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This article describes a series of more than 20 new compounds formed by the combination of 2,4,6-trihydroxybenzoic acid (H4thba) with metal ions in the presence of a base, with structures that include discrete molecular units, chains, and two- and three-dimensional networks. As a result of the presence of two ortho-hydroxy groups, H4thba is a relatively strong acid (pK a1 = 1.68). The carboxylate group in H3thba− is therefore considerably less basic than most carboxylates with intramolecular hydrogen bonds, conferring a rigid planar geometry upon the anion. These characteristics of H3thba− significantly impact upon the way it interacts with metal ions. In s-block metal compounds, where the interaction of the metal centres with the carboxylate O atoms is essentially ionic, the anion bonds to up to three metal centres via a variety of binding modes. In cases where the metal ion is able to form directional coordinate bonds, however, the carboxylate group tends to bond in a monodentate mode, interacting with just one metal centre in the syn mode. A dominant influence on the structures of the complexes seems to be the face-to-face stacking of the aromatic rings, which creates networks containing layers of metal–oxygen polyhedra that participate in hydrogen bonding. This investigation was undertaken, in part, by a group of secondary school students as an educational exercise designed to introduce school students to the technique of single-crystal X-ray diffraction and enhance their understanding of primary and secondary bonding.

The effect of core geometry constraints of hydrogenase H-cluster analogues on reduction chemistry have been explored by a combination of structural, electrochemical and IR spectro-electrochemical (IR-SEC) studies. A series of phosphido-bridged diiron hexacarbonyl complexes, Fe-2(mu(2)-PPh2(CH2)(x)PPh2)(CO)(6), x = 2 (2P) and 4 (4P) and previously reported with x = 3 (3P) and the unlinked bis-diphenylphosphido (DP) analogues were investigated. The X-ray structures of the neutral complexes demonstrate the effect of the linking group on the Fe2P2 core geometry with P-Fe-Fe-P torsion angles of 95 (2P), 101 (3P), 108 (4P) and 109 degrees (DP) and a twisting of the Fe(CO)(3) fragments from an eclipsed geometry (2P, 3P and DP) for 4P. For all four compounds the primary reduction process involves two close-spaced one-electron reactions (E-1 and E-2) with a systematic trend to more negative reduction potentials with a shorter link between the bridging phosphorus atoms. This reflects the greater constraint that the bridging group places on the adoption of a planar 2Fe2P geometry. The sensitivity of the core geometry is greater for E-2 than E-1 and this impacts the stability of the monoanion with respect to disproportion (K-disp(298 K) = 0.02 (2P), 2.4 (3P) and 3540 (4P and DP)). 4P has a stable dianion and gives reversible cyclic voltammetry at 298 K and is quasi-reversible at 253 K, whereas the response of 2P is irreversible at 298 K, with two distinct daughter products, but becomes quasi-reversible at 253 K. IR-SEC measurements enabled elucidation of the spectra and time evolution of the reduction products. These results are consistent with a bimolecular reaction giving a distinct reduced product modelled as a dimeric, 4Fe species. The sensitivity of the reduction chemistry of the bridged diiron compounds underpins their utility as catalytic proton reduction catalysts and the systematic trends delineated in this investigation provide the framework for charting the path of their redox-coupled chemical reactions.

The combination of 4-hydroxbenzoic acid with metal ions Li+, Mg2+ and Cu2+ leads to the formation of novel 2D and 3D networks.

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.

Using simple methods to obtain efficient catalysts has been a long-standing goal for researchers. In this work, the employment of a one-pot pyrolysis reaction to achieve molecular confinement, has led to the preparation of ruthenium (Ru)-based nanoclusters in a carbon matrix. A unique feature of the synthetic approach employed is that solvent and substrates were calcined together. As solvent evaporates, during calcination, the substrates form a dense solid which has the effect of limiting the aggregation of Ru centers during the carbonization process. The catalyst prepared in this simple manner showed an impressively high activity with respect to the hydrogen/oxygen evolution reaction (HER/OER). The Ru nanoclusters (Ru NCs), as the hydrogen evolution reaction (HER) catalysts, require ultralow overpotentials of 5 mV and 5.1 mV at −10 mA·cm−2 in 1.0 M KOH, and 0.5 M H2SO4, respectively. Furthermore, the catalyst prepared by the one-pot method has higher crystallinity, a higher Ru content and an ultrafine cluster size, which contributes to its exceptional electrochemical performance. Meanwhile, the RuOX nanoclusters (RuOX NCs), obtained by oxidizing the aforementioned Ru NCs, exhibited good oxygen evolution reaction (OER) performance with an overpotential of 266 mV at 10 mA·cm−2. When applied to overall water splitting, Ru/RuOX nanoclusters as the cathode and anode catalysts can reach 10 mA·cm−2 at cell voltages of only 1.49 V in 1 M KOH.

