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The paper describes a heterobimetallic mixed-ligand hexanuclear precursor [NaMn2(thd)4(OAc)]2 (1) (thd = 2,2,6,6-tetramethyl-3,5-heptadionate; OAc = acetate) that was designed based on its lithium homoleptic analogue, [LiMn2(thd)5], by replacing one of the thd ligands with an acetate group in order to accommodate 5-coordinated sodium instead of tetrahedral lithium ion. The complex, which is highly volatile and soluble in a variety of common solvents, has been synthesized by both the solid-state and solution methods. The unique “dimer-of-trimers” heterometallic structure consists of two trinuclear [NaMnII2(thd)4]+ units firmly bridged by two acetate ligands. X-ray diffraction techniques, DART mass spectrometry, ICP-OES analysis, and IR spectroscopy have been employed to confirm the structure and composition of the hexanuclear complex. Similar to the Li counterpart forming LiMn2O4 spinel material upon thermal decomposition, the title Na:Mn = 1:2 compound was utilized as the first single-source precursor for the low-temperature preparation of Na4Mn9O18 tunnel oxide. Importantly, four Mn sites in the hexanuclear molecule can be potentially partially substituted by other transition metals, leading to heterotri- and tetrametallic precursors for the advanced quaternary and quinary Na-ion oxide cathode materials.
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This content will become publicly available on February 28, 2026
Lithium-rich, oxygen-deficient spinel obtained through low-temperature decomposition of heterometallic molecular precursor
A heterometallic single-source molecular precursor Li2Mn2(tbaoac)6 (1 , tbaoac = tert -butyl acetoacetato) has been specifically designed to achieve the lowest decomposition temperature and a clean conversion to mixed-metal oxides. The crystal structure of this tetranuclear molecule was determined by single crystal X-ray diffraction, and the retention of heterometallic structure in solution and in the gas phase was confirmed by nuclear magnetic resonance spectroscopy and mass spectrometry, respectively. Thermal decomposition of this precursor at the temperatures as low as 310 oC resulted in a new metastable oxide phase formulated as lithium-rich, oxygen-deficient spinel Li1.5Mn1.5O3.5. This formulation was supported by a comprehensive suite of techniques including thermogravimetric/differential thermal analysis, elemental analysis, inductively coupled mass spectrometry, iodometric titration, X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy studies, and Rietveld refinement from powder X-ray diffraction data. Upon heating to about 400 oC, this new low-temperature phase disproportionates stoichiometrically, gradually converting to layered Li2MnO3 and spinel Li1+x Mn2-x O4 (x < 0.5). Further heating to 750 oC results in formation of thermodynamically stable Li2MnO3 and LiMn2O4 phases.
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- PAR ID:
- 10590122
- Publisher / Repository:
- OAE Publishing Inc.
- Date Published:
- Journal Name:
- Energy Materials
- Volume:
- 5
- Issue:
- 7
- ISSN:
- 2770-5900
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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