Syntheses,crystal structures,and photophysical properties of two 2-D coordination polymers with different geometries of lead(II)

Two complexes constructed from aromatic acid and N-heterocyclic ligands have been synthesized by hydrothermal reaction: [Pb(cipt)(NDC)]_n (1) [cipt?=?2-(3-chlorophenyl)-1H-imidazo[4,5-f][1,10]phenanthroline, NDC?=?naphthalene-1,4-dicarboxylic acid] and [Pb(ipm)(BDC)₂]_n (2) [BDC?=?terephthalic acid, ipm?=?5-(1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl)-2-methoxyphenol]. Single-crystal X-ray analysis shows that 1 exhibits an interesting arm-shaped chain structure. 1-D ladder chain structure is formed by N–H···O bonding interactions and further into a 2-D network by N–H···O hydrogen bonds and interchain π–π stacking interactions. Complex 2 shows a 2-D butterfly wings structure, which has been rarely reported. The structure in 2 has intermolecular N–H···O interactions, which help in construction of the 3-D framework. In 1, the coordination sphere of Pb(II) is hemi-directed, whereas the Pb(II) geometry in 2 is holo-directed. The solid-state fluorescence spectra of 1 and 2 are also investigated, as well as the ligands cipt and ipm.     

FTIR analysis of hydrogen bonding in amorphous linear aromatic polyurethanes. I. Influence of temperature

Fourier-transform infrared spectral studies of an amorphous linear aromatic polyurethane at various temperatures were performed. Hydrogen bonding was studied in the N? H stretching (3347 cm^?1) and the bending (1535 cm^?1) regions, using the band decomposition technique. The variations with temperature are used to calculate the ratio of the absorptivity coefficients for the H-bonded to the “free” N? H vibrations. This ratio is found to be independent of temperature. The enthalpy and the entropy of hydrogen bond dissociation are also obtained as 9.6 kJ mol^?1 and 44.8 J mol^?1 K^?1, respectively. Two C?C in-plane vibrational bands of the aromatic rings at 1614 and 1598 cm^?1 were studied at different temperatures. The integrated absorbance for both bands decreases clearly and regularly with increasing temperature, and both bands shift to lower wavenumbers. This strongly suggests a specific interaction for the aromatic rings, probably N? H … π hydrogen bonds, which will be discussed in detail in the second part of this series. © 1994 John Wiley & Sons, Inc.     

Molecular docking,quantum chemical computational and vibrational studies on bicyclic heterocycle “6-nitro-2,3-dihydro-1,4-benzodioxine”: Anti-cancer agent

The heterocyclic aromatic compounds are primarily used to make pharmaceutical and agrochemicals. In addition, these compounds can be chosen as antioxidants, corrosion inhibitors, electro and opto-electronic devices, polymer material, dye stuff, developers, etc. On the account of this, the heterocyclic aromatic 6-nitro-2,3-dihydro-1,4-benzodioxine (6N3DB) was chosen and the structure is optimized to predict the important properties of it. The structural parameters such as bond length and bond angle have been obtained by DFT/B3LYP/6-311++G(d,p) basis set to know the geometry and orientation of 6N3DB. The molecule has been characterized by FT-IR and FT-Raman spectroscopic techniques to predict the functional groups, vibrational modes and aromatic nature of 6N3DB. The chemical shifts of ¹H and ¹³C have been obtained experimentally and compared with the theoretical data. The parameters such as the band gap between HOMO-LUMO orbitals, λ_max, and electron transition probability in frontier orbitals have been estimated to know the NLO and corrosion inhibition activity. HOMO-LUMO orbital diagram has been obtained for different energy levels and their band gap energies have been compared with UV–vis band gap values. The chemical significance of the molecule has been explained using ELF, LOL, and RDG. The binding energy and intermolecular energy values indicate that the title compound possesses anti-cancer property through hydrolase inhibition activity.     

