Crystal-to-crystal transformation and linker exchange in Cd(II) coordination polymers based on flexible bis-pyridyl-bis-amide and 1,4-naphthalenedicarboxylate

Solvothermal reactions of Cd(ii) salts and naphthalene-1,4-dicarboxylic acid (1,4-H2NDC) with bis(N-pyrid-3-ylmethyl)adipoamide, L-1, and bis(N-pyrid-3-ylmethyl)suberoamide, L-2, afforded three Cd(II) coordination polymers, {[Cd(L-1)(1,4-NDC)(H2O)]center dot H2O}(n), 1, {[Cd(L-2)(1,4-NDC)]center dot 2H(2)O}(n), 2, and {[Cd-2(L-2)(1,4-NDC)(2)]3H(2)O}(n), 3, which have been structurally characterized using single-crystal X-ray crystallography. Complex 1 forms a 2D layer with 4(4)-sql topology, whereas 2 and 3 are 3D frameworks with rare {3(2)center dot 6(2)center dot 7(2)}{3(2)center dot 6(5)center dot 7(3)}(2)-4,5T61 and unique {3(2)center dot 5(4)}{3(4)center dot 4(6)center dot 5(8)center dot 6(6)center dot 7(4)}-sqc776 topologies, respectively. Complex 2 undergoes reversible crystal-to-crystal transformation to 3, while irreversible structural transformations from 1 to 2 and 3 to 1 can be carried out by linker exchange. Reorientation of the amide oxygen atoms that results in the change of the ligand conformation is proposed for the initiation of the crystal-to-crystal transformation. Complex 3 represents a unique example of a coordination polymer that is able to undergo both crystal-to-crystal transformation and linker exchange.