Prismatic Cage Research Articles

Synthesis and Characterization of an Isoreticular Family of Calixarene-Capped Porous Coordination Cages.

Functionalization of permanently porous coordination cages has been used to tune phase, surface area, stability, and solubility in this promising class of adsorbents. For many cages, however, these properties are intricately tied together, and installation of functional groups, for example, to increase solubility often leads to a decrease in surface area. Calixarene-capped cages offer the advantage in that they are cluster-terminated cages whose solid-state packing, and thus surface area, is typically governed by the nature of the capping ligand rather than the bridging ligand. In this work we investigate the influence of ligand functionalization on two series of isoreticular Ni(II)- and Co(II)-based calixarene-capped cages. The two types of materials described are represented as octahedral and rectangular prismatic coordination cages and can be synthesized in a modular manner, allowing for the substitution of dicarboxylate bridging ligands and the introduction of functional groups in specific locations on the cage. We ultimately show that highly soluble cages can be obtained while still having access to high surface areas for many of the isolated phases.

Self-assembled metallasupramolecular cages towards light harvesting systems for oxidative cyclization.

Designing artificial light harvesting systems with the ability to utilize the output energy for fruitful application in aqueous medium is an intriguing topic for the development of clean and sustainable energy. We report here facile synthesis of three prismatic molecular cages as imminent supramolecular optoelectronic materials via two-component coordination-driven self-assembly of a new tetra-imidazole donor (L) in combination with 180°/120° di-platinum(ii) acceptors. Self-assembly of 180° trans-Pt(ii) acceptors A1 and A2 with L leads to the formation of cages Pt4L2(1a) and Pt8L2(2a) respectively, while 120°-Pt(ii) acceptor A3 with L gives the Pt8L2(3a) metallacage. PF6− analogues (1b, 2b and 3b) of the metallacages possess a high molar extinction coefficient and large Stokes shift. 1b–3b are weakly emissive in dilute solution but showed aggregation induced emission (AIE) in a water/MeCN mixture as well as in the solid state. AIE active 2b and 3b in aqueous (90% water/MeCN mixture) medium act as donors for fabricating artificial light harvesting systems via Förster resonance energy transfer (FRET) with organic dye rhodamine-B (RhB) with high energy efficiency and good antenna effect. The metallacages 2b and 3b represent an interesting platform to fabricate new generation supramolecular aqueous light harvesting systems with high antenna effect. Finally, the harvested energy of the LHSs (2b + RhB) and (3b + RhB) was utilized successfully for efficient visible light induced photo-oxidative cross coupling cyclization of N,N-dimethylaniline (4) with a series of N-alkyl/aryl maleimides (5) in aqueous acetonitrile with dramatic enhancement in yields compared to the reactions with RhB or cages alone.

Self-assembly of a Mixed Valence Copper Triangular Prism and Transformation to Cage Triggered by an External Stimulus.

A triangular prismatic metal-organic cage based on mixed valence copper ions has been designed and synthesized by using metallocycle panels and pillar ligands. The triangular prism will be quickly transformed to a 10-nuclear cage upon an external chemical stimulus, which features a bicapped square antiprism structure. This prismatic cage can act as a catalyst for oxidation of aromatic alcohols to their corresponding aromatic aldehydes with high yields at room temperature under O2 atmosphere.

Catenated Cages Mediated by Enthalpic Reaction Intermediates

Catenated cages are generally considered thermodynamically more stable than their constituent monomeric cages. However, the catenation mechanism is yet to be elucidated; it would require systematic...

Preparation of cage-shaped hexakis(spiroborate)s.

