Triclinic P1 Research Articles

Investigations on (C6H9N2)2[MIIBr4] halogenometallate complexes with MII = Co, Cu and Zn: Crystal structure, thermal behavior and magnetic properties

Three complexes with the general formula (C6H9N2)2[MIIBr4] with MII = Cu (1), Co (2) and Zn (3) have been grown by the slow evaporation method at room temperature. These compounds were subjected to the following characterization techniques: single crystal X-ray diffraction, thermal analysis (ATG-TD), In situ X-ray powder diffraction and temperature dependent magnetic susceptibility measurements. The crystals of (C6H9N2)2[CuBr4] belong to the triclinic P1¯ space group, whereas (C6H9N2)2[CoBr4] and (C6H9N2)2[ZnBr4] crystallize in the orthorhombic system with the Pbcn space group. Molecular structures of the three coordination compounds consist of [MBr4]2- anions and 2-amino-6-methylpyridinium cations linked together via non-covalent interactions including hydrogen bonding, π···π stacking and halogen···halogen interactions which lead to three-dimensional supramolecular architecture. The thermal decomposition of the copper compound reveals the slow crystallization of CuBr at 130 °C. Both compounds 1 and 2 exhibit weak antiferromagnetic interactions.

High-pressure phase diagram, structural transitions, and persistent nonmetallicity of BaBiO3 : Theory and experiment

${\mathrm{BaBiO}}_{3}$ is a mixed-valence perovskite, which escapes the metallic state through a Bi valence (and Bi-O bond) disproportionation or CDW distortion, resulting in a semiconductor with a gap of 0.8 eV at zero pressure. The evolution of structural and electronic properties at high pressure is, however, largely unknown. Pressure, one might have hoped, could reduce the disproportionation, making the two Bi ions equivalent and bringing the system closer to metallicity or even to superconductivity, such as is attained at ambient pressure upon metal doping. We address the high-pressure phase diagram of pristine ${\mathrm{BaBiO}}_{3}$ by ab initio DFT calculations based on GGA and hybrid functionals in combination with crystal structure prediction methods based on evolutionary algorithms, molecular dynamics, and metadynamics. The calculated phase diagram from 0 to 50 GPa indicates that pristine ${\mathrm{BaBiO}}_{3}$ resists metallization under pressure, undergoing instead at room temperature structural phase transitions from monoclinic I2/m to nearly tetragonal P-1 at 7 GPa, possibly to monoclinic C2/m at 27 GPa, and to triclinic P1 at 43 GPa. Remarkably, all these phases sustain and in fact increase the inequivalence of two Bi neighboring sites and of their Bi-O bonds and, in all cases except semimetallic C2/m, the associated insulating character. We then present high-pressure resistivity data, which generally corroborate these results, and show that the insulating character persists at least up to 80 GPa, suggesting that the C2/m phase is probably an artifact of the small computational cell.

Supramolecular coordination polymers of La(III), Ce(III), Sm(III), Gd(III) and Eu(III) decorated with rigid 5-hydroxy-1,3-benzenedicarboxylate and flexible hexane-1,6-dicarboxylate linkers: Syntheses, structures, DFT study, luminescence and magnetic properties

Five new coordination polymers (CPs) with the formula [Ln (hip) (adip)0.5(H2O)2]n·nH2O [Ln=La (1), Ce (2), Sm (3) and Gd (4)] and [Ln2(hip)2 (adip)(H2O)4]n·2nH2O [Ln=Eu (5)] were synthesized by self-assembly of lanthanide salts with rigid [5-hydroxyisophthalic acid (H2hip)] and flexible [adipic acid (H2adip)] linkers under solvothermal condition. The CPs 1–4 crystallizes in monoclinic C2/c space group, whereas CP 5 has triclinic P1¯ space groups respectively. The CPs 1–4 exhibit 1D linear ladder shaped extension with the linkage of lanthanide carboxylate chains having the backbone of H2hip and H2adip ligands, whereas CP 5 shows linear orthogonally twisted ladder shaped chains. The 1D linear ladder chains are grafted into three dimensional (3D) supramolecular frameworks via significant π–π and hydrogen bonding interactions. The DFT calculations support structures adopted by polymers. The CPs 3 (Sm) and 5 (Eu) emit strong ligand sensitized characteristic f–f luminescence emission. The CP 4 exhibit weak ferromagnetic interactions at low temperatures.

