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), ZnI2 and Zn(NCS)(2), three luminescent complexes ZnI2(L-1)(2) (I), [Cd(L-1)(2)(mu(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 I2N2 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 mu(1,3)-SCN bridging coordination modes and the adjacent Cd(II) ions are bridged by double mu(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.