9‐Methyl‐3‐phenyl­diazenyl‐9H‐carbazole: X‐ray and DFT‐calculated structures

The title compound, C₁₉H₁₅N₃, was prepared by condensation of 3‐nitroso­carbazole and aniline with subsequent methyl­ation. The structure is built up of stacks of almost planar mol­ecules. Density functional theory (DFT) calculations predict a completely planar conformation, different from that observed in the crystal lattice. HOMA (harmonic oscillator model of aromaticity) indices, calculated for three aromatic rings, demonstrate the small influence of the azo substituent on π electrons in the carbazole system.     

Orthorhombic polymorphs of two trans‐4‐aminoazoxybenzenes

The two isomeric compounds 4‐amino‐ONN‐azoxy­benzene [or 1‐(4‐amino­phenyl)‐2‐phenyl­diazene 2‐oxide], i.e. the α isomer, and 4‐amino‐NNO‐azoxy­benzene [or 2‐(4‐amino­phenyl)‐1‐phenyl­diazene 2‐oxide], i.e. the β isomer, both C₁₂H₁₁N₃O, crystallized from a polar solvent in orthorhombic space groups, and their crystal and molecular structures have been determined using X‐ray diffraction. There are no significant differences in the bond lengths and valence angles in the two isomers, in comparison with their monoclinic polymorphs. However, the conformations of the mol­ecules are different due to rotation along the Ar—N bonds. In the α isomer, the benzene rings are twisted by 31.5 (2) and 14.4 (2)° towards the plane of the azoxy group; the torsion angles along the Ar—N bond in the β isomer are 24.3 (3) and 23.5 (3)°. Quantum‐mechanical calculations indicate that planar conformations are energetically favourable for both isomers. The N—H?O hydrogen bonds observed in both networks may be responsible for the deformation of these flexible mol­ecules.     

Substituent effects in trans‐p,p′‐disubstituted azobenzenes: X‐ray structures at 100 K and DFT‐calculated structures

The crystal and molecular structures of two para‐substituted azobenzenes with π‐electron‐donating –NEt₂ and π‐electron‐withdrawing –COOEt groups are reported, along with the effects of the substituents on the aromaticity of the benzene ring. The deformation of the aromatic ring around the –NEt₂ group in N,N,N′,N′‐tetraethyl‐4,4′‐(diazenediyl)dianiline, C₂₀H₂₈N₄, (I), may be caused by steric hindrance and the π‐electron‐donating effects of the amine group. In this structure, one of the amine N atoms demonstrates clear sp²‐hybridization and the other is slightly shifted from the plane of the surrounding atoms. The molecule of the second azobenzene, diethyl 4,4′‐(diazenediyl)dibenzoate, C₁₈H₁₈N₂O₄, (II), lies on a crystallographic inversion centre. Its geometry is normal and comparable with homologous compounds. Density functional theory (DFT) calculations were performed to analyse the changes in the geometry of the studied compounds in the crystalline state and for the isolated molecules. The most significant changes are observed in the values of the N=N—C—C torsion angles, which for the isolated molecules are close to 0.0°. The HOMA (harmonic oscillator model of aromaticity) index, calculated for the benzene ring, demonstrates a slight decrease of the aromaticity in (I) and no substantial changes in (II).     

4‐Benzoyl‐3,4‐dihydro‐2H‐1,4‐benzoxazine‐2‐carbonitrile: refinement using a multipolar atom model

The structural model for the title compound, C₁₆H₁₂N₂O₂, was refined using a multipolar atom model transferred from an experimental electron‐density database. The refinement showed some improvements of crystallographic statistical indices when compared with a conventional spherical neutral‐atom refinement. The title compound adopts a half‐chair conformation. The amide N atom lies almost in the plane defined by the three neighbouring C atoms. In the crystal structure, molecules are linked by weak intermolecular C—H...O and C—H...π hydrogen bonds.     

5‐(3,4‐Dimethoxybenzyl)‐7‐isopropyl‐1,3,5‐triazepane‐2,6‐dione acetonitrile solvate refined using a multipolar atom model

The crystal structure of the title compound, C₁₆H₂₃N₃O₄·CH₃CN, was refined using a multipolar atom model transferred from an experimental electron‐density database. The refinement showed some improvement in crystallographic statistical indices compared with the independent atom model. The triazepane ring adopts a twist‐boat conformation. In the crystal structure, the molecule forms intermolecular contacts with 14 different neighbours. There are two N—H...O and one C—H...O intermolecular hydrogen bond.     

Noise map validation by continuous noise monitoring

This paper presents a comparison of two noise assessments in the Gdansk agglomeration in Poland. One is based on the noise map produced by computational method for the city in 2007, the second one is based on real data from continuous measurements acquired by a noise monitoring network operating in the city since 2008. Differences are shown and analyzed. Additionally, seasonal and weekday influence on noise indicators (L_DEN, L_D, L_E and L_N) is analyzed and discussed in this paper.     

A vanadyl Schiff base complex: {2,2′‐[1,1′‐(o‐phenylenedinitrilo)bis(ethan‐1‐yl‐1‐ylidene)]diphenolato}oxovanadium(IV)

The green crystals of the title compound, [V(C₂₂H₁₈N₂O₂)O], represent a mononuclear oxovanadium complex. The central V^IV centre has a distorted square‐pyramidal coordination. Two N atoms and two O atoms of the Schiff base ligand define the base of the pyramid, and the oxide O atom is in the apical position. Density functional theory (DFT) calculations were performed to analyse the changes in the geometry of the ligand during the complex formation. The most significant changes are observed in the values of the torsion angles in the vicinity of the donor N atoms. The HOMA index (Harmonic Oscillator Model of Aromaticity) has been calculated to compare the aromaticity of the benzene rings in the complex and its ligand.