Lanthanide complexes hexamethylphosphoramide

FIG. 8. (a) Plot of log,0 1 against the 8-coordinate ionic radius of the lanthanide ion for Lnffod-dg) complexes. Ic, is the first-order rate constant for substrate exchange HMP = 1,2-hexamethylphosphoramide TMU = tetramethylurea. (b) Suggested energy profile for substrate exchange. (481)... 

Solutions of alkali metals in ammonia have been the best studied, but other metals and other solvents give similar results. The alkaline earth metals except- beryllium form similar solutions readily, but upon evaporation a solid ammoniate," MINI-lj),. is formed. Lanthanide elements with stable + 2 oxidation states (europium, ytterbium) also form solutions. Cathodic reduction of solutions of aluminum iodide, beryllium chloride, and tetraalkylammonium halides yields blue solutions, presumably containing Al, 3e Be", 2e and R4N, e respectively. Other solvents such as various amines, ethers, and hexamethylphosphoramide have been investigated and show some propensity to form this type of solution. Although none does so as readily as ammonia, stabilization of the cation by complexation results in typical blue solutions... 

The complexes of monodentate oxygen ligands are less stable than those of chelates and tend to dissociate in aqueous solution the ions associate in aqueous solution with both nitrate and sulfate to give species such as MNOj +, MS04, etc., and anionic carbonate complexes are known. Many crystalline compounds or salts have been obtained from the lanthanide salts in ethanolic solutions (a) with hexamethylphosphoramide,27 which appears to give 6-coordinate species, [M(HMPA)6](C104)3, (b) with triphenyl-... 

In the case of hexamethylphosphoramide ((Me2N)3PO), a maximum of six of these ligands coordinate to a lanthanide, as in [Ln(hmpa)6]X3 (Ln = La-Lu X = CIO4, Br04, Re04). The most interesting hmpa complexes are the chlorides, where both fac- and wer-[LnCl3(hmpa)3] can be isolated they isomerize in solution by an associative mechanism. [La(hmpa)3(N03)3] is nine coordinate and... 

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