Synthesis, structure and properties of [Zn(dpa)(N3)2] and [Zn(dpa)(N3)(NO3)]2 (dpa=2,2'-dipyridylamine):: composition tailored architectures

The synthetic details, characterization data and single crystal X-ray structural analyses of [Zn(dpa)(N-3)(2)] (1) and [Zn(dpa)(N-3)(NO3)](2) (2) (dpa=2,2'-dipyridylamine) are described. Structural study reveals that the zinc(II) centre in 1 is in a pseudotetrahedral ZnN4 environment ligated by two terminal azide N atoms and two pyridine N atoms of the chelator. The coordination polyhedron around each metal ion in dinuclear 2 is best described as a ZnN4O2 distorted octahedron linked by two endon azido bridges. The mononuclear units in 1 are engaged in bifurcated intermolecular hydrogen bonding (N-H...N) between amine N of dpa and coordinated N of azide along with aromatic pi-pi stacking leading to a 2D sheet. In 2, the dinuclear units participate in intermolecular N-H...O hydrogen bonding between amine N of dpa and bound O of bidentate nitrate in combination with pi-pi interactions resulting to a 3D supramolecular continuum. 1 and 2 display high energy intraligand (1)(pi-pi(*)) fluorescence and intraligand (3)(pi-pi(*)) phosphorescence in glassy solutions (DMF at 77 K). A band (372 nm) observed for both 1 and 2 in their solid-state emission spectra is an excimeric emission arising due to aromatic pi-pi interaction. The role of dpa, a tailored diimine (-N=C-NHC=N-) in 1 and 2 is discussed towards functionalisation on crystal engineering and luminescence behaviour. (C) 2003 Elsevier Ltd. All rights reserved.