The two-dimensional (2-D) framework, [Cu(BTDAT)(MeOH)] {BTDAT = bis-[1,2,5]-thiadiazolo-tetracyanoquinodimethane}, possesses remarkable multi-step redox properties, with electrochemical studies revealing six quasi-stable redox states in the solid state. In situ electron paramagnetic resonance and visible-near infrared spectroelectrochemistry elucidated the mechanism for these multi-step redox processes, as well as the optical and electrochromic behavior of the BTDAT ligand and framework. In studying the structural, spectroscopic, and electronic properties of [Cu(BTDAT)(MeOH)], the as-synthesized framework was found to exist in a mixed-valence state with thermally-activated semiconducting behavior. In addition to pressed pellet conductivity measurements, single-crystal conductivity measurements using a pre-patterned polydimethylsiloxane layer on a silicon substrate provide important insights into the anisotropic conduction pathways. As an avenue to further understand the electronic state of [Cu(BTDAT)(MeOH)], computational band structure calculations predicted delocalized electronic transport in the framework. On the balance of probabilities, we propose that [Cu(BTDAT)(MeOH)] is a Mott insulator (i.e., electron correlations cause a metal-insulator transition). This implies that the conductivity is incoherent. However, we are unable to distinguish between activated transport due to Coulombically bound electron-hole pairs and a hopping mechanism. The combined electrochemical, electronic, and optical properties of [Cu(BTDAT)(MeOH)] shine a new light on the experimental and theoretical challenges for electroactive framework materials, which are implicated as the basis of advanced optoelectronic and electrochromic devices.

Calcium acetate hemihydrate is found in the efflorescent salts that form on pottery and other calcareous heritage artefacts. The formation of these salts can lead to deterioration of these objects. A recent analysis of the structure of Ca(OAc)2·½H2O by X-ray powder diffraction (XRPD) has revealed it has a remarkable and surprisingly complex structure. Although the compound usually exists in powder or microcrystalline form, often in mixtures with other salts, we have serendipitously managed to grow crystals of a size suitable for single crystal X-ray diffraction. Our single crystal data show the structure is based on infinite supramolecular polymeric rods that are chiral. Each rod has a minimum diameter of 1.75 nm and the external surface of each rod features four parallel, hydrophobic domains separated by hydrophilic strips. Each hydrophilic strip consists of acetate oxygen atoms and coordinated water molecules that are able to form hydrogen bonding interactions with symmetry-related strips on a neighbouring rod in an arrangement that resembles a zipper. Within the extended crystal structure each rod is bound to four rods of opposite handedness to give a racemic mixture.

The elucidation of mechanisms to modulate the properties of multifunctional electroactive, conductive, and magnetic porous materials is desirable to aid their future application. The synthesis and ...

A serendipitous discovery has led to the generation of a family of four compounds in which six components combine to form symmetric metal-cyclotricatechylene (H6ctc) cages. The four compounds, which have the compositions, [Cs((CH3)2CO)6][K4(H6ctc)4(H2O)8][Cs4(H2O)6](PO4)3, [Rb((CH3)2CO)6][Rb2K2(H6ctc)4(H2O)6][Rb4(H2O)6](PO4)3, [Cs((CH3)2CO)6][K4(H6ctc)4(H2O)8]-[Cs(H2O)9](SO4)3 and [Rb((CH3)2CO)6][Rb2K2(H6ctc)4(H2O)6][Rb(H2O)9](SO4)3 possess cubic symmetry that arises from the complementary interactions that govern the assembly of the components. The cage cavities contain water molecules and either one or four large alkali metal ions (either Rb+ or Cs+) which interact with the internal aromatic surfaces of the cage. Each cage is linked to six tetrahedral anions (PO43&minus, or SO42&minus, ) through 24 equivalent hydrogen bonds and each anion bridges a pair of cages through eight such hydrogen bonds. An unusual octahedral complex M((CH3)2CO)6+ (M = Rb or Cs), in which the M-C=O link is linear, appears to be a key structural component. A feature of this family of crystalline compounds is the presence of a range of complementary interactions which combine to generate materials that exhibit high crystallographic symmetry.

An investigation of the adsorption properties of two structurally related, 3D coordination polymers of composition Zn(2-Mehba) and Zn(2,6-Me2hba) (2-Mehba = the dianion of 2-methyl-4-hydroxybenzoic acid and 2,6-Me2hba = the dianion of 2,6-dimethyl-4-hydroxybenzoic acid) is presented. A common feature of these structures are parallel channels that are able to accommodate appropriately sized guest molecules. The structures differ with respect to the steric congestion within the channels arising from methyl groups appended to the bridging ligands of the network. The host network, Zn(2-Mehba), is able to take up appreciable quantities of H2 (77 K) and CO2 and CH4 (298 K) in a reversible manner. In regard to the adsorption of N2 by Zn(2-Mehba), there appears to be an unusual temperature dependence for the uptake of the gas such that when the temperature is increased from 77 to 298 K the uptake of N2 increases. The relatively narrow channels of Zn(2,6-Me2hba) are too small to allow the uptake of N2 and CH4, but H2 molecules can be adsorbed. A pronounced step at elevated pressures in CO2 and N2O isotherms for Zn(2,6-Me2hba) is noted. Calculations indicate that rotation of phenolate rings leads to a change in the available intraframework space during CO2 dosing.

