Supramolecular Dimers of Copper(II) Complexes Resulting from Designed Host-Guest Interactions

Syntheses, characterization and crystal structures of four designed host-guest compounds of the compositions [{(CuLI)-L-II}(2)subset of(H3N(ethylene)NH3)](NO3)(2) (1), [{(CuLI)-L-II}(2)subset of(H3N-(propylene)NH3)] (NO3)(2) (2), [{(CuLI)-L-II}(2)subset of(H3N(butylene)-NH3)](NO3)(2) (3) and [{(CuL2)-L-II}(2)subset of(H3N(ethylene)NH3](NO3)(2) (4) are described in this investigation [H2L1 = N,N'-ethyl-enebis(3-methoxysalicylaldimine); H2L2 = N,N'-ethyl-enebis(3-ethoxysalicylaldimine); ethylene = (CH2)(2); propylene = (CH2)3; butylene = (CH,,)41, Compounds 2 and 3 crystallize in the orthorhombic Pcab and monoclinic C2/c systems, respectively, while the space group of compounds 1 and 4 is triclinic Pi. In all of these four compounds 1-4, the two +NH3 sites of the [H3N(CH2)(n)NH3](2+) dication (n = 2-4) behave as guests in the 04 compartment of two [(CuL1)-L-II/L-2] moieties through bifurcated N-H center dot center dot center dot O(phenoxo) and N-H center dot center dot center dot O(methoxy/ethoxy) hydrogen-bonding interactions. Evidently, two mononuclear copper(II) moieties are interlinked by bridging supramolecular synthons, resulting in the formation of a supramolecular dimer in the title compounds. From the extent of displacement of the N atoms of [H3N(CH2)(n)-NH3](2+) from the least-squares O(phenoxo)(2)O(methoxy/ethoxy)2 plane, it is clear that [(CuL1)-L-II] is a better host than [(CuL2)-L-II] for the diprotonated diamine guests. Comparison of the inclusion of water and diprotonated diamines in [(CuL1)-L-II/L-2] is also described in the present investigation. Interestingly, of the two guest species, water and diprotonated diamines, [(CuL2)-L-II] prefers the former and [(CuL1)-L-II] prefers the latter.