Synthesis and properties of a one-dimensional mixed-ligand Cd (II) complex with helical structure

The title complex, [[Cd (Him) (OH-BDC) (H₂O)₂]·3H₂O]_n (1) (Him is imidazole, OH-H₂BDC is 5-hydroxyisophthalic acid), was synthesized by liquid/liquid diffusion method at room temperature. The complex crystallizes in orthorhombic, space group P2₁2₁2₁, with a = 0.6716 (7), b = 1.3806 (2), c = 1.7421 (2) nm, V = 1.6152 (3) nm³, C₁₁H₁₈CdN₂O₁₀, M_r = 450.67, D_c = 1.853 g/cm³, μ = 1.407 mm^-1, F (000) = 904, Z = 4, the final R₁ = 0.0209 and wR₂ = 0.0453 for 3211 observed reflections (I > 2σ (I)). In the structure of 1, the OH-BDC ligands exhibiting bis-bidentate coordination mode bridge the adjacent Cd centers to form a one-dimensional helical chain and the second ligand Him acting as terminal ligands are attached to the helical chain. It is notable that a series of complicated hydrogen bonds (e.g., N-H ⋯ O, O-H ⋯ O) exist in the structure, which link neighboring helices into a three-dimensional supramolecular architecture. An observed intense blue luminescence with an emission band peaking at 390 nm for 1 may be resulted from ligand-to-metal charge transfer (LMCT).