Cyclotricatechylene (ctcH6 ) is a bowl-shaped macrocyclic compound that can be used as a building block for self-assembled capsules. ctcH6 and its derivatives in various protonation states - here collectively labeled as CTC - form dimers that resemble the shape of a clam. These clam-shaped entities have been studied experimentally by Abrahams, Robson, and co-workers [B. F. Abrahams, N. J. FitzGerald, T. A. Hudson, R. Robson and T. Waters, Angew. Chem. Int. Ed. 2009, 48, 3129-3132] where the capsules acted as an excellent host for large alkali-metal cations. In this study, we present a detailed analysis based on accurate dispersion-corrected Density Functional Theory approaches that reveals the factors that stabilise such CTC-based capsules at different protonation states and their interaction with various encapsulated guests. Our results show that the capsules' overall stability results as an interplay of hydrogen bonding, London dispersion, and electrostatic effects. The most stable capsules with group-1 and group-2 cations as guests contain only six phenolic hydrogens, as opposed to the maximum possible number of twelve. Inclusion of larger alkali-metal cations is favoured due to larger London-dispersion contributions. Cations are favoured as guests over isoelectronic neutral species, as the resulting host-guest complexes experience additional stability due to cooperative effects. In fact, using the latter to drive the formation of specific capsules could be used in future strategies aimed at synthesising similar aggregates; our results provide an insightful understanding and useful guidance for such future endeavours.

The synthesis, structure and properties of a 2D FeIII network material of composition [Fe(O-bipy)2Cl](TCNQ)2 (O-bipy = 4,4'-bipyridyl N,N'-dioxide; TCNQ = 7,7,8,8-tetracyanoquinodimethane) are presented. The structure consists of a square grid in which square pyramidal FeIII centers are linked to four equivalent centers through O-bipy ligands. Pairs of TCNQ radical anions are located within rectangular cavities of the 2D network. The apical position on each Fe center is occupied by a chloride ion. Magnetic studies are indicative of weak antiferromagnetic coupling. Electrical conductivity measurements reveal that the compound is a semiconductor and on the basis of DFT calculations it is proposed that electrical conduction occurs via charge hopping between interlayer TCNQ anions. Mossbauer spectra indicate a rare example of the Goldanskii–Karyagin effect and are suggestive of unusual dynamic processes.

Redox-active ligands are of interest for their ability to link metal centres and generate electroactive materials. We report the synthesis of 9-hydrogen-2,3,7-trihydroxyfluorone, which is able to serve as a bridging ligand and has the potential to exist in multiple oxidation states. Anionic [4+4] metallocycles in which Mo or W centres are linked by the trianion of this ligand are also described.

Designing and building unique cage assemblies attract increasing interest from supramolecular chemists but remain synthetically challenging. Herein, we propose the use of a flexible vertex with adjustable angles to selectively form highly distorted tetrahedral and octahedral cages, for the first time, in which the flexible vertex forms from the synergistic effect of coordination and covalent interactions. The inherent interligand angle of the vertex can be modulated by guest anions present, which allows for the fine-tuning of different cage geometries. Furthermore, the reversible structural transformation between tetrahedral and octahedral cages was achieved by anion exchange monitored by mass spectrometric technique, the smaller anions favoring tetrahedral cages, while the larger anions supporting octahedral cages. Additionally, the KBr-based cage thin films exhibited prominent enhancement of their third-order NLO responses in two or three orders of magnitude compared to those obtained for their corresponding solutions. This work not only provides a new methodology to build irregular polyhedral structures in a controlled and tunable way but also provides access to new kinds of promising functional optical materials.

A remarkably flexible, multifunctional, 2D coordination polymer exhibiting an unprecedented mode of reversible mechanical motion, enabling pores to open and close, is reported. Such multifunctional materials are highly sought after, owing to the potential to exploit coexisting electronic and mechanical functionalities that underpin useful technological applications such as actuators and ultrasensitive detectors. The coordination polymer, of composition Mn(F4TCNQ)(py)2 (F4TCNQ = 2,3,5,6-tetrafluoro-7,7,8,8-tetracycanoquinodimethane; py = pyridine), consists of Mn(II) centers bridged by F4TCNQ dianions and coordinated by py molecules that extend above and below the 2D network. Exposure of Mn(F4TCNQ)(py)2, in its collapsed state, to carbon dioxide results in a pore-opening process at a threshold pressure for a given temperature. In addition to carbon dioxide, a variety of volatile guests may be incorporated into the pores, which are lined with electron-rich F4TCNQ dianions. The inclusion of electron-deficient guests such as 1,4-benzoquinone, nitrobenzene, maleic anhydride, and iodine into the pores is accompanied by a striking color change associated with a new host-guest charge-transfer interaction and an improvement in the semiconductor behavior, with the iodine adduct showing an increase in conductivity of almost 5 orders of magnitude. Experimental and density functional theory calculations on this remarkable multifunctional material demonstrate a reduction in the optical band gap with increasing electron affinity of the guest.

