Perchlorates coordinating ability

In light of the great affinity of silylenium ions for electron-rich species, one could be also skeptical about the possibility of the existence of the tricoordinate Si+ species in solvents like acetonitrile (AN) and sulfolane. These solvents are known to have nucleophilic coordination ability. Gut-mann s donicity number (84), 14.1 and 14.8 for AN and sulfolane, respectively, is comparable to that for acetone, 17.0. Coordination of acetonitrile to silicon has been considered in some systems (85,86). The small equivalent conductance of triphenylsilyl perchlorate in CH2C12 may be explained by the domination of the covalent form (18). Consequently, the absence of the coordination of acetonitrile and sulfolane with the tricoordinate Si+ observed in CH2C12 (with 1 or 6 equiv of acetonitrile) may simply indicate that C104 coordinates to Si+ under these conditions more readily than acetonitrile and sulfolane [Eq. (15)]. The reverse situation in acetonitrile... 

The ratio of the size of the metal ion and the radius of the internal cavity of the macrocyclic polyether determines the stoichiometry of these complexes. The stoichiometry of these complexes also depends on the coordinating ability of the anion associated with the lanthanide. For example, 12-crown-4 ether forms a bis complex with lanthanide perchlorate in acetonitrile while a 1 1 complex is formed when lanthanide nitrate is used in the synthesis [66]. Unusual stoichiometries of M L are observed when L = 12 crown-4 ether and M is lanthanide trifluoroacetate [67]. In the case of 18-crown-6 ligand and neodymium nitrate a 4 3 stoichiometry has been observed for M L. The composition of the complex [68] has been found to be two units of [Nd(18-crown-6)(N03)]2+ and [Nd(NCh)<--)]3. A similar situation is encountered [69] when L = 2.2.2 cryptand and one has [Eu(N03)5-H20]2- anions and [Eu(2.2.2)N03]+ cations. It is important to note that traces of moisture can lead to polynuclear macrocyclic complexes containing hydroxy lanthanide ions. Thus it is imperative that the synthesis of macrocyclic complexes be performed under anhydrous conditions. 

Copper perchlorate and tetrafluoroborate salts have also been found to form coordination compounds with the neutral ligands L37 (n = 2 or 3), but the structures vary little due to nonparticipation of the counteranions C104 and BF4 for their weak coordinating ability 110, 111). In fact, they are 1 1 metal-ligand compounds in which... 

ESR spectra (Table 1). The JV-cyclohexylthiosemicarbazone, 13, complex formed the expected [Fe(13-H)2] with FeCl as the counterion [141]. However, [Fe(13) (13-H)H20]C104 was isolated from ethanol. Bulkiness of the cyclohexyl group, and the perchlorate ion s greater ability to hydrogen bond are probably both important to the stability of this cation. The iron(III) center is considered six-coordinate with a tridentate 13-H, bidentate 13, and a coordinated water molecule. 

Such effects on the catalytic ability of mercuric ion by solvent water have been demonstrated in the hydration of acetylenes catalyzed by mercuric perchlorate (132b). Large amounts of water impede reaction by competing too successfully with the acetylene for coordination sites around the mercuric ion. 

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