In previous research studies, various types of prismatic cage-shaped molecular containers have been prepared and evaluated in terms of their guest inclusion properties. Basically, most of these molecular cages have a cationic or electron-deficient nature, and exhibit strong affinity mainly toward electron-rich aromatic guests. On the other hand, there is no report concerning anionic prismatic cages that are expected to recognize cationic polyaromatic guests with various structures and functions. In this manuscript, we present the preparation of hexakis(spiroborate)-type molecular cages, which was achieved by the reaction of phenylene- or biphenylenebis(dihydroxynaphthalene), hexahydroxytriphenylene, and boric acid in N,N-dimethylformamide. Their triangular prismatic hollow structures were confirmed by X-ray crystallographic analysis, and it was found that both phenylene- and biphenylene-bridged spiroborate cages have internal cavities of the corresponding size. It was also revealed that tetra(n-butylammonium) cations located inside the cavity and between the two adjacent spiroborate cages resulted in the formation of a one-dimensional columnar array. The molecular recognition behavior of the spiroborate cages was evaluated using tris(pyridinium)triazines as tricationic aromatic guests. 1H NMR measurement implied that a discrete 1 : 1 host-guest complex was formed when 1 equiv. of guest was added to the cage, whereas infinite one-dimensional aromatic stacks were constructed by the addition of 2 equiv. of guest.

Theoretical study on prismatic (N6)n (n=16–35) molecules

As a continuation of our study on the stability of pure nitrogen molecules, twenty members of the (N6)n (n = 16–35) molecular sequence with D3h or D3d symmetry alternatively are studied in this work. The structures and energies are examined at the B3LYP/cc‒pvDZ computational level. “Natural Bond Orbital (NBO)” and “Atom In Molecule (AIM)” analyses are performed to investigate the bonding properties and the electronic topologies of the prismatic molecules. The van der Waals forces or the dispersion interactions are identified to be the dominant stabilizing factor for large prismatic nitrogen cages. The van der Waals forces interweave with covalent bonds to form a dense network which tightly bind nitrogen atoms at grid points, and consequently, to make the prismatic (N6)n molecules stable. The mechanism of generating van der Waals forces in the prismatic molecules is the focus of this paper. Geometrically, all the polygons on the prismatic surface are boat hexagons except the two caps. The van der Waals forces or dispersion interactions occur only between the nitrogen atoms at positions 1′,4′ of the boat hexagon on the surface. The atom‒atom proximity effect of nitrogen atoms at the positions 1′,4′ leads to the van der Waals interaction. Topologically, van der Waals forces are generated by partial overlap of sp3 hybrid orbitals of lone pairs of nitrogen atoms at positions 1′,4’. These large prism‒shaped nitrogen cages may also be novel beeline nanotubes which is environmentally friendly. This work is expected to open up a bright prospect of the study and applications of nitrogen nanofibers.

Anion Pairs Template a Trigonal Prism with Disilver Vertices.

Here we describe the formation of a trigonal prismatic cage, utilizing 2-formyl-1,8-naphthyridine subcomponents to bind pairs of silver(I) ions in close proximity. This cage is the first example of a new class of subcomponent self-assembled polyhedral structures having bimetallic vertices, as opposed to the single metal centers that typically serve as structural elements within such cages. Our new cage self-assembles around a pair of anionic templates, which are shown by crystallographic and solution-phase data to bind within the central cavity of the structure. Many different anions serve as competent templates and guests. Elongated dianions, such as the strong oxidizing agent peroxysulfate, also serve to template and bind within the cavity of the prism. The principle of using subcomponents that have more than one spatially close, but nonchelating, binding site may thus allow access to other higher-order structures with multimetallic vertices.

Coordination‐driven self‐assembly of Cp*Rh‐Based Rectangles, Cages and Their Host−Guest Binding Study

Supramolecular coordination‐driven self‐assembly rectangle 1a have be formation of distorted shapes, with a strong π···π interactions between the L1 and anthracene in 1b (1a ⊃ anthracene) that changed the size to desired and supported by single‐crystal Xray diffraction data. The formation of 1c(1a ⊃ DMF) has been further corroborated by the single‐crystal and 1b also can reaction with decaborane to form ortho‐carborane complex 1d. A self‐assembled triangular prism cage 2a consisting of binuclear half‐sandwich metal precursors [Cp*2Rh2(μ‐BiBzIm)]Cl2 (BiBzIm = 2,2′‐bisbenzimidazole) ligands and L2 were found to capsulated a triphenylene in cage. Another two kinds of prismatic cages (3a and 3b) were obtained from the reactions of the bis‐chelating‐coordinated [Cp*2Rh2(μ‐CA)]Cl2(CA = chloranilate) with L2 and L3 in the presence of AgOTf (OTf = CF3SO3) in CH3OH, and cage 3b have a perfect sized cavity to self‐assembled with anthracene in it.

