132038-47-2Relevant academic research and scientific papers
Ligation and Charge Separation of Alkali and Alkaline Earth Cations with Benzo-15-crown-5
Poonia, Narinder S.,Bajaj, Amritlal V.,Arora, Ashok K.,Joshi, Kalpana,Banthia, Anila
, p. 37 - 43 (2007/10/02)
Conditions for 1:1 complexation (ligation) and 1:2 sandwich encapsulation (charge separation) of Ca and Mg (M(2+)) with a macrocyclic multidentate - benzo-15-crown-5 (CROWN) - have been worked out.It is not strong solvation of M(2+) but its involvement with the counter anion which deters both the processes; water in the reaction medium favours the processes by aiding ion separation and ion stabilization.Conductance measurements in isopropanol and isopropanol-water mixtures (7:3 and 5:5) show that with CROWN each of Li, Na, K (M(+)) and M(2+) undergoes charge separation from picrate (Pic); Mg in isopropanol as well as in aqueous isopropanol whereas Na and Ca decisively in aqueous isopropanol.Although stability of M(Pic)2(CROWN)2 complexes in these media decreases with increase in water content yet the isolation is favoured; a novel product Li(Pic)(CROWN)*2aq has been isolated from almost pure water.Solid charge-separated M(Pic)(CROWN)2 product has been prepared only for K.X-ray diffraction analysis reveals cation-anion involvement to be profoundly strong for Ca in that the compounds Ca(Pic)2(CROWN)*3aq and Ca(3,5-dinitrobenzoate)2-(CROWN)2*3aq are both ion-paired and each contains an uncomplexed molecule of CROWN.CROWN/Ca(2+) ratio in the solid phase can be varied by controlling the 'effective charge density' of M(2+) through a change of the counter anion or by stabilizing the latter with a foreign proton donor.
