Structural Transformations of Pb(II)-trans-1,2-bis(4′-pyridyl)ethene Coordination Polymers in Solution

Reaction of bpe (bpe = trans-1,2-bis(4'-pyridyl)ethylene) with Pb(OAc)(2)center dot 3H(2)O in the presence of trifluoroacetic acid (HTFA) affords a triple stranded coordination polymer (CP) [Pb-3(mu-bpe)(3)(mu-bpe)(3) (mu-O2CCF3)(2)] (1) in two days, which undergoes structural transformation in solution to yield a two-dimensional (2D) sheet like CP [Pb(mu-bpe)(mu-O2CCH3)(O2CCF3)]center dot 0.25bpe center dot 1.75H(2)O (2) in three weeks; finally compound 2 rearranges to [Pb(mu-bpe)(O2CCH3)(O2CCF3)] (3) in the fourth week. Compound 3 has a molecular fabric-like interwoven structure formed by spiral, one-dimensional (1D) coordination polymeric chains. Reaction of bpe with Pb(O2CCF3)(2) and Pb(OAc)(2)center dot 3H(2)O respectively in equimolar ratio produces [Pb(mu-bpe)(mu-O2CCF3)(2)] (4) and [Pb(mu-bpe)(O2CCH3)(2)]center dot 0.25H(2)O (5). The compound 4 is a three-dimensional (3D) CP with a 4(2).6(3).8-sra (SrAl2) topology, whereas 5 has a double-stranded structure with Pb(II)center dot center dot center dot pi (pyridyl) interactions between 1D chains. The compounds [Pb(mu-bpe)(mu-O2CCH3)(O2CCF3)]center dot 0.25bpe (2a), 4, and 5 have been characterized by X-ray crystallography, while 1 and 3 were reported before. The factors influencing the rearrangement of CPS in solution have been discussed. The structural topological features observed in 2a, 4, and 5 have been attributed to the coordination preference of the Pb(II) and the carboxylate ligands.