Tunable Proton Conductivity and Color in a Nonporous Coordination Polymer via Lattice Accommodation to Small Molecules

Nonporous coordination polymers (npCPs) able to accommodate molecules through internal lattice reorganization are uncommon materials with applications in sensing and selective gas adsorption. Proton conduction, extensively studied in the analogue metal-organic frameworks under high-humidity conditions, is however largely unexplored in spite of the opportunities provided by the particular sensitivity of npCPs to lattice perturbations. Here, AC admittance spectroscopy is used to unveil the mechanism behind charge transport in the nonporous 1·2CH3 CN. The conductance in the crystals is found to be of protonic origin. A vehicle mechanism is triggered by the dynamics of the weakly coupled acetonitrile molecules in the lattice that can be maintained by a combination of thermal cycles, even at low humidity levels. An analogue 1·pyrrole npCP is formed by in situ exchange of these weakly bound acetonitrile molecules by pyrrole. The color and conduction properties are determined by the molecules weakly bonded in the lattice. This is the first example of acetonitrile-mediated proton transport in an npCP showing distinct optical response to different molecules. These findings open the door to the design of switchable protonic conductors and capacitive sensors working at low humidity levels and with selectivity to different molecules.

Dehydrohalogenation reactions in second-sphere coordination complexes

The latest advances of solid-state dehydrohalogenation and halogenation reactions of hydrogen bonded halometallate salts from the second sphere coordination perspective are reported. Since the second sphere englobes many different materials, our focus has been limited to outer sphere adducts where protonated organic cations act as outer sphere hydrogen bond donors and transition metal anions act as first sphere hydrogen bond acceptors. This is our attempt to analyze dehydrohalogenation/hydrohalogenation reactions viewed as transformations from the second sphere coordination to first sphere coordination of a complex and vice versa. The examples describe a unique solid-state chemistry and reactivity in outer sphere adducts where C-H, N-H and M-X chemical bonds are cleaved and new M-N and H-X bonds are formed (where M = Cu, Zn, Co, Pt, Pd, Hg and X = Cl, Br). The transformations are induced by external stimuli, mainly by mechanochemical and thermal methods. Different reactivities have been observed depending on the lability of the transition metals, the position of the reacting functional groups in the cations and the relative position of organic cations and metal anions. The reverse hydrohalogenation reactions (i.e., from the first sphere coordination to second sphere coordination) via the gas-solid chemisorption process occur even if the materials are non-porous implying a rather dynamic behaviour of these materials. Moreover, due to the implicit changes in the coordination sphere of transition metal ions, dehydrohalogenation/halogenation reactions allow structure-function correlation to be established, for instance involving optical, sensing and magnetic aspects.

Sequential single-crystal-to-single-crystal vapochromic inclusion in a nonporous coordination polymer: unravelling dynamic rearrangement for selective pyridine sensing

Unprecedent selective and reversible pyridine solid–vapor sequential inclusion in a nonporous Fe(ii) coordination polymer accompanied by a color change is presented. Although the internal reorganization is significant, the process remains SCSC.

Effect of stepwise protonation of an N-containing ligand on the formation of metal–organic salts and coordination complexes in the solid state

Controlled synthesis of a series of metal–organic salts and coordination complexes is tuned by the protonation of ligand, and their transformations are induced by the solid–gas and concentration of [H⁺].

Single-crystal-to-single-crystal transformation and proton conductivity of three hydrogen-bonded organic frameworks

In this communication, we report the SCSC transformation and proton conductivity of three H-bonded organic frameworks. The results show that H-bonded systems can improve their proton conductivity by uptaking water molecules based on the adaptability.

Selective signalling of alcohols by a molecular lattice and mechanism of single-crystal-to-single-crystal transformations

A molecular material undergoes spin-switching as it exchanges MeOH, EtOH or ⁿPrOH with acetone from the lattice. The subsequent thermal single-crystal-to-single-crystal desorption of ⁿPrOH is followed by single crystal X-ray diffraction snapshots.

