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)]·H2O·CH3CH2OH}n (M = Ni, 1a; Co, 1b, 1,4-H2BDC = benzene-1,4-dicarboxylic acid), {[Ni2(4-ampy)4(1,3-BDC)2]·H2O·CH3CH2OH}n (1,3-H2BDC = benzene-1,3-dicarboxylic acid), 2, [M2(4-ampy)4(1,2-BDC)2] (M = Ni, 3a; Co, 3b, 1,2-H2BDC = benzene-1,2-dicarboxylic acid), [Co(4-ampy)2(1,3-BDC)]n, 4, {[Cu(4-ampy)2(1,4-BDC)] CH3CH2OH}n, 5a, and {[Cu(4-ampy)2(1,4-BDC)]·H2O}n, 5b·H2O, 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-BDC2- 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·H2O are 1D linear and zigzag chains, in which the Cu2-1,4-BDC2- units adopt the cis and trans configurations, respectively. A novel irreversible structural transformation due to cis→trans isomerization of the Cu2-1,4-BDC2- units was observed in 5b⋅H2O and 5a upon water adsorption of the desolvated product of 5b·H2O.
Keywords: X-ray structure; coordination polymer; dinuclear metallocycle; structural transformation.