calculations were performed on several hydrogen-bonded systems. Different complexes were taken into account to analyze various types of hydrogen bonds, possessing different types of proton donors and proton acceptors as well as characterized by the broad range of the interaction energy. The Quantum Theory of Atoms in Molecules is applied. The results of the hybrid variational-perturbational approach are discussed. The unique properties of hydrogen bonds, where π-electrons act as the proton acceptor (X-H···π), are analyzed, and these interactions are compared with the other types of hydrogen bonds, mainly with C-H···Y interactions. It is shown that for X-H···π systems the ellipticity at the bond critical point of the proton···acceptor interaction is much greater than for the other types of hydrogen bonds. However, both X-H···π and C-H···Y interactions are characterized by the dominance of the dispersive energy.     

Single-turn helix-coil strands stabilized by metal···metal and π-π interactions of the alkynylplatinum(II) terpyridyl moieties in meta-phenylene ethynylene foldamers

Dinuclear alkynylplatinum(II) terpyridyl complexes with oligomeric bridge consisting of five repeating meta-phenylene ethynylene (mPE) units have been found to exhibit a strong tendency to fold back onto themselves to form short helical strands through the stabilization of Pt···Pt and π-π interactions. The steric bulk of the terpyridine ligands and the length of the oligomeric bridge have been found to affect the extent of the intramolecular Pt···Pt interaction that governs the stabilization of the short helical strand in solution. Their folding properties via Pt···Pt and π-π stacking interactions have been studied by (1)H NMR, 2D ROESY NMR, electronic absorption, and emission spectroscopies.     

Emerging supramolecular synthons: C-H···π(chelate) interactions in metal bis(1,1-dithiolates)

Crystal structures of transition and main group element 1,1-dithiolates are shown to be partially sustained by C-H···π(chelate) interactions. For the planar binary bisdithiocarbamates, C-H···π(MS(2)C) interactions lead to aggregation patterns ranging from a 0-D four molecule aggregate to a 3-D architecture but with the majority of structures featuring 1-D or 2-D supramolecular assemblies.     

Two-step electrosynthesis and catalytic activity of CoO−CoO • xH2O-supported Ag,Au, and Pd nanoparticles

Russian Chemical Bulletin - Two-step electrosynthesis of CoO-CoO?xH2O-supported metal nanoparticles (MNPs, M = Au, Ag, Pd) was carried out in N,N-dimethylformamide in the absence and in...     

Comparison of aromatic NH···π, OH···π, and CH···π interactions of alanine using MP2, CCSD, and DFT methods

A comparison of the performance of various density functional methods including long‐range corrected and dispersion corrected methods [MPW1PW91, B3LYP, B3PW91, B97‐D, B1B95, MPWB1K, M06‐2X, SVWN5, ωB97XD, long‐range correction (LC)‐ωPBE, and CAM‐B3LYP using 6‐31+G(d,p) basis set] in the study of CH···π, OH···π, and NH···π interactions were done using weak complexes of neutral (A) and cationic (A⁺) forms of alanine with benzene by taking the Møller–Plesset (MP2)/6‐31+G(d,p) results as the reference. Further, the binding energies of the neutral alanine–benzene complexes were assessed at coupled cluster (CCSD)/6‐31G(d,p) method. Analysis of the molecular geometries and interaction energies at density functional theory (DFT), MP2, CCSD methods and CCSD(T) single point level reveal that MP2 is the best overall performer for noncovalent interactions giving accuracy close to CCSD method. MPWB1K fared better in interaction energy calculations than other DFT methods. In the case of M06‐2X, SVWN5, and the dispersion corrected B97‐D, the interaction energies are significantly overrated for neutral systems compared to other methods. However, for cationic systems, B97‐D yields structures and interaction energies similar to MP2 and MPWB1K methods. Among the long‐range corrected methods, LC‐ωPBE and CAM‐B3LYP methods show close agreement with MP2 values while ωB97XD energies are notably higher than MP2 values. © 2010 Wiley Periodicals, Inc. J Comput Chem 2010     

Syntheses,structures, and catalytic activity in Friedel–Crafts acylations of substituted tetramethylcyclopentadienyl molybdenum carbonyl complexes

Reactions of the substituted tetramethylcyclopentadienes [C₅HMe₄R] [R =  ^t Bu, Ph, CH₂CH₂C(CH₃)₃] with Mo(CO)₃(CH₃CN)₃ in refluxing xylene gave a series of dinuclear molybdenum carbonyl complexes [(η⁵-C₅Me₄R)Mo(CO)₃]₂ [R =  ^t Bu (1), Ph (2), CH₂CH₂C(CH₃)₃ (3)], [(η⁵-C₅Me ^t Bu)Mo(μ-CO)₂]₂ (4)], and [(η⁵-C₅Me₄) ^t Bu]₂Mo₂O₄(μ-O) (5)], respectively. Complexes 1–5 were characterized by elemental analysis, IR, ¹H NMR, and ¹³C NMR spectroscopy. In addition, their crystal structures were determined by X-ray crystal diffraction analysis. The catalytic activities of complexes 1–3 in Friedel–Crafts acylation in the presence of o-chloranil has also been investigated; the reactions were achieved under mild conditions to give the corresponding products in moderate yields.