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

Abstract

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]·2.5H₂O}_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 [Cd₄(3-pbpmb)₄]_n chains as well as L linkers and displays an interesting 5-connected net with a 4⁶6⁴ 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 [Cd₂(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.