Crown ether chemistry of the alkaline earth nitrates

Crystallization of the alkaline earth nitrates M(NO3)(2). xH(2)O (M = Mg, x = 6; M = Ca, x = 4; M = Sr or Ba, x = 0) from an aqueous solution of either 15-crown-5 or 18-crown-6 resulted in complex formation in all cases. Thus, [Mg(H2O)(2)(15-crown-5)](3)[NO3](6) and [Mg(H2O)(5)(NO3)]NO3. 18-crown-6 . H2O, [Ca(NO3)(2)(15-crown-5)], [Sr(H2O)(NO3)(2)(15-crown-5)], [Sr(NO3)(2)(18-crown-6)], [Ba(15-crown-5)(2)][Ba(NO3)(3)(15-crown-5)](2) and [Ba(H2O)(NO3)(2)(18-crown-6)] have all been characterized using X-ray crystallography. Wide variations in the co-ordination sphere of the metals are observed as the ionic radius increases, and the mode of bonding to the crown ether varies considerably as the diameter of the crown is modified.