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

By self-assembly of delocalized organic ligands (L1 and L2) with Cd(SCN)2, ZnI2 and Zn(NCS)2, three luminescent complexes ZnI2(L1)2 (I), [Cd(L1)2(μ1,3-SCN)2]n (II) and Zn(NCS)2(L2)2 (III) were obtained (L1 = 2-{5,5-dimethyl-3-[2-(pyridine-4-yl)ethenyl]cyclohex-2-enylidene}propanedinitrile and L2 = 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 μ1,3-SCN bridging coordination modes and the adjacent Cd(II) ions are bridged by double μ1,3-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 N4 distorted tetrahedral geometry. Compared with the free ligands, the complexes show superior luminescent property with red-shift and enhancement of fluorescence intensity.