Distorted Square-antiprism Geometry Research Articles

Magnetic and photophysical properties of new TbIII –based two-dimensional hydrogen-bonded polymer

A new terbiumIII-based 2D hydrogen-bonded polymer formulated as {[TbIII(2-stp)(H2O)3].2(4,4′-bipy).5(H2O)}, (1) (4,4′-bipy = 4,4′-bipyridine and 2-stp = 2-sulfoterephthalate) was hydrothermally synthesized. This hydrogen-bonded TbIII–based polymer was characterized by X-ray crystallography, spectroscopic, magnetic and photoluminescence measurements. Field emission scanning electron microscopy (FESEM) was used for the morphological analysis. The crystal structure of 1 shows a distorted square-antiprism geometry about TbIII atom with two carboxylic oxygen atoms from the symmetry-related two 2-stp ligands and six oxygen atoms from the symmetry-related three coordinated water molecules. The magnetic behaviour of 1 reveals the antiferromagnetic interaction between TbIII magnetic centers. The photoluminescence spectrum of 1 exhibits strong characteristic green emission bands of TbIII with CIE chromaticity coordinates (0.185, 0.632).

Distorted square-antiprism geometry of new zirconium (IV) Schiff base complexes: Synthesis, spectral characterization, crystal structure and investigation of biological properties

A series of zirconium (IV) Schiff-base complexes formulated as [Zr (Lx)2] and [Zr (Lx′)2] were synthesized by reaction of tetradentate salicylaldimine Schiff-base ligands with [Zr (acac)4] in methanol. These ligands are as follows: H2Lx and H2Lx′ (x = x′ = 1,2,3,4). The new complexes have been characterized using FT-IR, lH NMR, 13C{1H} NMR spectroscopic techniques, elemental analyses (CHN) and the crystal structure of Zr (L3)2, Zr (L1′)2 and Zr (L3′)2 were determined by X-ray crystallography. The crystal structure analysis revealed that the coordination environment of the metal in all complexes is eight-coordinate occupied by N2O2 sets of the coordinated ligands in distorted square-antiprism geometry. The in vitro biological screening effects of the synthesized compounds were tested against different microbial kinds and the zirconium (IV) complexes exhibit antimicrobial activity.

Slow Relaxation of Magnetization in an Isostructural Series of Zinc-Lanthanide Complexes: An Integrated EPR and AC Susceptibility Study.

We report the synthesis, structure, and spectroscopic and dynamic magnetic properties of a series of heterodinuclear complexes, [ZnLn(LH4 )2 ](NO3 )3 ⋅6 H2 O (Ln=Nd, Tb, Dy, Ho, Er, and Yb), with the singly deprotonated form of a new compartmentalized Schiff-base ligand, LH5 . The Ln(III) ions in these systems show a distorted square-antiprism geometry with an LnO8 coordination sphere. EPR spectroscopy and DC magnetic studies have shown that the anisotropic nature of the complexes is far more complicated than predicted on the basis of a simple electrostatic model. Among the investigated systems, only the Dy(III) derivative showed single-ion magnet behavior, in zero and an applied magnetic field, both in pure polycrystalline samples and in a series of polycrystalline samples with different degrees of dilution at the single-crystal level in the isostructural Y(III) derivative. The rich dynamics observed as functions of frequency, field, and temperature reveals that multiple relaxation mechanisms are at play, resulting in a barrier of 189 cm(-1) , which is among the highest reported for a dinuclear Zn-Dy system. Analysis of the dynamic behavior as a function of dilution degree further evidenced the persistence of non-negligible intermolecular interactions, even at the lowest concentration of 1 %.

Crystal structures, spectroscopic, and thermal properties of Dysprosium (III) and Europium (III) complexes with 3-chloro-4-methoxybenzoic and 1,10-phenanthroline

Two lanthanide complexes with the formula [Dy(3-Cl-4-MOBA)3phen]2 (1) and [Eu (3-Cl-4-MOBA)3phen]2 (2) (3-Cl-4-MOBA=3-chloro-4-methoxybenzoate; phen=1,10-phenanthroline) were synthesized and characterized by elemental analysis, molar conductivity, ultraviolet spectra, infrared spectra, single crystal X-ray diffraction, and thermal analysis. The two complexes are isostructural. Two lanthanide cations are connected by four carboxylic groups through a bridging bidentate mode, resulting in distorted square-antiprism geometry. Under the excitation ultraviolet light, the two complexes exhibit characteristic emission of dysprosium or europium cation. The gaseous decomposition products of the two complexes were inferred by thermogravimetry and infrared spectrometry techniques. The heat capacity of the complexes was measured using differential scanning calorimetry technology. And the thermodynamic functions including entropy, gibbs free energy, and enthalpy relative to the reference temperature (298.15 K) were also calculated. In addition, the antifungal activities of the two complexes were also studied.

