Solid-state structural transformations and photoreactivity of 1D-ladder coordination polymers of Pb(II)

An attempt has been made to design double-stranded ladder-like coordination polymers (CPs) of hemidirected Pb(II) . Four CPs, [Pb(μ-bpe)(O2 C-C6 H5 )2 ]⋅2H2 O (1), [Pb2 (μ-bpe)2 (μ-O2 C-C6 H5 )2 (O2 C-C6 H5 )2 ] (2), [Pb2 (μ-bpe)2 (μ-O2 C-p-Tol)2 (O2 C-p-Tol)2 ]⋅ 1.5 H2 O (3) and [Pb2 (μ-bpe)2 (μ-O2 C-m-Tol)2 (O2 C-m-Tol)2 ] (4) (bpe=1,2-bis(4'-pyridyl)ethylene), have been synthesised and investigated for their solid-state photoreactivity. CPs 2-4, having a parallel orientation of bpe molecules in their ladder structures and being bridged by carboxylates, were found to be photoreactive, whereas CP 1 is a linear one-dimensional (1D) CP with guest water molecules aggregating to form a hydrogen-bonded 1D structure. The linear strands of 1 were found to pair up upon eliminating lattice water molecules by heating, which led to the solid-state structural transformation of photostable linear 1D CP 1 into photoreactive ladder CP 2. In the construction of the double-stranded ladder-like structures, the parallel alignment of CC bonds in 2-4 is dictated by the chelating and μ2 -η(2) :η(1) bridging modes of the benzoate and toluate ligands. The role of solvents in the formation of such double-stranded ladder-like structures has also been investigated. A single-crystal-to-single-crystal transformation occurred when 4 was irradiated under UV light to form [Pb2 (rctt-tpcb)(μ-O2 C-m-Tol)2 (O2 C-m-Tol)2 ] (5).