Gas-Conforming Transformability of an Ionic Single-Crystal Host Consisting of Discrete Charged Components

Controlled crystallisation of porous crystals of luminescent platinum(II) complexes by electronic tuning of ancillary ligands

Porous molecular crystals (PMCs) have gained significant importance as next-generation functional porous materials. However, the selective crystallisation of the PMC phase remains a challenge. Herein, we have systematically controlled the stability of the luminescent PMC phase prepared using the luminescent Pt(II) complex [Pt(pbim)(N^O)] (pbim = 2-phenylbenzimidazolate, N^O = N-heteroaryl carboxylate) with Pt⋯Pt electronic interactions. The PMC phase formation varied significantly among the complexes depending on the heteroaryl group of the ancillary N^O ligand; the oxazolyl-bearing complex did not form a PMC phase, whereas the pyrazyl- and 5-fluoropyridyl-bearing complexes spontaneously formed a porous structure. This difference was rationalised by the π-stacking capability of the heteroaryl group of the ancillary ligand. Furthermore, owing to the presence of the one-dimensional Pt⋯Pt chains in this PMC phase, the photophysical properties of PMCs resulting from the Pt⋯Pt interactions were also significantly changed by the ancillary ligands.

Benchmarks for transition metal spin-state energetics: why and how to employ experimental reference data?

Accurate prediction of energy differences between alternative spin states of transition metal complexes is essential in computational (bio)inorganic chemistry-for example, in characterization of spin crossover materials and in the theoretical modeling of open-shell reaction mechanisms-but it remains one of the most compelling problems for quantum chemistry methods. A part of this challenge is to obtain reliable reference data for benchmark studies, as even the highest-level applicable methods are known to give divergent results. This Perspective discusses two possible approaches to method benchmarking for spin-state energetics: using either theoretically computed or experiment-derived reference data. With the focus on the latter approach, an extensive general review is provided for the available experimental data of spin-state energetics and their interpretations in the context of benchmark studies, targeting the possibility of back-correcting the vibrational effects and the influence of solvents or crystalline environments. With a growing amount of experience, these effects can be now not only qualitatively understood, but also quantitatively modeled, providing the way to derive nearly chemically accurate estimates of the electronic spin-state gaps to be used as benchmarks and advancing our understanding of the phenomena related to spin states in condensed phases.

Thermally Tunable Adsorption of Xenon in Crystalline Molecular Sorbent

The thermostability of encapsulated xenon is investigated in a series of isostructural crystalline sorbents. These sorbents consist of metal-organic capsules, with the general formula of [ConFe4-nL6]4- (n = 1, 2, 3 and 4), where L2- is an organic linker with two sulfonate groups. In the crystalline sorbent, guanidinium cations form H-bond networks with the peripheral sulfonate groups in the solid state and trap xenon in the molecular cavities, which are at least 2.7 times the volume of xenon. When heated, the sorbent retains xenon up to 561 K, i.e., 396 K higher than the boiling point of xenon. Furthermore, the thermostability of trapped xenon can be modulated by varying the ratio of Co:Fe in the crystalline sorbent. Elemental analysis on a single crystal by energy dispersive X-ray spectroscopy confirms the homogeneous distribution of Co and Fe in the sorbent. Structural analyses reveal that the expansion of capsule cavity is proportional to the Co:Fe ratio, with increases of 0.049(1) Å and 6.4(8) Å3 in metal-metal distance and cavity volume, per substitution of Fe by Co center. Steric repulsion between peripheral sulfonate groups is found to render a hypothetical face-centered cubic structure of (C(NH2)3)4[Fe4L6] not accessible, which would have trapped xenon with exceptional thermostability. The stable and tunable trapping of xenon in crystalline sorbents by over-sized molecular cavities suggests a new strategy for separation and storage of xenon, through introduction of kinetic barriers, such as H-bond networks.

