Themed collection In celebration of Tony Cheetham’s 70th birthday

Welcome to this themed issue of Dalton Transactions entitled ‘Flexibility and Disorder in Metal–Organic Frameworks’.

Entropy is one of the fundamental quantities which links emerging research areas like flexibility and defect engineering in inorganic–organic hybrid materials. Here, we highlight the role of entropy in the past and discuss how computational methods can help us to understand entropic effects in inorganic–organic hybrid materials in the future.

The wide-ranging properties of metal organic frameworks (MOFs) rely in many cases on the presence of defects within their structures and the disorder that is inevitably associated with such defects.

We examine the emerging chemical and structural trends in the field of inorganic–organic framework structures and discuss some of the nascent applications of this vast and exciting class of materials.

Highlights of the recent results on the carbon-assisted synthesis of inorganic nanowires are presented. The illustration shows SEM images of nanowires of (a) Al₂O₃ and (b) AlN produced by carbon-assisted synthesis.

Establishing the fundamental structure–mechanical properties relationships in metal–organic frameworks (MOFs) and dense hybrids is central to the design, optimization and implementation of this new class of materials.

Poly(3,4-ethylenedioxythiophene) (PEDOT) is formed inside a metal–organic framework (MOF). MOF removal leads to sub-millimetre structures of the nanostructured conducting polymer.

Dispersion of the nanosheets exposes labile metal-sites which are shown to exchange solvent molecules allowing the nanosheets to act as sensors in suspension.

Density functional theory screening of the hybrid double perovskites (MA)₂B^IBiX₆ (B^I = K, Cu, Ag, Tl; X = Cl, Br, I) was performed and (MA)₂TlBiBr₆, isoelectronic with MAPbBr₃, was synthesised and found to have a band gap of ∼2.0 eV.

A Bi-based double perovskite provides a suitable approach to search for lead-free alternatives for photovoltaics.

The porosity of a glass formed by melt-quenching a metal–organic framework, has been characterized by positron annihilation lifetime spectroscopy.

Polymorphism in formate-based dense metal–organic frameworks with the general formula ABX₃ is predicted by quantum chemical calculations and confirmed experimentally.

We show controlled release over a 30 day period compared with the release from crystalline MOF, which occurs in less than 2 days.

Computed Kohn–Sham energies as a function of torsion angle for three rotational modes of the methylammonium group in orthorhombic CH₃NH₃PbI₃.

Owing to its thermal stability and structural flexibility, the original 3-D framework of lithium L-malate remains intact upon topotactic dehydration.

Anisotropic negative thermal expansion, driven by magnetoelastic coupling, has been found in cobalt adipate and interpreted through understanding its antiferromagnetic structure.

A lamellar pyrimidinethiolate coordination polymer has been exfoliated to form nanosheets and found to be electronically insulating.

Topotactic reactions can create nanomaterials having unique structure and properties that cannot be realized in bulk materials.

The robustness of F–H⋯F hydrogen bonds within bifluoride of a framework structure is probed via nanoindentation.

This paper presents utilization of carbonized metal–organic frameworks for sulphur loading to fabricate cathode structures for lithium–sulphur batteries.

Ball-milling induced amorphization of the prototypical substituted zeolitic imidazolate framework ZIF-8 results in a less porous framework, adopting a continuous random network topology.

The mechanical properties of isostructural MOFs adopting the perovskite ABX₃ topology are strongly correlated to the ligand field stabilization energy.

We show that dispersive interactions are an essential component in modelling zeolitic imidazolate frameworks and compare Zn-ZIFs to their LiB-ZIFs analogues.

High pressure, synchrotron X-ray studies of a zeolitic imidazolate framework reveal a new high pressure phase followed by reversible amorphization.

We report efficient white upconversion luminescence in Y₂BaZnO₅-based phosphors under near-infrared excitation and at low excitation power densities.

Simulated crystal structure of the zeolitic imidazole framework (ZIF) with the topology of the LTL-type zeolite.

A novel porous coordination polymer displays a high physisorptive H₂ adsorption enthalpy of 8 kJ/mol, due to fluorine atoms exposed to the pore surface and the structure's small pore size

We report the structures of a family of bimetallic 4- and 5-component coordination polymers of Cu and Zn with 5-hydroxyisophthalic acid, 4,4′-bipyridyl and oxalate, in which the metals and ligands occupy distinct sites.

Experimental and computational observations indicate that the formation of zinc 4-cyclohexene-1,2-dicarboxylates proceeds largely under thermodynamic control.

A nanoporous nickel coordination polymer demonstrates the utility of 5-sulfoisophthlate as a ligand for the synthesis of new hybrid systems.

Five unique structures of cobalt succinate may be prepared from one starting mixture simply by varying the synthesis temperature. The changes in bonding and composition for structures illustrate the important role of temperature in hybrid materials synthesis.

Open-framework zinc phosphates are typically made in the presence of amines and phosphoric acid. However, novel architectures can be created by using organophosphorus amides as a single source of amine and phosphorus.

We report how mechanical and dynamical properties in formate-based perovskites can be manipulated by the preparation of an A-site solid-solution.

Tolerance Factors of possible hybrid perovskites are calculated for over 2500 amine-metal-anion permutations of the periodic table.

A dense, insulating metal–organic framework (MOF), is successfully converted into a semiconducting amorphous MOF via a topochemical route.

