Complexation of sodium and potassium with macrocyclic polyethers; activation of the counter anions

Abstract

Complexation of inorganic salts of sodium and potassium, MX (X = NCS −, I −, Br −, Cl − and PO 4 −3) with benzo-15-crown-5 (I) and dibenzo-30-crown-10 (II) in ethanolic (methanolic) and aq-ethanolic (aq-methanolic) media has been carried out using diverse organic protonated molecules, HL, in the reaction medium. Polyethers I and II with potassium form [K−-I 2] + and [K-II] + which due to their low charge density fails to stabilise the counter anion, X. Consequently, reactions X −+HL=X...HL −=HX+L −  HL L,(HL) n − take place in this order. In addition to some new complexes of the old type, viz. [K-I 2]Benz,2 BenzH and [K-II]NCS, BenzH (BenzH = benzoic acid and Benz its anion) new series of complexes (i) [K-II]L,HL (HL = 2-nitrophenol (OnpH), 2,4-dinitrophenol (DnpH), or 2,4,6-trinitrophenol (PicH)), (ii) [K-II]Pic, and (iii) [K-R]X, (HL) n (for R = I, HL = a molecule of OnpH or DnpH for X = Cl −, and BenzH for X = NCS −; and for R = II, HL = two molecules of OnpH when X = NCS −) have been isolated. With I and II, sodium forms cations [Na-I] + and [Na 2-II] +, which possess nearly double the charge density compared to analogous potassium cations, activation of only Cl − and PO 4 3− could be noticed that too towards strong proton donor, PicH; Pic − produced in situ, however, is not allowed to undergo homoconjugation by the high charge density cations. The bimetallic compound [Na 2-II]2Pic so obtained is also the first of its type.