New examples of self-catenation in two three-dimensional polymeric co-ordination networks

Abstract

Among the new types of entanglements in polymeric architectures the phenomenon of self-interpenetration has attracted attention in recent times. Two new three-dimensional networks that present this unusual topological feature have been obtained. The first species, [Ag(2-ethpyz)₂][SbF₆] 1 (2-ethpyz = 2-ethylpyrazine), contains four-connected silver centres that give [Ag₄(2-ethpyz)₄] squares linked into double-crankshaft ribbons. Each of these ribbons is joined to parallel identical motifs to form a three-dimensional four-connected binodal frame of (4²,6³,8)(4²,6,8²,9) topology, the same as that of coesite, a high-pressure polymorph of silica, exhibiting self-catenated 8-membered circuits. The second species, [Cu(bpe)₂(SO₄)]·5H₂O 2 [bpe = 1,2-bis(4-pyridyl)ethane], is a nanoporous polymer based on copper(II) centres four-connected to pyridyl groups to give a [Cu(bpe)₂] three-dimensional binodal network with the unprecedented (6⁴,8²)(6,8⁵) topology, showing the unique feature that all the shortest circuits are self-catenated.