Template Cations Research Articles

Structures and cationic complexes of 18[(2,6)pyridino-6-corand-6] (‘sexipyridine’)

The conformers of the title compound and its (gas phase) complexes with alkali metal cations and some molecular cations have been structurally optimized at HF/3-21G and HF/6-31G* levels of theory, with extended basis set single-point DFT calculations to include some of the effects of electron correlation. The only stable conformer found for the free macrocycle has D3 symmetry, and stable complexes of the same symmetry are demonstrated for Na+ and K+. Stable complexes of lower (C3) symmetry are also found for the possible template cations H3O+ and NH4+. Binding energies for the alkali metal cations ions are significantly larger than those found in comparable computational studies on structurally-related macrocycles. Finally, the complex with another potential template cation, C(NH2)3+, is also explored.

Synthesis and Ion-Binding Properties of Polymeric Pseudocrown Ethers. III. Ion-Binding Studies

ABSTRACT An ion-induced templatization strategy was used to prepare crosslinked polymeric pseudocrown ethers (PCEs) in situ during a one-step free-radical polymerization. These studies bring to a conclusion the fundamental studies on the templatization process reported in the first two papers of this series. For the PCEs, with nickel as the templating ion and hydroxyethyl methacrylate as the monovinyl comonomer, the ion-binding studies revealed a significant enhancement in the ion-binding capacity associated with the inclusion of the template ion during synthesis. For example, a PCE synthesized with a monomer-to-solvent ratio of 20/80 exhibited an ion-binding capacity that was 7.5 times higher than a control polymer produced under identical conditions except for the absence of the template cations. A PCE synthesized with a monomer-to-solvent ratio of 20/80 exhibited a capacity of 0.3 mg/g polymer for Ni2+ cations. Finally, it was observed that the column could be fully regenerated by elution with a small volume of a 1 M HCL solution at 60°C, resulting in the recovery of the bound ions as a concentrated solution.

Construction of supramolecular copper architecture via tetrahedral Cu(CN) 4 building blocks and trigonal bipyramidal [R 3Sn] connecting units

The self assembly of the pyramidal tetrahedral Cu(CN) 4 building blocks, the trigonal bipyramidal [R 3Sn] connecting units and the guest–template–cations leads to the construction of new types of non-interpenetrating polymeric networks. Twelve polymers have been prepared, most of them, according to the desired stoichiometry while polymers 9–12 represent binuclear copper compounds. These polymers are formed when no suitable space-demanding alkyl groups are used. The structures of the polymers under investigation were confirmed by elemental analysis, IR and Raman spectra, thermal analysis and NMR spectroscopy.

Self-assembling iron and manganese metal–germanium–selenide frameworks: [NMe4]2MGe4Se10, where M = Fe or Mn

The hydrothermal synthesis mixture Ge–Se–(TMA)OH–H2O (TMA+ = NMe4+) yielded crystals of the material (TMA)4Ge4Se10. A single-crystal X-ray diffraction structure showed the presence of adamantanoid Ge4Se104– clusters and TMA+ cations. The TMA+ template-mediated aqueous synthesis of (TMA)2MGe4Se10 (M = Mn or Fe) from Ge4Se104– and M2+ building-blocks is described. Rietveld powder X-ray diffraction full profile structure refinements of (TMA)2MGe4Se10 established that these novel metal–germanium–selenide frameworks are isostructural with the analogous metal–germanium–sulfides, (TMA)2MGe4S10. The selenide materials have a zinc blende-type of open-framework structure. Charge-balance of the anionic open-framework [MGe4Se10]2– is maintained by two TMA+ template cations that reside within the cavity spaces. Trends in the tetragonal unit cell dimensions and metal–chalcogenide bond lengths of (TMA)2MGe4X10 (X = S or Se) are those expected based upon increases in metal and chalcogenide radii on passing from S–II to Se–II and FeII to MnII.

