Nitrogen Donor Atoms Research Articles

Preparation of nanoscale zero-valent iron supported on chelating resin with nitrogen donor atoms for simultaneous reduction of Pb2+ and [formula omitted

Polymeric ion exchanger has been proven to be an excellent carrier for metal nanoparticles due to chemical stability and robust mechanical strength. However, polymeric ion exchanger containing non-diffusible negatively or positively charged groups can only permit cation or anion contaminants to permeate into the polymer phase due to Donnan exclusion effect. In this study, zero-valent iron nanoparticles (NZVI) were immobilized within a chelating resin DOW 3N with pyridine functional groups through NaBH4 reduction. TEM indicated that Fe0 particles were clearly discrete and well dispersed on the surface of DOW 3N with grain size ranging from 10 to 30nm. The reduction ability of NZVI-DOW 3N for Pb2+, NO3- and their mixture were evaluated, respectively. The results showed that NO3- and Pb2+ can be reduced efficiently. In a binary solution, the removal efficiencies of NO3- and Pb2+ can reach 87% and 97%, respectively.

Searching for Vanadium‐Based Prospective Agents against Trypanosoma cruzi: Oxidovanadium(IV) Compounds with Phenanthroline Derivatives as Ligands

AbstractSearching for new promising metal‐based drugs for the treatment of parasitic diseases against Trypanosoma cruzi, three related oxidovanadium(IV) complexes, [VIVO(SO4)(H2O)2(NN)], with the phenanthroline derivatives (NN) 1,2,5thiadiazolo[3,4‐f]1,10phenanthroline (tdzp), 1,10‐phenanthroline‐5, 6‐dione (phendione), and 5,6‐epoxy‐5,6‐dihydro‐1,10‐phenanthroline (epoxyphen) are synthesized, characterized, and evaluated in vitro as anti‐T. cruzi agents. The compounds are characterized in the solid state and in solution by elemental analysis, electrospray ionization mass spectrometry (ESI‐MS), conductimetric measurements, and infrared (FTIR), UV/Vis, and electronic paramagnetic resonance (EPR) spectroscopy. EPR spectroscopy suggests that the ligands act as bidentate, binding through both nitrogen donor atoms in an axial‐equatorial mode. DFT calculations corroborate the structural assignments. The stability of the complexes in solution is evaluated by EPR and 51V‐ NMR spectroscopy and all complexes show reasonable stability. The anti‐T. cruzi activity of the complexes was tested by measuring the growth inhibitory effect on the epimastigote life cycle form of the parasite (Dm28c strain). All complexes show IC50 values in the micromolar range against T. cruzi and display activities of the same order of that of Nifurtimox, but lower than that of the previously reported analogue [VIVO(SO4)(H2O)2(dppz)] (dppz = dipyrido[3, 2‐a:2′,3′‐c]phenazine). Furthermore, DNA was evaluated as a potential target by using atomic force microscopy (AFM), showing that the complexes display ability to interact with this biomolecule.

Synthesis and structural characterization of dimethyltin(IV) complexes based on functionalized pyridyl ligands

The reaction of dimethyltin dichloride with 1,5-bis(2′-pyridyl)pentane-1,3,5-trione (Htrione) resulted in the formation of the dinuclear complex {[Me2ClSn(μ-trione)SnMe2Cl2]·Htrione} (1) in the solid state. The solid state X-ray determination of the complex {[Me2ClSn(μ-trione)SnMe2Cl2]·Htrione} (1) revealed that complex 1 contains the simultaneous presence of penta- and hexacoordinated tin(IV) atoms. Notably, trione acts as a bridging ligand through both oxygen and nitrogen donor atoms. While the hexacoordinated tin(IV) atom adopts an octahedral geometry with a trans-[SnMe2] configuration, the pentacoordinated tin(IV) atom exists in a highly distorted trigonal bipyramidal arrangement with equatorial methyl groups. It is also important to note that there is a free Htrione molecule as a co-crystal in the di-enol form. The complexes [SnMe2Cl(tpyCl)]+[SnMe2Cl3]− (2), [SnMe2Cl(tpyOH)]+Cl− (3) and [SnMe2Cl(tpySH)]+2(SnMe2Cl3)−Cl− (4) were also prepared from the reaction of SnMe2Cl2 with 4′-functionalized 2,2′:6′,2″-terpyridines (tpyX), where X=Cl, O, S. It is important to note that the formation of the anion depends upon the nature of 4′-substituted terpyridyl ligand. The resulting products have been fully characterized by IR, elemental analysis and multinuclear (1H, 13C, 119Sn) NMR spectroscopy. The X-ray crystal structure determination of [SnMe2Cl(tpyCl)]+[SnMe2Cl3]− reveals that the [SnMe2Cl(tpyCl)]+ moiety adopts an octahedral geometry about the tin atom with a trans configuration of the methyl ligands. In the [SnMe2Cl3]− moiety, the tin(IV) atom exists in a trigonal bipyramidal geometry with equatorial methyl groups.

