Crystalline Derivatives of Dipyrazolo-1,5-diazocine and Dipyrazolopyrimidine: A Case of Unexpected Synthesis and Isostructural Polymorphism

Abstract

Pyrazole-phenylmethanimines (Shiff bases), Py–N=CH–Ph, form molecular crystals whose supramolecular and self-assembly properties can be tuned according to the substitution made on the aromatic and pyrazole rings. In pursuit of the first pyrazole-pyridinemethanimine member, Py–N=CH–Pyr, by following the well-known synthetic scheme for these Shiff bases, two hitherto unknown crystalline derivatives of dipyrazolo-1,5-diazocine and dipyrazolopyrimidine were obtained instead, this depending on the use or not of acetic acid as the catalyst. 1,5-diazocine crystallizes in a single P-1 triclinic packing system (Z = 2, Z′ = 1), while dipyrazolopyrimidine exhibits isostructural dimorphic behavior by adopting two (pale pink and yellow) alike P21/c monoclinic systems (both Z = 4, Z′ = 1) as a function of the solvent used. Crystal structures were resolved by means of X-ray diffraction technique and their intramolecular, intermolecular, and supramolecular assemblies analyzed with the assistance of decorated Hirshfeld surfaces and the topology study of electron density using the quantum-theory of atoms in molecules (QTAIM). Although both dipyrazolopyrimidine polymorphs are stabilized by the same type of noncovalent motifs, the pale pink crystal has a slightly more compact structure, with more efficient inter- and intramolecular interactions.

N,N′-Bis(3-ethoxy-2-hydroxybenzylidene)-phenylene-1,3-diamine Methanol Solvate

“…The polymorphic compounds differ in their physicochemical properties, such as color, stability, solubility, crystal form, etc., which may be assigned to the different crystal packing arrangements. The different properties of the polymorphic compounds influence their potential applications [8][9][10][11]. The title compound, C 24 H 24 N 2 O 4 •MeOH (H 2 Lphen), is a methanol solvate that crystallizes in the triclinic space group P1, whereas the earlier-reported analogous Schiff base synthesized by Ha (the solvent-free compound) crystallizes in another space group, orthorhombic P2 1 2 1 2 1 [2].…”