Anion-dependent structural diversity of cadmium(II) complexes: synthesis, crystal structures, luminescence properties, and unusual C-H/σ supramolecular interactions involving σ-aromatic M2X2 cores

Four complexes based on N,N-bis(2-pyridylmethylene)-1,3-propanediamine (L) and different Cd(II) salts have been synthesized and characterized by single-crystal X-ray diffraction analysis. The complexes are [Cd-2(L)(2)(-Cl)(2)](ClO4)(2) (1), [Cd-2(L)(2)(-Br)(2)](ClO4)(2) (2), [Cd(L)I](ClO4) (3), and [Cd(L)(NCS)(2)] (4). L exhibits the same coordination mode in 1-4. The radius of each anion plays a role in affecting the structures and luminescent intensities of the final products. CdCl2, CdBr2, and CdI2 react with L to produce chloride or bromido-bridged binuclear complexes and mononuclear iodido complex, respectively, whereas an unusual mononuclear trigonal prismatic (TP) 4 is obtained when thiocyanate was used as a coligand. Photoluminescence properties of all the complexes show that the trend of fluorescence intensity is 1>4>2>3. All four complexes exhibit different supramolecular interactions such as C-H/sigma, pi-pi, and C-H/pi and hydrogen bonding interactions. The experimental findings are complemented by density functional theory (DFT) calculations.