The concept of tolerance factors is applied quantitatively to hybrid inorganic–organic materials that adopt perovskite-like architectures.

Single-crystal nanoindentation performed on a series of soft porous crystals reveals highly anisotropic mechanical properties of these frameworks as a function of the network geometry.

Hierarchical and thermally stable bicontinuous metal–organic frameworks were synthesized by using self-assembled functional block co-oligomer micelle templates.

Graphene is employed to create a new class of photocatalysts that truly advances semi-conductor photocatalysis to its next generation.

The effect of ligand length on two families of dense frameworks, several incorporating highly unusual MnO₅ trigonal bipyramids, is explored and the high magnetic ordering temperature of one of these is discussed.

The reversible pressure-induced phase transformation associated with bond rearrangement in a rare-earth formate framework was explored using first-principles calculations, which complement and help understand its experimental observations.

Three highly crystalline Cu(II)-polyoxometalate (POM) complexes, [Cu_1.5(H₂O)_7.5PW₁₂O₄₀]·4.75H₂O and cis- and trans-[Cu₂(H₂O)₁₀SiW₁₂O₄₀]·6H₂O, were successfully synthesized and characterized by single crystal and powder X-ray diffraction as well as thermogravimetric analysis.

Eleven novel coordination compounds, composed of chrysazin (1,8-dihydroxyanthraquinone) and different first-row transition metals (Fe, Co, Ni, Cu), were synthesised and the structures determined by single-crystal X-ray diffraction.

A catalytically active and super paramagnetic Co–carbon–rGO composite was synthesized and used as a nanoactuator to achieve simultaneous momentum-transfer and hydrolysis of NaBH₄ or H₃NBH₃ for hydrogen production.

Amorphization of zeolitic imidazolate frameworks during ball-milling is much more rapid than that of aluminosilicate zeolites.

Structural flexibility in pillared-layer metal–organic frameworks can be controlled via the concept of mixed-linker solid solutions.

A weak relationship between the longest C–O bond in an anionic organic ligand and the shortest Li–O bond was found.

Incorporating nanofillers into thermal-oxidatively crosslinked polymers of intrinsic microporosity (PIM-1) generates highly permeable and selective molecular sieves for gas separations.

The crystal structures of Na₃NpO₄ and Na₃PuO₄ have been solved for the first time ab initio, and the pentavalence of the neptunium cation has been confirmed using Mössbauer spectroscopy.

High resolution ¹³C and ¹⁵N CP MAS NMR spectra of ZIF-4, ZIF-8 and ZIF-zni are assigned on the basis of DFT calculations on the geometry-optimized structures.

Trends in the Young's Modulus and Hardness for the hybrid perovskites CH₃NH₃PbX₃ (X = I, Br and Cl) are assessed in relation to the underlying chemical bonding.

The deep red phosphor Sr₄(PO₄)₂O:Eu²⁺, which has an excitation peak around 450 nm for blue LED applications, is reported.

Elastic properties and acoustic dissipation associated with the disorder–order ferroelectric transition in a single crystal metal–organic framework (MOF), [NH₄][Zn(HCOO)₃], have been investigated using resonant ultrasound spectroscopy (RUS) in the temperature range between 10 K and 300 K.

A new blue-green phosphor, Ca₆BaP₄O₁₇:Ce³⁺, which can be prepared by conventional solid-state synthesis, is reported as a candidate phosphor for solid-state lighting with near-ultraviolet LEDs.

Hydrated interparticle phases are considered to make a considerable contribution to proton conduction in many metal-organic frameworks.

A new phase, Ca₆BaP₄O₁₇, was found in the CaO–BaO–P₂O₅ phase diagram and its Eu²⁺-doped derivative was evaluated as a possible phosphor for solid-state lighting.

Potassium and rubidium trithiocyanurate crystals exhibit proton conductivities, which are discussed on the basis of their crystal structures.

Two distinct adsorption sites and “breathing” within the flexible fluorinated MOF Znbpetpa are found through computational methods.

The origins of structural diversity of fourteen rare earth frameworks, exhibiting one, two and three dimensional connectivity, are explored and the luminescent properties of low dimensional frameworks described.

As-synthesised zeolitic imidazolate framework (ZIF-8) nanocrystals were dispersed into a polymer matrix forming nanocomposite membranes with enhanced gas permeability.

A family of layered frameworks has been created in which the topological diversity affects the size of nanosheets obtained by exfoliation; their layered structures support strongly coupled two-dimensional antiferromagnets.

The first transition metal frameworks containing two distinct linear dicarboxylate ligands are described and are antiferromagnets, which undergo different transitions with increasing applied field.

1- and 3-D coordination polymers containing monomeric bismuth–pyridinedicarboxylate units and lithium cations have been synthesized. Their gas sorption and photoluminescence properties have been described.

A 2D homochiral framework {[Mn(NPTA)(4,4′-bpy)(H₂O)]·(H₂O)₂}_n exhibits a spin–flop transition with a critical field of 23.6 kOe at 1.9 K.

The magnetic structure, hydrogen positions and cation valency of the transition metal gallates were elucidated using neutron diffraction, in conjunction with synchrotron techniques.

Five novel inorganic–organic frameworks based on anthraquinone dicarboxylic acid are presented and their photoluminescent properties investigated. The relationship between ligand flexibility and temperature dependent photoluminescence is examined.