Two novel tetranuclear zinc(II) clusters with different topological structures: Crystal structures and luminescence properties

Two novel tetranuclear zinc(II) clusters with different topological structures have been synthesized by using Zn(ClO4)2·6H2O, sodium azide and potentially multidentate Schiff base ligands containing different substituent groups. The two complexes have been characterized by elemental analysis, IR, single crystal X-ray diffraction and fluorescence studies. Structural studies reveal that [Zn4(HL1)4(μ1,1-N3)2(N3)2] (1) is a linear tetranuclear cluster whereas [Zn4(HL2)4(μ1,1-N3)4] (2) is a square-planar tetranuclear cluster. Both two complexes display intraligand (π → π*) fluorescence. Due to the heavy atom effect which increases the probability for intersystem crossing to the triplet state, the fluorescence intensity of complex 2 is much lower than that of complex 1.