Trigonal Prismatic Cage Research Articles

Computationally guided synthesis of a hierarchical [4[2+3]+6] porous organic ‘cage of cages’

Here we report a two-step, hierarchical synthesis that assembles a trigonal prismatic organic cage into a more symmetric, higher-order tetrahedral cage, or ‘cage of cages’. Both the preformed [2+3] trigonal prismatic cage building blocks and the resultant tetrahedral [4[2+3]+6]cage molecule are constructed using ether bridges. This strategy affords the [4[2+3]+6]cage molecule excellent hydrolytic stability that is not a feature of more common dynamic cage linkers, such as imines. Despite its relatively high molar mass (3,001 g mol−1), [4[2+3]+6]cage exhibits good solubility and crystallizes into a porous superstructure with a surface area of 1,056 m2 g−1. By contrast, the [2+3] building block is not porous. The [4[2+3]+6]cage molecule shows high CO2 and SF6 uptakes due to its polar skeleton. The preference for the [4[2+3]+6]cage molecule over other cage products can be predicted by computational modelling, as can its porous crystal packing, suggesting a broader design strategy for the hierarchical assembly of organic cages with synthetically engineered functions.

A redox-active organic cage as a cathode material with improved electrochemical performance.

Organic cages offer numerous opportunities for creating novel materials suitable for a wide range of applications. Among these, energy-related applications are beginning to attract attention. We report here the synthesis of a [3 + 6] trigonal prismatic cage constituted by three redox-active dibenzotetraazahexacene subunits. Cathodes formulated with the organic cage show enhanced performance compared to those formulated with the individual subunits, showing improvements in terms of electrochemical stability, lithium-ion diffusivity, and cathode capacity.

Hetero-Diels-Alder Reaction between Singlet Oxygen and Anthracene Drives Integrative Cage Self-Sorting.

A ZnII8L6 pseudocube containing anthracene-centered ligands, a ZnII4L'4 tetrahedron with a similar side length as the cube, and a trigonal prism ZnII6L3L'2 were formed in equilibrium from a common set of subcomponents. Hetero-Diels-Alder reaction with photogenerated singlet oxygen transformed the anthracene-containing "L" ligands into endoperoxide "LO" ones and ultimately drove the integrative self-sorting to form the trigonal prismatic cage ZnII6LO3L'2 exclusively. This ZnII6LO3L'2 structure lost dioxygen in a retro-Diels-Alder reaction after heating, which resulted in reversion to the initial ZnII8L6 + ZnII4L'4 ⇌ 2 × ZnII6L3L'2 equilibrating system. Whereas the ZnII8L6 pseudocube had a cavity too small for guest encapsulation, the ZnII6L3L'2 and ZnII6LO3L'2 trigonal prisms possessed peanut-shaped internal cavities with two isolated compartments divided by bulky anthracene panels. Guest binding was also observed to drive the equilibrating system toward exclusive formation of the ZnII6L3L'2 structure, even in the absence of reaction with singlet oxygen.

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.

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.

Ultrafine Pt Nanoclusters Confined in a Calixarene-Based {Ni24} Coordination Cage for High-Efficient Hydrogen Evolution Reaction.

To obtain stable and ultrafine Pt nanoclusters, a trigonal prismatic coordination cage with the sulfur atoms on the edges was solvothermally synthesized to confine them. In the structure of {Ni24(TC4A-SO2)6(TDC)12 (H2O)6} (H4TC4A-SO2 = p-tert-butylsulfonylcalix[4]arene; H2TDC = 2,5-thiophenedicarboxylic acid), three Ni4-(TC4A-SO2) SBUs are bridged by three TDC ligands into a triangle and two such triangles are pillared by three pairs of TDC ligands to form a trigonal prism. The cage cavity has 12 sulfur atoms on the surface. Because of the porous structure and strong covalent interaction between metal and sulfur, ultrafine Pt nanoclusters composed of less than ∼18 Pt atoms can be facilely confined in the present trigonal prismatic cage (Pt@CIAC-121). The as-synthesized Pt NCs exhibit higher electrocatalytic activity than commercial Pt/C toward hydrogen evolution reaction.

Template-free coordination-driven self-assembly of discrete hexanuclear prismatic cages employing half-sandwich octahedral RuII2 acceptors and triimidazole donors

Coordination-driven self-assembly of dinuclear half-sandwich p-cymene ruthenium(II) complexes [Ru2(μ-η4-C2O4)(CH3OH)2(η6-p-cymene)2](O3SCF3)2 (1a) and [Ru2(μ-η4-C6H2O4)(CH3OH)2(η6-p-cymene)2](O3SCF3)2 (1b) separately with imidazole-based tritopic donors (L1–L2) in methanol yielded a series of hexanuclear [3+2] trigonal prismatic cages (2–5), respectively [L1=1,3,5-tris(imidazole-1-yl)benzene; L2=4,4′,4″-tris(imidazole-1-yl)triphenylamine]. All the self-assembled cages 2–5 were characterized by various spectroscopic techniques (multinuclear NMR, Infra-red and ESI-MS) and their sizes, shapes were obtained through geometry optimization using molecular mechanics universal force field (MMUFF) computation. Despite the possibility due to the free rotation of donor sites of imidazole ligands, of two different atropoisomeric prismatic cages (C3h or Cs) and polymeric product, the self-selection of single (C3h) conformational isomeric cages as the only product is a noteworthy observation.

