Solid state transformations in crystalline salts

Abstract

Two examples are described of reactions which proceed in the crystalline state. In the first, a metal-organic salt CoH2O6X2 ⋅2bpdo ⋅2H2O X = Br − , Cl − transforms at room temperature into a coordination polymer CoX2bpdoH2O2 ⋅H2O with different connectivity. The process can be followed by powder x-ray diffraction. In the second example, we observed sublimation/dissociation and recrystallisation under ambient pressure when a single crystal of 4-(1-hydroxy-1,2-diphenylethyl)pyridinium chloride was heated and the pure organic moiety crystallized on the mother crystal surface providing an excellent example of molecular structure – macroscopical property relationship which can be explained by partial isostructurality. Under similar conditions the nitrate salt of the same compound, 4-(1-hydroxy-1,2-diphenylethyl)pyridinium nitrate sublimed and recrystallised without dissociation. The two crystal structure of the salts are isostructural but the Hirshfeld surface analysis shows significant differences between the intermolecular interactions which can explain the different thermal behavior of them in the crystalline phase while the computational studies explained their behavior in gas phase.