Advancing the coordination abilities of 2,6-diacetylpyridine bis(benzoylhydrazone) with tin through modifications of axial ligands: Synthesis, spectroscopic features, and structural profiling

A series of seven-coordinate pentagonal-bipyramidal (PBPY-7) Sn(IV) complexes with the pentadentate pyridine-based pro-ligand 2,6-diacetylpyridine bis(benzoylhydrazone), H₂L, and different axial ligands have been synthesized. Reactions of H₂L with R₂SnO (where R = Me, n-Bu, n-Oct, or Bz) in anhydrous toluene, or with RSnCl₃ (where R = n-Bu or Ph) in anhydrous toluene (or acetonitrile in the case of PhSnCl₃), produced a series of novel seven-coordinate complexes: [Me₂Sn(L)] (1), [n-Bu₂Sn(L)] (2), [n-Oct₂Sn(L)] (3), [Bz₂Sn(L)] (4), [n-BuSn(L)Cl]·0.5C₇H₈ (5), and [PhSn(L)Cl] (6). By taking advantage of lability of the axial Cl ligands in complex 5, two neutral PBP Sn(IV) complexes [n-BuSn(L)N₃] (7) and [n-BuSn(L)NCS] (8) with different axial ligands were obtained and characterized. In a separate effort to obtain single crystals of the dibenzyltin compound [Bz₂Sn(L)] (4), a few crystals were successfully extracted from crystallization experiments in chloroform. Diffraction studies of these crystals revealed a composition of [Sn(L)Cl₂]·CHCl₃ (9). In these complexes, the double-deprotonated chelating ligand occupies the equatorial plane, while the two axial ligands can be two R groups, two Cl ligands, or a combination of one R group with a Cl, N₃, or NCS ligand. The compounds 1–8 (9 only by IR) were fully characterized using Fourier transform infrared (FT-IR) spectroscopy, high-resolution mass spectrometry (HRMS), and solution-state Fourier transform nuclear magnetic resonance (FT-NMR) spectroscopy. Single crystal X-ray diffraction analysis confirmed that all complexes 1–9 exhibit a PBP geometry. Notably, all complexes display significant in-plane distortion of the SnN₃O₂ pentagon due to shifts in the Sn(IV) ion position.