Stereoisomerism in Tetrametallic Propeller-Like Complexes: A Solid-State and Solution NMR Study on a Tetragallium(III) Derivative

Tetragallium(III) complex in [Ga-4(L4-Py)(2)(dpm)(6)] . EtOH, with H3L4-Py=2-(hydroxymethyl)-2-(pyridin-4-yl)propane-1,3-diol and Hdpm=dipivaloylmethane, was investigated as a diamagnetic analogue of tetrametallic, propeller-like single-molecule magnets (SMMs). The chiral molecular structure partitions the six CH2 protons of each tripodal (L4-Py)(3-) ligand into two diastereotopic sets. The two signals were clearly detected by H-1 NMR spectroscopy in C6D6, proving that ? and Delta enantiomers interconvert slowly over NMR timescale. Density functional theory calculations provided quantitative agreement with the observed values of chemical shifts and scalar coupling constants across both geminal and long-range interaction pathways. The solid-state structure suggests the occurrence of a lower symmetry stereoisomer (27 mol%), which was clearly identified in the NMR spectra. Since high spin Fe3+ forms distinctly more inert complexes than Ga3+, comparable or greater configurational stability is expected for the isostructural Fe-4(III), (Fe3CrIII)-Cr-III, and (Fe3VIII)-V-III SMMs, which are difficult to investigate by solution NMR because of the strong paramagnetism.

Automated summary

The study investigates the diamagnetic analogue of tetrametallic, propeller-like single-molecule magnets [Ga-4(L4-Py)(2)(dpm)(6)] in EtOH. Through H-1 NMR spectroscopy and density functional theory calculations, it was found that the two enantiomers interconvert slowly. The solid-state structure suggests the existence of a lower symmetry stereoisomer, which needs to be clearly identified through NMR spectra.