Modulation of the Sorption Characteristics for an H-bonded porous Architecture by Varying the Chemical Functionalization of the Channel Walls

Five isostructural microporous supramolecular architectures prepared by H-bonded assembly between the hexa-anionic complex [Zr₂ (Ox)₇ ]^6- (Ox=oxalate, (C₂ O₄ )^2- ) and tripodal cations (H₃ -TripCH₂ -R)³⁺ with R=H, CH₃ , OH and OBn (Bn=CH₂ Ph) are reported. The possibility to obtain the same structure using a mixture of tripodal cations with different R group (R=OH and R=CH₃ ) has also been successfully explored, providing a unique example of three-component H-bonded porous framework. The resulting SPA-1(R) materials feature 1D pores decorated by R groups, with apparent pore diameters ranging from 3.0 to 8.5 Å. Influence of R groups on the sorption properties of these materials is evidenced through CO₂ and H₂ O vapor sorption/desorption experiments, as well as with I₂ capture/release experiments in liquid media. This study is one of the first to demonstrate the possibility of tuning the porosity and exerting precise control over the chemical functionalization of the pores in a given H-bonded structure, without modifying the topology of the reference structure, and thus finely adjusting the sorption characteristics of the material.

Synthesis, Structural Characterization, and Water Vapor Sorption Behavior of Two Ligand Ratio-Dependent Supramolecular Networks, [Cd(2,2'-bpym)1.5(BDC)]·0.5(2,2'-bpym)·5H2O and [Cd(2,2'-bpym)0.5(BDC)(H2O)3]

Two ligand ratio-dependent supramolecular networks, [Cd(2,2'-bpym)_1.5(BDC)]·0.5(2,2'-bpym)·5H₂O (1) and [Cd(2,2'-bpym)_0.5(BDC)(H₂O)₃] (2), (BDC^2- = dianion of terephthalic acid and 2,2'-bpym = 2,2'-bipyrimidine) have been synthesized and structurally characterized by the single-crystal X-ray diffraction method. Structural determination reveals that compound 1 is a two-dimensional (2D) layered metal-organic framework (MOF) constructed via the bridges of Cd(II) ions with 2,2'-bpym and BDC^2- ligands, and compound 2 is a zero-dimensional (0D) 2,2'-bpym-bridged di-Cd(II) monomeric complex. When the thermally dehydrated powders of 1 (at 100 °C) were immersed into water solution, most of the dehydrated powders of 1 underwent structural transformation back to rehydrated 1, but very little amounts of the dehydrated powders of 1 were decomposed to light-brown crystals of 2 or colorless crystals of a new coordination polymer (CP), [Cd(2,2'-bpym)(BDC)(H₂O)]·3H₂O (3), with its one-dimensional (1D) zigzag chain-like framework being constructed via the bridges of Cd(II) ions with the BDC^2- ligand. Structural analysis reveals that all 3D supramolecular networks of 1-3 are further constructed via strong intermolecular interactions, including hydrogen bonds and π-π stacking interactions. Compounds 1 and 2 both exhibit significant water vapor hysteresis isotherms, and their cyclic water de-/adsorption behavior accompanied with solid-state structural transformation has been verified by de-/rehydration TG analyses and powder X-ray diffraction (PXRD) measurements.

Inclusion of cyclodextrins in a metallosupramolecular framework via structural transformations

The inclusion of α-cyclodextrin and both α- and γ-cyclodextrins in a multilayer framework composed of d-penicillaminato AuI3CoIII2 complex anions and aqua sodium(i) cations via solvent-mediated structural transformations are reported.

Synthesis and structure determination of racemic (Δ/Λ)-tris-(ethyl-enedi-amine)-cobalt(III) trichloride hemi(hexa-aqua-sodium chloride)

The synthesis and crystal structure of the title racemic compound, [Co(C2H8N2)3]Cl3.{[Na(H2O)6]Cl}0.5, are reported. The trivalent cobalt atom, which resides on a crystallographic threefold axis, is chelated by a single ethyl-ene di-amine (en) ligand and yields the tris-chelate [Co(en)3]3+ cation with distorted octa-hedral geometry after the application of crystal symmetry. The sodium cation (site symmetry ), has a single water mol-ecule bound to it in the asymmetric unit and yields a distorted, octa-hedrally coordinated hydrated [Na(H2O)6]+ cation after the application of symmetry. One of the chloride ions lies on a general position and the other has site symmetry. An extensive array of C-H⋯O, N-H⋯Cl and O-H⋯Cl hydrogen bonds exists between the ethyl-ene di-amine ligands, the water mol-ecules of hydration, and the anions present, thereby furnishing solid-state stability.

