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.