Benzene-1,2,4,5-tetrol

The crystal structure of the title compound was determined at 120 K. It crystallizes in the triclinic space group P with four independent mol-ecules in the asymmetric unit. In the crystal, each symmetry-unique mol-ecule forms π-π stacks on itself, giving four unique π-π stacking inter-actions. Inter-molecular hydrogen bonding is observed between each pair of independent mol-ecules, where each hy-droxy group can act as a hydrogen-bond donor and acceptor.

Glycols in the Synthesis of Zinc-Anilato Coordination Polymers

We report the synthesis, structural investigation, and thermal behavior for three zinc-based 1D-coordination polymers with 3,6-di-tert-butyl-2,5-dihydroxy-p-benzoquinone, which were synthesized in the presence of different glycols. The interaction of zinc nitrate with glycols, followed by using the resulting solution in solvothermal synthesis with the anilate ligand in DMF, makes it possible to obtain linear polymer structures with 1,2-ethylene or 1,2-propylene glycols coordinated to the metal. The reaction involving 1,3-propylene glycol under similar conditions gives a crystal structure that does not contain a diol. The crystal and molecular structures of the synthesized compounds were determined using single crystal by X-ray structural analysis. The influence of glycol molecules coordinated to the metal on the thermal destruction of synthesized compounds is shown.

Mixed valency in a neutral 1D Fe-chloranilate coordination polymer

A neutral Fe-chloranilate chain, with triphenylphosphine oxide co-ligands, represents a rare example of a one-dimensional chain in which there is a temperature dependent electron transfer from the Fe(ii) centre to the bridging chloranilate ligand.

Magnesium and Nickel Complexes with Bis(p-iminoquinone) Redox-Active Ligand

Abstract

Poorly soluble in the most part of organic solvents dimeric complexes $${\text{M}}{{{\text{g}}}_{{\text{2}}}}{\text{L}}_{2}^{2}$$·4DMF (I) and $${\text{N}}{{{\text{i}}}_{{\text{2}}}}{\text{L}}_{2}^{2}$$·4DMF (II) (L is 4,4'-(1,4-phenylenebis(azanylylidene))bis(3,6-di-tert-butyl-2-hydroxycyclohexa-2,5-dien-1-one dianion)) are synthesized by the reactions of magnesium and nickel acetates with the ditopic redox-active ligand of the hydroxy-para-iminoquinone type in a DMF solution. The molecular and crystal structures of the synthesized compounds are determined by X-ray diffraction analysis (CIF files CCDC nos. 2045665 (I) and 2045666 (II·3DMF)). The thermal stability is studied by thermogravimetry. The redox-active character of the organic bridging ligand in the dimeric complexes $${\text{M}}{{{\text{g}}}_{{\text{2}}}}{\text{L}}_{2}^{2}$$·4DMF and $${\text{N}}{{{\text{i}}}_{{\text{2}}}}{\text{L}}_{2}^{2}$$·4DMF is confirmed by the data of solid-phase electrochemistry.

Reversible single crystal-to-single crystal double [2+2] cycloaddition induces multifunctional photo-mechano-electrochemical properties in framework materials

Reversible structural transformations of porous coordination frameworks in response to external stimuli such as light, electrical potential, guest inclusion or pressure, amongst others, have been the subject of intense interest for applications in sensing, switching and molecular separations. Here we report a coordination framework based on an electroactive tetrathiafulvalene exhibiting a reversible single crystal-to-single crystal double [2 + 2] photocyclisation, leading to profound differences in the electrochemical, optical and mechanical properties of the material upon light irradiation. Electrochemical and in situ spectroelectrochemical measurements, in combination with in situ light-irradiated Raman spectroscopy and atomic force microscopy, revealed the variable mechanical properties of the framework that were supported using Density Functional Theory calculations. The reversible structural transformation points towards a plethora of potential applications for coordination frameworks in photo-mechanical and photoelectrochemical devices, such as light-driven actuators and photo-valves for targeted drug delivery.

Porous coordination frameworks that undergo reversible structural transformations are promising for sensing, switching and separations. Here, the authors report an electroactive framework that exhibits a reversible single crystal-to-single crystal double [2+2] photocyclisation, leading to property changes.

2D-metal–organic coordination polymers of lanthanides (La(iii), Pr(iii) and Nd(iii)) with redox-active dioxolene bridging ligands

2D-coordination redox-active networks bearingt-Bu-substituted anilic bridged ligands and lanthanide ions were synthesized and characterized.

