Crystal structure showing cation positions

Several other polyiodide salts with cations not conventionally associated with ionic liquid behaviour are noted for completeness. These include the salt, bis(l,3-dimethylthiourea)iodinium triidodide [363], that melts at 87°C. The crystal structure shows that the closest approach of the positively charged iodine with any atom of the triiodide counter-ion is at, or greater than, the sum of the van der Waals radii for two iodine atoms, suggesting little interaction. The structure of the long-known [I(py)2][l7] [682] has been described [347]. 

X-ray structural analysis of the methylsulfate compound indicates the orthorhombic crystal unit cell contains two translationally inequivalent cations positioned on mirror planes and tilted at 3 ° relative to the two-fold screw (c) axis (23). This is a compromise orientation for simultaneously, rather than individually, maximizing x ccc and x /> bbc in this polar structure. This structure is therefore consistent with the extremely large SHG intensity reported in Table 1 while, also consistently, preliminary x-ray data show the perrhenate and tetrafluoroborate salts to be isostructural (23.). Details of the packing... 

Figure 2. (a) Crystal structure ofCClfSb(OTeFs)f (b) A view of the CClf cation, with key bond lengths and bond angles, showing the two-fold positional disorder around the crystallographic inversion center.82... 

Figure 7 shows a plot of x as a function of cp. A rough correlation can be seen if cp is positive then x is positive and if cp is negative then x is negative. The crystal structure of XAGWUX contains two independent molecules with opposite conformations. One of the molecules is syn-syn the other is anti-anti. This occurrence frustrates any attempts to correlate the conformation of the cation with the acidic strength of the anion or other counter ion effects. 

The first pentagonal bipyramidal complex of zinc, ZnLCl2 3H20, was reported in 1973, where L is the planar five-coordinate 2,6-diacetylpyridinebis(semicarbazone).346 The crystal structure determination shows the complex to contain the [LZnG(H2Q)]+ cation, with three bland two O-donor atoms forming a slightly distorted planar pentagon around the metal ion and the chlorine and water in axial positions. 

The X-ray crystal structure of protonated formic acid, acetic acid, and methyl formate has recently been determined by Minkwitz and co-workers. In agreement with NMR data discussed above, the nearly equal C—O bond lengths of protonated formic acid (1.239 and 1.255 A),573 protonated acetic acid 275 (1.251-1.291 A for various salts),574 and protonated methyl formate 276 (1.260 and 1.264 A)575 show efficient delocalization of the positive charge. Minkwitz et al.576 have also studied protonation of oxalic acid in HF-SbF5 and isolated the hexafluoroantimonate of the mono- and diprotonated acid at 75°C and 40°C, respectively. Structural characteristics are very similar to those of the other cations discussed. 

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