Recent advance in porous coordination polymers from the viewpoint of crystalline-state transformation

Topological transformations in metal–organic frameworks: a prospective design route?

We apply a topological approach based on the underlying net and transformation pattern concepts as well as on the ‘supernet–subnet’ formalism to uncover mechanisms of solid-state transformations in coordination polymers and metal–organic frameworks.

Tuning Semiconductor Performance of Nickel Complexes through Crystal Transformation

Crystal transformation between two polymorphs (green, 1-G, and red, 1-R) of the square-planar nickel complex NiL₂ (L = 2-ethoxy-6-( N-methyliminomethyl)phenolate) and their tuning effect to semiconductor properties were studied both experimentally and theoretically. When 1-G is heated to 413 K, it converts to 1-R, whereas soaking 1-R in several kinds of solvents causes it to revert to 1-G. Crystallographic and PXRD studies reveal the dramatic changes in crystal dimensions due to the changes of packing models. Heating device made from 1-G (D-1-G(298)) at 413 K significantly increases the electrical conductivity from 6.55 × 10^-4 S cm^-1 for D-1-G(298) to 1.11 × 10^-3 S cm^-1 for D-1-G(413), showing significant crystal form dependence. Heat-treating D-1-G and D-1-R devices at different temperatures clearly reveals the reason for the conductivity tuning. Thus, the conductivity of NiL₂-based devices could be well tuned through crystal transformation by heating or by soaking in solvent. Theoretical calculations clearly revealed the reason for such conductivity changes and also predicted that both polymorphs are good p-type semiconductors with hole mobilities of 1.63 × 10^-2 (1-G) and 2.11 × 10^-1 cm² V^-1 s^-1 (1-R).

Chemical reaction within a compact non-porous crystal containing molecular clusters without the loss of crystallinity

A yellow crystal with {FeII4O₄} cubes is modified to a black crystal with {FeIII4O₄} cubes via a SC–SC transformation.

The very rare occurrence of a gas–solid chemical reaction has been found to take place on a molecule within a compact non-porous crystal without destroying its long-range structural order and retaining similar crystal structures when yellow crystals of FeII4(mbm)₄Cl₄(MeOH)₄ were exposed to air to give black [FeIII4(mbm)₄Cl₄(OH)₄]·2H₂O. The latter cannot be synthesised directly. The original cluster underwent an exchange of methanol to hydroxide, an oxidation of Fe(ii) to Fe(iii), a change in stereochemistry and hydration while the packing and space-group remained unaltered.

Temperature-induced reversible single-crystal-to-single-crystal isomerisation of uranyl polyrotaxanes: an exquisite case of coordination variability of the uranyl center

A reversible solid-state isomerisation mediated by the change of uranyl-ligand coordination modes has been achieved in uranyl polyrotaxanes by a temperature-induced strategy.

Synthesis, structure and characterization of a layered coordination polymer based on Zn(ii) and 6-(methylmercapto)purine

A layered coordination polymer was synthesized from Zn(ii) and 6-(methylmercapto)purine (mMP-H) in N,N-dimethylformamide (DMF). Its structure and formula [Zn₂(μ₂-mMP)₃(NO₃)(DMF)(H₂O)]_n·nDMF were determined by single crystal X-ray diffraction.

Solvent diffusion through a non-porous crystal ‘caught in the act’ and related single-crystal-to-single-crystal transformations in a cationic dinuclear Ag(i) complex

A few snapshots of a dynamic solvent diffusion process through a seemingly non-porous crystal of a dinuclear, cyclic Ag(i) complex were revealed. These indicate the complexity of the process, which involves not only relocation of the molecules in the crystal lattice, but also conformational adjustments of the metallocycles in response to solvent uptake/release.

The concept of mixed organic ligands in metal–organic frameworks: design, tuning and functions

The mixed organic ligand strategy is significant for the rational construction of MOFs, and furthermore for their functionality and tunability.

Iterative mass spectrometry and X-ray crystallography to study ion-trapping and rearrangements by a flexible cluster

An important aspect of chemical reactions involves understanding the intermediate steps from reactants to products. The iterative use of mass spectrometry and X-Ray crystallography is demonstrated to be a powerful combination in this respect. We have applied them in identifying molecular clusters in solution followed by their solid-state structural characterizations. We used a key ligand, 2-[(2-hydroxy-3-methoxy-benzylidene)-amino]-ethanesulfonate (L), which serves as chelating/bridging units to stabilize the precursor [Li₄Ni₆(OH)₂(L)₆(CH₃CN)₆](ClO₄)₂·4CH₃CN. The results of subsequent reactions witness a cascade of processes involving fragmentation, inner bridging ligand substitution (OH⁻ to OCH₃⁻), changing modes of binding (chelate to monodentate) of the key ligand, ion-trapping and exchange (Li⁺, Na⁺ and Ca²⁺) and their site preferences, coordinating and non-coordinating solvents (CH₃CN to CH₃OH, H₂O and EtOH) replacement. The flexibility of the Ni₃OL₃ species in solution permits the formation of six derivatives. The complimentary techniques open a broader prospect for cluster design and applications.