Infrared fingerprint spectroscopy and theoretical studies of potassium ion tagged amino acids and peptides in the gas phase

Infrared multiple-photon dissociation spectroscopy is effected on the K(+) tagged aromatic amino acids tyrosine and phenylalanine, as well as the K(+) tagged peptides bradykinin fragment 1-5 and [Leu]-enkephalin. The fingerprint (800-1800 cm(-1)) infrared spectra of these species are compared to density-functional theory (DFT) calculated spectra to determine whether the complex is in the charge solvation (CS) or salt bridge (SB) (i.e. zwitterionic) configuration. For the aromatic amino acids the CS structure is favored and the tridentate N/O/ring structure is found to be the preferred binding geometry for K(+). The experimental and theoretical evidence for bradykinin fragment 1-5 tagged with K(+) suggests that the SB structure is favored; the calculations indicate a head-to-tail looped structure stabilized by a salt bridge between the protonated guanidine group and the deprotonated C-terminus, which allows K(+) to sit in a binding pocket with five C=O electrostatic interactions. For K(+) tagged [Leu]-enkephalin the spectroscopic evidence is not as clear. While the calculations clearly favor a CS structure and the observation of a weak carboxylic acid C=O stretching band in the infrared spectrum matches this finding, the prominence of a band at 1600 cm(-1) renders the analysis more ambiguous, and hence the presence of some salt bridge ions cannot be excluded. Another striking feature in the [Leu]-enkephalin spectrum is the high infrared activity of the tyrosine side-chain modes, which can be clearly identified from comparison to the [Tyr + K](+) experimental spectrum, but which is not reproduced by the DFT calculations.     

Structure and multinuclear solid-state NMR of a highly birefringent lead-gold cyanide coordination polymer

The coordination polymer Pb(H2O)[Au(CN)2]2 (1) was synthesized by the reaction of KAu(CN)2 and Pb(NO3)2. The structure contains 1-D chains of lead(II)-OH2 linked via Au(CN)2(-) moieties, generating a 2-D slab; weak aurophilic interactions of 3.506(2) and 3.4885(5) A occur within and between slabs. The geometry about each lead(II) is bicapped trigonal prismatic, having six N-bound cyanides at the prism vertices and waters at two of the faces. Dehydration at 175 degrees C yields microcrystalline Pb[Au(CN)2]2 (2), which, along with 1, was examined by 13C, 15N, 1H, and 207Pb solid-state NMR methods. Two 15N resonances are assigned to the mu2-bridging and hydrogen-bonding cyanides in 1. Upon dehydration, the 207Pb NMR spectrum becomes axially symmetric and yields a reduced shielding span, indicating higher site symmetry, while the 13C and 15N spectra reveal a single cyanide. Although no single-crystal X-ray structure of 2 could be obtained, a structure is proposed on the basis of the NMR and X-ray powder data, consisting of a lead(II) center in a distorted square-prismatic environment, with cyanides present at each corner. The birefringence of single crystals of 1 is found to be 7.0 x 10(-2) at room temperature. This value is large compared to that of most optical materials and can be attributed to the anisotropy of the 2-D slabs of 1, with all CN bonds aligned in the same direction by the polarizable lead(II) center.     

Cove-Edged Nanographenes with Localized Double Bonds

The efficient synthesis and electronic properties of two large-size cove-edged nanographenes (NGs), CN1 and CN2 , are presented. X-ray crystallographic analysis reveals a contorted backbone for both molecules owing to the steric repulsion at the inner cove position. Noticeably, the dominant structures of these molecules contain four (for CN1 ) or six (for CN2 ) localized C=C double bonds embedded in nine (for CN1 ) or twelve (for CN2 ) aromatic sextet rings according to Clar's formula, which is supported by bond length analysis and theoretical (NICS, ACID) calculations. Furthermore, Raman spectra exhibit a band associated with the longitudinal CC stretching mode of olefinic double bonds. Owing to the existence of the additional olefinic bonds, both compounds show a small band gap (1.84 eV for CN1 and 1.37 eV for CN2 ). They also display moderate fluorescence quantum yield (35 % for CN1 and 50 % for CN2 ) owing to the contorted geometry, which can suppress aggregation in solution.     