A high symmetry heterothiometallic cluster-based 3D framework of composition [WS4Cu4(μ-CN)2(bpea)2]·1.5DMF was obtained from the combination of (NH4)2WS4, CuCN and 1,2-bis(4-pyridyl)ethane (bpea). It holds an unusual topology with [WS4Cu4]2+ clusters linked by CN- and bpea bridging ligands. An interesting feature of this cubic structure is the presence of isolated hexagonal channels that extend in four distinct directions. Its desolvated sample demonstrated high performance in the adsorption of iodine from solution.

Although 4-hy­droxy­benzoic acid (H2hba) is a relatively simple organic mol­ecule, it displays remarkable coordinative flexibility in its reactions with alkali metal hydroxides, forming ionic networks containing the dianion (hba2−), the monoanion (Hhba−) or the neutral acid species (H2hba). A common feature of the structures of the lattices is their layered arrangement: alternating hydro­philic layers made up of closely packed metal–oxygen polyhedra are separated by the hydro­phobic nonpolar com­ponents of the hy­droxy­benzoate linking units., As part of an educational exercise designed to introduce school students to the technique of single-crystal X-ray diffraction and enhance their understanding of primary and secondary bonding, a group of nine secondary school students was given the opportunity to prepare new com­pounds and to solve and refine data collected on the crystalline materials they had prepared. Their investigation of the alkali metal salts of 4-hy­droxy­benzoic acid (H2hba) yielded nine new com­pounds and their structures are described in this article. Whilst the salts might be expected to have similar atomic arrangements, there are significant differences in their structures. Although H2hba is a relatively simple organic mol­ecule, it displays remarkable coordinative flexibility, forming ionic solids containing the uncharged mol­ecule, the monoanion Hhba− or the dianion hba2−. A common feature of the structures is their layered arrangement: alternating hydro­philic layers made up of closely packed metal–oxygen polyhedra separated by the hydro­phobic com­ponent of the hy­droxy­benzoate linking units. Close packing of these units seems to be a dominant influence in determining the overall structure. The hy­droxy­benzoate units are usually both parallel and anti­parallel with their immediate neighbours, with packing that can be edge-to-face, face-to-face or a mixture of the two. Hydrogen bonding plays a key role in the structure of most com­pounds and a short strong hydrogen bond (SSHB) is observed in two of the networks. The com­pounds of 4-hy­droxy­benzoic acid, C7H6O3, described here are: poly[di-μ-aqua-μ-4-oxidobenzoato-dilithium], [Li2(C7H4O3)(H2O)2] n , 1, poly[tri­aqua-μ-4-oxidobenzoato-dilithium], [Li2(C7H4O3)(H2O)3] n , 2, poly[μ-4-hy­droxy­benzoato-lithium], [Li(C7H5O3)] n , 3, catena-poly[4-hy­droxy­benzoate [[di­aqua­sodium]-di-μ-aqua]], {[Na(H2O)4](C7H5O3)} n , 4, poly[di-μ-aqua-aqua-μ-4-hy­droxy­benzoato-potassium], [K(C7H5O3)(H2O)3] n , 5, poly[μ-aqua-μ-4-hy­droxy­benzoato-potassium], [K(C7H5O3)(H2O)] n , 6, poly[aqua-μ-4-hy­droxy­benzoato-rubidium], [Rb(C7H5O3)(H2O)] n , 7, poly[aqua-μ-4-hy­droxy­benzoato-caesium], [Cs(C7H5O3)(H2O)] n , 8, poly[[μ-aqua-aqua­(μ-4-hy­droxy­benzoato)(4-hy­droxy­benzoic acid)sodium] monohydrate], {[Na(C7H5O3)(C7H6O3)(H2O)2]·H2O} n , 9, poly[[(μ-4-hy­droxy­benzoato)(μ-4-hy­droxy­benzoic acid)rubidium] monohydrate], {[K(C7H5O3)(C7H6O3)]·H2O} n , 10, and poly[[(μ-4-hy­droxy­benzoato)(μ-4-hy­droxy­benzoic acid)rubidium] monohydrate], {[Rb(C7H5O3)(C7H6O3)]·H2O} n , 11.