Three novel Ho(III) complexes with different auxiliary ligands: Synthesis, crystal structures and thermal properties

Three novel Ho(III) complexes, [(Ho(2-Br-5-MOBA)3(terpy)(H2O)] (1), [Ho(2-Br-5-MOBA)3(2,2′-bipy)]2 (2) and [Ho(2-Br-5-MOBA)3(5,5′-DM-2,2′-bipy)]2 (3) (2-Br-5-MOBA=2-bromine-5-methoxybenzoate, terpy=2,2:6′,2″-terpyridine, 2,2′-bipy=2,2′-bipyridine, 5,5′-DM-2,2′-bipy=5,5′-dimethy-2,2′-bipyridine), have been synthesized and characterized by single-crystal X-ray diffraction. Although 1–3 have the same triclinic crystal system and P1¯ space group, they show three different types of molecule structures. For 1, it is mononuclear and fake binuclear units constituted by the mononuclear molecules are stitched together via π–π stacking and C–H⋯O hydrogen bonding interactions to form the 1D, 2D supramolecular structure. Complexes 2 and 3 are binuclear structures with the different coordination numbers, which are assembled into 1D, 2D, 3D supramolecular structures by different intermolecular interactions. This is because of the different auxiliary ligands. The thermal decomposition mechanism of complexes 1–3 were studied by TG analysis and further authenticated by TG/DSC-FTIR techniques, indicating that the difference of the auxiliary ligand affects the thermal stabilities of complexes. The average molar heat capacity values of the complexes gradually increased with an increase of temperature, indicating the complexes have good thermal stability within this range of temperature. In addition, the IR, PXRD, and the antibacterial activities of complexes 1–3 were measured.

Effects of Halo-Substitution on 2′-Chloro-5′-halo-phenyl-1,2,3,5-dithiadiazolyl Radicals: A Crystallographic, Magnetic, and Electron Paramagnetic Resonance Case Study

The syntheses and characterization of the aryl-substituted dithiadiazolyls 2′-Cl-5′-X-C6H3CNSSN• [1 (X = F), 2 (X = Cl), 3 (X = Br), 4 (X = I)] are described. In all four cases the radicals adopt distorted stacks of π*−π* dimers with interstack S···X contacts. In 1 (monoclinic P2/c) S···Cl contacts are manifested through a noncrystallographic 3-fold axis forming supramolecular trimers, whereas the interstack S···X contacts in 2 (triclinic P1), 3 and 4 (which form an isostructural pair, orthorhombic Pna21) form supramolecular chains. While all the structures adopt π*−π* cis-oid dimer motifs, tuning the halogen modifies the intradimer S···S distance. Variable temperature SQUID magnetometry and X-band continuous-wave electron paramagnetic resonance studies revealed the presence of a thermally accessible triplet state in all cases, with the singlet–triplet separation appearing in the order 1 > 2 > 3 > 4, consistent with a reduction in the overlap integral with increasing intradimer S···S separation. Variable...

Base metal Schiff base complexes applied as catalysts for the oxidation of n-octane

The catalytic oxidation of n-octane to value-added oxygenates has been studied with a series of salen-type complexes of iron. The four iron Schiff base complexes N,N′-bis(salicylidene)-L-iron(III) chloride [L=1,2-phenylenediamine (5); ethylenediamine (6); propylenediamine (7) and butylenediamine (8)] were synthesised by variation of the bridging diamine backbone. All the complexes are fully characterised and the crystal structure of 7 is for the first time reported as a centrosymmetric dimer observed to crystallise in the triclinic P1‾ system. The application of 5–8 in this oxidation reaction represents a rare example of the systematic use of iron-salen complexes for the liquid-phase functionalisation of Csp3–H bonds of straight chain alkanes. All catalysts displayed activity with H2O2 and TBHP as oxidants that resulted in a mixture of oxygenated products dominated by the ketones (2-, 3- and 4-octanones). Observed trends and variations in catalytic activities of the complexes is related to differences in chemical/structural features and changes in reaction conditions. A detailed analysis of selectivity parameters of the complexes to the variety of oxygenates is also presented and rationalised.

