Fluoride coordination

The differences of the Ru—F-distances in RuFg and the octahedral distortions correspond closely to those of the MoFg-structure. The Ru—F-distances range from 1.78 A to 2.10 A for singly and doubly coordinated fluoride ions resp. The smallest F—F-distance in the linked RuFs-octa-hedra is reported to be 2,48 A. 

Fig. 16. Two-dimensional, tangent-circle representation of an electron-domain model of a coordinated fluoride ion...

Difluoro- and trifluorosilanes tend to coordinate fluoride anions under formation of five-and six-coordinate fluorosilicates88,89 (equations 53 and 54). 

An empirical set of effective ionic radii in oxides and fluorides, taking into account the electronic spin state and coordination of both the cation and anion, have been calculated (114). For six-coordinate Bk(III), the radii values are 0.096 nm, based on a six-coordinate oxide ion radius of 0.140 nm, and 0.110 nm, based on a six-coordinate fluoride ion radius of 0.119 nm. For eight-coordinate Bk(IV), the corresponding values are 0.093 and 0.107 nm, based on the same anion radii (114). Other self-consistent sets of trivalent and tetravalent lanthanide and actinide ionic radii, based on isomorphous series of oxides (145, 157) and fluorides (148, 157), have been published. Based on a crystal radius for Cf(III), the ionic radius of isoelectronic Bk(II) was calculated to be 0.114 nm (158). It is important to note, however, that meaningful comparisons of ionic radii can be made only if the values compared are calculated in like fashion from the same type of compound, both with respect to composition and crystal structure. 

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]. 

While it can be debated whether or not a PFf, counter anion actually provided the source of adventitious fluoride anion in the original Sessler-Ibers structure (see footnote 17 in reference 280), its very existence nonetheless stands as clear proof that the doubly protonated form of sapphyrin can indeed coordinate fluoride anion in the solid state. This seminal result thus led directly... 

The seven-coordinate fluoride K2WF7 was prepared by reaction of KWFe with LiF at high temperatures and under vacuum. 

Figure 2.19 The structure of the aluminophosphate fluoride UT-6 is based on the CHA framework but includes coordinated fluoride ions linking octahe-drally coordinated aluminium cations (white octahedra).

Metal complexes have a variety of stractures. Silver complexes are often linear beryllium complexes are usually tetrahedral iron forms a carbonyl compound that has a trigonal bipyramidal structure cobalt(lll) complexes are octahedral and tantalum forms an eight-coordinated fluoride complex (Figure 3.1). Although a variety of coordination numbers and structures have been observed in metal complexes, the only common coordination numbers are four and six the common structures corresponding to these coordination numbers are tetrahedral and square planar, and octahedral, respectively. In studying metal complexes, it soon becomes clear that the octahedral structure is by far the most common of these configurations. 

---