An N,N'-diethylformamide solvent-induced conversion cascade within a metal-organic framework single crystal

Crystals of a two-dimensional (2D) metal-organic framework (MOF) [Cd3(BTB)2(DEF)4]·2(DEF)0.5 (1; BTB = benzene-1,3,5-tribenzolate; DEF = N,N'-diethylformamide) immersed in a solution of trans-1,2-bis(4-pyridyl)ethylene (BPEE) yields an interpenetrated three-dimensional (3D) MOF of [Cd3(BTB)2(BPEE)(H2O)2]·(BPEE)·xSol (2). Crystals of MOF 2, in turn, undergo a cascade conversion when immersed in DEF, yielding [Cd3(BTB)2(BPEE)1.8(DEF)0.9(H2O)0.8]·xSol (3a) over 100 seconds and [Cd3(BTB)2(BPEE)2(DEF)2]·xSol (4) after one hour, before finally shuttling back to MOF 1 after six hours.

Tetraoxolene-bridged rare-earth complexes: a radical-bridged dinuclear Dy single-molecule magnet

Two families of neutral tetraoxolene-bridged dinuclear rare earth complexes of general formula [((HBpz₃)₂RE)₂(μ-tetraoxolene)] (RE = Y and Dy; HBpz₃^- = hydrotris(pyrazolyl)borate; tetraoxolene = fluoranilate (fa^2-; 1-RE) or bromanilate (ba^2-; 2-RE)) have been synthesised and characterised. In each case, the bridging tetraoxolene ligand is in the diamagnetic dianionic form and each rare earth metal centre has two HBpz₃^- ligands completing the coordination. Electrochemical studies on the soluble 2-RE family reveal a tetraoxolene-based reversible one-electron reduction. Bulk chemical reduction with cobaltocene affords the cobaltocenium (CoCp⁺) salt of the 1e-reduced analogue: [CoCp][((HBpz₃)₂RE)₂(μ-ba˙)] (3-RE) that incorporates a radical trianionic form of the bromanilate bridging ligand. Alternating current (ac) magnetic susceptibility studies of 2-Dy reveal slow magnetic relaxation only in the presence of an applied magnetic field, but reduction to radical-bridged 3-Dy affords frequency-dependent peaks in the out-of-phase ac susceptibility in zero applied field. Exchange coupling between the Dy(iii) ions and the radical bridging ligand thus reduces zero-field magnetisation quantum tunnelling and confers single-molecule magnet status on the complex. Comprehensive analysis of the magnetic relaxation data indicates that a combination of Orbach, Raman and direct relaxation processes are required to fit the data for both dysprosium bromanilate complexes.

A Strategic High Yield Synthesis of 2,5-Dihydroxy-1,4-benzoquinone Based MOFs

Metal organic frameworks (MOFs) of the type NBu₄M(DHBQ)_1.5 (M = Ni²⁺, Fe²⁺, and Co²⁺; DHBQ = 2,5-dihydroxy-1,4-benzoquinone) were prepared with improved yield up to 100% via a simple benchtop aqueous addition reaction. For the first time, the crystalline phase of this formula polymer was synthesized without in situ generation of the DHBQ ligand from 2, 5-diamino-1,4-benzoquinone (DABQ). Powder X-ray diffraction and elemental analysis confirm the crystalline phase and composition of products. Infrared and electron dispersive spectroscopy further confirm that the materials are homologous to the reported single crystalline polymers. The present MOF synthesis can be extended to halide-substituted ligands, i.e., 3,6-dichloro-2,5-dihydroxy-1,4-benzoquinone (chloranilic acid, CAN) and 3,6-difluoro-2,5-dihydroxy-1,4-benzoquinone (fluoranilic acid, FAN).

Square Grid Metal-Chloranilate Networks as Robust Host Systems for Guest Sorption

Reaction of the chloranilate dianion with Y(NO₃ )₃ in the presence of Et₄ N⁺ in the appropriate proportions results in the formation of (Et₄ N)[Y(can)₂ ], which consists of anionic square-grid coordination polymer sheets with interleaved layers of counter-cations. These counter-cations, which serve as squat pillars between [Y(can)₂ ] sheets, lead to alignment of the square grid sheets and the subsequent generation of square channels running perpendicular to the sheets. The crystals are found to be porous and retain crystallinity following cycles of adsorption and desorption. This compound exhibits a high affinity for volatile guest molecules, which could be identified within the framework by crystallographic methods. In situ neutron powder diffraction indicates a size-shape complementarity leading to a strong interaction between host and guest for CO₂ and CH₄ . Single-crystal X-ray diffraction experiments indicate significant interactions between the host framework and discrete I₂ or Br₂ molecules. A series of isostructural compounds (cat)[M^III (X-an)₂ ] with M=Sc, Gd, Tb, Dy, Ho, Er, Yb, Lu, Bi or In, cat=Et₄ N, Me₄ N and X-an=chloranilate, bromanilate or cyanochloranilate bridging ligands have been generated. The magnetic properties of representative examples (Et₄ N)[Gd(can)₂ ] and (Et₄ N)[Dy(can)₂ ] are reported with normal DC susceptibility but unusual AC susceptibility data noted for (Et₄ N)[Gd(can)₂ ].