Highly Porous Ionic Solids Consisting of AuI3CoIII2 Complex Anions and Aqua Metal Cations

Treatment of Na₃[Au₃Co₂(d-pen)₆] (Na₃[1]; d-H₂pen = d-penicillamine) with M(OAc)₂ (M = Ni^II, Mn^II) in water gave ionic crystals of [M(H₂O)₆]₃[1]₂ (2^M) in which [1]^3- anions are hydrogen-bonded with [M(H₂O)₆]²⁺ cations to form a 3D porous framework with a porosity of ca. 80%. Soaking crystals of 2^Ni in its mother liquor afforded crystals of [Ni(H₂O)₆]₂[{Ni(H₂O)₄}(1)₂] (3^Ni) in which [1]^3- anions are connected to trans-[Ni(H₂O)₄]²⁺ and [Ni(H₂O)₆]²⁺ cations through coordination and hydrogen bonds, respectively, to form a 1D porous framework with a porosity ca. 60%. Further soaking crystals led to [{Ni(H₂O)₄}₃(1)₂] (4^Ni), in which [1]^3- anions are connected to cis-[Ni(H₂O)₄]²⁺ and trans-[Ni(H₂O)₄]²⁺ cations through coordination bonds in a dense framework with a porosity of ca. 30%. A similar two-step crystal-to-crystal transformation mediated by solvent proceeded when crystals of 2^Mn were soaked in a mother liquor. However, the transformation of 2^Mn generated [{Mn(H₂O)₄}(H1)] (4'^Mn) as the final product, in which [H1]^2- anions are connected to cis-[Mn(H₂O)₄]²⁺ cations through coordination bonds in a very dense framework with a porosity ca. 5% by way of [Mn(H₂O)₆]₂[{Mn(H₂O)₄}(1)₂] (3^Mn), which is isostructural with 3^Ni. While all the compounds adsorbed H₂O and CO₂ depending on the degree of their porosity, unusually large NH₃ adsorption capacities were observed for 4^Ni and 4'^Mn, which have dense frameworks.

Rendering classical hydrophilic enantiopure Werner salts [M(en)3]n+nX- lipophilic (M/n = Cr/3, Co/3, Rh/3, Ir/3, Pt/4); new chiral hydrogen bond donor catalysts and enantioselectivities as a function of metal and charge

Known hydrophilic halide salts of the title compounds are converted to new lipophilic BArf- (B(3,5-C6H3(CF3)2)4-) salts. These are isolated as hydrates (Λ- or Δ-[M(en)3]n+nBArf-·zH2O; z = 17-9) and characterized by NMR (acetone-d6) and microanalyses. Thermal stabilities are probed by capillary thermolyses and TGA and DSC measurements (onset of dehydration 71-151 °C). In the presence of tertiary amines, they are effective catalysts for enantioselective Michael type carbon-carbon or carbon-nitrogen bond forming additions of 1,3-dicarbonyl compounds (acceptors: trans-β-nitrostyrene, di-tert-butylazodicarboxylate, 2-cyclopenten-1-one; average ee = 33%, 52%, 17%). Effects of the metal and charge upon enantioselectivities are analyzed. A number of properties appear to correlate to the NH Brønsted acidity order ([Pt(en)3]4+ > [Cr(en)3]3+ > [Co(en)3]3+ > [Rh(en)3]3+ > [Ir(en)3]3+).

Liquid–liquid interface-promoted formation of a porous molecular crystal based on a luminescent platinum(ii) complex

A Pt(ii)-based luminescent porous molecular crystal was selectively crystallised at the liquid–liquid interface, allowing control of porosity and luminescence.

Reversible Encapsulation of Xenon and CH2 Cl2 in a Solid-State Molecular Organometallic Framework (Guest@SMOM)

Reversible encapsulation of CH2 Cl2 or Xe in a non-porous solid-state molecular organometallic framework of [Rh(Cy2 PCH2 PCy2 )(NBD)][BArF4 ] occurs in single-crystal to single-crystal transformations. These processes are probed by solid-state NMR spectroscopy, including 129 Xe SSNMR. Non-covalent interactions with the -CF3 groups, and hydrophobic channels formed, of [BArF4 ]- anions are shown to be important, and thus have similarity to the transport of substrates and products to and from the active site in metalloenzymes.

