Alkali metal, crown ether complexes

The following reference gives an account of the coordination chemistry of alkali metal crown ether complexes ... 

Phosphorus tricyanide reacts with dialkyl phosphites at low temperatures to give the planar dicy-anophosphide anion P (CbOj which can conveniently be isolated as alkali metal/crown ether complexes (Figure 6.15). In the absence of a base the reaction products are quite different. 

Figure 4.11 Molecular structures of typical crown-ether complexes with alkali metal cations (a) sodium-water-benzo-I5-crown-5 showing pentagonal-pyramidal coordination of Na by 6 oxygen atoms (b) 18-crown-6-potassium-ethyl acetoacetate enolate showing unsymmelrical coordination of K by 8 oxygen atoms and (c) the RbNCS ion pair coordinated by dibenzo-I8-crown-6 to give seven-fold coordination about Rb.

Fig. 3.6-1. Topological relationship between conventional crown ether complexes and their inverse counterparts. M denotes an alkali metal circled M denotes Mg orZn.

Kollig, H.P., Ellington, J.J., Weber, E.J., and Wolfe, N.L. Environmental research brief - Pathway analysis of chemical hydrolysis for 14 RCRA chemicals. Office of Research and Development. U.S. EPA Report 600/M-89/009, 1990, 6 p. Kolthoff, I.M. and Chantooni, M.K., Jr. Crown ether complexed alkali metal picrate ion pairs in water-saturated dichloro-methane as studied by electrolytic conductance and by partitioning into water. Effect of lithium chloride on partitioning, J. Chem. Eng. Data, 42(l) 49-53, 1997. 

An important class of alkali and alkaline earth metal amides are Mulvey s inverse crown complexes (also discussed in Chapter 2, dealing with sodium and potassium amides), in which cationic homo- or heterometallic macrocycles are hosts to anionic guest moieties.The term inverse crown indicates that the Lewis acidic/Lewis basic sites are reversed or exchanged in comparison to conventional crown ether complexes. Scheme 3.9 illustrates the range of recently published alkali and alkaline earth metal amide inverse crown complexes (for related Zn species see Chapter 7 on group 12 amides). 

In contrast to the alkali metals, the lanthanides do not form crown ether complexes readily in aqueous solution, due to the considerable hydration energy of the Ln + ion. These complexes are, however, readily synthesized by operating in non-aqueous solvents. Because many studies have been made with lanthanide nitrate complexes, coordination numbers are often high. Thus 12-coordination is found in La(N03)3(18-crown-6) (Eigure 4.4), 11 coordination in La(N03)3(15-crown-5), and 10 coordination is found in La(N03)3(12-crown-4). Other complexes isolated include Nd(18-crown-6)o.75(N03)3, which is in fact [ Nd(18-crown-6)(N03)2 +]3 psid(N03)6]. Other lanthanide salts complex with crown ethers small crowns like 12-crown-4 give 2 1 complexes with lanthanide perchlorates, though the 2 1 complexes are not obtained with lanthanide nitrates where the anion can... 

The crown ether-complexed alkali metal ions are large and hydrophobic, and their salts tend to be soluble in organic solvents. For example, whereas KMn04 is water-soluble but insoluble in benzene, [K(18-crown-6)][Mn04] is soluble in benzene mixing benzene with aqueous KMn04 leads to the purple colour being transferred from the aqueous to the benzene layer. This phenomenon is very useful in... 

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