Lead(II) coordination polymers with imidazole-4- and pyrazole-3-carboxylate isomeric linkers: Structural diversity and luminescence properties

Abstract

Using 1H-imidazole-4-carboxylic acid (4imCOOH) and 1H-pyrazole-3-carboxylic acid (3pyrCOOH) coordination polymers [Pb(4imCOO)2(H2O)]n (1) and [Pb2(3pyrCOO)4]n (2) were constructed. Obtained polymers were characterized via FT-IR, X-ray, PL and TG methods. The coordination polyhedron around Pb(II) in 1 is described as distorted pentagonal pyramid with hemidirected coordination sphere (based on DFT calculations). Compound 2 consists of two crystallographically independent Pb(II) centres: Pb1 forms distorted monocapped pentagonal pyramid polyhedron (CN = 7, hemidirected), whereas the coordination polyhedron of Pb2 is distorted monocapped pentagonal pyramid (CN = 7) or tricapped octahedron (CN = 9, including secondary bonds) with holodirected geometry (confirmed by DFT calculations). Crystal structure of polymer 1 demonstrates a 1D structural motif with 2C1 topology while polymer 2 is a 2D compound with cpf topology. Polymer 1 presents blue-green emission at 485 nm at RT in the solid state, whereas polymer 2 exhibits two emission centres with maximum at 449 nm (blue fluorescence) and at 532 nm (green-yellow fluorescence), respectively.