Ferrocene as a Hydrophobic Templating Agent with Pyrogallol[4]arenes

Solution structure of zinc-seamed C-alkylpyrogallol[4]arene dimeric nanocapsules

The structural stability and solution geometry of zinc-seamed-C-propylpyrogallol[4]arene dimers has been studied in solution using in situ neutron scattering and 2D-DOSY NMR methods. In comparison with the structures of the analogous copper-/nickel-seamed dimeric entities, the spherical geometry of the PgC₃Zn species (R = 9.4 Å; diffusion coefficient = 1.05 × 10^-10 m² s^-1) is larger due to the presence of ligands at the periphery in solution. This enhanced radius in solution due to ligation is also consistent with the findings of model molecular dynamics simulations of the zinc-seamed dimers.

The borderline: exploring the structural landscape of triptycene in cocrystallization with ferrocene

When the effective packing of triptycene (TripH)–ferrocene chain oligomers in their cocrystal could not be achieved, we reached a borderline at the structural landscape of TripH, where the packing of TripH molecules reproduces the pattern in the native TripH crystal.

Encapsulation of ferrocenes by hydrogen-bonded pyrogallol[4]arene dimers

The treatment ofC-iso-butylpyrogallarene (PgC4) orC-ethylpyrogallarene (PgC2) with ferrocene (FcH) in a 2:1 molar ratio under different reaction conditions afforded the host–guest compounds FcH@(PgC4)2·CH3OH·3H2O (1) and FcH@(PgC2)2·3EtOH·2H2O (2), respectively. Complexes1and2are both pyrogallarene dimers providing capsule-type voids. Single crystal X-ray crystallography was used to investigate the role of hydrogen bonding networks in the assembly of the two host–guest systems.

Anionic Hosts for the Incorporation of Cationic Guests

Pentaphosphaferrocene [Cp*Fe(η5 -P5 )] (1 a) represents an excellent building block for the template-directed synthesis of spherical supramolecules. Here, the self-assembly of 1 a with CuI and CuII halides in the presence of the template complexes [FeCp2 ][PF6 ], [CoCp2 ][PF6 ] and [CoCp2 ] is reported, testifying to the redox behavior of the formed supramolecules. The oxidation or reduction capacity of these reactive complexes does not inhibit their template impact and, for the first time, the cationic metallocene [CoCp2 ]+ is enclosed in unprecedented anionic organometallic hosts. Furthermore, the large variety of structural motifs, as icosahedral, trigonal antiprismatic, cuboidal and tetragonal antiprismatic arrangements of 1 a units are realized in the supramolecules [FeCp2 ]@[{1 a}12 (CuBr)17.3 ] (3), [CoCp2 ]+3 {[CoCp2 ]+ @[{1 a}8 Cu24.25 Br28.25 (CH3 CN)6 ]4- } (4), {[Cp2 Co]+ @[{1 a}8 (CuI)28 (CH3 CN)9.8 ]}{[Cp2 Co]+ @[{1 a)}8 Cu24.4 I26.4 (CH3 CN)8 ]2- } (5), and [{1 a}3 {(1 a)2 NH}3 Cu16 I10 (CH3 CN)7 ] (6), respectively.

Application of ferrocene-resorcinarene in silver nanoparticle synthesis

An amphiphilic resorcinarene with ferrocene groups at the lower rim has been applied as both reductant and stabilizer in the synthesis of colloidal silver nanoparticles.

Establishing trends based on solvent system changes in cocrystals containing pyrogallol[4]arenes and fluorescent probes rhodamine B and pyronin Y

Eight cocrystal structures containing a pyrogallol[4]arene of varying aliphatic tail lengths and either fluorescent probes rhodamine B or pyronin Y in a range of solvent systems are examined. Trends based on probe, solvent, and aliphatic tail length are investigated.

