Guest Exchange in a Robust Hydrogen-Bonded Organic Framework: Single-Crystal to Single-Crystal Exchange and Kinetic Studies

The salt 3,4-lutidinium pamoate crystallizes as its hemihydrate, forming a hydrogen-bonded organic framework with tetrahydrofuran (THF) as a guest in channels in the structure (<b>1·THF</b>). Extensive investigation has shown this framework to be highly robust: the THF in the channels can be exchanged for 20 different compounds, with 13 of these exchanges occurring in a single-crystal to single-crystal manner. The THF can also be exchanged for the volatile solids pyrazine or iodine, both via single-crystal to single-crystal transformations. Stepwise exchange of solvents is also possible, with a sequence of five exchanges occurring before the crystals begin to deteriorate. Investigation of the kinetics of exchange in <b>1·THF</b> revealed that exchange occurs according to a deceleratory kinetic model for contracting volume

Selectivity Behavior of a Robust Porous Organic Salt Based on the Pamoate Ion

The selectivity of a porous hydrogen-bonded framework, <b>1</b>, toward various solvent mixtures has been investigated. Framework <b>1</b>, which is the hydrate of 3,4-lutidinium pamoate, crystallizes as its THF solvate, <b>1·THF</b>. Solvent exchange can take place either by exposing crystals of <b>1·THF</b> to solvent vapors or by immersing the crystals in a solvent. Framework <b>1</b> shows preferential inclusion of particular solvents when exposed to mixed solvent vapors, or to mixed solvents in the liquid form. Analysis showed that solvents are included in the same ratios when exposed to mixed solvents in the liquid or vapor phase, despite the significant differences in mole ratios between the liquid and vapor phases due to the different vapor pressures of the solvents investigated. In some cases, when immersed in solvent mixtures containing acetonitrile or acetone, <b>1·THF</b> recrystallizes as an acetonitrile or acetone solvate of 3,4-lutidinium pamoate. The crystal structures of these two new solvates are also reported

A Series of Polymorphs of Hexakis(4-fluorophenoxy)cyclotriphosphazene

A series of conformational polymorphs of hexakis­(4-fluorophenoxy)­cyclotriphosphazene have been identified and characterized. Three of the four polymorphs are previously unreported. Thermal analysis coupled with variable temperature powder X-ray diffraction has shown that conversion between polymorphs occurs at well-defined temperatures. The high temperature form is metastable at room temperature and is never obtained from solution. Two forms are observed in solution crystallization experiments, a monoclinic form and a triclinic form. Slurry experiments revealed that the triclinic form is the most stable at room temperature. The fourth polymorph is observed only at low temperatures. Interconversion between three of the polymorphs occurs in a single-crystal to single-crystal manner

A Series of Polymorphs of Hexakis(4-fluorophenoxy)cyclotriphosphazene

A series of conformational polymorphs of hexakis­(4-fluorophenoxy)­cyclotriphosphazene have been identified and characterized. Three of the four polymorphs are previously unreported. Thermal analysis coupled with variable temperature powder X-ray diffraction has shown that conversion between polymorphs occurs at well-defined temperatures. The high temperature form is metastable at room temperature and is never obtained from solution. Two forms are observed in solution crystallization experiments, a monoclinic form and a triclinic form. Slurry experiments revealed that the triclinic form is the most stable at room temperature. The fourth polymorph is observed only at low temperatures. Interconversion between three of the polymorphs occurs in a single-crystal to single-crystal manner