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)2·3H2O in the presence of trifluoroacetic acid (HTFA) affords a triple-stranded coordination polymer (CP) [Pb3(μ-bpe)3(μ-O2CCF3)2(μ-O2CCH3)2(O2CCF3)2] (1) in two days, which undergoes structural transformation in solution to yield a two-dimensional (2D) sheet-like CP [Pb(μ-bpe)(μ-O2CCH3)(O2CCF3)]·0.25bpe·1.75H2O (2) in three weeks; finally compound 2 rearranges to [Pb(μ-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)2·3H2O respectively in equimolar ratio produces [Pb(μ-bpe)(μ-O2CCF3)2] (4) and [Pb(μ-bpe)(O2CCH3)2]·0.25H2O (5). The compound 4 is a three-dimensional (3D) CP with a 42.63.8-sra (SrAl2) topology, whereas 5 has a double-stranded structure with Pb(II)···π (pyridyl) interactions between 1D chains. The compounds [Pb(μ-bpe)(μ-O2CCH3)(O2CCF3)]·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.