A Breathing Zirconium Metal–Organic Framework with Reversible Loss of Crystallinity by Correlated Nanodomain Formation

The isoreticular analogue of the metal–organic framework UiO‐66(Zr), synthesized with the flexible trans‐1,4‐cyclohexanedicarboxylic acid as linker, shows a peculiar breathing behavior by reversibly losing long‐range crystalline order upon evacuation. The underlying flexibility is attributed to a concerted conformational contraction of up to two thirds of the linkers, which breaks the local lattice symmetry. X‐ray scattering data are described well by a nanodomain model in which differently oriented tetragonal‐type distortions propagate over about 7–10 unit cells.     

Electron delocalization and aromaticity in low-lying excited states of archetypal organic compounds

Aromaticity is a property usually linked to the ground state of stable molecules. Although it is well-known that certain excited states are unquestionably aromatic, the aromaticity of excited states remains rather unexplored. To move one step forward in the comprehension of aromaticity in excited states, in this work we analyze the electron delocalization and aromaticity of a series of low-lying excited states of cyclobutadiene, benzene, and cyclooctatetraene with different multiplicities at the CASSCF level by means of electron delocalization measures. While our results are in agreement with Baird's rule for the aromaticity of the lowest-lying triplet excited state in annulenes having 4nπ-electrons, they do not support Soncini and Fowler's generalization of Baird's rule pointing out that the lowest-lying quintet state of benzene and septet state of cyclooctatetraene are not aromatic.     

Synthesis of the Natural Product Building Block 5‐(3‐Bromophenyl)‐4‐hydroxy‐5‐methylhexan‐2‐one and its Chiral Characterization by Using Chiroptical Spectroscopy

The absolute configuration of 5‐(3‐bromophenyl)‐4‐hydroxy‐5‐methylhexan‐2‐one, an intermediate in the synthesis of various natural products, is assigned by using vibrational circular dichroism (VCD), electronic circular dichroism (ECD), and optical rotatory dispersion (ORD). Experimental spectra were compared to density functional theory (DFT) calculations of the molecule with known configuration. These three techniques independently confirm that the absolute configuration is (S)‐5‐(3‐bromophenyl)‐4‐hydroxy‐5‐methylhexan‐2‐one, thus enabling us to assign the absolute configuration with high reliability. The reliability of the VCD analysis was assessed quantitatively by using the CompareVOA program. We found that, in cases in which the agreement between theory and experiment was very good, a value of 10 cm^?1 for the triangular weighting function gave a more‐realistic discriminative power between enantiomers than the default value of 20 cm^?1.     

The first examples of rhodium-catalyzed 1,4-conjugate addition reactions of arylboronic acids with ethenesulfonamides

An unprecedented rhodium-catalyzed 1,4-conjugate addition of arylboronic acids with ethenesulfonamides resulting in the corresponding 2-arylethanesulfonamides is described. The amino substituent, the applied arylboronic acid, the type of Rh-catalyst, and the experimental conditions all affected the reaction outcome.     

Partial chlorine-chlorine intermolecular scattering functions for XCl4 liquids (X = C,Si, Ge,V, Ti,Sn) from neutron diffraction and the RISM

Combining neutron diffraction intermolecular scattering functions with RISM partial scattering function for X-X and X-Cl atom paris the Cl-Cl partial scattering functions are obtained. The systematic trends in Cl-Cl partial scattering functions and radial distribution functions in six different tetrachloride liquids have been investigated. The intermolecular nearest neighbour Cl-Cl distance of 0·377(14) nm corresponds well with the value of 0·34 nm adopted for the chlorine hard sphere diameter in the RISM calculations.     

A computer method for estimating volumes and surface areas of complex structures consisting of overlapping spheres

A PASCAL program which calculates volumes and surface areas of structures consisting of overlapping spheres is designed. The calculation is done by modelling the structure in the memory of a computer and then scanning the memory bit- or bytewise. A brief discussion of the error is presented, and an example for testing the algorithm is provided.     

The coordination chemistry ofN-vinylimidazole

Summary The synthesis of coordination compounds of formula M(viz)_n(A)₂ is described, where viz. =N-vinylimidazole, M = Mn, Fe, Co, Ni, Cu, Zn or Cd, A = ClO ₄ ^– , BF ₄ ^– or NO ₃ ^– , and n varies from 3 to 6, depending upon the particular combination of cation and anion. The compounds are easily prepared in ethanol from the hydrated metal(II) salts and the ligand and the products were characterized using i.r., ligand-field, far-i.r. and e.p.r. spectra in conjunction with x-ray powder diagrams and magnetic techniques. Octahedral cations [M(viz)₆]²⁺ are formed in many cases, although square planar species Cu(viz)₄(A)₂ and tetrahedral species [M(viz)₄]²⁺ for M = Co and Zn are also found.Compared withN-alkylimidazole ligands, viz behaves differently in some cases, resulting in special effects in the crystal packing, and can be related to the quite rigid ligand structure. The pyridine-type N-atom of the imidazole ring appears to be coordinated; in all compounds no evidence is found for C=C double bond coordination.