Water Clusters Gather Luminescent Zinc(II) Complexes around Hydrogen-Bonded Framework Structures and Associated Fluorescence Modulation

2006-01-04T00:00:00Z (GMT) by Sanjib Das Parimal K. Bharadwaj
Luminescent complexes [Zn(phen)(dca)<sub>2</sub>] (<b>1</b>) and [Zn(bpy)(aba)<sub>2</sub>] (<b>2</b>) (phen = 1,10-phenanthroline, dca = 4-dimethylamino cinnamate, bpy = 2,2‘-bipyridyl, aba = 4-dimethylamino benzoate) are formed readily at room temperature when the reactants are allowed to react in a 1:1:2 molar ratio. Complex <b>1</b> self-assembles into a hydrogen-bonded framework structure in aqueous ethanol to form {[Zn(phen)(dca)<sub>2</sub>]·3H<sub>2</sub>O·EtOH}<i><sub>n</sub></i> (<b>3</b>), in which four complex units gather around tetrameric water clusters. Similarly, complex <b>2 </b>forms a different hydrogen-bonded framework structure with the empirical formula {[Zn(bpy)(aba)<sub>2</sub>]·4H<sub>2</sub>O}<i><sub>n</sub></i> (<b>4</b>), in which octameric water clusters assemble [Zn(bpy)(aba)<sub>2</sub>] complex units. Compounds <b>3 </b>and <b>4 </b>exhibit significant red shifts of the emission bands with respect to <b>1 </b>and <b>2</b>, respectively. On heating, compound <b>3 </b>loses water to form <b>1 </b>and then later upon recrystallization from aqueous ethanol forms <b>3 </b>as monitored by X-ray powder patterns. Similarly, the transformation between <b>2 </b>and <b>4</b> is also reversible.