Direct Evidence for Single-Crystal to Single-Crystal Switching of Degree of Interpenetration in a Metal–Organic Framework

Opening of an Accessible Microporosity in an Otherwise Nonporous Metal-Organic Framework by Polymeric Guests

The development of highly porous metal-organic frameworks (MOFs) is greatly sought after, due to their wide range of applications. As an alternative to the development of new structures, we propose to obtain new stable configurations for flexible MOFs by insertion of polymeric guests. The guests prevent the otherwise spontaneous closing of the host frameworks and result in stable opened forms. Introduced at a fraction of the maximal capacity, polymer chains cause an opening of the occupied nanochannels, and because of the MOF reticular stiffness, this opening is propagated to the neighboring nanochannels that become accessible for adsorption. Composites were obtained by in situ polymerization of vinyl monomers in the nanochannels of an otherwise nonporous MOF, resulting in homogeneously loaded materials with a significant increase of porosity (S_BET = 920 m²/g). In addition, by limiting the accessible configurations for the framework and forbidding the formation of a reactive intermediate, the polymeric guest prevented the thermal degradation of the host MOF even at very low loading (as low as 3 wt %) and increased its stability domain by more than 200 °C.

The impact of N,N′-ditopic ligand length and geometry on the structures of zinc-based mixed-linker metal–organic frameworks

A series of MOFs containing di(4-pyridyl)-1H-pyrazole linkers have been prepared and characterised.

A new multitalented azine ligand: elastic bending, single-crystal-to-single-crystal transformation and a fluorescence turn-on Al(iii) sensor

A multifunctional azine ligand with elastic bending with full phase retention, photoinduced SCSC transformation and sensitive Al³⁺ detection.

Coordination change, lability and hemilability in metal–organic frameworks

Deformation or cleavage/reformation of metal–ligand bonds in MOFs lies at the heart of chemical/thermal stability and dynamic/flexible behaviour, provides avenues for post-synthetic modification, and can enable novel or improved performance for a variety of applications.

A nanoporous Ag(i) coordination polymer for selective adsorption of carcinogenic dye Acid Red 26

This work presents a unique Ag(i) nanoporous coordination polymer, showing selective and complete removal of carcinogenic dye Acid Red 26 from aqueous solution upon the size-exclusion and charge-matching effect.

UV-induced single-crystal-to-single-crystal conversion from a coordination ladder to a two-dimensional network through an intermolecular carbon–carbon coupling reaction

UV-induced single-crystal-to-single-crystal transformation from a coordination ladder to a two-dimensional network accompanied by photocontrolled fluorescence.

A five-fold interpenetrated metal–organic framework showing a large variation in thermal expansion behaviour owing to dramatic structural transformation upon dehydration–rehydration

A five-fold interpenetrated MOF has the highest uniaxial negative thermal expansion coefficient reported for any interpenetrated MOF to date. Upon dehydration, the framework shows considerable change in the magnitudes of the thermal expansion coefficients.

Highly efficient Cr2O72−removal of a 3D metal-organic framework fabricated by tandem single-crystal to single-crystal transformations from a 1D coordination array

Tandem single-crystal to single-crystal (SC–SC) transformation of a 1D neutral chain affords a 3D cationic framework, showing highly efficient Cr₂O₇²⁻captureviaSC–SC anion-exchange.

A porous two-dimensional Zn(ii)-coordination polymer exhibiting SC–SC transmetalation with Cu(ii): efficient heterogeneous catalysis for the Henry reaction and detection of nitro explosives

The 2D Zn(ii)-CP, 1Zn and its Cu-analogue 1Cu exhibit efficient catalytic activity for the Henry reaction. 1Zn can be utilized for detecting trace amounts of nitro explosives in DMSO.

Dual structure evolution of a Ag(i) supramolecular framework triggered by anion-exchange: replacement of terminal ligand and switching of network interpenetration degree

Dual single-crystal to single-crystal transformations triggered by different anion-exchanges are achieved for a Ag(i) coordination framework, where switching of network interpenetration degree is observed.

Isolation of a structural intermediate during switching of degree of interpenetration in a metal-organic framework

A known pillared layered metal-organic framework [Co2(ndc)2(bpy)] is shown to undergo a change in degree of interpenetration from a highly porous doubly-interpenetrated framework (2fa) to a less porous triply-interpenetrated framework (3fa). The transformation involves an intermediate empty doubly-interpenetrated phase (2fa') which has been isolated for the first time for this kind of phenomenon by altering the conditions of activation of the as-synthesized material. Interestingly, all the transformations occur in single-crystal to single-crystal fashion. Changes in degree of interpenetration have not been explored much to date and their implications with regard to the porosity of MOFs still remain largely unknown. The present study not only provides a better understanding of such dramatic structural changes in MOF materials, but also describes an original way of controlling interpenetration by carefully optimizing the temperature of activation. In addition to studying the structural mechanism of conversion from 2fa to 3fa, sorption analysis has been carried out on both the intermediate (2fa') and the triply-interpenetrated (3fa) forms to further explain the effect that switching of interpenetration mode has on the porosity of the MOF material.

Double-step CO2 sorption and guest-induced single-crystal-to-single-crystal transformation in a flexible porous framework

A new 2D highly flexible and breathing porous framework [CuL(Me2NH)]·DMF·H2O () (H3L = 5-(4'-carboxylphenoxy)nicotinic acid) has been synthesized using a tritopic linker with a flexible joint. The desolvated framework, [CuL(Me2NH)] (), undergoes structural contraction, and exhibits selective and double-step hysteretic adsorption for CO2. Furthermore, on exposure to CH2Cl2 at room temperature, a unique single-crystal-to-single-crystal transformation occurred between and [Cu2L2(Me2NH)2(H2O)2]·5H2O ().

