A structural investigation of organic battery anode materials by NMR crystallography.

Conjugated alkali metal dicarboxylates have recently received attention for applications as organic anode materials in lithium- and sodium-ion batteries. In order to understand and optimise these materials, it is important to be able to characterise both the long-range and local aspects of the crystal structure, which may change during battery cycling. Furthermore, some materials can display polymorphism or hydration behaviour. NMR crystallography, which combines long-range crystallographic information from diffraction with local information from solid-state NMR via interpretation aided by DFT calculations, is one such approach, but this has not yet been widely applied to conjugated dicarboxylates. In this work, we evaluate the application of NMR crystallography for a set of model lithium and sodium dicarboxylate salts. We investigate the effect of different DFT geometry optimisation strategies and find that the calculated NMR parameters are not systematically affected by the choice of optimisation method, although the inclusion of dispersion correction schemes is important to accurately reproduce the experimental unit cell parameters. We also observe hydration behaviour for two of the sodium salts and provide insight into the structure of an as-yet uncharacterised structure of sodium naphthalenedicarboxylate. This highlights the importance of sample preparation and characterisation for organic sodium-ion battery anode materials in particular.

Effect of Transition Metal Substitution on the Flexibility and Thermal Properties of MOF-Based Solid-Solid Phase Change Materials.

A series of azobenzene-loaded metal-organic frameworks were synthesized with the general formula M2(BDC)2(DABCO)(AB)x (M = Zn, Co, Ni, and Cu; BDC = 1,4-benzenedicarboxylate; DABCO = 1,4-diazabicyclo[2.2.2]octane; and AB = azobenzene), herein named M-1⊃ABx. Upon occlusion of AB, each framework undergoes guest-induced breathing, whereby the pores contract around the AB molecules forming a narrow-pore (np) framework. The loading level of the framework is found to be very sensitive to the synthetic protocol and although the stable loading level is close to M-1⊃AB1.0, higher loading levels can be achieved for the Zn, Co, and Ni frameworks prior to vacuum treatment, with a maximum composition for the Zn framework of Zn-1⊃AB1.3. The degree of pore contraction upon loading is modulated by the inherent flexibility of the metal-carboxylate paddlewheel unit in the framework, with the Zn-1⊃AB1.0 showing the biggest contraction of 6.2% and the more rigid Cu-1⊃AB1.0 contracting by only 1.7%. Upon heating, each composite shows a temperature-induced phase transition to an open-pore (op) framework, and the enthalpy and onset temperatures of the phase transition are affected by the framework flexibility. For all composites, UV irradiation causes trans → cis isomerization of the occluded AB molecules. The population of cis-AB at the photostationary state and the thermal stability of the occluded cis-AB molecules are also found to correlate with the flexibility of the framework. Over a full heating-cooling cycle between 0 and 200 °C, the energy stored within the metastable cis-AB molecules is released as heat, with a maximum energy density of 28.9 J g-1 for Zn-1⊃AB1.0. These findings suggest that controlled confinement of photoswitches within flexible frameworks is a potential strategy for the development of solid-solid phase change materials for energy storage.

Twists to the Spin Structure of the Ln9-diabolo Motif Exemplified in Two {Zn2Ln2}[Ln9]{Zn2} Coordination Clusters.

Two pentadecanuclear Zn4Ln11 [with Ln = Gd(1) or Dy(2)] coordination clusters, best formulated as {Zn2Ln2}[Ln9]{Zn2}, are presented. The central {Ln9} diabolo core has a {Zn2Ln2} handle motif pulling at two outer Ln ions of the central core via two {ZnLn} units, which also invest the system with C2 point symmetry. The resulting cluster motif is supported on two Zn "feet", corresponding to the {Zn2} unit in the formula. A thorough investigation of the magnetic properties in the light of the properties of previously reported {Ln9} diabolo compounds was undertaken. Up to now, the spin structure of such diabolo motifs usually proves ambiguous. Our magnetic studies show that the orientation of the central spin in the {Gd9} diabolo plays a decisive role. In stabilizing the core by attachment of the {Zn}2+ "feet" and using the C2 symmetry related {ZnGd}5+ handles to influence the spin direction of the central Gd of the {Gd9} diabolo, we can understand why the "naked" {Gd9} diabolo shows ambiguous spin structure. This then allowed us to elucidate the single-molecule magnetic (SMM) properties of the Dy-based compound 2 through disentangling the magnetic properties of the isostructural Gd-based compound 1.

