Inorganic–organic hybrid materials based on PbBr2 and pyridine–hydrazone blocks – structural and theoretical study

Abstract

Five lead(II) coordination compounds based on PbBr₂ and a series of neutral hydrazone and hydrazine ligands (L1–L5) were prepared and structurally characterised, namely [Pb(μ₂-Br)(Br)(L1)]₂ (1), [Pb(μ₂-Br)(Br)(μ₂-L2)]_n (2), [Pb(μ₂-Br)(Br)(μ₃-L3)]_n (3), [Pb(μ₂-Br)(Br)(μ₂-L4)]_n (4) and [Pb₃(μ₃-Br)₂(μ₂-Br)₄(L5)₂]_n (5). In all compounds, there are bridging bromide ligands that interconnect Pb(II) centres and generate either [PbBr₂]₂ dimers (in 1, 2 and 3) or [PbBr₂]_n chain motifs (in 4) and [Pb₃Br₆]_n ribbons (in 5). These correspond to three structural fragments present in the lead(II) bromide structure. Depending on the terminal (in 1 and 5) or μ₂- and μ₃-bridging (in 2, 3 and 4) coordination modes of organic building blocks, the [PbBr₂]_n fragments constitute discrete molecules (1) or extend to structurally distinct 1D (2 and 5) or 2D (3 and 4) metal–organic networks. Topological analysis and classification of these networks in 2–5 were performed, disclosing underlying chains or layers with the 2C1, 3,4L83, hcb topologies, and a trinodal 3,4,6-connected net of unprecedented topology, respectively. Theoretical calculations (DFT) were employed to analyze some relevant noncovalent interactions observed in the solid state. In particular the inter-ligand π–π stacking interactions in 1 and the influence of the metal coordination on their strength were analyzed. In 3, the role of intramolecular tetrel and π–hole unconventional interactions in the solid state architecture was demonstrated.