Rational Synthesis and Investigation of Porous Metal–Organic Framework Materials from a Preorganized Heterometallic Carboxylate Building Block

Strategic design and synthesis of star-shaped organic linkers for mesoporous MOFs

In the process of designing new MOFs with the aim of having a specific morphology, the shape of the linkers and the choice of coordinating metals have major importance. In this study, the aim to create novel hnb non-interpenetrating MOFs led us to choose tritopic linkers. Novel star-shaped molecules, presenting trigonal geometry and based on aromatic rings, were synthesized. For more convenient synthesis of the library, C-C coupling reactions via a direct arylation methodology were performed. This new synthetic tool, together with the idea of a molecule as a modular combination of smaller building blocks, made possible the fast, cheap and reproducible production of this class of compounds and also its scale-up. With one of the compounds, a MOF was synthesized and characterised via its specific surface area, which varies between 1681 and 3770 m2 g-1.

Metal-Organic Frameworks for Highly Selective Separation of Xylene Isomers and Single-Crystal X-ray Study of Aromatic Guest-Host Inclusion Compounds

Separation of hydrocarbon molecules, such as benzene/cyclohexane and o-xylene/m-xylene/p-xylene, is relevant due to their widespread application as chemical feedstock but challenging because of their similar boiling points and close molecular sizes. Physisorption separation could offer an energy-efficient solution to this problem, but the design and synthesis of sorbents that exhibit high selectivity for one of the hydrocarbons remain a largely unmet challenge. Herein, we report a new heterometallic MOF with a unique tortuous shape of channels decorated with aromatic sorption sites [Li₂Zn₂(bpy)(ndc)₃] (NIIC-30(Ph), bpy = 4,4'-bipyridine, ndc^2- = naphthalene-1,4-dicarboxylate) and study of its benzene/cyclohexane and xylene vapor and liquid separation. For an equimolar benzene/cyclohexane mixture, it is possible to achieve a 10-fold excess of benzene in the adsorbed phase. In the case of xylenes, microporous framework NIIC-30(Ph) demonstrates outstanding selective sorption properties and becomes a new benchmark for m-/o-xylene separation. In addition, NIIC-30(Ph) is stable enough to carry out at least three separation cycles of benzene/cyclohexane mixtures or ternary o-xylene/m-xylene/p-xylene mixtures both in the liquid and in the vapor phase. Insights into the performance of NIIC-30(Ph) are gained from X-ray structural studies of each aromatic guest inclusion compound.

Influence of Substituents in Terephthalate Linker on the Structure of MOFs Obtained from Presynthesized Heterometallic Complex

The synthesis of new porous materials with desired properties is a challenging task. It becomes especially difficult if you need to combine several metals in one framework to obtain a heterometallic node. The use of presynthesized complexes for obtaining of new heterometallic metal–organic frameworks could be essential to solve the problem of tailored synthesis. In our study we use presynthesized heterometallic pivalate complex [Li2Zn2(piv)6(py)2] to obtain new MOFs with heterometallic core as a node of the framework. We are managed to obtain four new heterometallic MOFs: [H2N(CH3)2]2[Li2Zn2(bdc)4]·CH3CN·DMF (1), [Li2Zn2(H2Br2-bdc)(Br2-bdc)3]·2DMF (2), [H2N(CH3)2][LiZn2(ndc)3]·CH3CN (3) and [{Li2Zn2(dmf)(py)2}{LiZn(dmf)2}2 (NO2-bdc)6]·5DMF (4). Moreover three of them contain starting tetranuclear core {Li2Zn2} and saves its geometry. We also demonstrate the influence of substituent in terephthalate ring on preservation of tetranuclear core. For compound 1 it was shown that luminescence of the framework could be quenched when nitrobenzene is included in the pores.

Heterometallic MOFs constructed from thiophene and furandicarboxylate ligands for heavy metal luminescence sensing

A series of heterometallic porous MOFs were rationally designed from preorganized molecular complexes for heavy metal cation luminescence detection.

A Heterometallic Three-Dimensional Metal-Organic Framework Bearing an Unprecedented One-Dimensional Branched-Chain Secondary Building Unit

A heterometallic metal−organic framework (MOF) of [Cd₆Ca₄(BTB)₆(HCOO)₂(DEF)₂(H₂O)₁₂]∙DEF∙xSol (1, H₃BTB = benzene-1,3,5-tribenzoic acid; DEF = N,N′-diethylformamide; xSol. = undefined solvates within the pore) was prepared by solvothermal reaction of Cd(NO₃)₂·4H₂O, CaO and H₃BTB in a mixed solvent of DEF/H₂O/HNO₃. The compatibility of these two divalent cations from different blocks of the periodic table results in a solid-state structure consisting of an unusual combination of a discrete V-shaped heptanuclear cluster of [Cd₂Ca]₂Ca′ and an infinite one-dimensional (1D) chain of [Cd₂CaCa′]_n that are orthogonally linked via a corner-shared Ca²⁺ ion (denoted as Ca′), giving rise to an unprecedented branched-chain secondary building unit (SBU). These SBUs propagate via tridentate BTB to yield a three-dimensional (3D) structure featuring a corner-truncated P4₁ helix in MOF 1. This outcome highlights the unique topologies possible via the combination of carefully chosen s- and d-block metal ions with polydentate ligands.

