Classical tetradentate chelation and novel bis(bidentate) congregation motifs of a neutral N-donor Schiff base in dinuclear cadmium(II) complexes: Synthesis, structure and luminescence behaviour

Three dinuclear compounds [Cd2(bpbd)3](Y)4 (Y = image, 1; image, 2) and [Cd(bpbd)(Cl)]2(PF6)2 (3) [bpbd = N,N′-(bis(pyridine-2-yl)benzylidene)-1,4-butanediamine] are prepared and characterized. Structures of 1 and 3 are solved by X-ray study that reveals interesting variation in ligational motifs of bpbd from classical tetradentate chelation binding a single metal ion to bis(bidentate) congregation encapsulating two cadmium(II) centers. In the crystalline state, the dinuclear units of 1 pack through cooperative face-to-face π⋯π interactions and C–H⋯O hydrogen bonds whereas those of 3 are engaged in edge-to-face C–H⋯π interactions and C–H⋯F and C–H⋯Cl hydrogen bonds each leading to 2D sheet structure. High-energy intraligand 1(π–π∗) fluorescence at room temperature in DMF solutions and intraligand 3(π–π∗) phosphorescence in glassy solutions (DMF at 77 K) are seen in all the complexes.