Self-assembly of discrete metallamacrocycles employing half-sandwich octahedral diruthenium(II) building units and imidazole-based ligands

Equimolar combination of a series of binuclear half-sandwich p-cymene ruthenium(II) building units [Ru2(μ-η4-C2O4)(MeOH)2(η6-p-cymene)2](OTf)2[1a](OTf)2, [Ru2(μ-η4-N,N′-diphenyloxamidato)(MeOH)2(η6-p-cymene)2](OTf)2[1b](OTf)2 and [Ru2(μ-η4-C6H2O4)(MeOH)2(η6-p-cymene)2](OTf)2[1c](OTf)2 separately with imidazole-based ditopic ligands (L1–L2) in methanol yielded a series of tetranuclear metallamacrocycles [2–7](OTf)4, respectively [L1 = 1,4-bis(imidazole-1-yl)benzene; L2 = 4,4′-bis(imidazole-1-yl)biphenyl; OTf− = O3SCF3−]. Similarly, the reaction of [Ru2(μ-η4-C2O4)(MeOH)2(η6-p-cymene)2](OTf)2[1a](OTf)2 with a triazine-based tritopic ligand 1,3,5-tris(imidazole-1-yl)triazine (L3) in 3:2 M ratio afforded an unexpected tetranuclear macrocycle [8](OTf)4 instead of an expected trigonal prismatic cage [8a](OTf)6. All the self-assembled macrocycles [2−8](OTf)4 were isolated in moderate to high yields and were fully characterized by multinuclear [1H, 19F] NMR, IR and electrospray ionization mass spectrometry (ESI-MS). In addition, X-ray diffraction study on the single crystals of [3](OTf)4 and [8](OTf)4 also indicated the formation [2 + 2] self-assembled macrocycles. Despite the possibility of formation of different conformational isomeric macrocycles (syn- and anti) and polymeric product due to free rotation of ligand sites of imidazole linkers, the selective formation of single conformational isomer (anti) as the only product is quite interesting. Furthermore, the photo- and electrochemical properties of these assemblies have been studied using UV/Vis absorption and cyclic voltammetry analysis.

Trigonal prismatic Cu(i) and Ag(i) pyrazolato nanocage hosts: encapsulation of S8 and hydrocarbon guests

Two neutral hexanuclear trigonal prismatic cage molecules have been synthesized by coupling two planar triangular M3pz3-panels, M = Cu(I) and Ag(I), in eclipsed geometry. The ~230 Å(3) cage volume can be either vacant or occupied by neutral guests. The crystal structures of the M6-cyclohexane and Ag6-S8 host-guest species have been determined.

Coordination-driven self-assembly of M3L2 trigonal cages from preorganized metalloligands incorporating octahedral metal centers and fluorescent detection of nitroaromatics.

The design and preparation of novel M(3)L(2) trigonal cages via the coordination-driven self-assembly of preorganized metalloligands containing octahedral aluminum(III), gallium(III), or ruthenium(II) centers is described. When tritopic or dinuclear linear metalloligands and appropriate complementary subunits are employed, M(3)L(2) trigonal-bipyramidal and trigonal-prismatic cages are self-assembled under mild conditions. These three-dimensional cages were characterized with multinuclear NMR spectroscopy ((1)H and (31)P) and high-resolution electrospray ionization mass spectrometry. The structure of one such trigonal-prismatic cage, self-assembled from an arene ruthenium metalloligand, was confirmed via single-crystal X-ray crystallography. The fluorescent nature of these prisms, due to the presence of their electron-rich ethynyl functionalities, prompted photophysical studies, which revealed that electron-deficient nitroaromatics are effective quenchers of the cages' emission. Excited-state charge transfer from the prisms to the nitroaromatic substrates can be used as the basis for the development of selective and discriminatory turn-off fluorescent sensors for nitroaromatics.

Dative boron–nitrogen bonds in structural supramolecular chemistry: multicomponent assembly of prismatic organic cages

The multicomponent reaction of diboronic acids with a catechol and a tripyridyl linker results in the formation trigonal prismatic cages. The cages feature six dative boron–nitrogen bonds as structure-directing elements. The size of the cages can be varied by changing the diboronic acid building block. The cages are able to encapsulate polyaromatic molecules such as triphenylene or coronene.

