Analysis of the strengths and directionality of intermolecular interactions in the crystals containing only one type of supramolecular synthon allows the suggestion of a general classification of molecular crystals depending on type of their basic structural motifs. All crystals may be divided on four classes namely (I) crystals with isotropic packing of the building units; (II) columnar crystals where the basic structural motif (BSM) is a chain/column; (III) layered crystals with layers as the BSM; (IV) columnar-layered crystals containing chains/columns as the primary basic structural motif and layers as the secondary BSM. Taking into account the participation of different supramolecular synthons in the formation of different levels of the organization of molecular crystals, they may be considered as basic (responsible for the formation of molecular complexes as building units of crystals), primary, secondary and auxiliary, which are involved in the agglomeration of molecules in primary or secondary basic structural motifs or in the packing of these motifs, respectively. The ranking of supramolecular synthons depends on values of energies of intermolecular interactions and it is individual for each crystal.

Crystal structures of six new salts of 2‐methyl‐5‐nitroaniline with inorganic acids [(H2Me5NA)Br, (H2Me5NA)I, (H2Me5NA)NO3, (H2Me5NA)Cl, (H2Me5NA)HSO4 and (H2Me5NA)I3·0.5H2O] are determined by single‐crystal X‐ray diffraction. The most important hydrogen‐bonding patterns are formed by the ammonio group and respective anions composing 1D or 2D networks. The patterns are analysed using the graph‐set approach and mathematical interrelations between graph‐set descriptors are shown for comparative purposes. Analysis of IR spectra enables the strength of hydrogen bonds in the crystals to be assessed. The frequency of N—H and O—H stretching vibrations and NH3 group libration indicates that the strongest hydrogen bonds are present in (H2Me5NA)HSO4, whereas the weakest ones occur in (H2Me5NA)I3·0.5H2O. Hirshfeld surface analysis reveals that apart from obvious N—H…anion hydrogen bonds, the molecules are also connected to each other by exclusive C—H…ONO2 interactions. The opposite occurs in the crystal structure of 2‐methyl‐4‐nitroaniline salts, where a variety of ONO2…π(N)NO2 non‐hydrogen bonding interactions are observed.

In both independent mol­ecules of the title compound, [Nd(C9H11NO4P)3(C12H8N2)], the NdIII atom is coordinated by six O atoms belonging to three phosphoryl ligands and two N atoms of 1,10-phenanthroline in a dodeca­hedral geometry. In the phosphoryl ligands, the benzene rings are twisted with respect to the planes of the sp 2-hybridized C atoms of the chelate rings by 12.1 (1)–24.7 (1)°.

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Polymorphism represents an expanding area of crystal engineering and an opportunity for discovery of materials with interesting properties, thus giving a new perspectives for “old”, well-known compounds known by chemists...

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