Impact of Isomeric Dicarboxylate Ligands on the Formation of One-Dimensional Coordination Polymers and Metallocycles: A Novel cis→trans Isomerization.

A series of Co(II), Ni(II) and Cu(II) coordination polymers and dinuclear metallocycles containing 4-aminopyridine (4-ampy) and benzenedicarboxylate ligands, {[M(4-ampy)(2)(1,4-BDC)]·H(2)O·CH(3)CH(2)OH}(n) (M = Ni, 1a; Co, 1b, 1,4-H(2)BDC = benzene-1,4-dicarboxylic acid), {[Ni(2)(4-ampy)(4)(1,3-BDC)(2)]·H(2)O·CH(3)CH(2)OH}(n) (1,3-H(2)BDC = benzene-1,3-dicarboxylic acid), 2, [M(2)(4-ampy)(4)(1,2-BDC)(2)] (M = Ni, 3a; Co, 3b, 1,2-H(2)BDC = benzene-1,2-dicarboxylic acid), [Co(4-ampy)(2)(1,3-BDC)](n,) 4, {[Cu(4-ampy)(2)(1,4-BDC)] CH(3)CH(2)OH}(n), 5a, and {[Cu(4-ampy)(2)(1,4-BDC)]·H(2)O}(n), 5b·H(2)O, are reported, which were hydrothermally prepared and structurally characterized by using single crystal X-ray diffraction. Complexes 1a and 1b are isomorphous 1D zigzag chains, while 2 displays a concave-convex chain and 3a and 3b are dinuclear metallocycles that differ in the boding modes of the 1,2-BDC(2-) ligands, forming a 3D and a 2D supramolecular structures with the pcu and sql topologies, respectively. Complex 4 exhibit a 1D helical chain and complexes 5a and 5b·H(2)O are 1D linear and zigzag chains, in which the Cu(2)-1,4-BDC(2-) units adopt the cis and trans configurations, respectively. A novel irreversible structural transformation due to cis→trans isomerization of the Cu(2)-1,4-BDC(2-) units was observed in 5b⋠H(2)O and 5a upon water adsorption of the desolvated product of 5b·H(2)O.