Microporosity of a Guanidinium Organodisulfonate Hydrogen-Bonded Framework

Guanidinium organosulfonates (GSs) are a large and well-explored archetypal family of hydrogen-bonded organic host frameworks that have, over the past 25 years, been regarded as nonporous. Reported here is the only example to date of a conventionally microporous GS host phase, namely guanidinium 1,4-benzenedisulfonate ( p -G₂BDS ). p -G₂BDS is obtained from its acetone solvate, AcMe@ G₂BDS , by single-crystal-to-single-crystal (SC-SC) desolvation, and exhibits a Type I low-temperature/pressure N₂ sorption isotherm (SA_BET=408.7(2) m² g⁻¹, 77 K). SC-SC sorption of N₂, CO₂, Xe, and AcMe by p -G₂BDS is explored under various conditions and X-ray diffraction provides a measurement of the high-pressure, room temperature Xe and CO₂ sorption isotherms. Though p -G₂BDS is formally metastable relative to the “collapsed”, nonporous polymorph, np -G₂BDS , a sample of p -G₂BDS survived for almost two decades under ambient conditions. np -G₂BDS reverts to zCO₂@ p -G₂BDS or yXe@ p -G₂BDS (y,z=variable) when pressure of CO₂ or Xe, respectively, is applied.     

Mechanochemistry for Synthesis

Mechanochemical solvent‐free reactions by milling, grinding or other types of mechanical action have emerged as a viable alternative to solution chemistry. Mechanochemistry offers not only a possibility to eliminate the need for bulk solvent use, and reduce the generation of waste, but it also unlocks the door to a different reaction environment in which synthetic strategies, reactions and molecules previously not accessible in solution, can be achieved. This Minireview examines the potential of mechanochemistry in chemical and materials synthesis, by providing a cross‐section of the recent developments in using ball milling for the formation of molecules and materials based on covalent and coordination bonds.     

Mechanochemical Desymmetrization of Unbiased Bis- and Tris-alkynes to Access 3,5-Isoxazoles-Alkyne Adducts and Unsymmetrical Bis-3,5-isoxazoles**

A mechanochemical desymmetrization of symmetrical bis- and tris-alkynes by a controlled 1,3-dipolar cycloaddition reaction using nitrile oxide dipoles (NOs). This operationally simple protocol allows access to 3,5-isoxazole-alkyne adducts from easily prepared or commercially available symmetrical bis- and tris-alkynes in moderate to excellent yields. In addition, we have highlighted the synthetic utility of 3,5-isoxazole-alkyne by developing a route to access, for the first time, β-ketoenamine-alkyne derivatives, and unsymmetrical bis-3,5-isoxazoles.     

Towards the development of highly active copper catalysts for atom transfer radical addition (ATRA) and polymerization (ATRP)

Fundamentals of copper catalyzed atom transfer radical addition (ATRA) and mechanistically similar polymerization (ATRP) were discussed. Special emphasis was placed on structural characterization and electrochemical properties of copper complexes. Recent advances in the development of highly active copper complexes for both processes were also reviewed. It was found that electron-donating groups (methoxy and methyl in the 4 and 3,5 positions, respectively) of the pyridine rings in tris(2-pyridylmethyl)amine (TPMA) ligand, significantly increase the catalytic activity in copper mediated ATRA/ATRP.     

Solution of the generalized eigenvalue equation perturbed by a generalized low rank perturbation

Summary The problem of finding eigenvalues and eigenstates of the generalized perturbed eigenvalue equation = g3(+) is considered. The eigenvalues and the eigenstates of the unperturbed eigenvalue equation = are assumed to be known. Matrices , and can be arbitrary, except for the requirement that be nonsingular and that the eigenstates of the unperturbed equation be complete. It is shown that the eigenvalues and the eigenstates of the perturbed equation can be easily obtained if the rank of the generalized perturbation , is small. A special case of low rank perturbations are piecewise local perturbations which are common in physics and chemistry. If the perturbation is piecewise local with fixed localizability, the operation count for the derivation of a single eigenvalue and/or a single eigenstate is (n). If the perturbation has a fixed rank, the operation count for the derivation of all eigenvalues and/or all eigenstates is (n ²).Research supported by the Welch Foundation of Houston, Texas, and by the Yugoslav Ministry for Development (Grant P-96)     

New synthesis of 7-bromo-1, 3-dihydro-3-hydroxy-5-(2′-pyridyl)-2H-1,4-benzodiazepin-2-one

A new synthesis of 7-bromo-1,3-dihydro-3-hydroxy-5-(2′-pyridyl)-2H-1,4-benzodiazepin-2-one ( 5 ) is described. Starting from bromazepam ( 3 ), C(3) acylation with lead tetraacetate/potassium iodide in acetic acid affords 4 , while its mild hydrolysis according to our recently described method (5) gives 5 . Improved hexamine cyclization of 1 into 3 , via quaternary hexaminium salt 2 , is discussed, and identification of the intermediates 7 and 8 is performed. Compound 5 undergoes on melting, or on brief heating in glacial acetic acid, the thermal rearrangement into quinazolin-2-aldehyde ( 13 ), the structure of which is confirmed by oxidation into the ester 14 , which in turn was hydrolyzed to the acid 15 . The same compound ( 5 ) rearranges on heating with manganese(III) acetate in acetic acid into the 3-amino-2-quinolone derivative 6 . On heating in glacial acetic acid in the presence of lead tetraacetate/potassium iodide (or iodine), compound 4 , in addition to giving the aldehyde 13 , ester 14 and acid 15 rearrangement products, affords 1,2-dihydroquinazolin-2-carboxylic acid 16 .     

Reply to the comment on MORT treatment of bond length alternation in conjugated hydrocarbons

It is shown that in treating bond distortions in the framework of the approach suggested by Nakajima, the contributions of different terms to the total energy are highly sensitive to the choice of parameters and to variations in the functional dependence of the resonance integral as a function of bond length. Hence one can not unambiguously attribute the overall effect to any particular term or terms, and sometimes one has to make a rather careful adjustment in order to avoid qualitatively erroneous results. Though the simple molecular orbital resonance theory (MORT) approach is rather naive, it correctly predicts relative bond lengths in a range of molecules with essentially no parameter adjustment. This approach is hence a rather successful first order approximation to more sophisticated models which progressively incorporate missing contributions. The variation of the resonance integral with bond length and the -bond compression energy should be in these more sophisticated models undoubtedly taken into account. However, the contribution of the charge polarisation can not be totally disregarded, especially in the case of conjugated compounds containing small rings.Theoretica Chimica Acta 65, 77–80 (1984)     

Perfect Matchings in Bipartite Lattice Animals: Lower Bounds and Realizability

In the first part of this paper we establish sharp lower bounds on the number of perfect matchings in benzenoid graphs and polyominoes. The results are then used to determine which integers can appear as the number of perfect matchings of infinitely many benzenoids and/or polyominoes. Finally, we consider the problem of concealed non-Kekuléan polyominoes. It is shown that the smallest such polyomino has 15 squares, and that such polyominoes on n squares exist for all n ≥ 15.