Structure and NMR properties of the dinuclear complex di-?-azido-?4N1:N1-bis-[(azido-?N)(pyridine-2-carboxamide-?2N1,O)zinc(II)].
ABSTRACT: The new diamagnetic complex, [Zn2(N3)4(C6H6N2O)2] or [Zn2(pca)2(?1,1-N3)2(N3)2] was synthesized using pyridine-2-carboxamide (pca) and azido ligands, and characterized using various techniques: IR spectroscopy and single-crystal X-ray diffraction in the solid state, and nuclear magnetic resonance (NMR) in solution. The mol-ecule is placed on an inversion centre in space group P . The pca ligand chelates the metal centre via the pyridine N atom and the carbonyl O atom. One azido ligand bridges the two symmetry-related Zn2+ cations in the end-on coordination mode, while the other independent azido anion occupies the fifth coordination site, as a terminal ligand. The resulting five-coordinate Zn centres have a coordination geometry inter-mediate between trigonal bipyramidal and square pyramidal. The behaviour of the title complex in DMSO solution suggests that it is a suitable NMR probe for similar or isostructural complexes including other transition-metal ions. The diamagnetic nature of the complex is reflected in similar 1H and 13C NMR chemical shifts for the free ligand pca as for the Zn complex.
Project description:Synthesis of the new scorpiand ligand L composed of a aneN<sub>3</sub> macrocyclic ring bearing a CH<sub>2</sub>CH<sub>2</sub>NHCH<sub>2</sub>-anthracene tail is reported. L forms both cation (Zn<sup>2+</sup>) and anion (phosphate, benzoate) complexes. In addition, the zinc complexes of L bind these anions. The equilibrium constants for ligand protonation and complex formation were determined in 0.1 M NaCl aqueous solution at 298.1 ± 0.1 K by means of potentiometric (pH-metric) titrations. pH Controlled coordination/detachment of the ligand tail to Zn<sup>2+</sup> switch on and off the fluorescence emission from the anthracene fluorophore. Accordingly, L is able to sense Zn<sup>2+</sup> in the pH range 6-10 down to nM concentrations of the metal ion. L can efficiently sense Zn<sup>2+</sup> even in the presence of large excess of coordinating anions, such as cyanide, sulphide, phosphate and benzoate, despite their ability to bind the metal ion.
Project description:In the title polymeric Zn<sup>II</sup> compound, [Zn(C<sub>8</sub>H<sub>7</sub>O<sub>3</sub>)<sub>2</sub>(C<sub>12</sub>H<sub>12</sub>N<sub>2</sub>)] <sub><i>n</i></sub> , the Zn cation is coordinated by two N atoms from 1,2-bis-(pyridin-4-yl)ethane unit and four O atoms from two mandelate [or hy-droxy(phen-yl)acetate] anions in a slightly distorted octa-hedral coordination geometry. The 1,2-bis-(pyridin-4-yl)ethane unit bridges two Zn<sup>II</sup> cations, related by an inversion centre, to form a polymeric chain along . The crystal structure features extensive O-H?O and weak C-H ?O hydrogen bonds, with C-H ? ? inter-actions and ?-? inter-actions also being present. The centroid-centroid distance between the phenyl ring of the mandelate group and the 1,2-bis-(pyridine-4-yl)ethane moiety is 4.951?(2)?Å. The 1,2-bis-(pyridin-4-yl)ethane ligand is disordered over two positions, with a refined occupancy of 0.578?(14) for the major component.
Project description:Recent research has built a consensus that the binder plays a key role in the performance of high-capacity silicon anodes in lithium-ion batteries. These anodes necessitate the use of a binder to maintain the electrode integrity during the immense volume change of silicon during cycling. Here, Zn<sup>2+</sup>-imidazole coordination crosslinks that are formed to carboxymethyl cellulose backbones in situ during electrode fabrication are reported. The recoverable nature of Zn<sup>2+</sup>-imidazole coordination bonds and the flexibility of the poly(ethylene glycol) chains are jointly responsible for the high elasticity of the binder network. The high elasticity tightens interparticle contacts and sustains the electrode integrity, both of which are beneficial for long-term cyclability. These electrodes, with their commercial levels of areal capacities, exhibit superior cycle life in full-cells paired with LiNi<sub>0.8</sub>Co<sub>0.15</sub>Al<sub>0.05</sub>O<sub>2</sub> cathodes. The present study underlines the importance of highly reversible metal ion-ligand coordination chemistries for binders intended for high capacity alloying-based electrodes.