A 2-D coordination framework, (NEt4)2[Fe2(fan)3] (1·5(acetone); H2fan = 3,6-difluoro-2,5-dihydroxy-1,4-benzoquinone), was synthesized and structurally characterized. The compound is structurally analogous to a formerly elucidated framework, (NEt4)2[Fe2(can)3] (H2can = 3,6-dichloro-2,5-dihydroxy-1,4-benzoquinone), and adopts a 2-D (6,3) topology with the symmetrical stacking of [Fe2(fan)3]2- sheets that are held in position by the NEt4+ cations between the sheets. The investigation of the dc and ac magnetic properties of 1·5(acetone) revealed ferromagnetic ordering behavior and slow magnetization relaxation, as evinced from ac susceptibility measurements. Furthermore, the exposure of 1·5(acetone) to air led to the formation of a heptahydrate 1·7H2O which displayed distinct magnetic properties. The study of the redox state and extent of delocalization in 1·5(acetone) was undertaken via crystallography, in combination with Mossbauer and vis-NIR spectroscopy, to reveal the mixed-valence and delocalized nature of the as-synthesized material. As a result, the conductivity studies conducted on a pressed pellet showed a relatively high conductivity of 1.8 × 10-2 S cm-1 (300 K). In order to compare structurally related anilate-based structures, a relationship among the redox state, spectroscopic properties, and electronic properties was elucidated in this work. A preliminary investigation of 1·5(acetone) as a candidate anode material in lithium ion batteries revealed a high reversible capacity of 676.6 mAh g-1 and high capacity retention.

Regioselective photodimerization of trans-4-styrylpyridine (4-spy) derivatives is performed using pseudorotaxane-like Zn-based metal organic frameworks MOFs as templates. The formation of rctt-HT (head-to-tail) dimers is achieved by confining pairs of coordinated 4-spy derivative ligands within hexagonal windows and then irradiating them with UV light. It is also possible to achieve a photodimerization reaction where two different substituted 4-spy ligands are included in such a MOF material. The ether bond formation is employed to protect the sensitive -OH group of HO-spy and the methyl group of CH3 O-spy is subsequently removed after the formation of cyclobutane derivative in the CH3 O-spy-based MOF. Introducing substituents at the 2- or 3-position of the phenyl group of 4-spy does not significantly affect the rate of the dimerization process except in the case of the strongly electron-withdrawing nitro group where the rate is significantly decreased. These results are in striking contrast to the mixtures of photoproducts and low yields obtained by untemplated photodimerization in organic solvents.

In 2008 a new approach to generating tetracyanoquinodimethane (TCNQ)-based materials was described which involved the use of the diprotonated, reduced form of TCNQ (TCNQH2) as a reactant. Since the initial work, the dianionic forms of TCNQH2 and F4TCNQH2 have been incorporated into a wide assortment of coordination polymers in which the ligand, with four potential donor atoms, binds to a variety of metal centres. The structures of neutral 1D, 2D and 3D coordination polymers are described, in addition to the structures of anionic networks. Not surprisingly, the oxidation state of the metal ion as well as its preference for certain coordination geometries has a major influence upon the topology and geometry of the polymeric material. In addition to the identity of the metal centre, the type of structure obtained depends upon the nature of the co-ligand in the case of neutral polymers. For anionic networks the shape, charge and size of the counter-cation impacts upon the network connectivity. The large number of metal compounds formed with the dianions is in contrast with the relatively small number of metal complexes involving TCNQ and F4TCNQ in the 0 and −1 oxidation states. In addition to coordination polymers, organic salts of TCNQ2− and F4TCNQ2− have also been investigated. The packing within these crystalline salts has been categorised into four types. In both the case of the coordination polymers and the organic salts, charge transfer interactions are common with the electron-rich TCNQ2− and F4TCNQ2− dianions often serving as electron donors. The presence of various species in the crystal that can act as electron acceptors normally leads to intensely coloured crystals. Whilst TCNQ2− and F4TCNQ2− dianions have been shown to be versatile building blocks capable of yielding a variety of unusual and aesthetically appealing structures, the redox activity of these dianions offers the prospect of creating materials that possess fascinating electronic properties. An overview of the types of structures obtained since 2008 using the TCNQH2/F4TCNQH2 synthetic approach is presented.

The reaction of Mn(BF4 )2 ⋅x H2 O with (Pr4 N)2 TCNQF4 (TCNQF4 =2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane) in a mixture of CH3 OH/CH2 Cl2 gives a 2:3 stoichiometric complex of (Pr4 N)2 [Mn2 (TCNQF4 )3 (CH3 OH)2 ] (1). If the solvent system used for the crystallisation of 1 is changed to CH3 OH/DMF, then a different product, [Mn(TCNQF4 )(DMF)2 ]⋅(CH3 OH)2 (2), is obtained. The use of Li2 TCNQF4 instead of (Pr4 N)2 TCNQF4 leads to the generation of [Mn2 (TCNQF4 )2 (DMF)4 ]⋅3 DMF (3). An unexpected mixed oxidation state network with a composition of [MnII4 MnIII16 O10 (OH)6 (OCH3 )24 (TCNQF4 )2 ](NO3 )2 ⋅24 CH3 OH (4), is formed if Mn(NO3 )2 ⋅x H2 O is used in place of Mn(BF4 )2 ⋅x H2 O in the reaction that leads to the formation of 3. Compounds 1-3 have been characterised by X-ray crystallography; FTIR, Raman and UV/Vis spectroscopy; and electrochemistry. Compound 4 has only been analysed by X-ray crystallography and vibrational spectroscopy (Raman, FTIR), owing to rapid deterioration of the compound upon exposure to air. These results indicate that relatively minor changes in reaction conditions have the potential to yield products with vastly different structures. Compound 1 adopts an anionic 2D network with unusual π-stacked dimers of the TCNQF42- dianion, whereas 2 and 3 are composed of similar neutral sheets of [Mn(TCNQF4 )(DMF)2 ]. Interestingly, the solvent has a significant influence on the stacking of the sheets in the structures of 2 and 3. In compound 4, clusters with a composition of [MnII4 MnIII16 O10 (OH)6 (OCH3 )24 (CH3 OH)4 ]6+ serve as eight-connecting nodes, whereas TCNQF42- ligands act as four-connecting nodes in a 3D network that has the same topology as fluorite. Compound 3 exhibits an exceptionally high super-catalytic activity for the electron-transfer reaction between ferricyanide and thiosulfate ions in aqueous media.