Trigonal Prismatic Cu6L3 Coordination Cage: Encapsulation of Aromatic Molecules and Tuned Photoluminescence

AbstractA trigonal prismatic Cu6L3 coordination cage has been assembled from Cu(I) and semi‐rigid bipyrazolyl ligand. The X‐ray crystallography demonstrates that the cage has a cavity and can encapsulate the toluene as a guest, exhibiting thermochromism phenomenon. Empty cage can be obtained by expulsion of the guest through single crystal to single crystal transformation. After removed the guest, the empty cage shows a blue‐shifted emission (580 nm), in comparison to its parent cage (615 nm). The empty cage could further serve as a host to encapsulate other aromatic molecules (e. g. mesitylene), which shows new emission band. The trigonal prismatic Cu6L3 coordination cage provides a platform to make advanced luminescent materials.

Tris-triazolium Salts as Anion Receptors and as Precursors for the Preparation of Cylinder-like Coordination Cages

The synthesis and characterization of a “click chemistry” derived tripodal tris-1,2,3-triazolium bearing different counterions are described. The trifluoromethanesulfonate trisazolium salt is used as a receptor for halides and oxoanions, reflecting the formation of 1:1 complexes with binding affinities ranging between 200 and 1200 M–1 in CD3CN. The same tris-1,2,3-triazolium cation was used as precursor of a 1,2,3-triazolylidene ligand for the preparation of trinuclear prismatic cages of Ag and Au, via metal-controlled self-assembly.

Multicomponent Porphyrin-Based Tetragonal Prismatic Metallacages and their Photophysical Properties.

Multicomponent coordination-driven self-assembly has proved to be a convenient approach to prepare advanced supramolecular coordination complexes (SCCs), especially for those with three-dimensional structures. Herein, we report the preparation of three tetragonal prismatic cages via the self-assembly of Pt(PEt3)2(OTf)2, three different linear dipyridyl ligands and porphyrin-based sodium benzoate ligands. Due to the efficient charge separation in the coordination process of Pt(PEt3)2(OTf)2 with pyridine and carboxylic acid and the directionality of metal-coordination bonds, these cages were prepared in high isolated yields (more than 90%). The absorption and emission properties as well as the singlet oxygen quantum yields of these cages were also studied, showing their potential applications as contrast agents for bio-imaging and photosensitizers for photodynamic therapy.

Supramolecular Pt(II) and Ru(II) Trigonal Prismatic Cages Constructed with a Tris(pyridyl)borane Donor.

We report a novel example of supramolecular cages containing a Lewis acidic trigonal boron center. Self-assembly of the tris(pyridyl)borane donor 1 with diruthenium (2) or platinum (3), as an electron acceptor, furnished boron-containing trigonal prismatic supramolecular cages 5 and 6, which were characterized by 1H NMR and electrospray ionization time-of-flight mass spectroscopy and X-ray crystallography. The molecular structure of cage 5 was confirmed as a trigonal prismatic cage with an inner dimension of about 400 Å3. The fluoride binding properties of borane ligand 1 and Pt cage 6 were studied. UV/vis absorption titration studies demonstrated that the boron center of cage 6 undergoes strong binding interaction with the fluoride ion, with an estimated binding constant of 1.3 × 1010 M-2 in acetone based on the 1:2 binding isotherm. The binding was also confirmed by 1H NMR titration. Photoluminescence titration studies showed that cage 6 emitted borane-centered fluorescence (τ = 2.21 ns), which was gradually quenched upon addition of fluoride. When excess fluoride was added to a solution of 6, however, dissociation of the pyridyl ligand from the Pt(II) center was observed.

Coordination-driven self-assembly of discrete Ru6-Pt6 prismatic cages.

