The mononuclear-dinuclear dance: Twisting the backbone in metalloligands operates a coordination switch

The copper(II) complex [Cu{(R,R)-1}] in which (R)-H(2)1 is 1,6-bis(3-ethoxy-2-hydroxyphenyl)-(3R,4R)-(-)-cyclohexane-1,2-diyl-2,5-diazahexa-1,5-diene possesses an O-4-donor cavity that can bind Pb2+, Cd2+ and Eu3+. The single crystal structures of [Cu(OH2){(R,R)-1}Pb(ONO2)(2)], {[Cu{(R,R)-1}Cd(O-NO2)(OH2)(2)][NO3]center dot MeOH}center dot[Cu{(R,R)-1}] and [Cu{(R,R)-1}Eu(O2NO)(3)] are presented. The co-crystallization of [Cu{(R,R)-1}Cd(ONO2)(OH2)(2)][NO3] and [Cu{(R,R)-1}] appears to be driven by hydrogen-bonded host-guest interactions between each axial water ligand in [Cu{(R,R)-1}Cd(ONO2)(OH2)(2)](+) with the O-4-domain of [Cu{(R,R)-1}]. When the ligand scaffold is changed from cyclohexane-1,2-diyl to 1,1'-binaphthyl to give (R)-H(2)2, the N2O2-cavity is unable to bind copper(II) in its preferred square planar environment. The single crystal structure of [Zn{(R)-2}] confirms the presence of tetrahedral zinc(II). As a result, the spatial properties of the ethoxy arms in [Zn{(R)-2}] and [Cu{(R)-2}] are not suited to the facile formation of dimetallic complexes. (C) 2010 Elsevier B.V. All rights reserved.