Selective lanthanide sorption and mechanism using novel hybrid Lewis base (N-methyl-N-phenyl-1,10-phenanthroline-2-carboxamide) ligand modified adsorbent

This study aims to develop a highly selective Lewis base adsorbent to investigate the selective sorption and recovery of Eu(III) and Sm(III) from wastewater. The oxygen and nitrogen donor atoms containing Lewis base N-methyl-N-phenyl-1,10-phenanthroline-2-carboxamide (MePhPTA) ligand was synthesized and subsequently an adsorbent was prepared by direct immobilization onto mesoporous silica. Determined maximum adsorption capacities were 125.63 and 124.38mg/g for Eu(III) and Sm(III), respectively. Experiments with mixed-cations solutions showed that the sequence of preferential adsorption was Eu(III)>Sm(III). The lanthanide sorption by hybrid Lewis base adsorbent (HyLBA) was not adversely affected by the presence of sodium, potassium, calcium, magnesium, chloride, sulfate and nitrate ions due to strong affinity between hard Lewis acid lanthanide and hard Lewis base adsorbent. The crystallography for the Sm-MePhPTA complex suggested that MePhPTA was strongly coordinated to Sm(III) with oxygen and nitrogen by forming a stable complex with two 5-membered rings. The data clarified that bond lengths between Sm(III) and amide oxygen (2.475Å) were shorter than SmN (2.662Å) in phenanthroline moiety indicating strong oxygen driven HyLBA. The results suggested that HyLBA has a good prospect of promising applications for separation/sorption of lanthanide ions from effluents.

Synthesis and evaluation of gold(III) complexes as efficient DNA binders and cytotoxic agents

In recent years, great interest has been focused on gold(III) complexes as cytotoxic and antitumor drugs. Recent studies demonstrated that simple bidentate or polydentate ligands containing nitrogen donor atoms may offer sufficient redox stabilization to produce viable Au(III) anticancer drug targets under physiologic conditions. So, we have synthesized square planer Au(III) complexes of type [Au(An)Clx]·Cly and characterized them using UV–Vis absorption, C, H, N elemental analysis, FT-IR, LC–MS, 1H and 13C NMR spectroscopy. These compounds manifested significant cytotoxic properties in vitro for brine shrimp lethality bioassay. The metal complexes were screened for series of DNA binding activity using UV–Vis absorption titration, hydrodynamic measurement and thermal DNA denaturation study. The nucleolytic activity was performed on plasmid pUC19 DNA. The Michaelis–Menten kinetic studies were performed to evaluate rate of enhancement in metal complexes mediated DNA cleavage over the non-catalyzed DNA cleavage.

