Solid-state models of ion solvation: Crystal structures of dimethyl sulfoxide solvates of alkaline earth cations

Structural studies of the dimethyl sulfoxide solvates of the perchlorates of Mg, Sr and Ba show the presence of a variety of complex ion species indicative of the forms possible in solution. While Mg(ClO4)(2)(.)6dmso contains the expected [Mg(dmso)(6)](2+) cation, the crystallised strontium species contains a mononuclear [Sr(dmso)(6)](2+) cation and two dinuclear species, the complex [(dmso-O)(5)Sr(mu-dmso-O)(3)Sr(OH2)-(dmso-O)(3)](4+) containing both seven- and eight-coordinate Sr metal centres, and [{(dmso-O)(5)Sr(mu-dmso-O)}(2)](4+) containing seven-coordinate Sr metal centres. The barium complex, of empirical formula Ba(ClO4)(2)(.)5dmso, contains a centrosymmetric dimer, [Ba-2(dmso-O)(6)(mu-dmso-O)(4)(O2ClO2)(2)](2+), involving an unsymmetrically chelating perchlorate and a nine-coordinate Ba metal centre. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.