3d/4f Coordination Clusters as Cooperative Catalysts for Highly Diastereoselective Michael Addition Reactions.

Michael addition (MA) is one of the most well studied chemical transformation in synthetic chemistry. Here, we report the synthesis and crystal structures of a library of 3d/4f coordination clusters (CCs) formulated as [ZnII2YIII2L4(solv)X(Z)Y] and study their catalytic properties toward the MA of nitrostyrenes with barbituric acid derivatives. Each CC presents two borderline hard/soft Lewis acidic ZnII centers and two hard Lewis acidic YIII centers in a defect dicubane topology that brings the two different metals into a proximity of ∼3.3 Å. Density functional theory computational studies suggest that these tetrametallic CCs dissociate in solution to give two catalytically active dimers, each containing one 3d and one 4f metal that act cooperatively. The mechanism of catalysis has been corroborated via NMR, electron paramagnetic resonance, and UV-vis. The present work demonstrates for the first time the successful use of 3d/4f CCs as efficient and high diastereoselective catalysts in MA reactions.

Efficient Ni(II)2Ln(III)2 Electrocyclization Catalysts for the Synthesis of trans-4,5-Diaminocyclopent-2-enones from 2-Furaldehyde and Primary or Secondary Amines.

A series of heterometallic coordination clusters (CCs) [Ni(II)2Ln(III)2(L1)4Cl2(CH3CN)2] 2CH3CN [Ln = Y (1Y), Sm (1Sm), Eu (1Eu), Gd (1Gd), or Tb (1Tb)] were synthesized by the reaction of (E)-2-(2-hydroxy-3-methoxybenzylidene-amino)phenol) (H2L1) with NiCl2·6(H2O) and LnCl3·x(H2O) in the presence of Et3N at room temperature. These air-stable CCs can be obtained in very high yields from commercially available materials and are efficient catalysts for the room-temperature domino ring-opening electrocyclization synthesis of trans-4,5-diaminocyclopent-2-enones from 2-furaldehyde and primary or secondary amines under a non-inert atmosphere. Structural modification of the catalyst to achieve immobilization or photosensitivity is possible without deterioration in catalytic activity.

Heteronuclear 3 d/Dy(III) coordination clusters as catalysts in a domino reaction.

Three isoskeletal tetranuclear coordination clusters with general formula [M(II) 2 Dy(III) 2 L4 (EtOH)6 ](ClO4 )2 ⋅2 EtOH, (M=Co, 1; M=Ni, 2) and [Ni(II) 2 Dy(III) 2 L4 Cl2 (CH3 CN)2 ]⋅2 CH3 CN (3), have been synthesized and characterized. These air-stable compounds, and in particular 3, display efficient homogeneous catalytic behavior in the room-temperature synthesis of trans-4,5-diaminocyclopent-2-enones from 2-furaldehyde and primary or secondary amines under a non-inert atmosphere.

Understanding Solid-State Photochemical Energy Storage in Polymers with Azobenzene Side Groups.