Synthesis and structure of microporous layered tin(IV) sulfide materials

Synthetic methods have been developed which yield large single crystals and highly crystalline phase-pure microporous layered SnS-n materials. This allows study of the structure–property–function relations of these materials. The tin sulfide layer of the SnS-1 structure type contains hexagonally shaped 24-atom rings which are constituted by six Sn3S4 broken-cube cluster building units, linked together by double bridge Sn(µ-S)2Sn sulfur bonds. The SnS-3 structure type contains elliptically shaped 32-atom rings which are also constructed from six Sn3S4 broken-cube clusters. However, they are linked by double bridge Sn(µ-S)2Sn sulfur bonds as well as tetrahedral edge-bridging Sn(µ-S2SnS2)Sn spacer units. The SnS-1 structure type [A2Sn3S7 ] was obtained in the presence of A+=Et4N+ , DABCOH+ (protonated 1,8-diazabicyclooctane), and a mixed template system of NH4+ /Et4N+ , while the SnS-3 structure type [A2Sn4S9 ] emerged in the presence of A+=Prn4N+ and Bun4N+ . Various SnS-1 and SnS-3 structures are examined and compared in relation to the size/shape of constituent template cations. A particular kind of structure-directing function was observed, that is, larger template molecules create larger void spaces within and between the tin sulfide sheets. Unique framework flexibility was discovered for both structure types. In order to accommodate the size/shape changes of templates, the flexible porous tin(iv) sulfide layers are able to undergo a certain degree of elastic deformation to alter the architecture of void spaces within and between the layers, rather than forming a completely new porous structure type. This is believed to be responsible for the relatively small number of structure types so far discovered for tin(iv) sulfide-based microporous layered materials compared to the myriad of three-dimensional open-framework structure types found for the zeolites and aluminophosphates. The observed differences among the various SnS-1 or SnS-3 structures is significant and has resulted in distinct adsorption behavior towards guest molecules. The TPA-SnS-3 framework is also found to be pressure sensitive. This all bodes well for envisaged chemical sensor applications for this class of porous materials.

Intermediates in the formation of microporous layered tin(IV) sulfide materials

The formation pathway of microporous layered tin(iv) sulfides A2Sn3S7 and A2Sn4S9 (A=cation), respectively denoted SnS-1 and SnS-3, synthesized from elemental Sn and S sources in the presence of templates and mineralizers has been studied. Three types of reaction intermediates, dimeric [Sn2S6 ]4– , polysulfides [Sn(S4)3 ]2– /[Sn(S4)2(S6)]2– and thiosulfate [S2O3 ]2– , have been isolated and characterized by single crystal X-ray diffraction structure analysis. UV–VIS and 119Sn NMR studies of mother-liquors of representative SnS-n systems indicate that the dimeric [Sn2S6 ]4– anion is the predominant solution tin-containing species and a likely basic building unit for the SnS-n frameworks. The role of template cations has also been examined. The pH dependent condensation–polymerization of the dimeric [Sn2S6 ]4– precursor in the presence of template cations is believed to be responsible for the formation of the SnS-n structures. The dissolution and redox reactions of the elemental Sn metal and S8 powders are found to be extremely sensitive to pH, mineralizers and temperature. Reagents, such as sulfide, fluoride, hydroxide and amines that can react with tin, sulfur and various tin sulfide and polysulfide intermediates are good mineralizers. To produce large single crystals of the SnS-n materials, the concentration and strength of mineralizers need to be kept low, however, to prepare phase pure materials, the presence of excess mineralizer is required. In general, amine templates are strong mineralizers for tin metal particles, presumably through coordination to various tin polysulfide and sulfide intermediates. As a result, amine templates/mineralizers provide cleaner and smaller product crystals under reaction conditions that are similar to those used with tetraalkylammonium hydroxide templates. Surprisingly, it was found that (DABCOH)2Sn3S7 , denoted DABCOH-SnS-1, can be formed using ‘very soft chemistry’ at room temperature and atmospheric pressure conditions, from an aqueous solution of [Sn2S6 ]4– simply by the precise control of pH. The hydrothermal reaction conditions that are generally employed in the synthesis of SnS-n materials only serve to digest the starting material.

