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

Abstract

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 η²-nitrates, thus resulting in a distorted pentagonal-bipyramidal seven-co-ordination. The species [M₂(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 [Cd₂(bpethy)₃(NO₃)₄]·CH₂Cl₂ and [Cd₂(azpy)₃(NO₃)₄] contain undulated two-dimensional layers with an unprecedented tiled pattern, that give threefold interpenetration in a parallel fashion.