Synthesis, Structure and Luminescent Property of a 3D Layered-Pillared Cd(II) Metal–Organic Framework Derived from Mixed Rigid and Flexible Ligands

A new 3D Cd(II) metal–organic framework of [Cd2(HIDC)2(bibp)1.5]n (1) was synthesized hydrothermally by the reaction of imidazole-4,5-dicarboxylic acid (H2IDC) and 4,4′-bis(imidazol-1-ylmethyl)biphenyl (bibp) with Cd(NO3)2·4H2O. Single-crystal X-ray diffraction analysis reveals that this compound crystallizes in triclinic, space group Pī with a = 9.6610(3), b = 15.5866(5), c = 16.0228(6) Ǻ, α = 110.662(3), β = 101.521(3), γ = 107.115(3)˚, V = 2029.46(15) Ǻ3, Z = 2, Dc = 1.644 g cm−3, µ = 1.113 mm−1, F(000) = 1002, the final R1 = 0.0468 and wR2 = 0.0962 for 8932 observed reflections with I > 2σ(I). In 1, the alternately interconnection of Cd(II) ions by µ2-HIDC2− and µ3-HIDC2− anions resulted in the formation of 1D [Cd2(µ2-HIDC)(µ3-HIDC)]∞ with the right- and left-helical chains, which were further linked by the oxygen atoms derived from one of the carboxylate groups of µ3-HIDC2− anions, generating the 1D double helical chain structure of [Cd4(µ2-HIDC)2(µ3-HIDC)2]∞ along a axis. These adjacent 1D double chains are further linked by cis-µ2-bibp ligands to form a 2D network structure of [Cd4(µ2-HIDC)2(µ3-HIDC)2(cis-µ2-bibp)2]n, which are further pillared by trans-µ2-bibp ligands to generate a 3D layered-pillared metal–organic framework architecture of [Cd4(µ2-HIDC)2(µ3-HIDC)2(cis-µ2-bibp)2(trans-µ2-bibp)]n. Furthermore, the thermal stability and luminescent property of 1 have also been investigated. A 3D Cd(II) layered-pillared metal–organic framework was synthesized hydrothermally. This new compound displays high thermal stability and intense fluorescent emission.