Solar thermal fuel (STF) materials store energy through light-induced changes in the structures of photoactive molecular groups, and the stored energy is released as heat when the system undergoes reconversion to the ground-state structure. Solid-state STF devices could be useful for a range of applications; however, the light-induced structural changes required for energy storage are often limited or prevented by dense molecular packing in condensed phases. Recently, polymers have been proposed as effective solid-state STF platforms, as they can offer the bulk properties of solid materials while retaining the molecular-level free volume and/or mobility to enable local structural changes in photoresponsive groups. Light-induced energy storage and macroscopic heat release have been demonstrated for polymers with photoisomerizable azobenzene side groups. However, the mechanism of energy storage and the link between the polymer structure, energy density and storage duration has not yet been explored in detail. In this work, we present a systematic study of methacrylate- and acrylate-based polymers with azobenzene side groups to establish the mechanism of energy storage and release and the factors affecting energy density and reconversion kinetics. For polymers with directly attached azobenzene side groups, the energy storage properties are in line with previous work on similar systems, and the photoisomerization and reconversion properties of the azobenzene side groups mirror those of molecular azobenzene. However, the inclusion of an alkyl linker between the azobenzene side group and the backbone significantly increases the photoswitching efficiency, giving almost quantitative conversion to the Z isomeric state. The presence of the alkyl linker also reduces the glass transition temperature and leads to faster spontaneous thermal reconversion to the E isomeric form, but in all cases, half-lives of more than 4 days are observed in the solid state, which provides scope for applications requiring daily energy storage-release cycles. The maximum gravimetric energy density observed is 143 J g-1, which represents an increase of up to 44% compared to polymers with directly attached azobenzene moieties.

Systematic Investigation into the Photoswitching and Thermal Properties of Arylazopyrazole-based MOF Host-Guest Complexes.

A series of arylazopyrazole-loaded metal-organic frameworks were synthesized with the general formula Zn2(BDC)2(DABCO)(AAP)x (BDC = 1,4-benzenedicarboxylate; DABCO = 1,4-diazabicyclo-[2.2.2]octane; AAP = arylazopyrazole guest). The empty framework adopts a large pore tetragonal structure. Upon occlusion of the E-AAP guests, the frameworks contract to form narrow pore tetragonal structures. The extent of framework contraction is dependent on guest shapes and pendant groups and ranges between 1.5 and 5.8%. When irradiated with 365 nm light, the framework expands due to the photoisomerization of E-AAP to Z-AAP. The proportion of Z-isomer at the photostationary state varies between 19 and 57% for the AAP guests studied and appears to be limited by the framework which inhibits further isomerization once fully expanded. Interestingly, confinement within the framework significantly extends the thermal half-life of the Z-AAP isomers to a maximum of approximately 56 years. This finding provides scope for the design of photoresponsive host-guest complexes with high stability of the metastable isomer for long-duration information or energy storage applications.

Efficient solid-state photoswitching of methoxyazobenzene in a metal-organic framework for thermal energy storage.

Efficient photoswitching in the solid-state remains rare, yet is highly desirable for the design of functional solid materials. In particular, for molecular solar thermal energy storage materials high conversion to the metastable isomer is crucial to achieve high energy density. Herein, we report that 4-methoxyazobenzene (MOAB) can be occluded into the pores of a metal-organic framework Zn2(BDC)2(DABCO), where BDC = 1,4-benzenedicarboxylate and DABCO = 1,4-diazabicyclo[2.2.2]octane. The occluded MOAB guest molecules show near-quantitative E → Z photoisomerization under irradiation with 365 nm light. The energy stored within the metastable Z-MOAB molecules can be retrieved as heat during thermally-driven relaxation to the ground-state E-isomer. The energy density of the composite is 101 J g-1 and the half-life of the Z-isomer is 6 days when stored in the dark at ambient temperature.

Transformative 3d-4f coordination cluster carriers.

The aim of this perspective is to summarise the use of the reported 3d-4f Coordination Clusters (CCs) in catalytic reactions and to demonstrate the potential of this emerging field. The pioneering work of Shibasaki, Matsunaga and others, demonstrated the use of 3d-4f in situ systems to catalyse asymmetric organic transformations. Our recent studies show that well characterised 3d-4f CCs catalyse numerous organic transformations and useful mechanistic aspects of their catalysis can be obtained. Furthermore, we have shown that by manipulation of the metal ion coordination environment; the nature of the 3d and lanthanide ions and the organic periphery of the ligand can all improve the efficacy of a 3d-4f CC catalyst. All in situ formed and well characterized 3d-4f CCs involved in catalysis are discussed.

