Kitaigorodsky Revisited: Polymorphism and Mixed Crystals of Acridine/Phenazine

Abstract

Non-stoichiometric molecular mixed crystals have potential as functional materials, the properties of which can be tailored by rationally changing their composition. The guidelines for their preparation were summarized over thirty years ago by Alexander Kitaigorodsky. Here those principles are revised in light of new studies on the acridine/phenazine system, and solvent-assisted grinding is presented as a convenient synthetic procedure to afford a more homogeneous product than traditional solvent-evaporation methods. Finally, the proposed prerequisite of crystal isostructurality/isomorphicity for the pure compounds, which seems to be violated in the present case, is discussed.

Making crystals with a purpose; a journey in crystal engineering at the University of Bologna

“…The importance of non-stoichiometric molecular mixed crystals as novel functional materials has been recently emphasized in a study of mixed crystals of acridine and phenazine prepared mechanochemically (Schur et al, 2015). This approach has been expanded to the preparation of ternary mixed crystals of anthracene, phenazine and acridine (Lusi et al, 2015).…”

A mixed molecular salt of lithium and sodium breaks the Hume-Rothery rules for solid solutions

“…4,5 In molecular mixed crystals it has been suggested that molecular isostructurality is also required, 6 although exceptions are reported. 7 Such strict rules explain why solid solutions are rarer than single component crystals and co-crystals. Furthermore, the difficulty in finding molecular components that satisfy the above conditions is an obstacle to the development of solid solutions into products for real world applications.…”

Precessional Motion in Crystalline Solid Solutions of Ionic Rotors

“…The term isotypic is synonymous with isostructural]. The importance of solid solutions as a tool for modifying the physicochemical properties of materials has been recently emphasized in a series of studies on mixed crystals, where features such as melting point, polymorphic phase transition, enantioselectivity, mechanical, optical, magnetic, and thermosalient effects, among others, can be studied and finely “tuned” by controlling the composition. This approach has also been successfully applied to control the rotational frequency of 4,4′‐bipyridine rotators in porous coordination polymers .…”

“…Twoc rystalsa re said to be isostructural if they have the same structure, but not necessarily the same cell dimensions nor the same chemical composition, and with a"comparable" variability in the atomiccoordinates to that of the cell dimensions and chemical composition. The term isotypic is synonymous with isostructural].T he importanceo fs olid solutionsa satool for modifyingt he physicochemicalp roperties of materials has been recently emphasized in as eries of studies on mixed crystals,w here features such as meltingp oint, [24,25] polymorphic phase transition, [26,27] enantioselectivity, [28,29] mechanical, [30] optical, [31] magnetic, [32] and thermosalient effects, [33] among others, can be studied and finely "tuned" by controlling the composition. This approach has also been successfully appliedt oc ontrol the rotational frequency of 4,4'-bipyridine rotators in porous coordination polymers.…”