Syntheses, structures and luminescence behaviors of zinc(II) complexes containing a tetradentate Schiff base: Variation in nuclearity and geometry with the change of halide/pseudohalide/carboxylate and counter anion

A series of pentacoordinated mono-/dinuclear compounds, [Zn(L)(Br)]PF6 (1), [Zn(L)(NCS)]ClO4 (2) and [Zn2(L)2(μ-tp)](ClO4/PF6)2 (3/4) [L = N,N′-(bis(pyridin-2-yl)benzylidene)-1,3-propanediamine, tp = terephthalate dianion], have been synthesized using one-pot reactions of the building components. All the complexes are characterized using microanalytical, spectroscopic and other physicochemical results. Structures of 1–4 are solved by single crystal X-ray diffraction measurements. Structural analyses reveal that each zinc(II) center in 1 and 3 adopts a distorted trigonal bipyramidal geometry with ZnN4Br and ZnN4O chromophores, respectively, whereas zinc(II) centers in 2 and 4 have a distorted square pyramidal geometry with ZnN5 and ZnN4O chromophores, respectively. Intermolecular CH⋯Br, CH⋯F and CH⋯O hydrogen bondings along with CH⋯π and π⋯π interactions as the case in 1–4 lead to different crystalline aggregates. The compounds show intraligand π–π* fluorescence in solid states and in DMF solutions at room temperature.