Solid-State Structural Transformations and Photoreactivity of 1D-Ladder Coordination Polymers of PbII

An attempt has been made to design double-stranded ladder-like coordination polymers (CPs) of hemidirected PbII. Four CPs, [Pb(-bpe)(O2C-C6H5)2]2H2O (1), [Pb2(-bpe)2(-O2C-C6H5)2(O2C-C6H5)2] (2), [Pb2(-bpe)2(-O2C-p-Tol)2(O2C-p-Tol)2] 1.5H2O (3) and [Pb2(-bpe)2(-O2C-m-Tol)2(O2C-m-Tol)2] (4) (bpe=1,2-bis(4-pyridyl)ethylene), have been synthesised and investigated for their solid-state photoreactivity. CPs 24, 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 CC bonds in 24 is dictated by the chelating and 2-2:1 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)(-O2C-m-Tol)2(O2C-m-Tol)2] (5).