Design of weak interaction directed self-assemblies of nickel(II) complexes using diprotonated diamines as supramolecular tectons: Syntheses and crystal structures

The work in this paper reports syntheses, characterization and crystal structures of three designed host–guest compounds [(NiIIL)2 ⊂ (H3NCH2CH2NH3)](NO3)2 (1), [(NiIIL)2 ⊂ (H3NCH2CH2CH2NH3)](NO3)2 (2) and [(NiIIL)2 ⊂ (H3NCH2CH2CH2CH2NH3)](NO3)2 (3), where H2L is the compartmental Schiff base ligand N,N′-ethylenebis(3-ethoxysalicylaldimine). All three crystals are triclinic, compounds 1 and 3 are centrosymmetric (space group P1¯), whereas compound 2 is not (space group P1). In all of these three compounds 1–3, the two +NH3 sites of the [H3N(CH2)nNH3]2+ dication (n = 2–4) behave as guest in the O4 compartment of two [NiIIL] moieties through hydrogen bonds involving the two hydrogen atoms of the +NH3 site and the two phenoxo and two ethoxy oxygen atoms of the O4 compartment. Thus, the diprotonated diamines behave as tectons to interlink two mononuclear nickel(II) complex units to produce supramolecular self-assemblies. The title compounds are inorganic–organic cocrystals as well. Comparing with the previous report, the role of metal ion in the N2O2 compartment to stabilize a particular supramolecular self-assembly is also presented here.

► Diprotonated diamines as the supramolecular tectons.
► Three supramolecular self-assemblies of nickel(II) complexes.
► N,N′-ethylenebis(3-ethoxysalicylaldimine).
► Bifurcated hydrogen bonds between +NH3 sites and the phenoxo and ethoxy oxygen atoms.
► The title compounds are also inorganic–organic cocrystals.