A three body problem: a genuine hetero tri metallic molecule vs. a mixture of two parent hetero bi metallic molecules

This work raises a fundamental question about the "real" structure of molecular compounds containing three different metals: whether they consist of genuine hetero metallic species or of a mixture of parent hetero metallic species. Heterotrimetallic complex Li CoNi(tbaoac) ( , tbaoac = -butyl acetoacetate) has been designed based on the model tetranuclear structure featuring two transition metal sites in order to be utilized as a molecular precursor for the low-temperature preparation of the LiCo Ni O battery cathode material. An investigation of the structure of appeared to be very challenging, since the Co and Ni atoms have very similar atomic numbers, monoisotopic masses, and radii as well as the same oxidation state and coordination number/environment. Using a statistical analysis of heavily overlaid isotope distribution patterns of the [Li MM'L ] (M/M' = Co , Ni , and CoNi) ions in DART mass spectra, it was concluded that the reaction product contains both heterotrimetallic and bimetallic species. A structural analogue approach has been applied to obtain Li MMg(tbaoac) (M = Co ( ) and Ni ( )) complexes that contain lighter, diamagnetic magnesium in the place of one of the 3d transition metals. X-ray crystallography, mass spectrometry, and NMR spectroscopy unambiguously confirmed the presence of three types of molecules in the reaction mixture that reaches an equilibrium, Li M L + Li Mg L ↔ 2Li MMgL , upon prolonged reflux in solution. The equilibrium mixture was shown to have a nearly statistical distribution of the three molecules, and this is fully supported by the results of theoretical calculations revealing that the stabilization energies of hetero metallic assemblies fall exactly in between those for the parent hetero metallic species. The LiCo Ni O quaternary oxide has been obtained in its phase-pure form by thermal decomposition of heterometallic precursor at temperatures as low as 450 °C. Its chemical composition, structure, morphology, and transition metal distribution have been studied by X-ray and electron diffraction techniques and compositional energy-dispersive X-ray mapping with nanometer resolution. The work clearly illustrates the advantages of heterometallic single-source precursors over the corresponding multi-source precursors.