Replacing Two Chlorido Ligands by a Bipyridine Ligand in Ruthenium Nitrosyl Complexes with NO‐Release Capabilities: A Comparative Study

[RuII(FT)(bipy)(NO)][PF6]3 [FT is the electron‐rich 4′‐(2‐fluorenyl)‐2,2′:6′,2′′‐terpyridine ligand and bipy is 2,2′‐bipyridine] is synthesized and characterized. It crystallizes in the triclinic P1 space group [a = 9.5362(2) Å, b = 10.3946(4) Å, c = 22.5701(8) Å, α = 94.7400(10)°, β = 94.9400(10)°, γ = 101.0680(10)]. A photochemical study is presented in comparison with that of the parents cis(Cl,Cl)‐[RuII(FT)Cl2(NO)][PF6] and trans(Cl,Cl)‐[RuII(FT)Cl2(NO)][PF6]. The three derivatives release nitric oxide (·NO) under irradiation at λ = 405 nm with respective quantum yields of 0.06, 0.31, and 0.10. Their two‐photon absorption (TPA) cross‐sections (σTPA) were investigated by the Z‐scan technique on related derivatives in which two hexyl chains were introduced to improve their solubility while their spectroscopic properties remained almost unaffected. The resulting σTPA values of 100 GM at λ = 800 nm are in the window of transparency for human tissues, and the bipyridine‐based complex exhibits a slight tendency for higher efficiency. The replacement of the [RuII(Cl)2(NO)] core by [RuII(bipy)(NO)] provides a much simpler synthesis, and the TPA‐induced ·NO‐release capabilities are in the same range of magnitude. Therefore, it is envisioned that ·NO donors of greater complexity with several metal centers could be investigated in future.

Structural and magnetic properties of semiquinonate based Al(iii) and Ga(iii) complexes.

The reaction of anhydrous MCl3 (M = Al(iii) or Ga(iii)) with one-electron-reduced 3,5-di-tert-butyl-1,2-ortho-benzoquinone (using metallic sodium) led us to isolate two distinct metal complexes of Al(iii) and Ga(iii), which were structurally and magnetically characterized. Complex 1 crystallized in the monoclinic P21/n space group, whereas 2 crystallized in the triclinic P1[combining macron] space group. Interestingly, whereas the Al(iii) derivative was obtained as a dimer with the molecular formula [Al2(μ-HL-)2(L˙-)4] (1) (where L˙- is a semiquinonate radical and HL- is a monoanionic catecholate ligand), the Ga(iii) derivative crystallized as [Ga(L˙-)3] (2), which is a polymorph of a previously reported complex. The presence of both catecholate and/or semiquinonate ligands in 1 and 2 was confirmed by single-crystal X-ray diffraction, mass spectrometry, and NMR and infrared spectroscopy techniques. The crystalline phase purity of the complexes was confirmed by powder X-ray diffraction (PXRD). Measurements of direct-current magnetic susceptibility, which were performed on a polycrystalline samples, revealed that in both complexes the semiquinonate radical anions are coupled ferromagnetically via the diamagnetic metal ion. The magnetism data of both complexes were modelled using the Heisenberg-Van Vleck-Dirac (HDVV) Hamiltonian, and the extracted parameters are consistent with the literature reports. The details of the electronic structures of the ground states of 1 and 2 were further investigated via X-band (ca. 9 GHz) electron paramagnetic resonance (EPR). The EPR spectrum of 2 could be reproduced by considering a quartet ground state with zero-field splitting and hyperfine coupling, whereas attempts to simulate all the EPR spectral features observed in a frozen solution of 1 by assuming it was a pure phase failed. A correct simulation required the simultaneous inclusion of contributions from a quartet and a triplet state. This evidently suggests that the dimeric complex of 1 is in equilibrium with a monomeric [Al(L˙-)3] complex in solution.