Aluminum incorporation in MCM-41 mesoporous molecular sieves

Twelve MCM-41 samples with a Si Al ratio varying from 12 to 200 were prepared by using sodium aluminate in a tetramethylammonium hydroxide solution as aluminum source and an unexchanged CTMACl template solution. The thermogravimetric analysis (TGA) weight losses caused by thermal removal of the template cations, which are associated with the siloxy groups on the one hand and the aluminum sites on the other hand, correspond with these different Al contents. X-Ray diffraction (XRD) revealed that at Si Al = 5 , in addition to MCM-41, a lamellar phase and a dense crystalline tridymite structure are formed. 27Al Magic-angle spinning nuclear magnetic resonance (MAS NMR) indicates that upon calcination the tetrahedral aluminum sites are altered. Fourier transform infrared (FTIR) analysis of proton-exchanged MCM-41 with acetonitrile as probe molecule showed a very weak Brönsted and a rather strong Lewis acidity. The latter may be the result of the distortion of the aluminum sites by thermal treatment.

Molecular shape selectivity of EUO zeolites

The micropores of the EUO zeolite consist of 10-membered ring (10-MR) channels with deep side-pockets circumscribed by 12-MRs. In decane isomerization and hydrocracking EUO zeolites crystallized in the presence of hexamethonium (HM) and dibenzyldimethylammonium (DBDMA) exhibit different molecular shape selective properties. The catalytic sites of EUO specimens crystallized with DBDMA are located in more spacious cavities than those of EUO crystals synthesized with HM. This disparity in molecular shape selectivity is explained by a different location of the framework aluminium atoms in the two materials, viz. by the absence of aluminium in the 10-MR channels in EUO-DBDMA. Such aluminium siting is in agreement with the location of the organic template cations in the pores of the as-synthesized zeolites suggested in literature and revealed by a molecular graphics modeling.

Salt-Gel Synthesis of Porous Transition-Metal Oxides

Hydrothermal reaction of sodium metatungstate with the surfactant template cetyltrimethylammonium (CTA) hydroxide gave the salt (C{sub 19}H{sub 42}N){sub 6}(H{sub 2}W{sub 12}O{sub 40}). Despite the superficial similarity of TEM micrographs and powder X-ray patterns of this material to those of mesoporous silicates, the salt contains unconnected Keggin ions H{sub 2}W{sub 12}O{sub 40}{sup 6-}. These Keggin ions pack in a puckered layer arrangement and create roughly spherical cavities for the surfactant micelle counterions. Attempts to remove the template cations and condense the inorganic portion of the structure invariably lead to dense WO{sub 3-x} phases. Nb{sub x}W{sub 6-x}O{sub 19}{sup (2+x)-} (x = 2, 3, 4) clusters also formed layered salts with CTA cations, which were reacted with tetraethyl orthosilicate (TEOS). The TEOS molecules are absorbed, presumably into the hydrophobic portion of the structure, and can be hydrolyzed to form silica within the salt. Infrared and solid-state NMR double-resonance spectra show that the silica network is anchored to the clusters via covalent Nb-O-Si linkages. Extraction of the silica-modified salts with HCl/ethanol yields materials with both micropores and mesopores and specific surface areas up to 265 m{sup 2}/g. 34 refs., 10 figs., 1 tab.