Synthesis and Crystal Structure of a Nitronyl Nitroxide Complex {[Zn(NIT4Py)(fum)(H2O)2]·H2}n

The title compound {[Zn(NIT4Py)(fum)(H2O)2]·H2O}n, where N1T4Py=2-(4'-pyridinyl)-4,4,5,5-tetra-methylimidazoline-l-oxyl-3-oxide and rum=fumarate, has been prepared and structurally characterized by X-ray diffraction. It crystallizes in triclinic, space group P1 with a =6.9533(9), b=9.805(1), c=15.248(2)A, a=94.608(2), β=92.328(2),γ=105.840(2)°,C16H24N3O9Zn, Mr=467.75, V=994.8(2) A3, Z=2, Dc=1.562 g/cm3,μ(MoKa)=1.289 mm-1,F(000)=486, the final R=0.0243 and wR=0.0622 for 3505 independent reflections with Rint=0.0125. The Zn(Ⅱ) adopts a distorted five-coordinate triangle bipyramidal geometry. The basic framework structure of the complex is a 1-D chain. The intrachain hydrogen bonds are helpful to stabilize the 1-D chain structure. Furthermore, the chains are connected by O-H…O hydrogen bonds to give a 2-D double-layer network.     

Cyanide-bridged manganese(II) and chloride-bridged copper(II) complexes with 2-pyridineethanol: synthesis,structural characterization and C-H⋯M interactions

[Mn(hepH)₂Ni(μ-CN)₂(CN)₂]_n (1) and [Cu₂(μ-Cl)₂(μ-hep)₂]_n (2) (2-pyridineethanol abbreviated to hepH) have been synthesized and characterized by FT-IR and Raman spectroscopies, elemental analyses, and single-crystal X-ray diffraction. X-ray single-crystal structure analysis reveals that the structures of 1 and 2 consist of 1-D infinite chains. The coordination environment of Mn(II) was identified as distorted octahedral, whereas Ni(II) has a square planar geometry in 1. Each Cu(II) in 2 adopts a distorted square pyramidal geometry in which the basal plane is constructed by oxygen and nitrogen atoms from hep and a bridging chloride ligand, respectively, and the apical position is occupied by the other chloride. The 1-D chains in 1 and 2 are extended into a 2-D supramolecular network by O?H?N and weak C?H?Cl hydrogen bonds, respectively. Adjacent 2-D layers are further connected by C?H?M interactions resulting in the formation of 3-D supramolecular networks. The most remarkable properties of complexes are the presence of close C–H?M interactions with distance values of 2.58 and 2.93 Å between H?Ni and H?Cu, respectively. The H?Ni interaction distance is shorter than the corresponding values of other tetracyanonickelate(II) complexes.     

Defining rules of aromaticity: a unified approach to the Hückel, Clar and Randić concepts

The molecular structure of any system may be unambiguously described by its adjacency matrix, A, in which bonds are assigned entry a(ij) = 1 and non-bonded pairs of atoms entry a(ij) = 0. For π-electron-containing conjugated hydrocarbons, this matrix may be modified in order to represent one of the possible Kekulé structures by assigning entry 1 to double bonds and entry 0 to single bonds, leading to the Kekulé matrix K which can be obtained from the A matrix by subtracting 1 from elements a(pq) that represent single bonds in the Kekulé structure. The A and K matrices are the boundary cases of a general matrix A(ε), named perturbation matrix, in which from elements a(pq) that represent single bonds is subtracted a value ε∈<0,1> representing the magnitude of the perturbation. The determinant of the A(ε) matrix is unambiguously represented by an appropriate polynomial that, in turn, can be written in a form containing terms ±(1-ε)(N/2) that identify types of π-electron conjugated cycles (N is the corresponding number of π-electrons). If the sign before the term is (+), then the contribution is stabilizing, but if it is (-) the contribution is destabilizing. The approach shows why and how the Hückel rule works, how the Randi? conjugated circuits result from the analysis of canonical structures, and also how the Clar rule may be extended to include aromatic cycles larger than six-membered (aromatic sextet).     