Project description:A self-assembled Zn<sup>II</sup>-Nd<sup>III</sup> heterohexanuclear coordination compound [Zn?Nd?(L)?(bdc)?]·2NO? based on a hexadentate Salamo-like chelating ligand (H?L = 1,2-bis(3-methoxysalicylideneaminooxy)ethane]) and H?bdc (H?bdc = terephthalic acid) has been synthesized and characterized by elemental analyses, IR and UV/Vis spectra, and X-ray crystallography. Two crystallographically equivalent [Zn?Nd(L)?] moieties lie in the inversion center linked by two (bdc)<sup>2-</sup> ligands leading to a heterohexanuclear dimer in which the carboxylato group bridges the Zn<sup>II</sup> and Nd<sup>III</sup> atoms. The heteropolynuclear 3d-4f coordination compound includes four Zn<sup>II</sup> atoms, two Nd<sup>III</sup> atoms, four completely deprotonated (L)<sup>2-</sup> units, two fully deprotonated (bdc)<sup>2-</sup> units, and two crystalling nitrate ions. All of the Zn<sup>II</sup> atoms in the Zn<sup>II</sup>-Nd<sup>III</sup> coordination compound possess trigonal bipyramidal geometries and the Nd<sup>III</sup> atoms possess distorted bicapped square antiprism coordination arrangements. In addition, the fluorescence properties of the ligand and the Zn<sup>II</sup>-Nd<sup>III</sup> coordination compound were investigated.
Project description:Low-symmetry metal-organic architectures that feature unusual binding motifs are useful for exploring new modes of guest recognition. Such structures remain difficult to create using current rational design principles. One approach to constructing such architectures is to employ ligands with coordination vectors oriented to preclude the formation of simple, low nuclearity molecular assemblies upon complexation to metal ions. Here we report two new supramolecular assemblies generated from such a ligand: a simple metastable [Zn<sub>3</sub>L<sub>3</sub>]<sup>6+</sup> assembly, which was observed to convert to a more complex [Zn<sub>9</sub>L<sub>5</sub>(?-OH)<sub>6</sub>]<sup>12+</sup> twisted half-pipe architecture. Two chemically distinct stimuli-an anionic template and a base-must be applied for the conversion to occur. Perchlorate, perrhenate, trifluoromethanesulfonate and 2-naphthalenesulfonate were found to act as competent templates for the [Zn<sub>9</sub>L<sub>5</sub>(?-OH)<sub>6</sub>]<sup>12+</sup> structure.
Project description:Coordination of FeCl<sub>3</sub> to the redox-active pyridine-aminophenol ligand NNO<sup>H2</sup> in the presence of base and under aerobic conditions generates FeCl<sub>2</sub>(NNO<sup>ISQ</sup>) (1), featuring high-spin Fe<sup>III</sup> and an NNO<sup>ISQ</sup> radical ligand. The complex has an overall S = 2 spin state, as deduced from experimental and computational data. The ligand-centered radical couples antiferromagnetically with the Fe center. Readily available, well-defined, and air-stable 1 catalyzes the challenging intramolecular direct C(sp<sup>3</sup>)-H amination of unactivated organic azides to generate a range of saturated N-heterocycles with the highest turnover number (TON) (1 mol% of 1, 12 h, TON = 62; 0.1 mol% of 1, 7 days, TON = 620) reported to date. The catalyst is easily recycled without noticeable loss of catalytic activity. A detailed kinetic study for C(sp<sup>3</sup>)-H amination of 1-azido-4-phenylbutane (S<sub>1</sub>) revealed zero order in the azide substrate and first order in both the catalyst and Boc<sub>2</sub>O. A cationic iron complex, generated from the neutral precatalyst upon reaction with Boc<sub>2</sub>O, is proposed as the catalytically active species.
