Crystal structures and enhanced luminescence of Zn(II) and Cd(II) complexes containing conjugated organic ligands

By self-assembly of delocalized organic ligands (L 1 and L 2 ) with Cd(SCN) 2 , ZnI 2 and Zn(NCS) 2 , three luminescent complexes ZnI 2 (L 1 ) 2 ( I ), [Cd(L 1 ) 2 (μ 1,3 -SCN) 2 ] n ( II ) and Zn(NCS) 2 (L 2 ) 2 ( III ) were obtained (L 1 = 2-{5,5-dimethyl-3-[2-(pyridine-4-yl)ethenyl]cyclohex-2-enylidene}propanedinitrile and L 2 = 2-{5,5-dimethyl-3-[2-(pyridine-3-yl)ethenyl]cyclohex-2-enylidene}propanedinitrile). The structures of the complexes were determined by single crystal X-ray diffraction analysis (CIF files CCDC nos. 1406116 ( I ), 1406115 ( II ), and 1400360 ( III )). In complex I , Zn(II) is coordinated by two functional organic ligands and two I – ions, to form a I 2 N 2 distorted tetrahedral geometry. In 1D coordination polymer II , the Cd(II) centers show six-coordinated geometries, two organic ligands and four SCN – ions involve in coordination with each Cd(II) center. The thiocyanate groups show μ 1,3 -SCN bridging coordination modes and the adjacent Cd(II) ions are bridged by double μ 1,3 -SCN ions to form an infinite chain. In complex III , Zn(II) is coordinated by two functional organic ligands and two NCS – groups, to form a N 4 distorted tetrahedral geometry. Compared with the free ligands, the complexes show superior luminescent property with red-shift and enhancement of fluorescence intensity.