Design of novel nano-sorbents based on nano-magnetic iron oxide–bound-nano-silicon oxide–immobilized-triethylenetetramine for implementation in water treatment of heavy metals

Novel nano-sorbents were synthesized from the direct surface impregnation of magnetic nano-iron oxide (Nano-Fe3O4) with nano-silicon oxide (Nano-SiO2) for the formation of (Nano-Fe3O4–SiO2) sorbent. The product material was further functionalized with target nitrogen donor atoms via covalent surface binding and immobilization of triethylenetetramine (TETA) for the formation of (Nano-Fe3O4–SiO2–TETA) sorbent. Functionalized magnetic nano-sorbents were collected by facile separation under the influence of an external magnetic field. The magnetic nano-sorbents were identified by using FT-IR, SEM technique and TGA. The average particle size was found in the range of 14–40nm based on the SEM analysis. All synthesized nano-sorbents were examined to evaluate their selectivity and efficiency in removal of some heavy metal ions such as Cu(II) and Pb(II) from water samples by the batch equilibrium and micro-column techniques. (Nano-Fe3O4–SiO2–TETA) sorbent was identified by a high Cu(II) sorption capacity (480μmolg−1) in pH 7.0, while (Nano-Fe3O4) and (Nano-Fe3O4–SiO2) sorbents were characterized by high affinity to Pb(II). The contributions of various controlling factors such as solution pH, contact time and sorbent dosage on the extraction and sorption processes of metal ions were also studied and optimized.

A Bis(hexadentate) Biphenyl‐Based N12 Ligand and Its FeII Complexes

AbstractThe novel biphenyl‐based ligand N,N′,N″,N″′‐tetrakis(2,2′‐bipyridin‐6‐ylmethyl)‐4,4′‐dimethyl‐1,1′‐biphenyl‐2,2′,6,6′‐tetramine (6) with 12 nitrogen donor atoms has been synthesized. Ligand 6 is able to host two metal ions in an octahedral coordination sphere. This was shown by the synthesis of the dinuclear iron(II) complex 5 ([Fe2(6)]4+). Furthermore, the corresponding mononuclear iron(II) complex 4 ([Fe(6)]2+), where one coordination site is free, was obtained. Both FeII complexes show spin‐crossover behaviour, which was shown by 1H NMR spectroscopy and Evans' measurements. A comparison of the two complexes gives evidence of a sterically induced cooperative behaviour in the dinuclear complex 5.

Cd(II) complexes with pendant armed oxa- and azamacrocyclic ligands

The coordination capability of the pendant-arm macrocyclic ligands – with different sizes, nature and number of the donor atoms – dioxotriaza 17-membered (L1) and pentaaza 17-membered (L2) towards nitrate and perchlorate Cd(II) salts, has been investigated. The complexes were prepared in 1:1 metal/ligand molar ratio. The characterization carried out by elemental analysis, FAB mass spectrometry, IR and NMR spectroscopy, conductivity measurements, together with the crystal structure of the complexes [CdL1(CH3CN)](ClO4)2·CH3CN and [CdL2](ClO4)2 confirms the formation of mononuclear complexes in all cases. The X-ray diffraction of [CdL1(CH3CN)](ClO4)2·CH3CN complex presents a mononuclear endomacrocyclic structure with the metal ion coordinated by the five donor atoms from the macrocyclic framework, the amine group from the pendant-arm and one acetonitrile molecule, in a distorted pentagonal bipyramid geometry. The complex [CdL2](ClO4)2 is also mononuclear, but the cadmium ion is in a distorted trigonal prism environment coordinated by the six nitrogen donor atoms from the ligand. In both cases, the perchlorate ions do not participate in the coordination to the metal ion, but they are involved in numerous hydrogen bond interactions inter- and intramolecular with phenoxy and amino-groups.

Trace copper(II) ions detection and removal from water using novel ligand modified composite adsorbent

A highly selective mesoporous composite adsorbent is proposed for simultaneous detection and removal of Cu(II) ions in natural waters. The adsorbent was developed using the synthesized ligand 3-(((5-ethoxybenzenethiol)imino)methyl)-salicylic acid (EBMS) immobilization onto mesoporous silica monoliths. The data clarified the nitrogen donor atom in EBMS ligand made the strong and stable complexation mechanism with Cu(II) ions during detection and removal systems. Therefore, Cu(II) bonding with EBMS to enhance color formation and make the ligand as metal-ligand [Cu(II)-EBMS]n+ complexes. The solid material has spherical cavities to showed the rapid response and transport of Cu(II) to network sites easily with high sorption efficiency without loss of cage cavities. The influence of pH, kinetics parameters, limit of detection, Cu(II) sorption capacity, bond distances between ligand and Cu(II) and the effect of eluent for the stripping of Cu(II) ion from adsorbent over elution efficiency were evaluated. The adsorbent offered a simple procedure in ultra-trace Cu(II) sensing optically without using high tech instruments. The adsorbent offered a simple procedure in ultra-trace Cu(II) sensing optically without using high tech instruments. The data also revealed that the adsorbent exhibited high sorption capacity (182.15mg/g) and extreme high selectivity in high concentration ionic competition. The adsorbent materials has retaining their functionality in terms of Cu(II) detection and recovery after multiple reuse cycles without deterioration in its significant performances. Moreover, the present adsorbent was successfully applied to the determination, removal and elution Cu(II) ions in environmental samples.