Solution structures of nanoassemblies based on pyrogallol[4]arenes

Nanoassemblies of hydrogen-bonded and metal-seamed pyrogallol[4]arenes have been shown to possess novel solution-phase geometries. Further, we have demonstrated that both guest encapsulation and structural rearrangements may be studied by solution-phase techniques such as small-angle neutron scattering (SANS) and diffusion NMR. Application of these techniques to pyrogallol[4]arene-based nanoassemblies has allowed (1) differentiation among spherical, ellipsoidal, toroidal, and tubular structures in solution, (2) determination of factors that control the preferred geometrical shape and size of the nanoassemblies, and (3) detection of small variations in metric dimensions distinguishing similarly and differently shaped nanoassemblies in a given solution. Indeed, we have shown that the solution-phase structure of such nanoassemblies is often quite different from what one would predict based on solid-state studies, a result in disagreement with the frequently made assumption that these assemblies have similar structures in the two phases. We instead have predicted solid-state architectures from solution-phase structures by combining the solution-phase analysis with solid-state magnetic and elemental analyses. Specifically, the iron-seamed C-methylpyrogallol[4]arene nanoassembly was found to be tubular in solution and predicted to be tubular in the solid state, but it was found to undergo a rearrangement from a tubular to spherical geometry in solution as a function of base concentration. The absence of metal within a tubular framework affects its stability in both solution and the solid state; however, this instability is not necessarily characteristic of hydrogen-bonded capsular entities. Even metal seaming of the capsules does not guarantee similar solid-state and solution-phase architectures. The rugby ball-shaped gallium-seamed C-butylpyrogallol[4]arene hexamer becomes toroidal on dissolution, as does the spherically shaped gallium/zinc-seamed C-butylpyrogallol[4]arene hexamer. However, the arenes are arranged differently in the two toroids, a variation that accounts for the differences in their sizes and guest encapsulation. Guest encapsulation of biotemplates, such as insulin, has demonstrated the feasibility of synthesizing nanocapsules with a volume three times that of a hexamer. The solution-phase studies have also demonstrated that the self-assembly of dimers versus hexamers can be controlled by the choice of metal, solvent, and temperature. Controlling the size of the host, nature of the metal, and identity of the guest will allow construction of targeted host-guest assemblies having potential uses as drug delivery agents, nanoscale reaction vessels, and radioimaging/radiotherapy agents. Overall, the present series of solid- and solution-phase studies has begun to pave the way toward a more complete understanding of the properties and behavior of complex supramolecular nanoassemblies.

Cocrystallization of pyrogallol[4]arenes with 1-(2-pyridylazo)-2-naphthol

Mapping the effects of various solvent systems and varying aliphatic tails lengths of cocrystals composed of pyrogallol[4]arenes and 1-(2-pyridylazo)-2-naphthol.

Illuminating host–guest cocrystallization between pyrogallol[4]arenes and the ionic liquid 1-ethyl-3-methylimidazolium ethylsulfate

Symmetry-generated packing of a cocrystal composed of c-butyl-pyrogallol[4]arene and the ionic liquid, 1-ethyl-3-methylimidazolium ethylsulfate.

Zinc-seamed pyrogallol[4]arene dimers as structural components in a two-dimensional MOF

Computational methods were used as a proof of principle in the synthesis of a two-dimensional coordination polymer constructed from zinc-seamed pyrogallol[4]arene dimeric nanocapsules and 4,4′-bipyridine.

Investigating structural alterations in pyrogallol[4]arene-pyrene nanotubular frameworks

Small-angle neutron scattering (SANS) and diffusion NMR studies are performed to investigate the stability and geometry of hydrogen-bonded pyrene-guest-containing C-hexylpyrogallol[4]arene (PgC(6) -pyrene) nanotubular frameworks in solution. In the solid state, hydrogen-bonded pyrogallol[4]arene tubes are formed; however, the scattering data for PgC(6) -pyrene assemblies in acetone are best modeled as dimeric spheres of PgC(6) with no pyrene guest. The result of diffusion NMR study also indicates the rearrangement of tubular entity into spherical framework in acetone. This is the first example of structural transformation of pyrogallol[4]arene nanotubes (guest-exo) in solution. Individual hydrogen-bonded spheres of PgC(6) exhibits a uniform radius of ca. 8.6 Å and a diffusion coefficient of 9.12 × 10(-10) m(2) s(-1) in acetone. The diffusion NMR measurements further gave, for the first time, insights into how the type of solvent (acetone vs. methanol vs. acetontitrile/D(2) O) governs the structural differences in these nanoassemblies. Solution-phase structural alteration observed for PgC(6) -pyrene gives evidence of enhanced stability of pyrogallol[4]arene nanocapsules over nanotubes.