Sponge-Like Water De-/Ad-Sorption versus Solid-State Structural Transformation and Colour-Changing Behavior of an Entangled 3D Composite Supramolecuar Architecture, [Ni₄(dpe)₄(btc)₂(Hbtc)(H₂O)₉]·3H₂O

An entangled composite compound, [Ni₄(dpe)₄(btc)₂(Hbtc)(H₂O)₉]·3H₂O (1), where H₃btc = 1,3,5-benzenetricarboxylic acid and dpe = 1,2-bis(4-pyridyl)ethane, has been synthesized and structurally characterized. Single-crystal structural determination reveals that compound 1 consists of four coordination polymers (CPs), with two two-dimensional (2D) (4,4) layered metal-organic frameworks (MOFs) of [Ni(dpe)(Hbtc)(H₂O)] and [Ni(dpe)(btc)(H₂O)]^- anion, and two one-dimensional (1D) polymeric chains of [Ni(dpe)(btc)(H₂O)₃]^- anion and [Ni(dpe)(H₂O)₄]²⁺ cation, respectively. The three-dimensional (3D) supramolecular architecture of 1 is constructed via the inter-penetration of inter-digited, double-layered, 2D rectangle-grid MOFs by two 1D coordination polymeric chains, and tightly entangled together via the combination of inter-CPs π⁻π stacking and hydrogen bonding interactions. The ad-/de-sorption isotherms of 1 for water displays a hysteresis profile with a maximum adsorption of 17.66 water molecules of per molecule unit at relative P/P₀ < 0.89. The reversible de-/re-hydration processes in 1 monitored by cyclic water de-/ad-sorption TG analysis and PXRD measurements evidence a sponge-like water de-/ad-sorption property associated with a thermal-induced solid-state structural transformation. The magnetic property of 1 suggests that the ferromagnetic coupling might refer to a stronger inter-Ni(II) interaction, which could be along the btc^3- or Hbtc^2- ligands; the antiferromagnetic coupling corresponding to the weaker inter-Ni(II) interactions, which could be the dpe ligands for the 2D framework.

Structural characterization of framework-gas interactions in the metal-organic framework Co2(dobdc) by in situ single-crystal X-ray diffraction

The crystallographic characterization of framework-guest interactions in metal-organic frameworks allows the location of guest binding sites and provides meaningful information on the nature of these interactions, enabling the correlation of structure with adsorption behavior. Here, techniques developed for in situ single-crystal X-ray diffraction experiments on porous crystals have enabled the direct observation of CO, CH4, N2, O2, Ar, and P4 adsorption in Co2(dobdc) (dobdc4- = 2,5-dioxido-1,4-benzenedicarboxylate), a metal-organic framework bearing coordinatively unsaturated cobalt(ii) sites. All these molecules exhibit such weak interactions with the high-spin cobalt(ii) sites in the framework that no analogous molecular structures exist, demonstrating the utility of metal-organic frameworks as crystalline matrices for the isolation and structural determination of unstable species. Notably, the Co-CH4 and Co-Ar interactions observed in Co2(dobdc) represent, to the best of our knowledge, the first single-crystal structure determination of a metal-CH4 interaction and the first crystallographically characterized metal-Ar interaction. Analysis of low-pressure gas adsorption isotherms confirms that these gases exhibit mainly physisorptive interactions with the cobalt(ii) sites in Co2(dobdc), with differential enthalpies of adsorption as weak as -17(1) kJ mol-1 (for Ar). Moreover, the structures of Co2(dobdc)·3.8N2, Co2(dobdc)·5.9O2, and Co2(dobdc)·2.0Ar reveal the location of secondary (N2, O2, and Ar) and tertiary (O2) binding sites in Co2(dobdc), while high-pressure CO2, CO, CH4, N2, and Ar adsorption isotherms show that these binding sites become more relevant at elevated pressures.

Synergetic effect in heterogeneous acid catalysis by a porous ionic crystal based on Al(iii)–salphen and polyoxometalate

A porous ionic crystal with Al(salphen) and polyoxometalate shows high activity as a heterogeneous catalyst, while the components are much less active, suggesting a synergetic effect.