Copper(II) ions capturing from water using ligand modified a new type mesoporous adsorbent

Highly selective mesoporous adsorbent design is necessary for selective detection and removal of toxic metals from drinking water with high efficiency and cost-effective. The mesoporous adsorbent was fabricated by direct immobilization of a synthesized (3-(3-(methoxycarbonyl)benzylidene) hydrazinyl)benzoic acid onto mesoporous silica monoliths and tested for its potential application of Cu(II) ions sensing and removal from wastewater. Specific nitrogen donor atoms containing novel ligand onto mesoporous silica transformed the ion-sensing systems optically remove Cu(II) ions with stable assemblies and complexation mechanism. The Cu(II) bonding with ligand to enhanced color formation and capturing corresponding to formation of [Cu(II)-ligand]n+ complexes. The variation of pH, contact time, detection limit and initial Cu(II) concentration parameters were measured in sorption experiments. The sorption data revealed that the new type mesoporous adsorbent was able to remove Cu(II) with high sorption capacity and extreme selectivity in ionic competition. Therefore, design of mesoporous adsorbent offered a simple procedure in such low-level Cu(II) sensing and removal without using sophisticated instruments. The effective pH range for Cu(II) capturing was neutral region and the maximum sorption capacity of the adsorbent was as high as 145.98mg/g. The new type adsorbent exhibited good recyclability for several cycles use after sensing and removal operation without deterioration in its significant performances. Therefore, the adsorbent can be used effectively for sensitive and efficient Cu(II) sensing and removal in water and wastewater treatment.

New sulfanyl- and selanyl-substituted Schiff bases derived from 2-chalcogenoalkylamines and aromatic aldehydes. Synthesis and complex formation reactions

A number of β-phenyl(or benzyl)selanyl- and β-phenylsulfanyl-substituted imines possessing an additional donor nitrogen, oxygen, or sulfur atom were synthesized by reaction of 2-phenylsulfanylethanamine, 2-phenylsulfanylcyclohexanamine, 2-phenylselanylcyclohexanamine, and 2-benzylselanylaniline with salicylaldehyde, 2-pyridinecarbaldehyde, or 2-tert-butylsulfanylbenzaldehyde. The resulting Schiff bases were tested as ligands in the complex formation with nickel(II) and copper(II), and mononuclear (L-H)MCl or LMCl2 coordination compounds were isolated (L = sulfur- or selenium-containing imine). The redox properties of the selenium-containing ligands and complexes were studied by cyclic voltammetry. The complexes were found to undergo reduction of the metal ion in two one-electron steps. The reduction is reversible for copper complexes and irreversible for nickel complexes.

An insight into coordination ability of dicyanoimidazolato anions toward lithium in presence of acetonitrile. Crystal structures of novel lithium battery electrolyte salts

New generation of imidazole-derived salts was characterized by single-crystal X-ray diffraction experiments for the first time. Herein, we present crystal structures of lithium salts containing original 4,5-dicyanoimidazolato anions substituted with trifluoromethyl, pentafluoroethyl and heptafluoropropyl groups. Studied compounds crystallize as acetonitrile-solvated dimers with four-coordinate lithium cations. Structures of crystalline materials were examined with regard to the fine properties of electrolyte providing valuable information about coordination ability of substituted 4,5-dicyanoimidazolato anions. Anions act as ditopic N donor ligands containing additional weak fluorine donor-centers. Donor nitrogen atoms of imidazole and cyano groups, show slightly lower basicity than electroneutral acetonitrile solvent molecules coordinated to lithium. Presence of bulky substituents does not alter crystal structure and close-packed arrangement is observed.

