Hydrogen fluoride Crystal structure

The crystal structure of many compounds is dominated by the effect of H bonds, and numerous examples will emerge in ensuing chapters. Ice (p. 624) is perhaps the classic example, but the layer lattice structure of B(OH)3 (p. 203) and the striking difference between the a- and 6-forms of oxalic and other dicarboxylic acids is notable (Fig. 3.9). The more subtle distortions that lead to ferroelectric phenomena in KH2PO4 and other crystals have already been noted (p. 57). Hydrogen bonds between fluorine atoms result in the formation of infinite zigzag chains in crystalline hydrogen fluoride... 

The Crystal Structure of Ammonium Hydrogen Fluoride, NH4HF2... 

Hassel and Luzanski obtained quadratic tabular crystals on evaporation of an aqueous solution containing excess hydrogen fluoride. Laue photographs with the incident beam normal to the basal plane showed rhombic symmetry, with, however, appreciable approximation to ditetragonal symmetry. The unit of structure has the dimensions... 

Following the discovery of the above solid-state fluoride anion complex, the authors succeeded in crystallizing the bishydrochloride salt of this same system, 3. The X-ray structure of this derivative revealed the presence of two chloride counterions bound via hydrogen bonds to the diprotonated macrocycle (Figure 2). In contrast to what was seen in the case of the fluoride anion structure, in this instance neither of the counteranions is located in the plane of the sapphyrin macrocycle. Rather, they are found in near symmetric fashion ca. 1.8 A above and below the mean Nj plane. This out-of-plane binding reflects, presumably, the fact... 

The X-ray crystal structures of the F", Cl , and Br" cryptates of 19-6H demonstrate the inclusion of one of the halide anions in an unsymmetrical fashion. In the case of the small fluoride ion complex a tetrahedral coordination environment is observed for the guest anion with a mean N(H) - P hydrogen-bonding distance of 2.72(8) A. The CP and Br" cryptates exhibit octahedrally coordinated halide ions situated more centrally within the host framework with N(H) - X" distances in the ranges 3.19-3.39 A (X = CP) and 3.33-3.47 A (X = Br ). It is noteworthy that the hydrogen-bonded distances for the anion within the cryptand host are longer by up to ca 0.15 A than those for the other anions in the lattice, suggesting a particularly... 

More recently, the crystal structure of atactic polyvinyl fluoride, which is highly crystalline under ordinary conditions, was reported (49) here the atoms replacing each other randomly are hydrogen and fluorine, whose van der Waals radii are also similar ( 1.25 and 1.35 A respectively (48)). 

PF6, SbF6, C104-, FSO3 counterions. The X-ray crystal structure of nitronium ion is known with hydrosulfate anion.515 The most widely used tetrafluoroborate nitronium salt (N02+BF4 ) is prepared by treating a mixture of nitric acid and anhydrous hydrogen fluoride wit boron trifluoride516 [Eq. (4.145)]. 

In the structure of [PSH][TFA] (Fig. 3) [50] the expected tetrahedral anion was confirmed. Not surprisingly, the F-Al-F bond angles were approximately 109°, with equivalent Al-F distances of around 1.62 A. The closest contact between the coordinated fluoride and the chelated proton of the cation was 2.77 A, which could be considered a long hydrogen bond. The crystal structures of [Ph4P][TFA], [Ph4As][TFA], and [n-Bu4N][TFA] (Fig. 4) have also been reported and are similar to that of [PSH][TFA] with discrete cations and anions [8]. 

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