Host-guest chemistry of a chiral Schiff base copper(II) complex: can chiral information be transferred to the guest cation?

The in situ formation of [Cu{(R,R)-1}] through the reaction of copper(II) acetate with 1,6-bis(3-ethoxy-2- hydroxyphenyl)-(3R,4R)-(-)-cyclohexane-1,2-diyl-2,5-diazahexa-1,5-diene, (R,R)-H(2)1, followed by reaction with NH(4)PF(6), NaClO(4), KBr, KSCN, CsCl, Ca(NO(3))(2)center dot 4H(2)O or BaI(2) leads to the isolation of crystalline products, which illustrate the ability of the vacant O(4)-donor cavity in [Cu{(R,R)-1}] to host ammonium or s-block metal cations in a variety of manners. The smallest cations (Na(+) and Ca(2+)) are bound in the plane of the O(4)-donor set, with axial sites being occupied by methanol or coordinating anions. The bridging mode adopted by [NO(3)](-) anions results in the assembly of a chiral, one-dimensional coordination polymer. Larger cations ([NH(4)](+), K(+), Cs(+), Ba(2+)) are sited above the plane of the O(4)-donor cavity and give rise to either sandwich-type complexes (both transoid and cisoid) or, in the case of Ba(2+), to a 1 : 2 complex in which the [Cu{( R,R)-1}] ligands tend towards a mutually orthogonal arrangement. The 9-coordinate Ba(2+) coordination environment is completed by a methanol ligand. In all but the latter complex, a common feature of the molecular packing is the ability of the O(4)-domain to host a cyclohexane-1,2-diyl unit through C-H center dot center dot center dot O non-classical hydrogen bonds. The O(4)-donor set appears to be too distant from the chiral auxiliary for its stereochemical information to be recognized by the cation hosted within the O(4)-cavity.