The design and performance of QENS, a medium resolution, inverted geometry, tof quasielastic and inelastic spectrometer at IPNS

A multidetector, medium resolution, quasielastic and inelastic neutron scattering spectrometer has been designed and built at the Intense Pulsed Neutron Source of Argonne National Laboratory. The main objective in the design is to combine a moderate resolution around zero energy transfer with relatively uniform and high resolution at finite energy transfer up to about 1000 wave numbers. By using the principles of time and energy focusing together with pyrolytic graphite monochrometers and small detectors, we achieve a best resolution at the quasielastic peak of 56 μeV at the final energy of E f = 3.63 meV. The relative energy resolution at finite energy transfer, Δ E/ E, is fairly constant varying between 2% and 4%. The spectrometer has three arms which rotate around the sample covering the angular range 20°–155°. Two of the arms have 13 detectors and the third has 9 detectors. The q range at the elastic position varies from 0.4 to 2.6 Å −1. The incident neutron intensity on the sample area of 1 cm×10 cm is about 10 6 neutrons/s. Results of preliminary measurements on n-butane in the plastic phase, on crystallized Kaolinite, and on tetramethylammonium template cations occluded within zeolites are outlined.

Alkali cation binding of polymers with different sized crown ethers and photodimerizable units

AbstractThe polymers which have different sized crown ethers as alkali cation binding sites and photodimerizable cinnamoyl units were prepared by the cationic copolymerization of corresponding monomers. The crown–cation complexation ratio (1:1 or 2:1) was investigated by measuring quantum yields ϕ of the photodimerization of the crown‐connected cinnamoyl units in the presence of alkali metal chlorides and also by measuring the shift of λmax of alkali metal picrates in THF on addition of the crown polymers. A significant 1:2 complex formation of alkali cations with two different sized crown ether units in the side chain of the polymers was confirmed. The alkali metal cation binding ability and selectivity of the polymers, which were studied by a method of picrate salts extraction, were markedly different from those expected from the combination of polymers of same ring‐size crown ether units. When irradiated with ultraviolet (UV) light, the cinnamic acid ester groups of the polymers caused dimerization even in dilute solutions. The cation binding ability of the polymers was largely enhanced by the photodimerization of the cinnamoyl moieties with suitable template cations.

Poly(crown ether)s with rubidium cation selectivity

AbstractPolymers having both crown ether moieties as cation binding sites and cinnamoyl moieties as photodimerizable pendant groups were prepared by cationic polymerization of 2‐vinyloxyethyl 3‐(2,3‐benzo‐1,4,7,10,13‐pentaoxacyclopentadecen‐4′‐yl)acrylate (1) or 2‐vinyloxyethyl 3‐(2,3‐benzo‐1,4,7,10,13,16‐hexaoxacyclooctadecen‐4′‐yl)acrylate (2). The copolymer 3a was also prepared from 1 and 2. On irradiation with UV light, the cinnamoyl moieties of the polymers undergo dimerization in solution. The cation binding properties were investigated by using a fluorescent probe, 8‐anilino‐1‐naphthalenesulfonate. The cation binding ability of the photoreacted polymers was found to be higher than that of the original polymers. A significant template effect of alkali metal chlorides during photodimerization reaction on the cation binding ability was observed. The copolymers 4a, prepared by irradiation with template cations, show a remarkable rubidium cation selectivity, which is not observed for polymers with only 15‐crown‐5 or 18‐crown‐6 moieties.

Cation binding properties of polyesters with photodimerizable groups and oxyethylene units. Effect of photocrosslinking with template cations

Polyesters with p-phenylene diacrylate units as photodimerizable groups and oxyethylene units as cation binding sites were prepared, COCHCHC 6H 4CHCHCOO+CH 2CH 2O+ m . The numbers m of repeating oxyethylene units in the oligoethylene glycols were 4, 5, 6 and 7. The alkali cation binding ability of the polymers increased with increases of m for all alkali metal cations examined. The cation selectivity order was found to be K + ≈ Rb + > Cs + > NH 4 + > Na + for all the polymers used. On irradiation with u.v. light, the polymers became insoluble. The polymer ( m = 7) which was crosslinked photochemically in the presence of potassium acetate as a template showed enhanced cation binding ability for alkali cations, especially for K + and Rb + cations, compared with the photocrosslinked polymers without templates.