Cove‐Edged Nanographenes with Localized Double Bonds

The efficient synthesis and electronic properties of two large‐size cove‐edged nanographenes (NGs), CN1 and CN2 , are presented. X‐ray crystallographic analysis reveals a contorted backbone for both molecules owing to the steric repulsion at the inner cove position. Noticeably, the dominant structures of these molecules contain four (for CN1 ) or six (for CN2 ) localized C=C double bonds embedded in nine (for CN1 ) or twelve (for CN2 ) aromatic sextet rings according to Clar's formula, which is supported by bond length analysis and theoretical (NICS, ACID) calculations. Furthermore, Raman spectra exhibit a band associated with the longitudinal CC stretching mode of olefinic double bonds. Owing to the existence of the additional olefinic bonds, both compounds show a small band gap (1.84 eV for CN1 and 1.37 eV for CN2 ). They also display moderate fluorescence quantum yield (35 % for CN1 and 50 % for CN2 ) owing to the contorted geometry, which can suppress aggregation in solution.     

A molecular orbital study comparing the effects of heteroatom substitution in trans-1,3-butadiene,all-trans-1,3,5-hexatriene,and benzene

To gain more understanding of the nature of the perturbation that results from heteroatom substitution in conjugated polyenes and in an aromatic ring environment, we have carried out calculations ontrans-H₂C=X(H)-CH=CH₂, all-trans-H₂C=CH-X(H)=CH-CH=CH₂, and with X = C, N, Si, and P, using the 6-31G^*(5D) basis set with full geometry optimization. Linear relationships are found between (a) the C-X and C-C bond lengths, (b) the total overlap population in the C-C, C-N, C-Si, and C-P bonds and the bond length, and (c) the total atomic charge on the N, Si, and P atoms and the corresponding C atom in the various structures, and the electronegativity of N, Si, P and C. Whereas Si is more strongly bonded in the diene and triene compared to the aromatic ring, P, like N, appears to be bonded equally well in all three structural environments.     

Bis(1,3,5‐triazine‐2,4,6‐triamine‐κN1)silver(I) nitrate

The title compound, [Ag(C₃H₆N₆)₂]NO₃, has an alternating two‐dimensional bilayer structure supported by extensive hydrogen bonds. The [Ag(melamine)₂]⁺ cationic monomers (melamine is 1,3,5‐triazine‐2,4,6‐triamine) are connected via N—H...N hydrogen bonds to form two‐dimensional sheets. Nitrate groups are sandwiched between two sheets through N—H...O hydrogen bonds. An almost perfectly linear coordination geometry is found for the Ag^I ions. The triazine ligands are slightly distorted due to π–π interactions.     

Supramolecular architecture built of Co(II) and a tripodal ligand containing 1-D water tapes with (H2O)16 cluster units

The reaction of Co(NO₃)₂?·?6H₂O with a tripodal ligand leads to a new complex {[Co(L)]?·?2NO₃?·?8H₂O} (1) confirmed by single-crystal X-ray diffraction, infrared spectroscopy, and elemental analysis. The particular interest of 1 is in the formation of a 1-D water tape consisting of (H₂O)₁₆ cluster units, the neighboring water tapes are connected by free nitrate anions via hydrogen bonds into a 2-D guest layer. These guest layers are alternately packed face-to-face with the 2-D host layers along the a-axis to form a 3-D supramolecular architecture. There exist C–H?···?N and C–H?···?O weak hydrogen bonds between the guest layer and host layer. These weak hydrogen bonds and water–nitrate, water–water hydrogen bonds are important for the stability of the overall structure.     

