Positional isomeric effect on the structural variation of Cd(II) coordination polymers based on flexible linear/V-shaped bipyridyl benzene ligands

Self-assembly of Cd((II))) ions with five positional isomeric flexible bipyridyl benzene and 2,2'-azodibenzoic acid ligands yielded five interesting coordination polymers: [Cd2L2(3-pbpmb)(3)](n) (1), [Cd2L2(2-pbpmb)](n) (2), {[CdL.4-mbpmb)(2)].MeOH}n (3), {[ Cd2L2(3-mbpmb)(3)]2.5H(2)O)(n) (4) and [Cd2Cl2L(3-obpmb)(2)](n) (5) where H2L = 2,2'-azodibenzoic acid, 3-pbpmb = 1,4-bis(pyridine-3-ylmethoxy) benzene, 2-pbpmb = 1,4-bis(pyridine-2-ylmethoxy)benzene, 4-mbpmb = 1,3-bis(pyridine-4-ylmethoxy)benzene, 3-mbpmb = 1,3-bis(pyridine-3-ylmethoxy) benzene and 3-obpmb = 1,2-bis(pyridine-3-ylmethoxy) benzene. Their structures have been determined by single-crystal X-ray diffraction analyses, elemental analyses, IR spectroscopy, powder X-ray diffraction (PXRD) and thermogravimetric analyses (TGA). Compound 1 has a 3D architecture constructed by 1D ladder-like(Cd-4(3-pbpmb)(4)](n) chains as well as L linkers and displays an interesting 5-connected net with a 4(6)6(4) topology. Compound 2 comprises a 3D framework built from 2D wrinkled [Cd2L4](n) networks and 2-pbpmb bridges with a 6-connected pcu net. Compound 3 bears a 2D network based on (Cd-2(4-mbpmb)(2)] building units and 1D [CdL](n) chains. Compound 4 features a 2D network in which the helical [Cd(3-mbpmb)](n) chains are alternately arranged in a right-and left-handed sequence. Compound 5 exhibits a 2D network constructed by 1D [Cd2Cl2(3-obpmb)(2)](n) chains and L linkers. The results reveal that the diverse coordination networks of 1-5 can be adjusted by the positional isomeric effect of flexible bipyridyl benzene building blocks. Moreover, the luminescence properties of compounds 1-5 in the solid state have also been investigated.