Solvothermal synthesis, crystal structures and photoluminescence properties of the novel Cd/X/α,ω-bis(benzotriazole)alkane hybrid family (X = Cl, Br and I)

Seven organic-inorganic hybrid solids, namely, [(CdI2)(2)(L1)(2)] (1), [(CdBr2)(3)(L1)(2)](n) (2), [(CdCl2)(5)(L1)(2)](n) (3), [(CdI2)(L2)](n) (4), [(CdBr2)(L3)](n) (5), [(CdBr2)(2)(L4)(2)](n) (6), and [(CdI2)(4)(L4)(4)](n) (7), have been obtained via the self-assembly of CdX2 (X = Cl, Br or I) with the four structurally related flexible organic ligands 1,2-bis(benzotriazole) ethane (L1), 1,3-bis(benzotriazole) propane (L2), 1,4-bis(benzotriazole)butane (L3) and 1,6-bis(benzotriazole) hexane (L4) under solvothermal conditions. Compound 1 presents a binuclear structure with a [Cd2N12C4] 18-membered cycle. In 2, the L1 ligands locate alternately on the two sides of the 1-D inorganic chain formed by papilionaceous [Cd2Br2] subunits. The 1-D hexagonal [CdCl2](n) grid inorganic chains in 3 are generated by vertex-loss cubane-like [Cd3Cl4] motifs through sharing faces, which are further connected by L1 ligands to give a 2-D hybrid layer. For compound 4, the L2 ligands and 4-connected Cd centres link each other to give a 1-D single chain. In 5 and 6, [Cd2Br4] units are connected by L3 and L4 to generate a 2-D (4, 4) net and 1-D double chain structure, respectively. Four independent [CdI2] centres and four L4 ligands in 7 generate an extraordinarily large [Cd4N24C24] 52-membered cycle. The varying structures of 1-7 indicate that the spacer length of the bis(benzotriazole) alkane ligands and counter-anions play an essential role in the formation of the framework of the Cd(II) hybrid materials. Strong pi-pi stacking interactions between the benzotriazole ligands pack these low-dimensional hybrid chains or layers into high-dimensional supramolecular frameworks. The UV-vis diffuse reflectance spectra and solid state luminescence measurements show that compounds 1-7 are potential semiconductor and photoluminescence materials.