Project description:A series of racemic, heteronuclear complexes [Zn?Nd(ac)?(HL)?]NO?·3H?O (<b>1</b>), [Zn?Sm(ac)?(HL)?]NO?·3CH?OH·0.3H?O (<b>2</b>), [Zn?Ln(ac)?(HL)?]NO?·5.33H?O (<b>3</b>?<b>5</b>) (where <b>HL</b> is the dideprotonated form of <i>N</i>,<i>N</i>'-bis(5-bromo-3-methoxysalicylidene)-1,3-diamino-2-propanol, ac = acetate ion, and Ln = Eu (<b>3</b>), Tb (<b>4</b>), Dy (<b>5</b>), respectively) with an achiral multisite coordination Schiff base ligand (<b>H?L</b>) were synthesized and characterized. The X-ray crystallography revealed that the chirality in complexes is centered at lanthanide(III) ions due to two vicinally located <i>?</i>-acetato-bridging ligands. The presented crystals have isoskeletal coordination units but they crystallize in monoclinic (<b>1</b>, <b>2</b>) or trigonal crystal systems (<b>3</b>?<b>5</b>) with slightly different conformation. In <b>1</b> and <b>2</b> the Zn<sup>II</sup>?Ln<sup>III</sup>?Zn<sup>II</sup> coordination core is linear, whereas in isostructural crystals <b>3</b>?<b>5</b> the chiral coordination cores are bent and lie on a two-fold axis. The complexes <b>1</b>, <b>3</b>?<b>5</b> show a blue emission attributed to the emission of the ligand. For Zn<sup>II</sup>?Sm<sup>III</sup> complex (<b>2</b>) the characteristic emission bands of f-f* transitions were observed. The magnetic properties for compounds <b>1</b>, <b>4</b> and <b>5</b> are characteristic for the paramagnetism of the corresponding lanthanide(III) ions.
Project description:The asymmetric unit of the title compound, [Zn(C<sub>6</sub>H<sub>8</sub>N<sub>4</sub>B)<sub>2</sub>(C<sub>12</sub>H<sub>8</sub>N<sub>2</sub>)], comprises one half of a Zn<sup>II</sup> cation (site symmetry 2), one di-hydro-bis-(pyrazol-1-yl)borate ligand in a general position, and one half of a phenanthroline ligand, the other half being completed by twofold rotation symmetry. The Zn<sup>II</sup> cation is coordinated in form of a slightly distorted octa-hedron by the N atoms of a phenanthroline ligand and by two pairs of N atoms of symmetry-related di-hydro-bis-(pyrazol-1-yl)borate ligands. The discrete complexes are arranged into columns that elongate in the <i>c-</i>axis direction with a parallel alignment of the phenanthroline ligands, indicating weak ?-? inter-actions.
Project description:The title Zn<sup>II</sup> complex, [Zn(NCS)<sub>2</sub>(C<sub>20</sub>H<sub>21</sub>N<sub>3</sub>)], has been characterized by synchrotron single-crystal diffraction and FT-IR spectroscopy. The central Zn<sup>II</sup> ion has a distorted square-pyramidal coordination geometry, with three N atoms of the chiral (<i>S</i>) 1-phenyl-<i>N</i>,<i>N</i>-bis-[(pyridin-2-yl)meth-yl]ethanamine (<i>S</i>-ppme) ligand and one N atom of a thio-cyanate anion in the equatorial plane, and one N atom of another thio-cyanate anion at the apical position. The average Zn-N <sub><i>S</i>-ppme</sub> and Zn-N<sub>NCS</sub> bond lengths are 2.183?(2) and 1.986?(2)?Å, respectively. In the crystal, inter-molecular C-H?S hydrogen bonds and a face-to-face ?-? inter-action [centroid-centroid distance = 3.482?(1)?Å] link the mol-ecules and give rise to a supra-molecular sheet structure parallel to the <i>ac</i> plane.
Project description:The synthesis, characterization, and catalytic activity of pyridine(diimine) iron piperylene and isoprene complexes are described. These diene complexes are competent precatalysts for (i) the selective cross-[2+2]-cycloaddition of butadiene or <i>(E)</i>-piperylene with ethylene and ?-olefins and (ii) the 1,4-hydrovinylation of isoprene with ethylene. In the former case, kinetic analysis implicates the diamagnetic ?<sup>4</sup>-piperylene complex as the resting state prior to rate-determining oxidative cyclization. Variable temperature <sup>1</sup>H NMR and EXSY experiments established that diene exchange from the diamagnetic, 18e<sup>-</sup> complexes occurs rapidly in solution at ambient temperature through a dissociative mechanism. The solid-state structure of (<sup>Me</sup>(Et)PDI)Fe(?<sup>4</sup>-piperylene) (<sup>Me</sup>(Et)PDI = 2,6-(2,6-Me<sub>2</sub>-C<sub>6</sub>H<sub>3</sub>N?CEt)<sub>2</sub>C<sub>5</sub>H<sub>3</sub>N), was determined by single-crystal X-ray diffraction and confirmed the s-<i>trans</i> coordination of the monosubstituted 1,3-diene. Possible relationships between ligand-controlled diene coordination geometry, metallacycle denticity, and chemoselectivity of iron-mediated cycloaddition reactions are discussed.