Heterometallic molecular precursors for a lithium–iron oxide material: synthesis, solid state structure, solution and gas-phase behaviour, and thermal decomposition. Issue 17 (1st February 2017)

• Record Type: Journal Article
• Authors: Han, Haixiang; Wei, Zheng; Barry, Matthew C.; Filatov, Alexander S.; Dikarev, Evgeny V.
• Is Part Of: Dalton transactions. Volume 46:Issue 17(2017)
• Page Start: 5644
• Page End: 5649
• Publication Date: 2017-02-01
• Subjects: Chemistry, Inorganic -- Periodicals; Chemistry, Physical and theoretical -- Periodicals; Chemistry, Inorganic -- Periodicals; 546.05
• DOI: 10.1039/c6dt04602a
• Languages: English
• ISSNs: 1477-9226

Abstract

Abstract : Heterometallic single-source precursors with the appropriate Li : Fe ratio were shown to yield the target LiFeO2 cathode material upon thermal decomposition. Abstract : Three heterometallic single-source precursors with a Li : Fe = 1 : 1 ratio for a LiFeO2 oxide material are reported. Heterometallic compounds LiFeL3 (L = tbaoac (1 ), ptac (2 ), and acac(3 )) have been obtained on a large scale, in nearly quantitative yields by one-step reactions that employ readily available reagents. The heterometallic precursor LiFe(acac)3 (3 ) with small, symmetric substituents on the ligand (acac = pentane-2, 4-dionate), maintains a 1D polymeric structure in the solid state that limits its volatility and prevents solubility in non-coordinating solvents. The application of the unsymmetrical ligands, tbaoac ( tert -butyl acetoacetate) and ptac (1, 1, 1-trifluoro-5, 5-dimethyl-2, 4-hexanedionate), that exhibit different bridging properties at the two ends of the ligand, allowed us to change the connectivity pattern within the heterometallic assembly. The latter was demonstrated by structural characterization of heterometallic complexes LiFe(tbaoac)3 (1 ) and LiFe(ptac)3 (2 ) that consist of discrete heterocyclic tetranuclear molecules Li2 Fe2 L6 . The compounds are highly volatile and exhibit a congruent sublimation character. DART mass spectrometric investigation revealed the presence of heterometallic molecules in the gas phase. The positive mode spectra are dominated by the presence of [M − L] + peaks (M = Li2 Fe2 L6 ). In accord with their discrete molecular structure, complexes1 and2 are highly soluble in nearly all common solvents. In order to test the retention of the heterometallic structure in solution, the diamagnetic analog of1, LiMg(tbaoac)3 (4 ), has been isolated. Its tetranuclear molecular structure was found to be isomorphous to that of the iron counterpart. 1 H and 7 Li NMR spectroscopy unambiguously confirmed the presence of heterometallic molecules in solutions of non-coordinating solvents. The heterometallic precursor1 was shown to exhibit clean thermal decomposition in air that results in phase-pure α-modification of layered oxide LiFeO2, the prospective cathode material for lithium ion batteries.