A functional mesoporous ionic crystal based on polyoxometalate

A mesoporous ionic crystal is synthesized with a polyoxometalate and a macrocation with polar cyano groups. The compound possesses one-dimensional mesopores and shows high proton conductivity and catalytic activity, which are due to the water molecules in the mesopores.

Construction of porous cationic frameworks by crosslinking polyhedral oligomeric silsesquioxane units with N-heterocyclic linkers

In fields of materials science and chemistry, ionic-type porous materials attract increasing attention due to significant ion-exchanging capacity for accessing diversified applications. Facing the fact that porous cationic materials with robust and stable frameworks are very rare, novel tactics that can create new type members are highly desired. Here we report the first family of polyhedral oligomeric silsesquioxane (POSS) based porous cationic frameworks (PCIF-n) with enriched poly(ionic liquid)-like cationic structures, tunable mesoporosities, high surface areas (up to 1,025 m(2) g(-1)) and large pore volumes (up to 0.90 cm(3) g(-1)). Our strategy is designing the new rigid POSS unit of octakis(chloromethyl)silsesquioxane and reacting it with the rigid N-heterocyclic cross-linkers (typically 4,4'-bipyridine) for preparing the desired porous cationic frameworks. The PCIF-n materials possess large surface area, hydrophobic and special anion-exchanging property, and thus are used as the supports for loading guest species PMo10V2O40(5-); the resultant hybrid behaves as an efficient heterogeneous catalyst for aerobic oxidation of benzene and H2O2-mediated oxidation of cyclohexane.

Anion-dependent host-guest properties of porous assemblies of coordination complexes (PACs), [Cu(A)₂(py)₄] (A = PF₆, BF₄, CF₃SO₃, and CH₃SO₃; py = pyridine), based on Werner-type copper(II) complexes in the solid state

We report the syntheses and crystal structures of novel porous assemblies of coordination complexes (PACs) with/without guest molecules, α-[Cu(A)₂(py)₄] (α-PAC-2-A (A = PF₆, BF₄, CF₃SO₃, and CH₃SO₃); py = pyridine), γ-{[Cu(PF₆)₂(py)₄]·2guest} (γ-PAC-2-PF₆ ⊃ 2guest (guest = acetone and py)), γ-{[Cu(BF₄)₂(py)₄]·2acetone} (γ-PAC-2-BF₄ ⊃ 2acetone), and β-{[Cu(CH₃SO₃)₂(py)₄]·2.67H₂O} (β-PAC-2-CH₃SO₃ ⊃ 2.67H₂O). The single-crystal X-ray diffraction analyses of α-PAC-2-A show that α-PAC-2-A have dense packing structures, in which anions of the discrete coordination complexes form weak hydrogen-bonding and anion-π interactions. In contrast, γ-PAC-2-PF₆ ⊃ 2guest, γ-PAC-2-BF₄ ⊃ 2acetone, and β-PAC-2-CH₃SO₃ ⊃ 2.67H₂O form guest-including structures with coordination environments around the Cu(II) atoms similar to the α-forms. The vapour adsorption measurements for MeCN and acetone in α-PAC-2-A suggest that the adsorption associated with structural transformations is induced by weak Lewis-base PF₆⁻ and BF₄⁻ anions covered only with fluorine atoms, which weaken the host-host interactions.

Tris(ethyl-enedi-amine)-cobalt(II) dichloride

The title compound, [Co(II)(C2H8N2)3]Cl2, was obtained unexpectedly as the product of an attempted solvothermal synthesis of cobalt selenide from the elements in the presence of NH4Cl in ethyl-enedi-amine solvent. The three chelate rings of the distorted octa-hedral [Co(C2H8N2)3](2+) complex cation adopt twisted conformations about their C-C bonds. The spread of cis-N-Co-N bond angles [80.17 (6)-98.10 (6)°] in the title compound is considerably greater than the equivalent data for [Co(III)(C2H8N2)3]Cl3 [Takamizawa et al. (2008 ▶). Angew. Chem. Int. Ed. 47, 1689-1692]. In the crystal, the components are linked by numerous N-H⋯Cl hydrogen bonds, generating a three-dimensional network in which the cationic complexes are stacked in columns along [010] and separated by columns of chloride anions.