Clathrate formation—the formation of crystalline inclusion compounds—is one approach to chemical sensing of vapors and gases. The synthesis of a new diol host compound is described and absorptive clathrate formation and thermal clathrate decomposition are reported for acetone as the guest. It is shown that the sorptive uptake of a guest vapor by the crystalline host compound is not merely surface adsorption but true clathrate formation, involving a solid‐state transformation. It is suggested that the use of the host as a chemical sensor is not far off.
Inclusion compounds have significant potential as chemical receptors for sensors; however, it is necessary to understand the encapsulation and release processes for such applications. These authors have utilized the powerful combination of simultaneous thermogravimetry and differential scanning calorimetry and X‐ray diffraction to study the decomposition mechanism of the clathrates between 1,1′‐binaphthyl‐2,2′‐dicarboxylic acid (BNDA) and dimethyl formamide (DMF). Decomposition was found to proceed via three intermediate phases whose structures were determined by single crystal X‐ray crystallography.
The 2,2'-bis(9-hydroxy-9-fluorenyl)biphenyl host compound (1) was found to form various crystalline inclusion compounds with acetone depending on the crystallization conditions or on the method of preparation (inclusion of acetone vapour, co-crystallization from solution). In order to understand and control the formation of these pseudopolymorphic phases regarding potential uses, single crystals of the existing phases (two 1:2 and one 1:1 compound) were prepared, their structures were solved by single-crystal x-ray diffraction (XRD) analysis and the desolvation and phase transformations were studied using simultaneous thermogravimetry-differential scanning calorimetry (TG-DSC) and variable-temperature powder XRD. The results explain the inclusion and desolvation behaviour and also clarify the observed, apparently accidental formation of a 1:1 or 1:2 inclusion compound at ambient temperature.
The following MX · MgX2 · 6H2O compounds (double salt hexahydrates) were synthesized by variation of the M+ and X− ions: CsCl · MgCl2 · 6 H2O, Li(H2O)Cl · MgCl2 · 6H2O, NH4Br · MgBr2 · 6 H2O, RbBr · MgBr2 · 6 H2O, CsBr. MgBr2 · 6 H2O, KI · MgI2 · 6 H2O, NH4I. Mgl2 · 6 H2O and RbI · MgI2 · 6H2O. By X‐ray analysis of powder samples the lattice parameters and the space group were determined. On the basis of the results thus obtained, an identification with structural types was carried out. In accordance with the findings, the structure is made up of (M+)X6−octahedra which are linked into perovskite type units by sharing vertices. Their interstices are occupied by the Mg(H2O)62+ octahedra. A “tolerance factor” t which has been calculated on the basis of the proportion of radii and which attains values between 1.045 and 1.061 is a criterion for the upper limit of the area of existence of this structure. Carnallite has a higher to value and, therefore, a different structure.
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