Using microscopic techniques to reveal the mechanism of anion exchange in crystalline co-ordination polymers

Reversible transformation between Cu(i)-thiophenolate coordination polymers displaying luminescence and electrical properties

The direct self-assembly between CuI with thiophenol produces two different 1D coordination polymers (CPs) with multifunctional properties; the ratio CuI in acetonitrile is the key factor determining the reversible conversion between both CPs.

Mechanisms of Solvent-Mediated Structural Transformations for Dynamic Crystals of Supramolecular Coordination Systems

Thus far, reports about the transformations for dynamic crystals of supramolecular coordination systems mainly include single-crystal-to-single-crystal reactions, and solvent-mediated processes. This Concept focuses on the mechanisms for solvent-mediated structural transformations of dynamic crystals, which can be classified into two categories, that is, core-on-shell and core-to-core. The core-on-shell mechanism means that the core of the new crystal is generated from the shell of original crystal, being concomitant with the dissolution of the mother crystal. In contrast, for the core-to-core case, the growth of new crystal core and the dissolution of original crystal core will proceed simultaneously, but they are physically separated. Herein, the two mechanisms are elucidated in detail, with some typical examples from recent advances.

Anion exchange dynamics in the capture of perchlorate by a cationic Ag-based MOF

We report a detailed study of the host-guest interaction for a cationic metal-organic framework that can reversibly capture perchlorate. The structural transformation and flexibility of silver 4,4'-bipyridine nitrate (SBN) upon formation of silver 4,4'-bipyridine perchlorate (SBP) was evaluated by monitoring the anion exchange dynamics using a combination of powder X-ray diffraction (PXRD) with multinuclear 13C, 15N and 109Ag solid-state NMR spectra at different time intervals of the anion exchange. The structural transformation from SBN to SBP is complete within 70 minutes and was determined to take place by a solvent-mediated process. This pathway is confirmed by the morphological changes of the two crystalline materials observed by SEM. This key understanding may lead to application of this material towards perchlorate capture.

Anion exchange coupled with the reduction and dimerisation of a copper(ii) nitrate complex of tripyridyl dithioether via a single-crystal-to-single-crystal transformation

It is a challenge to develop methodologies involving multiple transformations for preparing new materials that cannot be obtained via direct synthesis. Herein, we report an anion exchange process accompanying cation reduction and dimerisation via a single-crystal-to-single-crystal transformation. First, a direct reaction of the flexible tripyridyl dithioether ligand L with CuI afforded a mixture of four bis(ligand) complexes (1a-1d). To avoid the formation of undesired mixed products, a copper(ii) nitrate complex-mediated approach involving anion exchange and cation reduction was employed to generate a monomeric complex, [CuII(L)NO3]NO3·toluene (2). When the dark blue crystals of 2 were immersed in an aqueous NaI solution, the crystals were transformed to a pale yellow dimeric copper(i) iodide complex, [(μ-CuI2I2)(L)2] (3). The observed anion exchange promotes the reduction of copper(ii) to copper(i) at the expense of I-/I3- oxidation as well as dimerisation via the formation of a Cu2I2 cluster. This result corresponds to the synthesis of a compound that otherwise was not able to be prepared via a direct synthetic procedure.

Solvent-vapour-assisted pathways and the role of pre-organization in solid-state transformations of coordination polymers

A family of one-dimensional coordination polymers, [Ag4(O2C(CF2)2CF3)4(phenazine)2(arene) n ]·m(arene), 1 (arene = toluene or xylene), have been synthesized and crystallographically characterized. Arene guest loss invokes structural transformations to yield a pair of polymorphic coordination polymers [Ag4(O2C(CF2)2CF3)4(phenazine)2], 2a and/or 2b , with one- and two-dimensional architectures, respectively. The role of pre-organization of the polymer chains of 1 in the selectivity for formation of either polymorph is explored, and the templating effect of toluene and p-xylene over o-xylene or m-xylene in the formation of arene-containing architecture 1 is also demonstrated. The formation of arene-free phase 2b , not accessible in a phase-pure form through other means, is shown to be the sole product of loss of toluene from 1-tol·tol [Ag4(O2C(CF2)2CF3)4(phenazine)2(toluene)]·2(toluene), a phase containing toluene coordinated to Ag(I) in an unusual μ:η(1),η(1) manner. Solvent-vapour-assisted conversion between the polymorphic coordination polymers and solvent-vapour influence on the conversion of coordination polymers 1 to 2a and 2b is also explored. The transformations have been examined and confirmed by X-ray diffraction, NMR spectroscopy and thermal analyses, including in situ diffraction studies of some transformations.

Topological Control in Heterometallic Metal−Organic Frameworks by Anion Templating and Metalloligand Design

Several new heterometallic metal-organic frameworks (MOFs) based on tris(dipyrrinato) metalloligands and Ag+ salts are reported. MOFs were prepared systematically to examine the effects of the core metal ion, counteranion, and ligand structure on the topology of the resultant network. The effect of the metal ion (Fe3+ vs Co3+) on MOF structure was generally found to be negligible, thereby permitting the facile synthesis of trimetallic Fe/Co/Ag networks. The choice of anion (e.g., silver salt) was found to have a pronounced effect on the MOF topology. Networks prepared with salts of AgO3SCF3 and AgBF4 reliably formed three-dimensional (10,3) nets, whereas use of AgPF6 and AgSbF6 produced two-dimensional (6,3) honeycomb nets. The topology generated upon formation of the MOF was found to be robust in certain cases, as demonstrated by anion-exchange experiments. Anion exchange was confirmed by X-ray crystallography in a rare set of apparent single-crystal-to-single-crystal transformations. The data presented here strongly suggest that the coordinative ability of the anion does not play a significant role in the observed templating effect. Finally, changes in the length of the tris(dipyrrinato) metalloligand were found to override the anion templating effect, resulting exclusively in two-dimensional (6,3) nets. These studies provide a basis for the rational design of MOF topologies by choice of ligand structure and anion templating effects. Furthermore, the results demonstrate the ability of carefully designed metalloligands to generate MOFs of structure strikingly similar to that of their organic counterparts.