A group of bis(aryl)acenaphthenequinonediimine (Ar‐BIAN) ligands were synthesized through a modified procedure, which bypasses the need for absolutely dry conditions during the initial template synthesis. The molecular and electronic structure of the corresponding homoleptic [Cu(Ar‐BIAN)2]BF4 complexes were probed by means of a variety of spectroscopic methods. In accord with solution 13C NMR spectra, X‐ray crystallography reveals D2 or approximate D2 symmetry for the [Cu(p‐Cl‐BIAN)2]+ and [Cu(p‐Me‐BIAN)2]+ cations and noncrystallographic C2 symmetry for the [Cu(o‐Ph‐BIAN)2]+ cation. The structures of the p‐Cl‐, p‐Me, and o‐Ph‐BIAN complexes agree with the presence of ligands in their neutral form according to the lengths of the relevant C–C and C=N bonds of the organic skeleton. The concerted stereo–electronic effects of the substituents on the aryl rings affect the electron donor/acceptor capacities of the ligands and the structures of the complexes, as the study of the visible absorption spectra of the complexes indicates. The spectra of the complexes are dominated by intense and broad metal‐to‐ligand charge transfer (MLCT) bands that enter the near‐infrared (NIR) region. Additionally, electrochemical studies undertaken reveal several successive electron capture and release processes, which further manifest the redox versatility of the ligands.

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The molecular recognition process and the ability to form multicomponent supramolecular systems have been investigated for the amide of triphenylacetic acid and l-tyrosine (N-triphenylacetyl-l-tyrosine, TrCOTyr). The presence of several supramolecular synthons within the same amide molecule allows the formation of various multicomponent crystals, where TrCOTyr serves as a chiral host. Isostructural crystals of solvates with methanol and ethanol and a series of binary crystalline molecular complexes with selected organic diamines (1,5-naphthyridine, quinoxaline, 4,4′-bipyridyl, and DABCO) were obtained. The structures of the crystals were planned based on non-covalent interactions (O–H···N or N–H+···O− hydrogen bonds) present in a basic structural motif, which is a heterotrimeric building block consisting of two molecules of the host and one molecule of the guest. The complex of TrCOTyr with DABCO is an exception. The anionic dimers built off the TrCOTyr molecules form a supramolecular gutter, with trityl groups located on the edge and filled by DABCO cationic dimers. Whereas most of the racemic mixtures crystallize as racemic crystals or as conglomerates, the additional tests carried out for racemic N-triphenylacetyl-tyrosine (rac-TrCOTyr) showed that the compound crystallizes as a solid solution of enantiomers.

p‐Phenylenediamine can be obtained as the dihydrate, C6H8N2·2H2O, (I), and in its anhydrous form, C6H8N2, (II). The asymmetric unit of (I) contains one half of the p‐phenylenediamine molecule lying about an inversion centre and two halves of water molecules, one lying on a mirror plane and the other lying across a mirror plane. In (II), the asymmetric unit consists of one molecule in a general position and two half molecules located around inversion centres. In both structures, the p‐phenylenediamine molecules are arranged in layers stabilized by N—H...π interactions. The diamine layers in (I) are isostructural with half of the layers in (II). On dehydration, crystals of (I) transform to (II). Comparison of their crystal structures suggests the most plausible mechanism of the transformation process which requires, in addition to translational motion of the diamine molecules, in‐plane rotation of every fourth p‐phenylenediamine molecule by ca 60°. A search of the Cambridge Structural Database shows that the formation of hydrates by aromatic amines should be considered exceptional.

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