Entanglement and Irreversible Structural Transformation in Co(II) Coordination Polymers Based on Isomeric Bis-pyridyl-bis-amide Ligands

Four coordination polymers constructed from the flexible isomeric bis-pyridyl-bis-amide (bpba) ligands, N,N'-di(3-pyridyl)suberoamide (L-1) and N,N'-di(4-pyridyl)suberoamide (L-2), and the auxiliary 1,4-naphthalenedicarboxylic acid (1,4-H2NDC), including [Co(L-1)(1.5)(1,4-NDC)(H2O)](n), 1, [Co-3(L-1)(1.5)(1,4-NDC)(3)(EtOH)(n), 2, {[Co(L-2)(1.5)(1,4-NDC)]center dot H2O}(n), 3, and {[Co(L-2)(0.5)(1,4-NDC)]center dot EtOH}(n), 4, have been synthesized and structurally characterized by using single crystal X-ray crystallography. Complex 1 forms a two-dimensional layer with double edges and 2 exhibits a unique three-dimensional (3D) self-catenated framework with the (4(8).6(6).8)-6T60 topology, while 3 displays a 3D framework with the highest 5-fold interpenetration for the bnn topology and 4 shows a 3D 2-fold interpenetrated framework with the pcu topology. The donor atom positions of the L-1 and L-2 ligands and the identity of the solvents play important roles in determining the structural diversity. Moreover, irreversible structural transformation from 2 to 1 has been verified by immersing crystals of 2 into water. The coordination ability of the CH3CH2OH molecule in 2 and the thermal stability of 1 govern the irreversible structural transformation.