Structures and Dynamic Behavior of Large Polyhedral Coordination Cages: An Unusual Cage-to-Cage Interconversion

The bis-bidentate bridging ligand L {α,α'-bis[3-(2-pyridyl)pyrazol-1-yl]-1,4-dimethylbenzene}, which contains two chelating pyrazolyl-pyridine units connected to a 1,4-phenylene spacer via flexible methylene units, reacts with transition metal dications to form a range of polyhedral coordination cages based on a 2M:3 L ratio in which a metal ion occupies each vertex of a polyhedron, a bridging ligand lies along every edge, and all metal ions are octahedrally coordinated. Whereas the Ni(II) complex [Ni(8)L(12)](BF(4))(12)(SiF(6))(2) is an octanuclear cubic cage of a type we have seen before, the Cu(II), Zn(II), and Cd(II) complexes form new structural types. [Cu(6)L(9)](BF(4))(12) is an unusual example of a trigonal prismatic cage, and both Zn(II) and Cd(II) form unprecedented hexadecanuclear cages [M(16)L(24)]X(32)(X = ClO(4) or BF(4)) whose core is a skewed tetracapped truncated tetrahedron. Both Cu(6)L(9) and M(16)L(24) cages are based on a cyclic helical M(3)L(3) subunit that can be considered as a triangular "panel", with the cages being constructed by interconnection of these (homochiral) panels with additional bridging ligands in different ways. Whereas [Cu(6)L(9)](BF(4))(12) is stable in solution (by electrospray mass spectrometry, ES-MS) and is rapidly formed by combination of Cu(BF(4))(2) and L in the correct proportions in solution, the hexadecanuclear cage [Cd(16)L(24)](BF(4))(32) formed on crystallization slowly rearranges in solution over a period of several weeks to the trigonal prism [Cd(6)L(9)](BF(4))(12), which was unequivocally identified on the basis of its (1)H NMR spectrum. Similarly, combination of Cd(BF(4))(2) and L in a 2:3 ratio generates a mixture whose main component is the trigonal prism [Cd(6)L(9)](BF(4))(12). Thus the hexanuclear trigonal prism is the thermodynamic product arising from combination of Cd(II) and L in a 2:3 ratio in solution, and arises from both assembly of metal and ligand (minutes) and rearrangement of the Cd(16) cage (weeks); the large cage [Cd(16)L(24)](BF(4))(32) is present as a minor component of a mixture of species in solution but crystallizes preferentially.

Tellurasiloxane Cages Containing Te6Si4O12 and Te6Si6O15 Frameworks

Reaction of the silanetriol t-BuSi(OH)(3) with (p-Me(2)NC(6)H(4))(2)TeO in a 4:6 ratio resulted in the formation of [((p-Me(2)NC(6)H(4))(2)Te)(6)(t-BuSiO(3))(4)].1.5 C(7)H(8) (1.1.5C(7)H(8)). In contrast, the reaction of tetrahydroxy-1,3-disiloxane, [t-BuSi(OH)(2)](2)O with (p-MeOC(6)H(4))(2)TeO in a 3:6 ratio afforded [((p-MeOC(6)H(4))(2)Te)(6)(t-BuSi)(6)O(15)] . 2 C(7)H(8) (2.2C(7)H(8)). 1 possesses a tetrahedron cage structure in which the vertices of the tetrahedron are occupied by silicon atoms. Each pair of silicon atoms is connected to each other by a R(2)TeO(2) motif. The six O-Te-O bridges occupy the edges of the tetrahedron. In contrast to 1, the structure of 2 can be described as a trigonal prismatic cage. The latter consists of two Te(3)Si(3)O(6) rings that are interconnected to each other through three Si-O-Si linkages. The structure of 2 is reminiscent of a double-six-ring (D6R) secondary building unit (SBU) framework found in zeolites such as faujasite. Reaction of (p-Me(2)NC(6)H(4))(2)TeO or (p-MeOC(6)H(4))(2)TeO with the disiloxane-1,3-diol, [Ph(2)Si(OH)](2)O in a 2:2 ratio afforded [((p-Me(2)NC(6)H(4))(2)Te)(OPh(2)Si-O-SiPh(2)O)](2) (3) and [((p-MeOC(6)H(4))(2)Te)(OPh(2)Si-O-SiPh(2)O)](2).CH(3)CN (4.CH(3)CN). In contrast to 1 and 2, the compounds 3 and 4 contain puckered 12-membered Te(2)Si(4)O(6) rings.

Structures and magnetism of two novel heptanuclear lanthanide-centered trigonal prismatic clusters: [LnCu6(mu 3-OH)3(HL)2(L)4](ClO4)2.25H2O (Ln = La, Tb; H2L = iminodiacetic acid).

The new heteronuclear iminodiacetic acid (H2L) complexes [LnCu6(mu 3-OH)3(HL)2(L)4](ClO4)(2).25H2O with Ln = La (1) and Tb (2) have been prepared in aqueous solution and characterized by single-crystal X-ray diffraction to be isomorphous (crystallographic data for 1 and 2: hexagonal, P63/m; a = b = 12.6425(14) A, c = 24.541(5) A, Z = 2 (1); a = b = 12.5802(9) A, c = 24.285(4) A, Z = 2 (2)). Ln3+ was found to be located in the center of the trigonal prismatic cage formed by six Cu2+ ions, with a tricapped trigonal prismatic coordination environment of nine O atoms. The magnetic properties of complexes 1 and 2 have been studied. The results indicate the presence of ferromagnetic couplings between Tb3+ and Cu2+ in compound 2.