Some aspects of the formation and structural features of low nuclearity heterometallic carboxylates

Heterometallic carboxylate complexes are of paramount interest in pure and applied coordination chemistry. Despite that plurality of such type compounds have been published to date, synthetic aspects of their chemistry often remain in the shadow of intriguing physical properties manifesting by these species. Present review summarizes reliable data on direct synthesis of low nuclearity molecular compounds as well as coordination polymers on their base with carboxylate-bridged {M2Mg} (M = Co2+, Ni2+, Cd2+), {M2Li2} (M = Co2+, Ni2+, Zn2+, VO2+), {M2Ln2} and {M2Ln} (M = Cu2+, Zn2+, Co2+) metal cores. Structural features and stabilization factors are considered and principal outcomes are confirmed by quantum-chemical calculations. Particular attention is paid to consideration of ligand-exchange reactions that allow controllable modification of heterometallic metal core under mild conditions giving diverse molecular complexes with modified ligand environment or Metal-Organic Frameworks with permanent porosity.

Exceptionally effective benzene/cyclohexane separation using a nitro-decorated metal-organic framework

Using a series of isoreticular MOFs with void connections of varying diameters, the selective separation of benzene and cyclohexane in both liquid and vapor phases is shown. The driving force of the highly efficient adsorption process is the formation of weak interactions between the adsorbed benzene molecules and the host framework.

Tuning the Molecular and Cationic Affinity in a Series of Multifunctional Metal-Organic Frameworks Based on Dodecanuclear Zn(II) Carboxylate Wheels

A series of new zinc(II)-thiophene-2,5-dicarboxylate (tdc) MOFs based on novel dodecanuclear wheel-shaped building blocks has been synthesized in almost quantative yields. Single-crystal X-ray diffraction analyses reveal 3D porous frameworks with a complex composition [Zn₁₂(tdc)₆(glycolate)₆(dabco)₃] where glycolate is a deprotonated polyatomic alcohol (ethylene glycol, EgO₂, 1; 1,2-propanediol, PrO₂, 2; 1,2-butanediol, BuO₂, 3; 1,2-pentanediol, PeO₂, 4; glycerol, GlO₂, 5) and dabco is 1,4-diazo[2.2.2.]bicyclooctane. All compounds 1-5 are isostructural except for pendant groups of the diols decorating the surface of channels. The adsorption of small gases (N₂, CO₂, CH₄, C₂H₂, C₂H₄, C₂H₆) and larger hydrocarbons (benzene, cyclohexane) both in liquid and vapor phases was thoroughly investigated for all compounds. The zero-coverage adsorption enthalpies, Henry constants, and selectivity factors by various models are calculated and discussed. The versatile adsorption functionality of the title series results from the variable nature of the diol and could be tailored for a specific adsorbate system. For example, 1 shows excellent selectivity of benzene over cyclohexane (20:1 for vapors, 92:1 for liquid phase), while 4 demonstrates unprecedented adsorption preference of cyclohexane over benzene (selectivity up to 5:1). The compound 5 demonstrates great adsorption selectivity for CO₂/N₂ (up to 75.1), CO₂/CH₄ (up to 7.7), C₂H₂/CH₄ (up to 14.2), and C₂H₄/CH₄ (up to 9.4). Also, due to polar nature of the pores, 5 features size-selective sorption of alkaline metal cations in order Li⁺ > Na⁺ > K⁺ > Cs⁺ as well as a notable luminescent response for cesium(I) ions and urea.

Rational synthesis and dimensionality tuning of MOFs from preorganized heterometallic molecular complexes

Rational synthesis of heterometallic MOFs was carried out by the judicious choice of pivalate complexes and a tricarboxylate linker defining their dimensionality.

Smoothing the single-crystal to single-crystal conversions of a two-dimensional metal–organic framework via the hetero-metal doping of the linear trimetallic secondary building unit

Doping of Co²⁺ in the linear Cd₃ cluster secondary building units lowers the single-crystal to single-crystal conversion reactivity of the resulting metal–organic framework.

Incorporation of an intact dimeric Zr12 oxo cluster from a molecular precursor in a new zirconium metal–organic framework

A dimeric Zr₁₂ oxo cluster was used as new molecular building block in construction of metal–organic frameworks utilizing the precursor approach.