Three structurally related Copper complexes with two isomers: DNA/BSA binding ability, DNA cleavage activity and excellent cytotoxicity

Three Cu(II) complexes of [Cu(L1)(Br)2]·CH3CN (1), [Cu(L2)2(OAc)](PF6)·2C2H5OH (2), and [Cu(L1)(L2)](PF6)2 (3) (L1=2-(6-(pyridine-2-yl)-4-p-tolylpyridin-2-yl)pyridine, L2=2-(4-(pyridine-2-yl)-6-p-tolylpyridin-2-yl)pyridine) were designed and synthesized as anti-cancer drugs. All complexes were structurally characterized by X-ray crystallography showing that three complexes were the mononuclear compounds with the triclinic crystal system p1¯ space group. The interaction between each of these three complexes and calf thymus DNA (CT-DNA) was investigated via spectroscopic techniques and viscosity measurement, which indicated that these complexes could bind to CT-DNA by intercalation. Moreover, DNA cleavage experiment showed that, in the natural light under an aerobic environment, all complexes could cleave DNA in the absence of exogenous oxidant agent, and that singlet oxygen (1O2) might serve as the major cleavage active species. Protein binding experiment indicated that 1–3 could bind to bovine serum albumin (BSA) with moderate bonding via the static quenching mechanism. In addition, the IC50 values of these three complexes were significantly lower which denoted highly anti-cancer activities in comparison to cisplatin. And each of these complexes could individually inhibit proliferation potential of cancer cells by promoting G1-phase cell cycle arrest (G1 arrest) and inducing apoptosis through the production of reactive oxygen species (ROS) and the activation of caspase-3

Crystallographic Structure, Intermolecular Packing Energetics, Crystal Morphology and Surface Chemistry of Salmeterol Xinafoate (Form I)

Single crystals of salmeterol xinafoate (form I), prepared from slow cooled supersaturated propan-2-ol solutions, crystallize in a triclinic P1¯ symmetry with 2 closely related independent salt pairs within the asymmetric unit, with an approximately double-unit cell volume compared with the previously published crystal structure. Synthonic analysis of the bulk intermolecular packing confirms the similarity in packing energetics between the 2 salt pairs. The strongest synthons, as expected, are dominated by coulombic interactions. Morphologic prediction reveals a plate-like morphology, dominated by the {001}, {010}, and {100} surfaces, consistent with experimentally grown crystals. Although surface chemistry of the slow-growing {001} face comprises large sterically hindering phenyl groups, although weaker coulombic interactions still prevail from the alcohol group present on the phenyl and hydroxymethyl groups. The surface chemistry of the faster growing {010} and {100} faces are dominated by the significantly stronger cation/anion interactions occurring between the carboxylate and protonated secondary ammonium ion groups. The importance of understanding the cohesive and adhesive nature of the crystal surfaces of an active pharmaceutical ingredient, with respect to their interaction with other active pharmaceutical ingredient crystals and how that may affect formulation design, is highlighted.

Structural phase transitions and photoluminescence properties of oxonitridosilicate phosphors under high hydrostatic pressure.

Spectroscopic properties of a series of (Sr0.98-xBaxEu0.02)Si2O2N2 (0 ≤ x ≤ 0.98) compounds has been studied under high hydrostatic pressure applied in a diamond anvil cell up to 200 kbar. At ambient pressure the crystal structures of (Sr0.98-xBaxEu0.02)Si2O2N2 (0 ≤ x ≤ 0.98) are related to the ratio of strontium to barium and three different phases exists: orthorhombic Pbcn(0.78 ≤ x ≤ 0.98), triclinic P1 (0 < x ≤ 0.65) and triclinic P1 (0.65 < x < 0.78). It was found that Eu2+ luminescence reveals abrupt changes under pressure (decay time, energy and shape) which indicate the variation of the local symmetry and crystal field strength in Eu2+ sites. These changes are attributed to the reversible pressure-induced structural phase transitions of triclinic (Sr0.98-xBaxEu0.02)Si2O2N2 into orthorhombic structure. Pressure in which phase transition occurs decreases linearly with increasing of Ba composition in (Sr0.98-xBaxEu0.02)Si2O2N2 series. Additionally, very different pressure shifts of the Eu2+ luminescence in different phases of (Sr0.98-xBaxEu0.02)Si2O2N2:Eu from −40 cm−1/kbar to 0 cm−1/kbar have been observed. This effect is explained by different interaction of the Eu2+ 5d electron with the second coordination sphere around the impurity cations.