A series of binuclear lanthanide(III) complexes: Crystallography, antimicrobial activity and thermochemistry properties studies

A series of novel lanthanide complexes with the general formula [Ln(3,4-DClBA)3phen]2 (Ln=Ho(1), Nd(2), Sm(3), Dy(4), Eu(5), Tb(6), Yb(7) and Er(8), 3,4-DClBA=3,4-dichlorobenzoate, phen=1,10-phenanthroline) were prepared at room temperature and characterized. The crystal structures of complexes 1–8 have been determined by single crystal X-ray diffraction. These complexes are isomorphous and lanthanide ions are all eight-coordinated to oxygen atoms and nitrogen atoms with distorted square-antiprism geometry. The thermal decomposition mechanism and TG-FTIR spectra of gaseous products of thermal decomposition processes for complexes 1–8 were acquired through TG/DSC-FTIR system. The heat capacities of complexes 1–8 were measured using DSC technology and fitted to a polynomial equation by the least-squares method. Complexes 3–6 display characteristic lanthanide emission bands in the visible region. Meanwhile, these complexes exhibit in good antimicrobial activity against Candida albicans, Escherichia coli, and Staphylococcus aureu.

Crystal structures, thermal behavior and biological activities of lanthanide compounds with 2,4-dichlorobenzoic acid and 1,10-phenanthroline

Five new binuclear lanthanide compounds [Ln(2,4-DClBA)3phen]2 (Ln = Pr(1), Eu(2), Tb(3), Ho(4) and Er(5); 2,4-DClBA = 2,4-dichlorobenzoate; phen = 1,10-phenanthroline) have been synthesized and structurally characterized by X-ray crystallography. And all of them were carefully investigated by elemental analysis, molar conductance, IR, UV and TG/DSC-FTIR technology. Single-crystal X-ray diffraction studies revealed that compounds 1–5 were binuclear molecules with an inversion center and the Ln3+ ions contained two kinds of coordination environment that was a distorted monocapped square-antiprism in the compounds 1–2, and a distorted square-antiprism geometry in the compounds 3–5. The 3D surface graphs for the FTIR spectra of gaseous products for the compounds 1–5 were recorded using simultaneous TG/DSC-FTIR technique which is intended to further analysis of the thermal decomposition processes. Hence the gaseous products were identified by the solved single IR spectra obtained at different temperatures from the 3D surface graphs. Furthermore, the Eu(III) and Tb(III) ternary compounds exhibited intense luminescence under the radiation of UV light. And the results for antimicrobial test show that these compounds exhibit good bacteriostatic activity against Staphylococcus aureus, and better antimicrobial activity against Escherichia coli and Candida albicans.

Structural reinvestigation of the photoluminescent complex [NdCl2(H2O)6]Cl

The structure of the photoluminescent compound hexaaquadichloridoneodymium(III) chloride has been redetermined from single-crystal X-ray diffraction data at 100 K, with the aim of providing an accurate structural model for the bulk crystalline material. The crystal structure may be described as a network of [NdCl2(H2O)6](+) cations with distorted square-antiprism geometry around the Nd(III) centre. The Nd(III) cation and the nonbonded Cl(-) anion are both located on twofold symmetry axes. The crystal packing consists of three different neodymium pairs linked by a three-dimensional network of O-H···Cl intermolecular interactions. The pair distribution function (PDF) calculated from the experimentally determined structure is used for the discussion of the local structure.

Cyanide-Bridged WVMnIII Bimetallic Chains Composed of a Blocked W Hexacyanide Precursor: Geometry-Related Magnetic Couplings and Magnetostructural Correlation

Five one-dimensional bimetallic W(V)Mn(III) complexes 1-5, consisting of [W(CN)6(bpy)](-) anions and [Mn(Schiff base)](+) cations, were prepared. The central coordination geometry around each W atom is determined as a distorted dodecahedron (DD) for 1 and 2, and a distorted square antiprism (SAPR) for 3-5. Magnetic analyses demonstrate that compounds 1, 4, and 5 exhibit antiferromagnetic interactions between magnetic centers, which are different from the ferromagnetic couplings in 2 and 3. For the distorted DD geometry, the Mn-N(ax) (ax = axial) bond length increases when moving from 1 to 2, with the Mn-N(ax)-C(ax) angle remaining constant. The elongation of the bond length is responsible for the reduction in orbital overlap and consequent ferromagnetic coupling in 2. In comparison, for 3-5 with the distorted SAPR geometry, given that the Mn-N(ax) bond lengths are similar across all the samples, the increase in the Mn-N(ax)-C(ax) angles accounts for the enhanced magnetic strength. Notably, a correlation between structure and magnetic exchange coupling is established for the first time in W(V)Mn(III) bimetallic systems based on the [W(CN)6(bpy)](-) precursor.

