Cobalt(II) coordination polymers constructed from bis(N-pyrid-3-ylmethyl)adipoamide and polycarboxylic acids: reversible structural transformation upon proton delivery and removal

Hydrothermal reactions of cobalt(II) salts and bis(N-pyrid-3-ylmethyl)adipoamide (L) with various polycarboxylic acids in water and NaOH solutions afforded {[Co(L)(0.5)(1,3,5-HBTC)(H2O)]center dot H2O}(n) (1,3,5-H3BTC = benzene-1,3,5-tricarboxylic acid), 1, {[Co-1.5(L)(1.5)(1,3,5-BTC)(H2O)(4)]center dot 4H(2)O}(n), 2, [Co(L)(5-tert-IPA)(H2O)(2)](n) (5-tert-H(2)IPA = 5-tert-butylbenzene-1,3-dicarboxylic acid), 3, and {[Co(L)(5-NH2-IPA)]center dot H2O}(n) (5-NH2-H(2)IPA = 5-aminoisophthalic acid), 4, respectively, which have been structurally characterized by using single crystal X-ray crystallography. Complexes 1-3 display two-dimensional (2D) networks, showing bey, bex and hcb topologies, respectively, while complex 4 exhibits a three-dimensional (3D) framework with the xww topology (standard representation), which can be further simplified as the tfz-d topology (cluster representation), revealing the structure-directing roles of the substituent groups on the polycarboxylate ligands. Reversible structural transformation upon delivery and removal of H+ in 1 and 2 is observed, which can be ascribed to the various bonding modes of the benzene-1,3,5-tricarboxylate anions and the flexible nature of L.