Two-dimensional hydrogen bonded sheet structures in nickel(II)- and zinc(II)-2,2′-dipyridylamine-azido complexes

Abstract

One-pot reactions of metal acetate, 2,2′-dipyridylamine (dpa) and NaN 3 in a 1:2:2 ratio in aqueous-acetonitrile solutions result in mononuclear complexes of the type [M(dpa) 2(N 3) 2] · H 2O [M = Ni ( 1), Zn ( 2)]. Structural analyses reveal that both the metal centres adopt distorted octahedral MN 6 environments coordinated through four N atoms of two dpa units and two azide N atoms as terminal ligands – the latter occupying mutual cis positions. The crystal packing shows that the mononuclear units self-assemble through hydrogen bonds to afford infinite two-dimensional (2D) sheets. Additionally, the pyridyl planes of adjacent sheets are engaged in face-to-face π⋯π and C–H⋯π interactions leading to a 3D supramolecular continuum. Complexes 1 and 2 exhibit high-energy intraligand 1(π–π*) fluorescence and intraligand 3(π–π*) phosphorescence in glassy solutions (DMF at 77 K). A band (374 nm) observed in their solid-state emission spectra is an excimeric emission originating from an aromatic π⋯π interaction. The role of dpa is highlighted in controlling crystalline aggregation and in arousing luminescence characteristics.