Neutral and ionic hydrogen bonding in Schiff bases

Low-temperature, high-resolution X-ray studies of charge distributions in the three Schiff bases, the dianil of 2-hydroxy-5-methylisophthaldehyde, 3,5-dinitro-N-salicylidenoethylamine and 3-nitro-N-salicylidenocyclohexylamine, have been carried out. These structures exhibit interesting weak interactions, including two extreme cases of intramolecular hydrogen bonds that are ionic N(+)-H...O- and neutral O-H...N in nature. These two types of hydrogen bond reflect differences in geometrical parameters and electron density distribution. At the level of geometry, the neutral O-H...N hydrogen bond is accompanied by an increase in the length of the C(1)-O(1) bond, opening of the ipso-C(1) angle, elongation of the aromatic C-C bonds, shortening of the C(7)-N(2) bond and increased length of the C(1)-C(7) bond, relative to the ionic hydrogen bond type. According to the geometrical and critical point parameters, the neutral O-H...N hydrogen bond seems to be stronger than the ionic ones. There are also differences between charge density parameters of the aromatic rings consistent with the neutral hydrogen bond being stronger than the ionic ones, with a concomitant reduction in the aromaticity of the ring. Compounds with the ionic hydrogen bonds show a larger double-bond character in the C-O bond than appears in the compound containing a neutral hydrogen bond; this suggests that the electronic structure of the former pair of compounds includes a contribution from a zwitterionic canonical form. Furthermore, in the case of ionic hydrogen bonds, the corresponding interaction lines appear to be curved in the vicinity of the hydrogen atoms. In the 3-nitro-N-salicylidenocyclohexylamine crystal there exists, in addition to the intramolecular hydrogen bond, a pair of intermolecular O...H interactions in a centrosymmetric dimer unit.     

Surface-enhanced Raman scattering of 4,4′-bipyridine on gold nanoparticle surfaces

The adsorption structure and mechanism of 4,4′-bipyridine (BiPy) on gold nanoparticle surfaces has been investigated by means of surface-enhanced Raman scattering (SERS). The aromatic ring of BiPy appeared to assume a perpendicular orientation with respect to the gold surface from the presence of the ν(CH) band at ∼3060 cm⁻¹. The SERS intensities of several vibrational modes of BiPy on Au were found to vary as the bulk concentration. The SERS intensities for BiPy on Au could be ascribed to both the electromagnetic (EM) and charge transfer (CT) enhancement mechanism.     

Ab initio study on the structural and electronic properties of Li3GaP2 compared with Li3GaN2

Structural and electronic properties of Li₃GaP₂ and Li₃GaN₂ have been investigated by the first-principles calculations within the density functional theory. The calculated lattice parameters of the two compounds are in excellent agreement with the available experimental data. Both Li₃GaP₂ and Li₃GaN₂ are direct band gap semiconductors with the band gaps of 1.26 eV and 2.37 eV, respectively. The Ga–P (Ga–N) and Li–P bonds consist of a mixture of ionic character and covalent nature, while the Li–N bond exhibits almost ionic. The bonds in the Li₃GaP₂ are shown to have stronger covalency and weaker ionicity as compared to the corresponding ones in the Li₃GaN₂.     

A 1:1 cocrystal of 4‐(dimethylamino)benzaldehyde and 6‐phenyl‐1,3,5‐triazine‐2,4‐diamine

The crystal structure of the title compound, C₉H₁₁NO·C₉H₉N₅, contains one molecule of each component in the asymmetric unit. Approximately planar clusters of four molecules are formed by N—H...N and N—H...O hydrogen bonds, and further N—H...N hydrogen bonds link adjacent clusters to form pleated ribbons. π–π interactions are found between triazine and aldehyde benzene rings in different clusters, generating stacks along the monoclinic b axis. The intramolecular geometry of the two components is similar to that found in other crystal structures containing these molecules. Both molecules are approximately planar, except for methyl H atoms, with a small twist about the C—C bond linking the phenyl and triazine rings.     

