s-Block chalcogenoether chemistry--thio- and selenoether coordination with hard Group 2 ions

A highly unusual series of Group 2 complexes with soft thio- and selenoether coordination, [MI(2)([18]aneO(4)E(2))] (M = Ca or Sr; E = S or Se), [CaI(2)([18]aneO(2)S(4))] and [MI(2)([15]aneO(3)S(2))], has been prepared by reaction of anhydrous MI(2) with the macrocycle in dry MeCN solution. The complexes have been characterised via(1)H NMR and IR spectroscopy, microanalysis and crystallographic studies which provide unambiguous confirmation of the M-S/Se coordination. The neutral complexes are seven- or eight-coordinate with the iodo ligands cis. The long M-E bond distances of ∼3.0 Å indicate weak interactions, but they are significantly less than the sum of the van der Waals radii for M and E, and are important in facilitating isolation of the complexes. Trace hydrolysis of [MI(2)([18]aneO(4)E(2))] and [SrI(2)([15]aneO(3)S(2))] leads, unexpectedly, to displacement of the iodo ligands rather than the S/Se donor functions, and the resulting dicationic [Ca(H(2)O)(2)([18]aneO(4)S(2))]I(2), [Sr(H(2)O)(3)([18]aneO(4)S(2))]I(2)·H(2)O, [Sr(H(2)O)(3)([18]aneO(4)Se(2))]I(2) and [Sr(H(2)O)(3)([15]aneO(3)S(2))]I(2) complexes have been structurally characterised, forming eight- and nine-coordinate cations, with all the macrocyclic donor atoms coordinated. Reaction of Ca(CF(3)SO(3))(2) with [18]aneO(4)S(2) in anhydrous MeCN solution similarly affords [Ca(CF(3)SO(3))(2)([18]aneO(4)S(2))], albeit in low yield, also proven crystallographically. Using the MI(2) precursors provides a general entry into this area of coordination chemistry of these Group 2 ions, owing in part at least to their higher solubility in the weak donor (weakly competing) MeCN solvent. While CaCl(2) reacts with 18-crown-6 either directly in MeCN giving [CaCl(2)(18-crown-6)], or in the presence of SbCl(5) (to form trans-[Ca(MeCN)(2)(18-crown-6)][SbCl(6)](2)), neither of these routes works with the oxa-thia or oxa-selena crowns.