Synthesis, crystal structure, thermal and physical properties of (C6H18N2)3[Sb4Cl18

The crystal structure of tris (N, N, N’, N’-tetramethylethylenediammonium) octadecachloridotetraantimonate (III) is built up of [(CH3)2NH(CH2)2NH(CH3)2]2+ cations connected to the one [Sb4Cl18]6n−n anionic chains by N—H⋯Cl hydrogen bonds. In this study, we found that this ionic compound exhibits a triclinic P1¯↔ monoclinic P21/n structural phase transition at about (T1=356±2K) which has been characterized by X-rays powder analysis, DSC, AC conductivity and dielectric measurements. The optical band gap determined by diffuse reflection spectroscopy is 4.38eV for a direct allowed transition. Impedance spectroscopy measurements of (C6H18N2)[Sb4Cl18] were conducted under various frequency settings (from 20Hz to 2MHz) and over the temperature range 309–398K. The Cole-Cole (Z” versus Z’) plots are fitted to two equivalent circuits models. Combined impedance and modulus plots were used as tools to analyze the sample behaviour as a function of frequency at different temperatures. The frequency dependence of the AC conductivity is interpreted in terms of Jonscher’s law. The temperature dependence of the DC and the bulk σp conductivities are well explained by Arrhenius law. The conduction mechanisms are attributed to the quantum mechanical tunnelling (QMT) model in phase I and to the small polaron tunnelling (SPT) model in phase II. Our study has also revealed that the relaxation times are thermally activated and that the dipole process has a non-Debye behaviour.

Supramolecular Interactions Direct the Formation of Two Structural Polymorphs from One Building Unit in a One-Pot Synthesis.

Two polymorphs of supramolecular isomers, a discrete dimer and a zig-zag chain, having the same chemical composition, [Mn(Hbit)Cl2 ] (Hbit=1-methyl-2-(1H-1,2,3-triazol-4-yl)-1H-benzo[d]imidazole), were obtained solvothermally in a one-pot synthesis. The isomers differ in a number of ways: orange blocks versus pale-yellow needles, triclinic P1‾ versus orthorhombic Pbcn, double μ2 -Cl versus alternate single and triple μ2 -Cl, coordination number 5 versus 6, and antiparallel versus parallel near-neighbor orientation of Hbit. The packing in each case is driven by the supramolecular interactions, H-bonds (N-H⋅⋅⋅Cl, C-H⋅⋅⋅Cl) and π⋅⋅⋅π overlaps, calculated to be in the range 20-36 kcal mol-1 . Calculations gave a difference of only 2 kcal mol-1 in favor of the dimer, which confirms with the observation of principally the dimer at short reaction time. ESI-MS spectra of the dissolved crystals reveal the same fragments with similar distributions. The presence of two fragments at m/z 286.96 [MnIV (Hbit)Cl-2H]+ and 323.94 [MnIII (Hbit)Cl2 ]+ indicates that [Mn(Hbit)Cl2 ] is the building unit in both cases; thus, the different orientations of the ligands lead to the two polymorphs stabilized by the respective supramolecular interactions. Importantly, the chain form represents the first example with alternate single and triple μ2 -Cl bridges. The magnetic interactions are weakly antiferromagnetic in both cases, with J in the range 0.07-0.34 cm-1 ; however, high-field EPR analysis reveals moderate magneto-anisotropy with D=0.26(1) cm-1 , E=0.06(1) cm-1 and D=0.17(1) cm-1 , E=0.03(1) cm-1 , respectively.

Structural Diversity and Magnetic Properties of Seven Coordination Polymers Based on the 2,2′-Phosphinico-dibenzoate Ligand

Seven novel coordination polymers based on 2,2′-phosphinico-dibenzoic acid (H3L), namely, {[Zn3L2(H2O)4]·2H2O}n (1), [Zn3L2(4,4′-bipy)2]n (2), [Zn(HL)(2,2′-bipy)(H2O)]n (3), {[Cd9L6(H2O)8]·4H2O}n (4), [Cd8L4(OH)2(OAc)2(4,4′-bipy)]n (5), [Mn3L2(4,4′-bipy)(EtOH)(H2O)2]n (6), and [Mn(HL)(2,2′-bipy)(H2O)]n (7), were synthesized under hydro(solvo)thermal conditions. These compounds crystallize in the triclinic P1 space group for 1, 4, 5, and 6, the monoclinic space group C2/c for 2, and the monoclinic P21/c space group for 3 and 7. The L3– ligand displays versatile binding modes in 1–7. Compound 1 is a one-dimensional (1-D) chain coordination polymer with a three-dimensional (3-D) supramolecular framework. Compound 2 is a 3-D porous metal–organic framework (MOF) with two different 4,4′-bipyridine linkers. Compounds 3 and 7 show 1-D zigzag chain structures. Compound 4 exhibits a sophisticated 3-D MOF constructed from two types of Cd8 clusters and one Cd2 dimer, which is the first example exhibiting the coexist...