Nitrogen defect levels in InN: XANES study

The local and electronic structure of nitrogen-related defects in thin film of InN (0 0 0 1) has been studied using synchrotron-based X-ray absorption near edge structure (XANES) spectroscopy. Several defect levels within the band gap and the conduction band of InN were clearly resolved in XANES spectra around the nitrogen K-edge. Theoretical analysis of XANES data includes advanced “ab initio” simulations: self-consistent full multiple scattering calculations using muffin-tin approximation, non-muffin-tin finite difference approach to study the influence of non-muffin-tin effects on XANES shape as well as advanced local density approximation scheme for optimization of initial geometry around nitrogen defects. Theoretical analysis of XANES data allows to attribute the level observed at 1.7 eV above the conduction band mimimum to antisite nitrogen and a sharp resonance at 3.2 eV above the conduction band minimum to molecular nitrogen.     

Synthesis and characterization of self-assembled coordination polymers of N-diaminomethylene-4-(3-formyl-4-hydroxy-phenylazo)-benzenesulfonamide

The azo dye ligand N-diaminomethylene-4-(3-formyl-4-hydroxy-phenylazo)-benzenesulfonamide (HL) and Cu(II), Co(II), and Mn(II) coordination polymers were synthesized in addition to a non-polymeric Pd(II) complex. In all complexes, the ligand bonds to the metal ion through the formyl and α-hydroxy oxygen atoms. The sulfonamide oxygen also coordinates to the metal. The complexes are formulated as [ML₂] _n , where M?=?Cu(II), Co(II), and Mn(II), and [ML(Cl)(H₂O)], where M?=?Pd(II). On the basis of spectral studies and magnetic susceptibility measurements, an octahedral geometry was assigned to Co(II) and Mn(II) complexes, tetragonally elongated octahedral geometry for Cu(II) complex, while the Pd(II) complex was found to be square planar. Crystallization of Cu(II) complex from DMF afforded single crystals of general formula {[Cu(L)₂]?·?3DMF} _n (2). X-ray structural analysis of 2 revealed that each Cu(II) adopts elongated octahedral geometry affording 1-D chains. The chains are connected by hydrogen bonds, resulting in the formation of 2-D supramolecular assemblies. The crystal structure of HL has also been determined and discussed. Cyclic voltammetric behavior of the ligand and some complexes are also discussed.     

Polymeric and monomeric dipicolinate complexes with 4-hydroxymethyl pyridine: spectral, structural, thermal and electrochemical characterization

Polymeric copper(II), [Cu(μ-dpc)(μ-4-hymp)] _n (1), and monomeric nickel(II), [Ni(dpc)(4-hymp)(H₂O)₂]·H₂O (2), (dpc: dipicolinate, 4-hymp: 4-hydroxymethyl pyridine), dipicolinate complexes have been prepared and characterized by spectroscopic (IR, UV–Vis, EPR), thermal (TG/DTA), X-ray diffraction technique and electrochemical methods. In both the dipicolinate complexes, the dpc dianion acts as a tridentate ligand. In polymeric copper(II) complex, the 4-hymp and dpc ligands adopt a bridging position between the Cu(II) centers, forming the elongated octahedral geometry. The polymeric chains are linked to one another via O–H···O hydrogen bond interactions, forming the 3-D polymeric structure. The Ni(II) ion is bonded to dpc ligand through pyridine N atom together with one O atom of each carboxylate group, two aqua ligands and N pyridine atom of 4-hymp, forming the distorted octahedral geometry. The Ni(II) complexes are connected to one another via O–H···O hydrogen bonds, forming R ₄²(18) motifs in 2-D pattern. The powder EPR spectra of copper(II) complex have indicated that the paramagnetic center is in rhombic symmetry with the Cu²⁺ ion having distorted octahedral geometry. IR and UV–Vis spectroscopes all agree with the observed crystal structure.