Self-assembly of novel co-ordination polymers containing polycatenated molecular ladders and intertwined two-dimensional tilings

Four novel co-ordination polymers have been obtained from the reactions of M-II(NO3)(2) salts (M-II = Zn, Co or Cd) and the bidentate spacer ligands 1,2-bis(4-pyridyl)ethyne (bpethy) and trans-4,4'-azobis(pyridine) (azpy), all exhibiting the same metal-to-ligand molar ratio of 2:3. Crystal structure analyses, however, have revealed two quite different polymeric motifs, in spite of the presence of similar co-ordination geometries of the metal ions, that are bound to three pyridyl groups, with a T-shaped disposition, and to the oxygen atoms of two eta(2)-nitrates, thus resulting in a distorted pentagonal-bipyramidal seven-co-ordination. The species [M-2(bpethy)(3)(NO3)(4)] (M = Zn or Co) consist of ladder-like polymers that interpenetrate in an unprecedented fashion to produce an overall three-dimensional array. On the other hand, the species [Cd-2(bpethy)(3)(NO3)(4)]. CH2Cl2 and [Cd-2(azpy)(3)(NO3)(4)] contain undulated two-dimensional layers with an unprecedented tiled pattern, that give threefold interpenetration in a parallel fashion.