Synthesis, Crystal Structures and DNA-Cleaving Activities of [Cemp]<sub>2</sub>[MCl<sub>4</sub>] (Cemp=<i>N</i>-Carbethoxymethyl-1,10-phenanthrolinium, M=Cu<sup>II</sup>, Zn<sup>II</sup>, Co<sup>II</sup>, Ni<sup>II</sup> and Mn<sup>II</sup>)

N-Carbethoxymethyl-1,10-phenanthrolinium bromide (CempBr) and its five ionic metal complexes, [Cemp]2[MCl4] where M = Cu(II) (1), Zn(II) (2), Co(II) (3), Ni(II) (4) and Mn(II) (5) were synthesized and fully characterized. Complexes 1-5 have similar structures, and consist of isolated [Cemp](+) cations and [MCl4](2-) anions in which there are no obvious interactions between the oxygen or nitrogen donor atoms in [Cemp](+) and the metal center in [MCl4](2-). Agarose gel electrophoresis studies on the cleavage of plasmid pBR322 DNA by complexes 1-5 indicated that complex 1 was capable of efficiently cleaving DNA under physiological conditions, most probably via an oxidative mechanism. Kinetic assay of complex 1 afforded the maximal catalytic rate constant kmax of 0.55 h(-1) and Michaelis constant KM of 47.6 µM, respectively, which gives about 1.5×10(7)-fold rate acceleration over uncatalyzed cleavage of supercoiled DNA. Ethidium bromide displacement experiments indicated that complex 1 had a binding affinity of (1.58±1.12)×10(6) M(-1) toward calf-thymus DNA, 20-100-fold higher than those shown by CempBr and complexes 2-5. The high cleaving efficacy of complex 1 is thought to be due to the efficient catalysis of the copper(II)-coordinated center and the efficient binding of the quaternized 1,10-phenanthroline cation to DNA.

Organosilver(I) Framework Assembly with Multinuclear Heteroaryl Ethynide Supramolecular Synthon R–C≡C⊃Agn (n=4, 5)

A series of six silver(i) trifluoroacetate complexes containing new ligands each composed of a quinolinyl or pyridyl nucleus bearing one or two terminal ethynyl substituent(s) has been synthesised. Single-crystal X-ray analysis of the complexes established the coordination preferences of the ethynide substituent(s) at variable positions with respect to the nitrogen donor atom, which serve as dominant factors in directing the construction of multi-dimensional organosilver(i) networks, which are consolidated by weak intermolecular interactions in supramolecular assembly.

Influencing the coordination mode of tbta (tbta = tris[(1-benzyl-1H-1,2,3-triazol-4-yl)methyl]amine) in dicobalt complexes through changes in metal oxidation states

The complexes [(tbta)Co(μ-CA(-2H))Co(tbta)(CH3CN)](BF4)2 1 and [(tbta)Co(μ-OH)2Co(tbta)](BF4)4 2 (tbta = tris[(1-benzyl-1H-1,2,3-triazol-4-yl)methyl]amine and CA = chloranilic acid) were synthesized and characterized by X-ray crystallography, SQUID magnetometry and NMR spectroscopy. The reactions to form these complexes deliver 1 as a paramagnetic species containing two high spin Co(II) centers, and 2 as a diamagnetic compound with two low spin Co(III) centers. Structural analysis shows that in 1 the capped-octahedral environment around the Co(II) centers is highly distorted with rather long bonds between the metal and donor atoms. The tbta ligand binds to the Co(II) centers through the three triazole nitrogen donor atoms in a facial form, with the Co-N(amine) distance of 2.494(2) Å acting as a capping bond to the octahedron. In the crystal an unusual observation of one acetonitrile molecule statistically occupying the coordination sites at both Co(II) centers is made. 1 displays a series of intermolecular C-H···Cl and π-π interactions leading to extended three-dimensional structures in the solid state. These interactions lead to the formation of voids and explain why only one acetonitrile molecule can be bound to the dinuclear complexes. In contrast to 1, the cobalt centers in 2 display a more regular octahedral environment with shorter cobalt-donor atom distances, as would be expected for a low spin Co(III) situation. The tbta ligand acts as a perfect tetradentate ligand in this case with the cobalt-N(amine) distance of 2.012(3) Å falling in the range of a normal bond. Thus, we present the rare instances where the ligand tbta has been observed to bind in a perfectly tetradentate fashion in its metal complexes. The room temperature magnetic moment of 6.30 μB for 1 shows values typical of two high spin Co(II) centers, and this value decreases at temperatures lower than 30 K indicating a weak antiferromagnetic coupling and zero field splitting. Mass spectrometric analysis of 2 provided evidence for the formation of an oxo-bridged dicobalt complex in the gas phase.