A tetranuclear CuDy coordination cluster as a Suzuki (C-C) coupling reaction promoter.

The air-stable tetranuclear coordination cluster [CuDyL4(NO3)2(CH3CN)2]·2(CH3CN), which can be obtained in high yield, promotes the Suzuki coupling reaction of phenylboronic acid with substituted aryl halides under environmentally benign conditions.

Dinucleating Schiff base ligand in Zn/4f coordination chemistry: synthetic challenges and catalytic activity evaluation.

Four Zn/4f polynuclear coordination clusters (PCCs) formulated as [ZnII2DyIII2L2(CO3)2(NO3)2] (1), [ZnIIYIIIL(NO3)2(o-van) (MeOH)] (MeOH) [2 (MeOH)] and [ZnIILnIIIL(NO3)2Cl(EtOH)] where Ln is Dy (3) and Y (4) and where H2L is the dinucleating Schiff base ligand N,N'-bis(3-methoxysalicylidene)cyclohexane-1,2-diamine and o-van is ortho-vanillin, were prepared and fully characterised for the first time. These air-stable heterometallic PCCs, obtained in high yields from commercially available materials, were shown to remain stable in solution in their dinuclear [ZnIILnIIIL] form. Their catalytic activity was evaluated in various catalytic transformations including the Friedel-Crafts alkylation of 2-acyl imidazoles with indoles.

Tetranuclear Zn/4f coordination clusters as highly efficient catalysts for Friedel-Crafts alkylation.

A series of custom-designed, high yield, isoskeletal tetranuclear Zn/4f coordination clusters showing high efficiency as catalysts with low catalytic loadings in Friedel-Crafts alkylation are described for the first time. The possibility of altering the 4f centers in these catalysts without altering the core topology allows us to further confirm their stability via EPR and NMR, as well to gain insights into the plausible reaction mechanism, showcasing the usefulness of these bimetallic systems as catalysts.

A new family of high nuclearity Co(II)/Dy(III) coordination clusters possessing robust and unseen topologies.

Mixing Co(NO3)2·6H2O/Dy(NO3)3·6H2O/(E)-4-(2-hydroxy-3-methoxybenzylideneamino)-2,3-dimethyl-1-phenyl-1,2-dihydropyrazol-5-one (HL)/pivalic acid/Et3N in various solvents results in the synthesis of seven compounds formulated as [CoII2DyIII2(µ3-MeO)2(L)2(piv)4(NO3)2] (3), [CoIIDyIII3(µ3-MeO)2(µ2-MeO)2(L)2(piv)2(NO3)3]·2(CH3OH) (4·2CH3OH), 2[CoII4DyIII4(µ2-O)2(µ3-OH)4(L)4(piv)8][CoII2DyIII5(µ3-OH)6(L)2(piv)8(NO3)4] (5), [CoII4DyIII4(µ2-O)2(µ3-OH)4(L)4(piv)8]·2(CH3CN) (6·2CH3CN), [CoII2DyIII5(µ3-OH)6(L)2(piv)8(NO3)4]·4(CH3CN) (7·4CH3CN), [CoII2DyIII2(µ3-OH)2(L)2(piv)2(NO3)2(EtOH)2(H2O)2](NO3)2·(EtOH) (8·EtOH) and [CoII4DyIII4(µ2-O)2(µ3-OH)4(L)4(piv)8] (9) with robust and unseen topologies. These show that the temperature and reaction time influence the formation of the final product. Preliminary magnetic studies, performed for 6 and 7 in the temperature range 2­300 K, are indicative of Single Molecule Magnet (SMM) behaviour. Moreover, analysis of the catalytic properties of compound 3 as an efficient catalyst for the synthesis of trans-4,5-diaminocyclopent-2-enones from 2-furaldehyde and primary amines has been carried out.