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

Abstract

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 π–π 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.