Tailoring the structures and transformations between copper complexes in gas–solid reactions and solid-state synthesis

A series of unusual structures and transformations between several copper salts and complexes induced in the solid–gas and solid-state reactions were investigated.

Thermal Reactivity in Metal Organic Materials (MOMs): From Single-Crystal-to-Single-Crystal Reactions and Beyond

Thermal treatment is important in the solid-state chemistry of metal organic materials (MOMs) because it can create unexpected new structures with unique properties and applications that otherwise in the solution state are very difficult or impossible to achieve. Additionally, high-temperature solid-state reactivity provide insights to better understand chemical processes taking place in the solid-state. This review article describes relevant thermally induced solid-state reactions in metal organic materials, which include metal organic frameworks (MOFs)/coordination polymers (CPs), and second coordination sphere adducts (SSCs). High temperature solid-state reactivity can occur in a single-crystal-to-single crystal manner (SCSC) usually for cases where there is small atomic motion, allowing full structural characterization by single crystal X-ray diffraction (SC-XRD) analysis. However, for the cases in which the structural transformations are severe, often the crystallinity of the metal-organic material is damaged, and this happens in a crystal-to-polycrystalline manner. For such cases, in the absence of suitable single crystals, structural characterization has to be carried out using ab initio powder X-ray diffraction analysis or pair distribution function (PDF) analysis when the product is amorphous. In this article, relevant thermally induced SCSC reactions and crystal-to-polycrystalline reactions in MOMs that involve significant structural transformations as a result of the molecular/atomic motion are described. Thermal reactivity focusing on cleavage and formation of coordination and covalent bonds, crystalline-to-amorphous-to-crystalline transformations, host-guest behavior and dehydrochlorination reactions in MOFs and SSCs will be discussed.

Qualitative Guest Sensing via Iron(II) Triazole Complexes

The pyridazine-pyridine triazole-based Rat ligand, L^pydzpy [4-(4-methylphenyl)-3-(3-pyridazinyl)-5-(2-pyridinyl)-1,2,4-triazole], is potentially ditopic. Nevertheless, L^pydzpy is shown herein to exclusively form mononuclear iron(II) complexes, [Fe^II(L^pydzpy)₂(NCE)₂]·solvent, in the presence of coordinating NCE anions (E = S or Se). Specifically, a new family of 10 mononuclear complexes, in which L^pydzpy binds in a monotopic bidentate manner, has been made: two solvent-free complexes, [Fe^II(L^pydzpy)₂(NCS)₂] (1) and [Fe^II(L^pydzpy)₂(NCSe)₂] (2); six solvatomorphs, 1·4CH₃CN, 2·4CH₃CN, 1·2.25CH₃CN, 2·3CH₃CN, 2·tetrahydrofuran, and 2·CHCl₃; and a pair of desolvated polymorphs, 1' and 2'. Seven of them are spin crossover-active, the exceptions being 1, 2, and 2'. This is confirmed by single-crystal X-ray diffraction (XRD) for 1, 2, 1·4CH₃CN, and 2·4CH₃CN and is consistent with variable-temperature optical microscopy observations on single crystals of 1·4CH₃CN and 2·4CH₃CN and on samples of 1' and 2'. Powder XRD, thermogravimetric analysis, and solid-state magnetometry reveal that desolvated 1' and 2' are capable of absorbing and desorbing a range of volatile guests: CH₃CN in both cases and also tetrahydrofuran and CHCl₃ in the case of 2'.

Reactivity among first and second coordination spheres using a multiprotonated ligand and Cu(ii) in the solid-state

The solid-state reactivity among nonporous Cu(ii) second and first sphere adducts has been studied using a multidentate flexible ligand in combination with quantum mechanics.

Dynamic behaviour in nonporous hybrid metal–organic materials via mechanochemical and gas–solid reactions

Nonporous hybrid metal organic materials have been studied in the solid-state by mechanochemical reactions, chemisorption and release of HCl by heating. The dynamic behavior of the hybrid materials allows the breaking and formation of chemical bonds.