Correlating Structural Features and ²⁰⁷Pb NMR Parameters with the Stereochemical Activity of Pb^II Lone Pairs in Birefringent Pb[2,6‐bis(benzimidazol‐2‐yl)pyridine] Complexes

Abstract

A series of Pb II materials containing the highly anisotropic tridentate ligand 2,6‐bis(benzimidazol‐2‐yl)pyridine (bbp) and [Au(CN) 2 ] – , Hg(CN) 2 or halide bridging units, [Pb(bbp)Br 2 ] · 2H 2 O, Pb(bbp)I 2 , [Pb(bbp)I] 2 (µ‐I)[Au(CN) 2 ], [Pb(bbp)Br] 2 (µ‐Br)[Au(CN) 2 ], [Pb(bbp)Br 2 ][Hg(CN) 2 ], Pb(bbp)Cl[Au(CN) 2 ] · 0.25H 2 O and Pb(H 2 O)(bbp) 2 [Au(CN) 2 ] 2 , have been prepared, structurally characterised and investigated spectroscopically by 207 Pb solid‐state NMR spectroscopy. Of these, five possess similar coordination geometries, providing an ideal series to investigate structural parameters as indicators for stereochemical activity by correlation with the 207 Pb chemical shift span parameter ( Ω ). The bond length of the substituent opposite to the stereochemically active lone pair and the angle between axial ligands were found to correlate weakly with Ω for these compounds ( R 2 = 0.85 and 0.66, respectively) and an expanded set of compounds with varying components and structures ( R 2 = 0.60 and 0.67, respectively), which indicates that these (or similar) structural parameters or Ω can be used to estimate the degree of lone‐pair activity. Compounds were also found to be highly birefringent with values ranging from 0.31(5) for Pb(H 2 O)(bbp) 2 [Au(CN) 2 ] 2 to 0.660(4) for [Pb(bbp)Br 2 ] · 2H 2 O, the latter being amongst the most birefringent compounds reported.