Structural characterization, vibrational studies and optical properties of a new luminescent organic-inorganic material [C6H20N3]BiI6·H2O

The (C6H20N3)BiI6·H2O compound is a new crystal belonging to the large hybrid organic-inorganic compounds family, which has been synthesized by the solvent evaporation method and characterized by single crystal X-ray diffraction at room. It crystallizes in the zero-dimensional (0-D) triclinic P1¯ space group. The cell dimensions are: a = 8.572 (5) Å, b = 11.838 (5) Å, c = 12.707 (5) Å, α = 74.317 (5)°, β = 71.043 (5)° and γ = 71.419 (5)°. The crystal structure consists of a discrete ionic layer of bis(3-azaniumylpropyl)azanium cations, hexa-iodobismuthate anions and neutral water molecules linked via simple and bifurcated NH⋯I(OW) and O(W)H⋯I hydrogen bonds. The structure of the prepared compound has been investigated using the group theory and IR and Raman spectroscopic techniques. The detailed interpretation of the vibrational modes was carried out. The optical absorption measurements on a (C6H20N3)BiI6·H2O pellet have revealed two absorption bands at 2.27 and 2.78 eV. In the end, two room temperature photoluminescence emissions attributed to the excitonic transition in the [BiI6]3− anions, were observed in the red spectral range at energy values of 1.87 and 2.05 eV.

Methyl carbazate energetic complexes: Transition metal perchlorates – Syntheses, crystal structures and properties

A series of transition metal (1 Mn(II), 2 Ni(II), 3 Cu(II), 4 Zn(II) and 5 Cd(II)) methyl carbazate perchlorate energetic complexes were synthesized in aqueous solution. The crystal structures were determined by single-crystal X-ray diffraction. The complex [Cu(MCZ)2](ClO4)2 belongs to the triclinic P1¯ space group. The Mn(II), Ni(II), Zn(II) and Cd(II) complexes all are monoclinic, P21/c space group. Their thermal stabilities were investigated using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). All the compounds show good thermal stabilities (1, 2, 4 and 5 under 200°C; 3 under 160°C). Non-isothermal reaction kinetics parameters, the critical temperatures of thermal explosion, ΔS≠, ΔH≠ and ΔG≠ were calculated. Their impact and friction sensitivities were tested, and their sensitivity levels are acceptable. The coordinated perchlorates reduce the thermal stability, but improve the decomposition rate immensely as well as the sensitivities.

Synthesis, physicochemical and biological studies of a ternary Co(II) complex with sulfaquinoxaline and 2,2′-bipyrimidine as ligands

A novel ternary complex of Cobalt(II) with 4-amino-N-2-quinoxalinylbenzenesulfonamide (sulfaquinoxaline, SQO), and 2,2′-bipyrimidine (Bpym) as ligands has been prepared. The complex has been characterized based on elemental analyses, FTIR and Raman spectroscopy. Its structure, [Co(SQO)2(Bpym)] was determined by X-ray diffraction methods. It crystallizes in the triclinic P1¯ space group with a=10.5381(2), b=13.6469(2), c=13.8409(3)Å, α=95.058(2)°, β=93.769(2)°, γ=93.750(2)° and Z=2 molecules per unit cell. Thermogravimetric (TG) and differential thermal analysis (DT) were also studied.The aquatic toxicity of the complex was evaluated on the two following test organisms: Danio rerio (cebritas) y Cyprinus carpio haematopterus (carpas koi). Antibacterial activity was screened against Escherichia coli (ATCC 8739), Salmonella typhimurium (ATCC 14028), Staphylococcus aureus (ATCC 49775) and Bacillus cereus (ATCC 10987). The antiproliferative effect of the tested complex [Co(SQO)2(Bpym)] in the human osteoblast (MG-63) cell line was also studied.

