Crown solvent molecule

From the method of preparation of [BeCl(12-crown-4)]+ (179), it is known that the Cl ligand can be substituted by a solvent molecule. We applied our most common test solvents water and NH3 to a Be2+ cation, where most coordination sites are occupied by a chelating ligand, in this case the crown ether 12-crown-4. In contrast to the tetrahedral [Be(solvent)4]2+ solvated complexes, the precursor complexes [Be(solvent)(12-crown-4)]2+ are quadratic pyramidal, where four oxygen donor atoms of the crown ether form the quadratic basis, while Cl- or a coordinating solvent molecule occupies the apical position. Addition of one water or ammonia molecule to [Be(12-crown-4)]2+ is exothermic (see Table IX). 

Addition of a second water or ammonia molecule results in the formation of [Be(solvent)(12-crown-4)---(solvent )]2+, where the second solvent molecule, is regarded as present in the second solvation sphere and is very loosely attached ([Be(H20)(12-crown-4)---(H20)]. 3.71 A [Be(NH3)(12-crown-4) (NH3)]2+ 5.06A)... 

An interesting question is whether the peroxo ligand in our [Fe (Porph)(02 )] complex is coordinated in a side-on or end-on fashion. Taking into consideration the DMSO coordination and the electrophilic potassium cation in the crown ether lying above the peroxo ligand, [Fe (Porph)(02 )] may in a way represent a model for the proposed (59) nucleophilic attack of the end-on peroxo form, with an axially coordinated solvent molecule, to an electron-deficient substrate (Scheme 14). 

The same authors have found that the inhibition effect of crown ethers [230] and crown esters [229] on cadmium electrodeposition from water-AN mixtures was caused by the competitive adsorption of macrocycles and organic solvents molecules. The effect of structure and concentration of crown ethers on the cadmium electrodeposition from aqueous sulfate solutions was also studied [231]. 

In these equations, Cr refers to a crown ether ligand while S denotes a solvent molecule. The notation Sn following Fl, Na+ signifies that In solvents such as dloxane, ethyl ether, tetra-hydropyran (THP) or tetrahydrofuran (THF) the tight ion pairs, especially when small alkali Ions are Involved, contain externally complexed solvent molecules. These must be removed before... 

Figure 10. Solvation of twelve 18C6 crowns "diluted" in dry versus humid [BMI][PF6] solutions. Typical snapshots of die "first shell" solvent molecules and radial distribution functions "RDFs" around the center of the crown 18C6 BMI (bold), 18C6 F (dotted), 18C6 P (plain) and Sr OH2 (inversed ordinate).

The crown-shaped molecule Se8 has long been known to crystallize in two monoclinic lattices termed a- and jS-Se8, respectively (see Table II). Crystals of various sizes have been obtained from CS2 solutions prepared by dissolution of either red amorphous Se (22) or of vitreous selenium in CS2 and subsequent cooling or evaporation of the solvent (3a,b, 4a, 5). Red amorphous Se is readily soluble in CS2, but since both vitreous and red amorphous Se do not contain more than small amounts of Se8, the dissolution must be accompanied by a chemical interconversion. It has, however, been reported (26) that the dissolution of red amorphous Se in CS2 requires illumination with photons of energies in excess of 2.3 eV, ambient room light levels being sufficient. 

The electrode is deactivated during massive reduction of solution species when polarized to low potentials (as happens with PC solutions) [356-357], The detrimental effect of co-intercalation of solvent molecules in this case is proven by the fact that, in PC solutions containing crown ethers (which solvate... 

This preorganization principle not only affects the thermodynamic stability of the complex but also has a pronounced effect on the kinetic stability of the alkali complexes of the spherands. The anisyl groups in the spherands provide the preorganized ligating donor sites, and they shield the cavity from solvent molecules. As a result, the rates of complexation by the spherands are decreased and the rates of decomplexation are decreased even more when compared with related flexible crown ethers. 

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