Analysis of in situ neutron powder diffraction data collected for the porous framework material Zn(hba) during gas adsorption reveals a two-stage response of the host lattice to increasing CO2 guest concentration, suggesting progressive occupation of multiple CO2 adsorption sites with different binding strengths. The response of the lattice to moderate CH4 guest concentrations is virtually indistinguishable from the response to CO2, demonstrating that the influence of host–guest interactions on the Zn(hba) framework is defined more strongly by the concentration than by the identity of the guests.

A pair of coordination polymers of composition (NBu4)2[M2(fan)3] (fan = fluoranilate; M = Fe and Zn) were synthesized and structurally characterized. In each case the compound consists of a pair of interpenetrating three-dimensional, (10,3)-a networks in which metal centers are linked by chelating/bridging fluoranilate ligands. Tetrabutylammonium cations are located in the spaces between the two networks. Despite the structural similarity, significant differences exist between (NBu4)2[Fe2(fan)3] and (NBu4)2[Zn2(fan)3] with respect to the oxidation states of the metal centers and ligands. For (NBu4)2[Fe2(fan)3] the structure determination as well as Mossbauer spectroscopy indicate the oxidation state for the Fe is close to +3, which contrasts with the +2 state for the Zn analogue. The differences between the two compounds extends to the ligands, with the Zn network involving only fluoranilate dianions, whereas the average oxidation state for the fluoranilate in the Fe network lies somewhere between −2 and ...

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 we have investigated 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. 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.

In the presence of the Et4N+ cation the chloranilate dianion (can2–) associates with a range of divalent cations, M2+, to yield an isomorphous series of crystalline compounds of composition (Et4N)2[M2(can)3] (M = Mg, Mn, Fe, Co, Ni, Cu, and Zn). The fluoranilate dianion (fan2–) likewise affords the closely related (Et4N)2[Zn2(fan)3]. The structures of (Et4N)2[Zn2(can)3], (Et4N)2[Fe2(can)3], and (Et4N)2[Zn2(fan)3] were determined by single crystal X-ray diffraction. Powder X-ray diffraction indicates that all the members of the can2– series are isomorphous. The structure of (Et4N)2[Zn2(fan)3] is very closely related to the structures of the can2– compounds. The [M2(can)32–]n component is present as chicken-wire-like sheets with (6,3) topology. The Et4N+ cation binds sheet to sheet and aligns them so that the large holes within the sheets are arranged one above another, thereby generating spacious channels running perpendicular to the sheets. The solvent molecules present in the channels are ill-defined and...

A high symmetry heterothiometallic cluster-based 3D framework of composition [WS

The single crystal X-ray structure determination of {[Cu(tpt)(o-phthalate)]·31/3(C2H2Cl4)}n (tpt = 2,4,6-tri-4-pyridyl-1,3,5-triazine, C2H2Cl4 = 1,1,2,2-tetrachloroethane = TCE) shows a 3D network in which CuII centres are linked by 3-connecting tpt ligands with the topology of a 12,3 net. CuII centres are further linked by o-phthalate dianions. The copper coordination geometry is square pyramidal, with o-phthalate oxygen donors trans to each other in the basal plane and the remaining positions taken by the pyridines of three linking tpt units. The solvent accessible void space is ∼65 %. The pale blue-green crystalline desolvate, obtained by heating to 200°C or washing the TCE solvate with acetone is formulated as [Cu(tpt)(o-phthalate)]n. Powder X-ray diffraction and electron paramagnetic resonance spectroscopy show that the crystal structure and the CuII geometry changes upon desolvation. The crystalline desolvated phase sorbs two equivalents of ammonia per copper ion. The adduct, mauve [Cu(tpt)(o-phthalate)(NH3)2]n, shows reasonable crystallinity and is stable up to ∼150°C under ambient conditions before the reversible desorption (minimum 10 cycles) of the guest ammonia. The colour change and high desorption temperature, along with changes in g values, is suggestive of chemisorption in two steps with Cu-ammine bonding in the loaded phase.

