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 [{Cu II L 1 } 2 ⊂(H 3 N(ethylene)NH 3 )](NO 3 ) 2 (1), [{Cu II L 1 } 2 ⊂(H 3 N-(propylene)NH 3 )](NO 3 ) 2 (2), [{Cu II L 1 } 2 ⊂(H 3 N(butylene)-NH 3 )](NO 3 ) 2 (3) and [{Cu II L 2 } 2 ⊂(H 3 N(ethylene)NH 3 )](NO 3 ) 2 (4) are described in this investigation [H 2 L 1 = N,N'-ethylenebis(3-methoxysalicylaldimine); H 2 L 2 = N,N'-ethylenebis(3-ethoxysalicylaldimine); ethylene = (CH 2 ) 2 ; propylene = (CH 2 ) 3 ; butylene = (CH 2 ) 4 ]. 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 + NH 3 sites of the [H 3 N(CH 2 ) n NH 3 ] 2+ dication (n = 2-4) behave as guests in the 0 4 compartment of two [Cu II L 1 /L 2 ] moieties through bifurcated N-H···O(phenoxo) and NH···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 [H 3 N(CH 2 ) n- NH 3 ] 2+ from the least-squares O(phenoxo) 2 O(methoxy/ ethoxy) 2 plane, it is clear that [Cu II L 1 ] is a better host than [Cu II L 2 ] for the diprotonated diamine guests. Comparison of the inclusion of water and diprotonated diamines in [Cu II L 1 / L 2 ] is also described in the present investigation. Interestingly, of the two guest species, water and diprotonated diamines, [Cu II L 2 ] prefers the former and [Cu II L 1 ] prefers the latter.