Counter anion structures

The x-ray crystal structures of the hexaethyl- and hexabutenylbenzene complexes show noteworthy conformational effects [78] (Fig. 6). The hexaethylbenzene complex has four distal chains [76] contrary to all the previous conformations of C6Et6 and (M)C6Et6 of C3 symmetry. This conformation also depends on the counter-anion as the three conformations with four, five, and six distal ET groups have close energies and can be observed by low-temperature 1H NMR. The hexabutenyl benzene complex has five distal chains [77]. 

Fig.1. Structures of porphyrin 1, chlorophyll 2, and phthalocyanine 3. In the presence of metal salts M"+X (M=metal, X=counter anion, n=oxidation state or number of counter anions), porphyrins produce chelate complexes. Some metal chelates of the porphyrins, such as ZnPor, form further coordination bonds with other ligands such as pyridines...

Open chain polyamine ligands have been widely studied. Often the coordination of zinc is compared with other first row transition metals and factors, such as behavior across a pH range, studied. The protonation patterns and stability constants are of particular interest. Octahedral zinc tris(ethylenediamine) structures have been characterized by X-ray diffraction with a number of different counter anions.94 The X-ray structure of zinc tris(ethylenediamine) with fluoride counter ions reveals extensive hydrogen bonding.95... 

Siderophore-ionophore supramolecular assembly formation via host-guest complexation of the pendant protonated amine arm of ferrioxamine B has been confirmed by X-ray crystallography (Fig. 28) (203). The stability and selectivity of this interaction as a function of ionophore structure, metal ion identity, and counter anion identity were determined by liquid-liquid extraction, isothermal calorimetry, and MS (204 -211). Second-sphere host-guest complexation constants fall in the range 103— 106M-1 in CHC13 and methanol depending on ionophore structure. 

The structure of the compound consists of two residues, one cationic (PYS-PYSH)+, containing the S-S bond linking the two 2-mercapto-pyridine molecules one of which is protonated and Ij as a counter anion. In the crystal lattice there are four symmetry-independent cation-anion pairs. There are only a few crystal structures reported in the literature containing open chain stable cations of DS-SD dimers, such as the monocationic [(C HgN S-SNjC Hj) ) ) [15]. The two I-I bond distances of the Ij" in the four components of complex (26) are 2.887(4) and 2.944(3) A in component a, 2.874(4) and 2.957(3) A in b, 2.968(3) and 2.862(3) A in c and 2.855(4) and 2.927(3) A in d, respectively, indicating a slight asymmetry of I3 in this complex (covalent hnear asymmetric). 

Work with supported ionic liquids was extended to a cationic polymer, poly (diallyldimethylammonium chloride), which has quaternary ammonium functional groups (Fig. 16) 268). The extra-structural counter anion is Cl . The polymer was applied to simultaneously incorporate an ionic liquid and a transition-metal catalyst via a simple mixing of the components. Wilkinson s catalyst and [BMIM]PF6 were... 

Other aspects related to the packing of these grid structures, the presence of a multitude of interactions between the tetranuclear cations and the counter-anions not hosted in the cavities, and with the crystallization solvent molecules, are beyond the scope of this discussion. In general all of these solids can be considered as microporous and the anions and solvent molecules located within these pores are normally very disordered. Figure 3.7 shows two selected examples, where channels are formed along the c axis in complexes 49 and 40. In the former, disordered triflate anions located in the channels are drawn in grey. In the second example, the regular... 

Figure 3.6 Full space representation of the structure of 40, showing the cavities of the grid formed by four camphor groups and two counter-anions where the external-grid toluene molecules are trapped. In (b) the face-to-face re stacking (A) of these toluene molecules with the pyrimidines is emphasized.

The grid compounds described in this chapter exhibit limited solubility in most organic solvents but are sufficiently soluble in acetone-dg to record H NMR spectra and spectra in the majority of cases. In dmso-dg and acetonitrile-dj they decompose, releasing the free ligands. Evidence for the stability of the structures in acetone solutions, at least when the counter-anion has a low coordinating ability (PFfi-, BF,, trifiate, CIO4 ), is obtained from the spectra (a) The chemical shifts of... 

A relative selectivity toward one of the anions, which depends on the grid-complex used as the starting material, was observed in these experiments. It is interesting to compare the results of tests 2 and 3, on the one hand, and those of tests 4 and 5 on the other. These correspond to experiments in which the same cationic grid is used as the starting material but with a different counter-anion. The data are clearly different, indicating that the solid state structure of the starting material is very important in the selectivity towards a specific anion. 

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