The combination of lightweight metal cations with a range of dicarboxylate ligands has led to the generation of ionic network materials that possess channels occupied by solvent molecules. The compounds [Li2 (2,2-bpdc)(DMF)2 ] and [Mg(2,2-bpdc)(DMF)2 ] (2,2-bpdc=2,2-dipyridyl-4,4-dicarboxylate) adopt a similar structure in which parallel metal-carboxylate chains are linked to four equivalent chains to generate a 3 D network in which DMF molecules occupy channels. [Li4 (3,5-pdc)2 (DMF)]⋅solvate (3,5-pdc=3,5-pyridine dicarboxylate) adopts a similar structure but the chains are more complex. As with the other structures, coordinated DMF molecules occupy network channels. [Li4 (3,5-pdc)2 (DMF)]⋅solvate is able to adsorb carbon dioxide at elevated pressures with the adsorption following a type V isotherm; hysteresis is apparent upon desorption. The final compound, Li[Mg3 OH(2,2-bqdc)3 (DMF/H2 O)3 ]⋅solvate (2,2-bqdc=2,2-biquinoline-4,4-dicarboxylate) has a distinctly different structure in which a trio of magnesium centres bound to a central μ3 -hydroxide ion serves as a 6-connecting, trigonal prismatic node within a 3 D network that has the point symbol, 49 66 . Solvent-filled intraframework spaces represent over 50 % of the crystal volume and are occupied by highly disordered solvent and Li+ ions. Immersion of Li[Mg3 OH(2,2-bqdc)3 (DMF/H2 O)3 ]⋅solvate in a solution of Fe(2,2-bipyridine)32+ results in the incorporation of the FeII complex into the large channels of the anionic network.

The structures and optical band gaps of twelve radical anionic 7,7,8,8-tetracyanoquinodimethane (TCNQ) and 7,7,8,8-tetracyano-2,3,4,5-tetrafluoroquinodimethane (F4TCNQ) based charge-transfer complexes are reported. The compounds described have been categorised into three general types based upon solid-state arrangements of the donor and acceptor molecules. Crystallographic, EPR and IR spectroscopic investigations indicated that both TCNQ and F4TCNQ in each of the compounds described exist in the radical monoanion form. Visible-NIR absorption measurements indicate optical band gaps in the range of 0.79 to 1.08 eV. Whilst the packing arrangements in CT complexes are known to affect the band gap, in the cases considered here no clear relationship between the packing arrangement and the optical band gap is apparent. The results suggest that in the absence of mixed valency the packing arrangement does not impact significantly upon the magnitude of the optical band gap.

Two cationic networks, [Cu(I)Cu(II)(4,4'bipy)4(H2O)2](3+) and [Cu(II)(4,4'bipy)2(H2O)2](2+) have been formed from a solution in which Cu(I) undergoes aerial oxidation. Whilst the topologies of the two networks are different the arrangement of Cu centres is almost identical, a structural feature which presumably allows for [Cu(I)Cu(II)(4,4'bipy)4(H2O)2](3+) to serve as a crystalline template for [Cu(II)(bipy)2(H2O)2](2+).

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)[MIII (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 robust, nano-sized covalent cage, of composition, [(PhSi)6(ctc)4]6- (H6ctc = cyclotricatechylene) has been prepared in a simple reaction in good yield. The tetrahedral anionic cage is stable in both the solid and solution state and exhibits an affinity for Cs+ ions which bind to the internal surface of the cage.

Reversible cycloaddition reactions between 1,4-bis[2-(3-pyridyl)ethenyl]benzene and its photodimers were performed within a pair of three-dimensional coordination polymers with retention of single crystal character. In each case, switching between two crystalline forms could be followed by monitoring the flourescence behaviour.

Coordination frameworks containing DCNQI2– (DCNQI = N,N′-dicyanoquinonediimine ligand) are produced by deprotonation of DCNQIH2 in the presence of a metal center and a co-ligand. This approach has yielded two-dimensional (2D) sheet compounds [Cd(DCNQI)(L)2] (where L = pyridine (py) or isoquinoline (isoquin)) that can be partially oxidized via solid-state electrochemical and in situ spectroelectrochemical methods to materials that contain DCNQI as its radical monoanion. The new frameworks display charge-transfer bands that are indicative of interligand charge-transfer interactions as supported by TD-DFT computational calculations. The redox-state dependent spectral properties of the frameworks have been probed using a newly developed solid-state spectroelectrochemical cell. Coupled with computational calculations, the experimental data provide an understanding of the fundamental charge-transfer processes that may underpin long-range functional properties such as conductivity in framework materials.

The structure of Li(inox)⋅2/3 DMF (inox(-) =the N-oxide of the isonicotinate anion) consists of a 3D framework with solvent-filled, square cross-section channels of approximate dimensions 5.5×5.5 Å. Unfortunately, the Li(inox) framework is unstable upon removal of DMF from the channels. When the structurally related 4-hydroxybenzoic acid (H2 hba) was used in place of Hinox, and Zn(2+) in place of the Li(+) , a structurally similar but more robust network, Zn(hba), was obtained; the isostructural compound, Co(hba), may also be prepared. Longer ligands with phenolate and carboxylate functional groups at opposite ends, such as the dianions of 4-coumaric acid (H2 cma) and 4'-hydroxy-4-biphenylcarboxylic acid (H2 hbpc), in combination with Zn(2+) yield Zn(cma) and Zn(hbpc) frameworks, respectively, with the same PtS topology but with larger channels. The coordination polymers remain intact after desolvation and exhibit microporosity, showing the ability to sorb significant quantities of CO2 , CH4 , and H2 .