Crystal Structures, Thermal Properties, and Biological Activities of a Series of Lanthanide Compounds with 2,4-Dichlorobenzoic Acid and 1,10-Phenanthroline

A new family of binuclear lanthanide compounds of general formula [Ln(2,4-DClBA)3phen]2 (Ln(III) = Nd (1), Sm (2), Dy (3), Yb (4); 2,4-DClBA = 2,4-dichlorobenzoate; phen = 1,10-phenanthroline) have been synthesized and characterized by elemental analysis, molar conductance, infrared spectroscopy, ultraviolet spectra, thermogravimetric analysis, and single-crystal X-ray diffraction. On the basis of X-ray crystallography, compounds 2–4 belong to the triclinic crystal system, PI̅ space group. In compound 2, the Sm3+ ion adopted a distorted monocapped square-antiprism coordination geometry. Compounds 3 and 4 are isomorphous whose central ions (Dy3+ and Yb3+) formed a distorted square-antiprism geometry. The heat capacities of compounds 1–4 are measured using DSC technology and fitted to a polynomial equation by the least-squares method. The smoothed molar heat capacities and thermodynamic function data of compounds 1–4 relative to the reference temperature 298.15 K are then calculated. Meanwhile, these compounds exhibit in good antifungal activity against C. albicans, good antibacterial activity against S. aureus, and better antibacterial activity against E. coli. The fluorescence spectra of the samarium and dysprosium compounds behave as characteristic transitions of Sm(III) and Dy(III) ions.

A series of 1D Dy(iii) compound showing slow magnetic relaxation: synthesis, structure, and magnetic studies

In this work, we present the synthesis, structure, and magnetic studies of three 1D homo-spin Dy(III) compounds in detail. For 1, one crystallography-independent Dy(III) site is contained and the coordination surrounding is a distorted square-antiprism geometry. Within 2, four crystallography-independent Dy(III) sites with largely distorted square-antiprism geometry are observed. As for 3, two crystallography-independent Dy(III) sites showing bicapped triangular-prism geometry are involved. The magnetic studies suggest weak ferromagnetic interactions for 1 and weak antiferromagnetic interactions for 2 and 3. Their dynamic magnetic properties are investigated by means of alternating current (ac) susceptibility measurement, revealing their slow magnetic relaxation. Moreover, a field-dependent ac signal is observed in 1, when by applying a static dc = 1000 Oe field, strong frequency-dependent ac signals and the peak of out-of-phase (χ'') can be clearly found. Ultimately, by fitting the Arrhenius law the energy barrier and relaxation time are estimated.

Crystal Structures and Thermal Properties of Two Transition-Metal Compounds {[Ni(DNI)(2)(H(2)O)(3)][Ni(DNI)(2) (H(2)O)(4)]}.6H(2)O and Pb(DNI)(2)(H(2)O)(4) (DNI = 2,4-Dinitroimidazolate).

Two transition-metal compounds derived from 2,4-dinitroimidazole, {[Ni(DNI)(2)(H(2)O)(3)][Ni(DNI)(2) (H(2)O)(4)]}.6H(2)O, 1, and Pb(DNI)(2)(H(2)O)(4), 2, were characterized by elemental analysis, FT-IR, TG-DSC and X-ray single-crystal diffraction analysis. Crystal data for 1: monoclinic, space group C2/c, a = 26.826(3), b = 7.7199(10), c = 18.579(2) A, beta = 111.241(2) degrees and Z = 4; 2: monoclinic, space group C2/c, a = 6.5347(6), b = 17.1727(17), c = 14.1011(14) A, beta = 97.7248(10) and Z = 4. Compound 1 contains two isolated nickel centers in its structure, one being six-coordinate and another five-coordinate. The structure of 2 contains a lead (II) center surrounded by two chelating DNI ligands and four water molecules in distorted square-antiprism geometry. The abundant hydrogen bonds in two compounds link the molecules into three-dimensional network and stabilize the molecules. The TG-DSC analysis reveals that the first step is the loss of water molecules and the final residue is the corresponding metal oxides and carbon.

Interactions of Calcium Ions with Carbohydrates: Crystal Structure of Calcium d-Glucarate Tetrahydrate

Abstract The crystal structure of calcium d-glucarate tetrahydrate has been determined from three dimensional X-ray data, and refined by the least squares method including an anisotropic temperature factor. The crystals are orthorhombic, space group P212121 with a=16.09, b=11.36 and c=6.68Å. The calcium ion is bound to two glucarate molecules and three water molecules. The eight oxygen atoms form the calcium coordination shell of a distorted square-antiprism geometry. The carboxyl group including C(1) of d-glucarate has an eclipsed conformation relative to C(2) and O(2), and is coordinated with one calcium ion through the carboxyl oxygen O(1) and the α-hydroxyl oxygen O(2), and with the other calcium ion through the carboxyl oxygen O′(1) and the hydroxyl oxygens O(3) and O(4). The other carboxyl group including C(6) has an unusual staggered conformation relative to C(5) and O(5), and is not coordinated with calcium ions. However the oxygen atoms of the latter carboxyl group are attached by hydrogen bonds to a number of hydroxyl groups and water molecules, all of which are coordinated with calcium ions.