A Series of Early Lanthanide Chloranilate Frameworks with a Square Grid Topology

A series of lanthanide chloranilate frameworks containing a (4,4)-net with LaIII, CeIII, NdIII, SmIII, and EuIII have been synthesised and structurally characterised. Two structure types of square grids were obtained for these frameworks. Type 1 consists of the formula (Et4N)[Ln(can)2(H2O)] (Ln=LaIII, CeIII, NdIII; H2can=chloranilic acid) and crystallised in the tetragonal space group I4/m, featuring a nine-coordinate lanthanide ion with a coordinated water molecule and four chloranilate ligands. Type 2, (Et4N)[Ln(can)2] (SmIII and EuIII) crystallised in the I4/mcm space group, and contains an eight-coordinate lanthanide ion without a coordinated water molecule. A single-crystal-to-single-crystal transformation was carried out for (Et4N)[Nd(can)2(H2O)] on removal of the coordinated aqua ligand.

Solid-State Gas Adsorption Studies with Discrete Palladium(II) [Pd2 (L)4 ]4+ Cages

The need for effective CO₂ capture systems remains high, and due to their tunability, metallosupramolecular architectures are an attractive option for gas sorption. While the use of extended metal organic frameworks for gas adsorption has been extensively explored, the exploitation of discrete metallocage architectures to bind gases remains in its infancy. Herein the solid state gas adsorption properties of a series of [Pd₂ (L)₄ ]⁴⁺ lantern shaped coordination cages (L = variants of 2,6-bis(pyridin-3-ylethynyl)pyridine), which had solvent accessible internal cavities suitable for gas binding, have been investigated. The cages showed little interaction with dinitrogen gas but were able to take up CO₂ . The best performing cage reversibly sorbed 1.4 mol CO₂ per mol cage at 298 K, and 2.3 mol CO₂ per mol cage at 258 K (1 bar). The enthalpy of binding was calculated to be 25-35 kJ mol^-1 , across the number of equivalents bound, while DFT calculations on the CO₂ binding in the cage gave ΔE for the cage-CO₂ interaction of 23-28 kJ mol^-1 , across the same range. DFT modelling suggested that the binding mode is a hydrogen bond between the carbonyl oxygen of CO₂ and the internally directed hydrogen atoms of the cage.

Dihydroxybenzoquinone as Linker for the Synthesis of Permanently Porous Aluminum Metal-Organic Frameworks

Two new dihydroxybenzoquinone-based metal-organic frameworks, ((CH3)2NH2)3[Al4(L1)3(L1(•))3]·3DMF (1, denoted CAU-20) and ((CH3)2NH2)3[Al4(L2)3(L2(•))3]·9DMF (2, denoted CAU-20-Cl2), were synthesized at 120 °C in DMF using 2,5-dihydroxy-p-benzoquinone ((C6H2(OH)2(O)2), H2L1) and 2,5-dichloro-3,6-dihydroxy-p-benzoquinone ((C6Cl2(OH)2(O)2), H2L2), respectively. Compared to other Al-MOFs, which contain carboxylate or phosphonate groups that connect the metal sites, in 1 and 2 the Al(3+) are coordinated by oxido groups. The metal ions are octahedrally surrounded by oxygen atoms of the deprotonated linker molecules to generate honeycomb layers with a metal to linker ratio of Al: L1/L2 = 2:3. The layers contain L1(2-) and L2(2-) ions as well as linker radical ions L1(•3-) and L2(•3-) in a molar ratio of 1 to 1. The presence of radical ions was confirmed by EPR and UV-vis-spectroscopic measurements, and the composition was determined from a combination of PXRD, (1)H NMR, TG, and elemental analyses. Charge balance is accomplished through intercalation of (CH3)2NH2(+) ions which are formed by partial hydrolysis of DMF. In the structures of 1 and 2 the eclipsed layers are AA and ABAB stacked, respectively, and one-dimensional hexagonal channels with diameters of ca. 9 and 6 Å are formed. Both compounds exhibit permanent porosity and have specific surface areas of 1440 and 1430 m(2) g(-1), respectively.