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

摘要

Five lead( II ) coordination compounds based on PbBr _(2) and a series of neutral hydrazone and hydrazine ligands ( L1–L5 ) were prepared and structurally characterised, namely [Pb(μ _(2) -Br)(Br)( L1 )] _(2) ( 1 ), [Pb(μ _(2) -Br)(Br)(μ _(2) - L2 )] _( n ) ( 2 ), [Pb(μ _(2) -Br)(Br)(μ _(3) - L3 )] _( n ) ( 3 ), [Pb(μ _(2) -Br)(Br)(μ _(2) - L4 )] _( n ) ( 4 ) and [Pb _(3) (μ _(3) -Br) _(2) (μ _(2) -Br) _(4) ( L5 ) _(2) ] _( n ) ( 5 ). In all compounds, there are bridging bromide ligands that interconnect Pb( II ) centres and generate either [PbBr _(2) ] _(2) dimers (in 1 , 2 and 3 ) or [PbBr _(2) ] _( n ) chain motifs (in 4 ) and [Pb _(3) Br _(6) ] _( 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 μ _(2) - and μ _(3) -bridging (in 2 , 3 and 4 ) coordination modes of organic building blocks, the [PbBr _(2) ] _( 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.