Synthesis and Characterization of Copper Complexes of a Tetrapyridyl Ligand, and Their Use in the Catalytic Aerobic Oxidation of Benzyl Alcohol

AbstractThe synthesis and characterization of new copper complexes of the tetrapyridyl ligand N,N′‐di(pyridin‐2‐yl)‐2,2′‐bipyridine‐6,6′‐diamine (bapbpy) is reported. The crystal structures of the compounds [Cu(bapbpy)(H2O)]Cl2·H2O (1), [Cu(bapbpy)(H2O)]Br2·H2O (2) and [Cu(bapbpy)(H2O)](NO3)2·H2O (3) have been elucidated and show the copper(II) ions to be in a distorted square‐pyramidal geometry with the tetradentate ligand in the equatorial plane. Conductivity measurements on 1 revealed that it is fully ionized in methanol, i.e., the chloride ions are not coordinated to copper(II) in methanolic solutions. The room temperature electron paramagnetic resonance (EPR) spectra of methanol solutions of the complexes show a copper signal with a giso value of 2.110; it shows hyperfine splitting into four lines (ACu = 77 G) and superhyperfine splitting into nine lines (AN = 12 G) owing to the interaction with the nuclear spin of the four nitrogen donor atoms of the bapbpy ligand. The catalytic activity of 1, 2 and 3 in the aerobic homogeneous oxidation of benzyl alcohol in presence of the TEMPO radical [(2,2,6,6‐tetramethylpiperidin‐1‐yl)oxidanyl] was investigated. Benzaldehyde is obtained selectively and the production of benzoic acid is not observed during 24 h of reaction. EPR analyses, carried out under stoichiometric conditions, show that the TEMPO radical does not interact with the copper centre. These data suggest that oxidation of the substrate may occur in the second coordination sphere of the copper complex.

Zinc, Cadmium, and Mercury Complexes of a Pyridyloxy-Substituted Cyclotriphosphazene: Syntheses, Structures, and Fluxional Behavior

The synthesis and characterization of the fluxional, d(10) cyclotriphosphazene complexes, [MLCl(2)] (M = Zn, Cd, and Hg; L = spiro-[(1,1'-biphenyl)-2,2'-dioxy]tetrakis(4-methyl-2-pyridyloxy)cyclotriphosphazene), are described. Single-crystal X-ray structures show that the zinc complex has crystallized into two crystal forms: one as a tetrahedral species, with a N(2)Cl(2) donor set in which a geminal pair of the pendant pyridyloxy nitrogen atoms binds to the zinc, and the other as a trigonal-bipyramidal (tbp) one, with an N(3)Cl(2) donor set. The third nitrogen atom comes from the phosphazene ring and the two pyridyl ligands are non-geminal. The asymmetric unit of the cadmium complex contains three structurally distinct molecules. One molecule has a tbp structure similar to that of the zinc complex. The second molecule has a six-coordinate, distorted octahedral geometry around the cadmium center with a N(4)Cl(2) donor set, with three of the nitrogen donor atoms coming from the pendant pyridyloxy arms. The third site contains a tbp complex and a distorted octahedral species with a relative occupancy of 3:1. The identification of these three different forms in the one crystal suggests that the energy difference between the tbp and distorted octahedral isomers is not large. Quantitative analysis of the (1)H NMR and variable-temperature (31)P NMR spectra of the zinc, cadmium, and mercury complexes in a CD(2)Cl(2) solution, coupled with the X-ray structural results, shows that an associative fluxional mechanism (ΔS(++) < -65 J mol(-1) K(-1)) is operating.