Cation-Exchange Porosity Tuning in a Dynamic 4d-4f-3d Framework for Ni(II) Ion-Selective Luminescent Probe

A heterometallic complex {[Yb2(L)6Cd2][Cd(H2O)6]·6H2O}n (Yb-Cd) (H2L = oxidiacetic acid) was synthesized under hydrothermal conditions. In Yb-Cd, each L chelates to one Yb(3+) center and bonds to two Cd(2+) ions in an anti-anti configuration. Yb and Cd atoms are arrayed alternatively and connected by O-C-O bridges to form a cubic octahedral cage as the secondary building unit. Consequently, topological NaCl nets with high symmetry in the cubic space group Fd-3c have been constructed. The [Cd(H2O)6](2+) moieties lying in the porosity of anionic metal-organic framework (MOF) act as the thermodynamically stable species, required to balance the two negative charges of [Yb2(L)6Cd2](2-) in Yb-Cd. Interestingly, when Yb-Cd was employed as a precursor and emerged in the aqueous solution of Mn(ClO4)2·6H2O or Zn(ClO4)2·6H2O, a reversible single-crystal-to-single-crystal transformation process driven by [Cd(H2O)6](2+) cations has been exhibited to generate the heterotrimetallic coordination polymer {[Yb2(L)6Cd2][Mn(H2O)6]·6H2O}n (Yb-Cd-Mn) or {[Yb2(L)6Cd2][Zn(H2O)6]·6H2O}n (Yb-Cd-Zn). To the best of out knowledge, Yb-Cd-Mn and Yb-Cd-Zn are the first examples representing 4d-4f-3d polymers based on multicarboxylic acid. Luminescent studies reveal that Yb-Cd-Zn may serve as a good candidate of Ni(2+) a luminescent probe. To our knowledge, Yb-Cd-Zn represent the fist example of the 4d-4f-3d framework to exhibit luminescent selectivity for Ni(2+).

A Temperature-Responsive Smart Europium Metal-Organic Framework Switch for Reversible Capture and Release of Intrinsic Eu3+ Ions

Stimuli-responsive structural transformations are emerging as a scaffold to develop a charming class of smart materials. A EuL metal-organic framework (MOF) undergoes a reversible temperature-stimulated single-crystal to single-crystal transformation, showing a specific behavior of fast capture/release of free Eu3+ in the channels at low and room temperatures. At room temperature, compound 1a is obtained with one free carboxylate group severing as further hook, featuring one-dimensional square channels filled with intrinsic free europium ions. Trigged by lowering the ambient temperature, 1b is gained. In 1b, the intrinsic free europium ions can be fast captured by the carboxylate-hooks anchored in the framework, resulting in the structural change and its channel distortion. To the best of our knowledge, this is the first report of such a rapid and reversible switch stemming from dynamic control between noncovalent and covalent Eu-ligand interactions. Utilizing EuL MOF to detect highly explosive 2,4,6-trinitrophenol at room temperature and low temperature provides a glimpse into the potential of this material in fluorescence sensors.

Solvent-induced single-crystal to single-crystal transformation of a Zn4O-containing doubly interpenetrated metal–organic framework with a pcu net

A present metal–organic framework with an interpenetrating pcu net showed the structural change in single-crystal to single-crystal manner upon guest-exchange.

Can the thermal expansion be controlled by varying the hydrogen bond dimensionality in polymorphs?

A higher dimensional (1-D) hydrogen bonded form shows smaller thermal expansion than a lower dimensional (0-D) hydrogen bonded form of 2-butynoic acid.

Dynamic structural transformations of coordination supramolecular systems upon exogenous stimulation

This feature article comments on the dynamic structural transformations of coordination supramolecular systems, which can be triggered by exposure to various exogenous stimuli such as concentration, temperature, light and mechanical force, as well as their synergic effect.

Controlling the flexibility and single-crystal to single-crystal interpenetration reconstitution of metal–organic frameworks

By controlling the guest accessibility to open metal sites, MOFs can select interpenetration reconstitution or not.

Novel mode of 2-fold interpenetration observed in a primitive cubic network of formula [Ni(1,2-bis(4-pyridyl)acetylene)2(Cr2O7)]n

A novel mode of inclined interpenetration in a primitive cubic network affords 1D ultramicropores that provide insight into gas sorption of CO₂.

Solvent induced single-crystal to single-crystal structural transformation and concomitant transmetalation in a 3D cationic Zn(ii)-framework

Guest solvent triggered reversible structural transformation and concomitant Zn(ii) to Cu(ii) transmetalation has been realized through single-crystal to single-crystal fashion in an imidazolium functionalized 3D cationic Zn(ii)-framework.

p-Benzoquinone adsorption–separation, sensing and its photoinduced transformation within a robust Cd(ii)-MOF in a SC–SC fashion

p-Benzoquinone (Q) adsorption–separation, sensing and its photoinduced transformation within a robust Cd(ii)-MOF (1) is reported.

Synthesis of an exceptional water-stable two-fold interpenetrated Zn(ii)-paddlewheel metal–organic framework

An exceptional water-stable two-fold interpenetrated Zn(ii)-paddlewheel metal–organic framework was obtained via the facile conversion of its non-interpenetrated isomer at ambient temperature, showing high CO₂ and CH₄ uptake capacities.

Hetero-nuclear coordinated compounds for use in high-performance supercapacitor electrode material design

Ni–Co complexes are prepared using cobalt coordination complex as precursors by nickel exchange method. Single-crystal to single-crystal transformation had been achieved. Using Ni–Co complex as the precursors, we have synthesized a series of 3D hierarchical Ni_xCo_3−xS₄ microflowers electrode materials for supercapacitors.