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)-H21, followed by reaction with NH4PF6, NaClO4, KBr, KSCN, CsCl, Ca(NO3)2·4H2O or BaI2 leads to the isolation of crystalline products, which illustrate the ability of the vacant O4-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 Ca2+) are bound in the plane of the O4-donor set, with axial sites being occupied by methanol or coordinating anions. The bridging mode adopted by [NO3]− anions results in the assembly of a chiral, one-dimensional coordination polymer. Larger cations ([NH4]+, K+, Cs+, Ba2+) are sited above the plane of the O4-donor cavity and give rise to either sandwich-type complexes (both transoid and cisoid) or, in the case of Ba2+, to a 1 : 2 complex in which the [Cu{(R,R)-1}] ligands tend towards a mutually orthogonal arrangement. The 9-coordinate Ba2+ 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 O4-domain to host a cyclohexane-1,2-diyl unit through C–H⋯O non-classical hydrogen bonds. The O4-donor set appears to be too distant from the chiral auxiliary for its stereochemical information to be recognized by the cation hosted within the O4-cavity.