Gallium–Gallium Bonds As Effective Templates for the Generation of Macrocycles and Supramolecular Entities

Treatment of the tetraalkyldigallium(4) compound R2Ga–GaR2 [1; R = CH(SiMe3)2] with the highly functionalized acids 3- and 4-carboxyphenylthiourea, 7-azaindole-3-carboxylic acid, and 6-aminonicotinic acid afforded macrocyclic compounds in which two or four Ga–Ga bonds are bridged by the respective number of organic spacer ligands. In each reaction two equivalents of CH2(SiMe3)2 per formula unit of 1 were released. The Ga–Ga bonds of the products 2 to 5 are bridged by a carboxylato group and a chelating ligand containing two nitrogen donor atoms or the sulfur and nitrogen atoms of a thiourea group. The thiourea derivatives afforded different species with four or eight gallium atoms in the heterocycles (2 and 3) depending on their substitution patterns (1,3- versus 1,4-positions at the benzene rings). Supramolecular aggregates resulted that had up to 12 THF molecules encapsulated in the heterocycles or bonded to the surface of the molecules via hydrogen bonding or orthogonal dipolar interactions.

Nature of the Te⋯N intramolecular interaction in organotellurium compounds. A theoretical investigation by NBO and AIM methods

The nature and the strength of intramolecular Te⋯N interactions in three series of o-substituted organotellurium compounds [2-(di-methyl)C6H4TeX (1a–f), 2-(oxa)C6H4TeX (2a–f), 2-(py)C6H4TeX (3a–f); X=Cl, Br, Me, CN, SPh and TePh; Me: Methyl, Ph: Phenyl] have been studied using density functional theory. The effect of substituents (X) and different nitrogen donors are predicted using B3LYP/LanL2DZ method. The Natural Bond Orbital (NBO) analysis demonstrated that the nN→σTeX∗ electron delocalization is the key contributing factor for Te⋯N non-bonding interactions. The NBO second-order perturbation energy ETe⋯N (as well as NBO deletion energy Edel) correlates with Te⋯N distance on a single curve irrespective of the donor nitrogen atom. The values of ETe⋯N (as well as Edel) approximately follow the trend Br>Cl>TePh>SPh>CN>Me for a given nitrogen donor, and 3>2>1 for a given X. Both NBO and Atoms-in-Molecule (AIM) methods suggest that the Te⋯N interactions in these compounds have a dominant covalent character. Studies on the effect of solvent on the Te⋯N interaction show that polar solvent stabilizes the Te⋯N interactions by shortening the Te⋯N atomic distance. Comparison with the corresponding Se counterpart shows that the strength of Te⋯N interactions is stronger than those of Se⋯N interactions.

Methyl- and methoxysalicylatocopper complexes with 2-pyridylmethanol: Synthesis, spectral properties, structure and EPR characterization in solid-state and in solution

Abstract The syntheses and characterizations of salicylatocopper(II) complexes of the formula Cu(X-sal)2(2-pyme)2 (X = 3-MeO (1), 4-MeO (2), 3-Me (3), 4-Me (4) and 5-Me (5), where 3-MeOsal− = 3-methoxysalicylate, 4-MeOsal− = 4-methoxysalicylate, 3-Mesal− = 3-methylsalicylate, 4-Mesal− = 4-methylsalicylate, 5-Mesal− = 5-methylsalicylate anion, and 2-pyme = 2-pyridylmethanol) are reported. The composition was determined by elemental analysis, and ligand coordination modes have been determined by spectroscopic methods (IR, UV-VIS). The crystal structure determination of [Cu(3-MeOsal)2(2-pyme)2] (1) and [Cu(5-Mesal)2(2-pyme)2] (5) have confirmed conclusions originally based on spectral data. EPR measurements of frozen water/methanol solutions containing different copper(II): 2-pyme molar ratios have indicated presence of complexes with only two nitrogen donor atoms bonded to each central atom.