Synthesis, structure and properties of [Zn(dpa)(N3)2] and [Zn(dpa)(N3)(NO3)]2 (dpa=2,2<f>′</f>-dipyridylamine): composition tailored architectures

The synthetic details, characterization data and single crystal X-ray structural analyses of [Zn(dpa)(N3)2] (1) and [Zn(dpa)(N3)(NO3)]2 (2) (dpa=2,2<f>′</f>-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 end-on 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 <f>π–π</f> 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 <f>π–π</f> interactions resulting to a 3D supramolecular continuum. 1 and 2 display high energy intraligand 1(<f>π–π*</f>) fluorescence and intraligand 3(<f>π–π*</f>) 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 <f>π–π</f> interaction. The role of dpa, a tailored diimine (–N<f>&z.dbnd6;C, upper limit | </f>–NH–<f>C, upper limit | &z.dbnd6;</f>N–) in 1 and 2 is discussed towards functionalisation on crystal engineering and luminescence behaviour. [Copyright &y& Elsevier]