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Topologies of ladder packing arrangements in crystal structures of five azaheterocyclic phosphonates were characterized by four geometrical descriptors introduced in the paper. The structural analysis was augmented by detailed calculations on interactions stabilizing the molecular assemblies. Intermolecular energies were evaluated using PIXEL and DFT(M062x-GD3) methods. Additionally, fingerprint plots derived from the Hirshfeld surfaces were generated for each structure to characterize the crystal packing arrangement in detail. All structures are stabilized by the relatively weak hydrogen bonds and nonbonding interactions involving aromatic rings, i.e., π···π, C-H···π, and (lp)···π effects. Distribution of the molecular electrostatic potential demonstrates that positively charged, endocyclic sulfur atoms are prone to chalcogen-chalcogen (S···O) bonding. Analysis of the supramolecular motifs shows the lack of a common synthon responsible for the ladder packing arrangements. However, the striking geometry similarity of all molecules indicates that ladder packing is based on a shape oriented molecular recognition and mostly driven by the van der Waals forces. The intermolecular electrostatic effects are crucial for stabilizing and fixing geometry of the already formed molecular clusters. [ABSTRACT FROM AUTHOR]

Atropisomers of three Blatter radicals were obtained by the addition of 8-substituted 1-naphthyllithiums to 3-phenyl and 3- t -butylbenzo[ e ][1,2,4]triazine and separated by chiral high-performance liquid chromatography. Their absolute configurations were assigned by a comparison of experimental and time-dependent density functional theory calculated electronic circular dichroism spectra. The free energy of activation, Δ G ‡ 298 , and the half life of racemization, t 1/2 , at 298 K were determined at ∼25 kcal mol -1 and <130 h, respectively. Intramolecular π-π interactions in radicals were evident from single-crystal X-ray diffraction, density functional theory, and electrochemical analyses.

A series of 19 structurally diverse C(3)-substituted derivatives of benzo[ e][1,2,4]triazine were synthesized from 3-chloro- (1c) and 3-iodobenzo[ e][1,2,4]triazine (1d) obtained in three steps from 2-nitroaniline in 37-55% yields. Nucleophilic aromatic substitution and metal-catalyzed (Pd, Cu) reactions led to functional derivatives that include alkyl (C 5 H 11 ), (het)aryl (Ph, 2-thienyl, ferrocenyl), ArC≡C, amine (NHPh and morpholine), PO(OEt) 2 , sulfanyl (SBu- t), alkoxide (OEt, OMe), and CN. The synthesis of C(3)-CF 3 derivative 1g via the Ruppert reaction with 1d and its 1-oxide analogue 2d led to the substitution followed by formal addition of HCF 3 to the C═N bond. Pd-catalyzed carbonylation reactions of 1d and 2d did not give the corresponding C(3)-carboxylic acids. Therefore, acid 1f was obtained through hydrolysis of the CN. The substituent effect on the electronic structure of the benzo[ e][1,2,4]triazine ring was investigated by spectroscopic methods (UV-vis and NMR) augmented with density functional theory calculations. Results show significant effect of the C(3) substituent on the π-π*(1) transition energy and good correlation of the 1 H NMR chemical shift with the substituent constant σ p . Molecular and crystal structures of six derivatives were established with the single-crystal X-ray diffraction method, and the substituent impact on the molecular geometry was investigated.