The coordination-driven self-assembly of two new Ru6–Pt6 hexanuclear trigonal prismatic cages comprising arene–ruthenium(II) clips (1a(NO3)2 and 1b(NO3)2) and a tritopic platinum(II) metalloligand 2 has been performed in methanol at room temperature. The [3 + 2] hexanuclear cages 3a and 3b were isolated in good yields and characterized by well-known spectroscopic techniques including multinuclear NMR, mass spectrometry, UV–vis and infrared studies. Geometry optimization revealed the shapes and sizes of these hexanuclear prismatic cages. The combination of ruthenium and platinum metal center in a one-pot self-assembly reaction showcases the construction of aesthetically elegant heterometallic structures in supramolecular chemistry leading to the formation of a single major product.

Fluorescent Metallacage-Core Supramolecular Polymer Gel Formed by Orthogonal Metal Coordination and Host-Guest Interactions.

Herein, we report the preparation of a multifunctional metallacage-core supramolecular gel by orthogonal metal coordination and host-guest interactions. A tetragonal prismatic cage with four appended 21-crown-7 (21C7) moieties in its pillar parts was first prepared via the metal-coordination-driven self-assembly of cis-Pt(PEt3)2(OTf)2, tetraphenylethene (TPE)-based sodium benzoate ligands and linear dipyridyl ligands. Further addition of a bisammonium linker to the cage delivered a supramolecular polymer network via the host-guest interactions between the 21C7 moieties and ammonium salts, which formed a supramolecular gel at relatively higher concentrations. Due to the incorporation of a TPE derivative as the fluorophore, the gel shows emission properties. Multiple stimuli responsiveness and good self-healing properties were also observed because of the dynamic metal coordination and host-guest interactions used to stabilize the whole network structure. Moreover, the storage and loss moduli of the gel are 10-fold those of the gel without the metallacage cores, indicating that the rigid metallacage plays a significant role in enhancing the stiffness of the gel. The studies described herein not only enrich the functionalization of fluorescent metallacages via elegant ligand design but also provide a way to prepare stimuli-responsive and self-healing supramolecular gels as robust and smart materials.

Cage Doubling: Solvent-Mediated Re-equilibration of a [3 + 6] Prismatic Organic Cage to a Large [6 + 12] Truncated Tetrahedron

We show that a [3 + 6] trigonal prismatic imine (a) cage can rearrange stoichiometrically and structurally to form a [6 + 12] cage (b) with a truncated tetrahedral shape. Molecular simulations rationalize why this rearrangement was only observed for the prismatic [3 + 6] cage TCC1 but not for the analogous [3 + 6] cages, TCC2 and TCC3. Solvent was found to be a dominant factor in driving this rearrangement.

Coordination-Driven Self-Assembly of Heterotrimetallic Barrel and Bimetallic Cages Using a Cobalt Sandwich-Based Tetratopic Donor.

Three-dimensional molecular architectures self-assembled with tripodal and tetratopic donors are valuable because of their encapsulation properties. Here, we present Co(I)-Fe(II)-Pd(II) heterotrimetallic trifacial barrel 1, which was self-assembled using a newly synthesized tetratopic donor [CpCo(CbR4)] [L; Cp = cyclopentadienyl, Cb = cyclobudiene, and R = 4-(4-pyridylphenyl)] and a 90° acceptor [ cis-(dppf)Pd(OTf)2] (A1; dppf = (diphenylphosphino)ferrocene and OTf = CF3SO3-). The heterotrimetallic barrel 1 exhibited selective 1:1 interaction with a N, N'-dimethyl-1,4,5,8-naphthalenetetracarboxylic diimide guest, as revealed by 1H NMR analysis. The self-assembly of donor L with two other Ru(II)-based 180° acceptors [( p-cymene)2Ru2(OO∩OO)(OTf)2] [OO∩OO = 6,11-dioxido-5,12-naphthacenedione (A2) and oxalate (A3)] resulted in tetragonal-prismatic cages. Self-assembly using the longer acceptor A2 provided rare isomers of a tetragonal-prismatic cage by varying the orientation of the cyclopentadienyl moiety out-out (2a) or out-in (2b) of the cavity, whereas self-assembly using the shorter acceptor A3 selectively resulted in the tetragonal-prismatic cage 3. The three-dimensional molecular architectures 1-3 were characterized by combined spectroscopic and elemental analyses. The structures of molecular barrel 1 and prismatic cage 3 were elucidated by single-crystal X-ray analysis.