Coordination chemistry of natural polyphenols and transition metals allows rapid self-assembly of conformal coatings on diverse substrates. Herein, we report that this coordination-driven self-assembly process applies to simple phenolic molecules with monotopic or ditopic chelating sites (as opposed to macromolecular, multitopic polyphenols), leading to surface-confined amorphous films upon metal coordination. Films fabricated from gallic acid, pyrogallol, and pyrocatechol, which are the major monomeric building blocks of polyphenols, have been studied in detail. Pyrocatechol, with one vicinal diol group (i.e., bidentate), has been observed to be the limiting case for such assembly. This study expands the toolbox of available phenolic ligands for the formation of surface-confined amorphous films, which may find application in catalysis, energy, optoelectronics, and the biomedical sciences.

Coordination polymer strips of composition ...Cu+2·lig2–·Cu+2·lig2–·Cu+2·lig2–... (where lig2– = TCNQ2– or its 2,3,4,5-tetrafluoro analogue) are observed with a wide range of coligands (monodentate, bidentate, and tridentate). Interdigitation of “thin”, planar N-heteroaromatic coligands on one strip with those on a neighbor is a common structural feature. Coligands too bulky to allow interdigitation give either non-interdigitating strips or 2D sheet structures. Both strips and sheets have 2-connecting Cu centers and 4-connecting tetracynano ligands. As a consequence of the great flexibility of the Cu/tetracyano ligand association, the geometries of the sheet structures vary widely from almost coplanar to highly corrugated and convoluted, despite which the same topology is present in all.

Five coordination polymers [Zn(oba)(4-spy)]2·(4-spy)0.25·(H2O) (1), [Zn2(oba)2(HT-ppcb)]2·(4-spy)0.25 (1a), [Zn(oba)(4-(2-npy))]2·(4-(2-npy))0.25·(H2O)1.25 (2), [Zn(oba)(4-npy)]2·(4-npy)0.25 (3) and [Zn2(oba)2(HT-pncb)]· (4-npy)0.25 (3a) (H2oba = 4,4′-oxydibenzoic acid; 4-spy = (E)-4-styrylpyridine; HT-ppcb = 1,3-bis(4-pyridyl)-2,4-bis(phenyl)cyclobutane; 4-(2-npy) = (E)-4-(2-(naphthalen-2-yl)vinyl)pyridine; 4-npy = (E)-4-(2-(naphthalen-1-yl)vinyl)pyridine; HT-pncb = rctt-1,3-bis(4-pyridyl)-2,4-bis(1-naphthyl)cyclobutane) were structurally determined. In each case, pairs of Zn(II) centres are linked by oba2− anions to form a 2D network. Olefinic pyridyl ligands bound to Zn(II) extend above and below the mean plane of the network and are located within the windows of adjacent parallel networks. Each window contains a pair of vinyl-pyridyl ligands that are tethered to networks that lie above and below and arranged in a head-to-tail manner. 1–3 show different alignments of the CC bond pair achieved by introducing olefinic ligands with different sizes of their terminal groups. In 1, the CC bonds are parallel and close enough for a [2 + 2] cycloaddition reaction to occur upon exposure to UV light. The CC bonds in 2 are too far apart to combine and no reaction occurs upon UV irradiation. In 3, the CC bonds are less than 4.0 A apart and has a criss-cross arrangement. Exposure of 3 to UV light leads to a [2 + 2] cycloaddition reaction. Analysis of the “before” and “after” structures shows a large conformational change associated with the rotation of the olefinic bonds and/or the naphthyl groups when the photodimerization of criss-cross CC bonds is undergone.

A new piperazine-derived ligand has been prepared and used to synthesise a porous coordination polymer which displays selective carbon dioxide uptake after solvent exchange and thermal activation. The ligand N,N′-bis(4-carboxyphenylmethylene)piperazine H2L1 was prepared from piperazine in three steps and good yield. A structure containing the deprotonated form K2L1·2H2O was determined and consists of a three-dimensional coordination polymer containing inorganic K2(COO)2(OH2) layers separated by the long organic bridging linker. The free compound H2L1 displays a one-dimensional hydrogen-bonded polymeric structure in the solid state with hydrogen bonding interactions between carboxylic acids and piperazine groups tightly linking molecules together. The two-dimensional polymeric complex [Zn3(L1)2(OH)2]·2DMF·0.5H2O 1 was prepared and analysed in the solid state to reveal tubular one-dimensional channels which, when activated by solvent exchange and evacuation, displayed selective affinity for CO2 over N2 and H2.

The reaction of Mn(BF

The need for effective CO