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Cocrystallization of all-cis-tetraisopropylcyclotetrasiloxanetetraol and diisopropylsilanediol gave single crystals, which were proved to have a nano-size tube-like aggregate structure. Six molecules of the cyclic tetraol and four molecules of the diol form an asymmetric unit by means of hydrogen bonding. The structure and properties of the aggregates are discussed in detail, and also the possibility of solid-state synthesis of siloxanes is described. [ABSTRACT FROM AUTHOR]

Synthesis of novel cage and cyclic silanols bearing Tip (2,4,6-triisopropylphenyl) groups was performed. Tip-substituted silanetriol, TipSi(OH)3 (1) was prepared from TipSiCl3, and can be handled without special care in the air. The versatility of this silanol is amply demonstrated as a starting material of various silanols with novel frameworks. Thus, the condensation of 1 using 2-chloro-1,3-dimethylimidazolinium chloride as a dehydrating agent afforded (TipSi)5O7OH (2) in 45% yield. When 1 was treated with (TipSiCl2)2O, cis,trans-cyclotrisiloxanetriol (3) as well as a novel incompletely condensed silsesquioxane, (TipSi)4O5(OH)2 (4) were obtained. In addition, the dehydrochlorinative condensation of (TipSiCl2)2O and (TipSi(OH)2)2O afforded 4 as single product. The structures of all these novel silanols were determined by X-ray crystallography, and their unique structures (hydrogen-bonded aggregates or intramolecular hydrogen bonding) were demonstrated. [Copyright &y& Elsevier]

Tetrachloro- and tetraazide-substituted all-cis-tetraphenylcyclotetrasiloxanes (all-cis-T4) 2 and 3 were synthesized in high yields and were fully characterized. Then the precursor 3 underwent CuAAC click reaction with monopropargyl BINOL 4 and dipropargyl BINOL 6 to give the novel BINOL and triazole-containing all-cis-T4 cyclic siloxane 5 and the 29-8-29-membered-ring ladder-type hybrid siloxane 7. The sensing ability of compounds 5 and 7 towards anions was studied as well, and it was observed that 7 could selectively recognize iodides through synergistic C–H⋯I hydrogen bonding, resulting in an impressive fluorescence quenching with a Ksv of 8.10 × 104 M−1. [ABSTRACT FROM AUTHOR]

Abstract: Anion recognition properties of d-ribose-based receptors α- and β-1 were measured by 1H NMR in CDCl3 and MeCN-d 3. Receptor β-1 showed effective binding with anions by cooperative hydrogen bonds of cis-diol. The anomeric isomer α-1 is a less effective anion receptor which has similar cis-diol as a recognition site, indicating that the stereo configuration of the anomeric position is of significant influence on the anion recognition ability. [Copyright &y& Elsevier]

Siloxane-based materials have a wide range of applications. Cage-type oligosiloxanes have attracted significant attention as molecular building blocks to construct novel siloxane-based nanoporous materials with promising applications such as in catalysis and adsorption. This paper reviews recent progress in the preparation of siloxane-based nanoporous materials using alkoxy- and silanol-functionalized cage siloxanes. The arrangement of cage siloxanes units is controlled by various methods, including amphiphilic self-assembly, hydrogen bonding of silanol groups, and regioselective functionalization, toward the preparation of ordered nanoporous siloxane-based materials. [ABSTRACT FROM AUTHOR]

Abstract: Synthesis and anion recognition properties of 2,2′-binaphthalene derivatives bearing two thiourea (1) and urea (2) groups at 8- and 8′-positions were studied. The structure of receptor 1 was determined by X-ray crystallography. UV–vis spectra of the receptors showed characteristic changes around 300–400nm through isosbestic points upon the addition of biologically relevant anions such as acetate, dihydrogenphosphate, and chloride in MeCN and DMSO due to restriction of the rotation around the single bond connecting two naphthyl moieties by cooperative guest binding of two recognition sites. Job’s plots showed 1:1 complexation for guest anions. The fluorescence quantum yields of free form of 1 and 2 in MeCN were determined to be 0.021 and 0.57, respectively. The fluorescence intensities of the receptors diminished upon the addition of anions in MeCN. The association constants of receptors 1 and 2 were one or two orders of magnitude greater than the corresponding monothiourea and urea receptors 3 and 4 indicating cooperative hydrogen bonding with guest anions. The selectivity trends of association of anions were F−>AcO−>H2PO4 −>Cl−>>HSO4 −≈NO3 −≈Br−≈I− for 1, and F−>AcO−≈Cl−>H2PO4 −>Br−>HSO4 −>I−≈NO3 − for 2. Receptor 2 showed remarkable Cl− selectivity presumably owing to suitable orientation for effective hydrogen bond formation with Cl−. [ABSTRACT FROM AUTHOR]

Abstract: Anion recognition by 1,3-disiloxane-1,1,3,3-tetraols has been elucidated by 1H NMR titrations and ESI-MS in organic solvents. The association constants of the receptors for halide anions are larger than those of silanediol and 1,3-disiloxane-1,3-diol due to the cooperative hydrogen bonds by four silanol hydroxy groups of 1,3-disiloxane-1,1,3,3-tetraols. [Copyright &y& Elsevier]