Tuning the structural and lanthanide luminescence properties of macrocyclic tetraiminodiphenolate europium(III) complexes

The synthesis, structural characterization, and luminescence properties of two novel macrocyclic tetraiminodiphenolate europium(III) complexes are reported. The macrocyclic ligands studied bind the lanthanide through four or five donor atoms, leaving space for additional nitrate ions or, in solution, solvent molecules within the inner coordination sphere of the Eu3+ ion. Structural aspects of the complexes, [Eu-TIDP-Pr-tBu(NO3)3] (3) and [Eu-TIDP-PrOH-tBu(NO3)3] (4), are probed in solution via absorption and fluorescence measurements, and in the solid state by IR spectroscopy and X-ray crystallography. Complex 3 crystallizes in the monoclinic P21/n space group with four molecules in the unit cell and cell dimensions a=9.6309(3) Å, b=21.4708(7) Å, c=21.4442(7) Å, β=94.565° and V=4420.2(2) Å3. Complex 4 crystallizes in the triclinic P1¯ space group, also with four molecules per unit cell and cell dimensions a=13.3847(2) Å, b=16.1381(2) Å, c=20.5803(3) Å, α=82.674(1)°, β=72.787(1)°, γ=71.871(1)° and V=4032.45(10) Å3. As confirmed by the crystal structure, an extra hydroxyl oxygen atom within the propanol linked derivative binds the metal center, leading to a significant decrease in solvent mediated quenching of the Eu3+ luminescence of complex 4. Finally, preliminary anion binding studies were conducted and suggest potential application of such complexes in the area of anion sensing via changes in emission intensity when select anions such as phosphate replace metal-bound water molecules in solution.

Investigation of structural, electronic, and optical properties of the monoclinic and triclinic polymorphs of hexamethylenetetraminium 2,4-dinitrophenolate monohydrate [formula omitted] compound: A DFT approach

We have investigated the structural, electronic and optical properties for two phases of polymorphs of hexamethylenetetraminium 2,4-dinitrophenolate monohydrate (C6H13N4+·C6H3N2O5−·H2O) compound which were synthesized by Hoong-Kun Fun's group. The first phase possesess monoclinic P21/m space group, while the other phase has triclinic P1 space group. The all electron full potential linearized augmented plane wave (FP-LAPW + lo) method within the local density approximation (LDA) and the Perdew-Burke-Ernzerhof generalized gradient approximation (PBE-GGA) were used. Calculation shows that the conduction band minimum (CBM) for the two phases is located between D and Z points of the Brillouin zone (BZ) while the valence band maximum (VBM) is located at the center of the BZ, resulting in an indirect band gap. It has been found that the monoclinic (300 K) polymorph possesses a band gap of about 1.884 (LDA) and 1.935 (PBE-GGA) eV while triclinic (143 K) polymorph has a band gap of about 1.720 (LDA) and 1.773 (PBE-GGA) eV. For a deeper insight into the electronic structure, we have performed comprehensive optical properties calculations. These confirm the band gap reduction during the phase transition (300 K→143 K). The bond lengths and angles are calculated and compared with the experimental data; good agreement was found which reveals the accuracy of the calculations.

Crystallographic evidence for β-cyclodextrin inclusion complexation facilitating the improvement of antioxidant activity of tea (+)-catechin and (−)-epicatechin

Single-crystal X-ray analysis to 0.6Å resolution using synchrotron radiation of the inclusion complexes of β-cyclodextrin (β-CD) with (+)-catechin (CA) and (−)-epicatechin (EC) has been carried out to gain atomistic insight into how the inclusion complexation helps to improve tea catechin antioxidant activity. The β-CD–CA complex crystallizes in the monoclinic P21 space group, whereas the β-CD–EC complex crystallizes in both the monoclinic P21 and triclinic P1 space groups. In comparing the inclusion structures, the β-CD–EC dimeric structure having higher numbers of OH⋯O hydrogen bonds combined with π⋯π interactions is associated with its greater interaction energy, as derived from DFT/B3LYP single-point energy calculations. Detailed structural analysis of the CA, EC conformation and inclusion geometry reveals that the interplay of the intermolecular OH⋯O hydrogen bond stabilized catechol moiety and the protection of OH groups in the β-CD cavity plays a key role in the improvement of antioxidant capacity upon inclusion complexation.