Concentration dependent supramolecular interconversions of triptycene-based cubic, prismatic, and tetrahedral structures.

The quantitative, single step, self-assembly of a shape-persistent, three-dimensional C3v-symmetric, triptycene-based tris-terpyridinyl ligand initially gives a platonic-based cubic architecture, which was unequivocally characterized by 1D and 2D NMR spectroscopy, mass spectrometry, and single crystal X-ray structural analysis. The unique metal-ligand binding properties of the Cd2+ analogue of this construct give rise to a concentration-dependent dynamic equilibrium between cube, prism, and tetrahedron-shaped architectures. Dilution transforms this cube into two identical tetrahedra through a stable prism-shaped intermediate; increasing the concentration reverses the process.

Temperature-dependent self-assembly of a purely organic cage in water.

Using a novel dynamic covalent approach relying on reversible hydrazone formation, a purely organic 3-dimensional prismatic cage was developed in water at elevated temperatures. By lowering the temperature, the hydrazone bond becomes kinetically inert. This self-assembled cage acts as an effective receptor for donor-acceptor pairs, whose interactions are weak in the absence of the cage.

Family of penta- and hexanuclear metallasilsesquioxanes: Synthesis, structure and catalytic properties in oxidations

The deliberate synthesis of two types of prismatic cage-like metallasilsesquioxanes (hereinafter, referred to as CLMSs), viz., penta- and hexanuclear ones, is reported. It is shown that the size of the prismatic cage can be readily and reliably controlled by synthesis parameters. More specifically, the nuclearity shift from six, which is most common in CLMS chemistry (complexes 1–6, 8), to five, which is observed significantly more rarely, is achieved by applying pyridine as a key solvent/crystallization medium (complexes 7, 9–12). Structures of 1–12 were established by single-crystal X-ray diffraction. In sum, their composition could be described as [PhSiO1.5]12[CuO]6 (for hexanuclear products) or [RSiO1.5]10[MO]5 (R = Ph, Vin, M = Cu, Ni, Co for pentanuclear products). Compounds 7, 9–10 represent the rare examples of cage silsesquioxanes comprising pentagonal metalla-oxa rings of Cu(II) ions. The complex 10 is the very first observation of a co-crystal composed of different CLMS (i.e., two Co(II)5 and one Cu(II)5 prismatic cages). The compound 12 (Co5 cage with vinyl substituents at the silicon atoms) is the very first example of a pentanuclear CLMS-based coordination polymer. Complex 7 efficiently catalyzes oxidation of secondary alcohols to the corresponding ketones and alkanes to the corresponding alkyl hydroperoxides.

Cage-opening supramolecular isomerism in Cu(II) complexes

Reactions of Cu(NO3)2·3H2O or Cu(CF3SO3)2·6H2O with semirigid ligands 2,6-bis(pyridin-3-ylmethyl)-3a,4,4a,7a,8,8a-hexahydro-4,8-ethenopyrrolo[3,4-f]isoindole-1,3,5,7(2H,6H)-tetraone (L1) and 2,6-bis(pyridin-4-ylmethyl)-3a,4,4a,7a,8,8a-hexahydro-4,8-ethenopyrrolo[3,4-f]isoindole-1,3,5,7(2H,6H)-tetraone (L2) result in 0D tetragonal prismatic cage (1, 4), 1D loop-and-chain (2, 5, 6), and 2D (4,4) network (3) metal-organic complexes, which comprise of Ua, Ub or Z type ligand conformations, respectively. Solid state X-ray diffraction and solution state ESI-MS analyses manifest the ring-opening isomerization mechanism among the complexes, and photoluminescence properties are also studied.