XRD-pure Li(4)Mn(5)O(12) spinels are obtained below 600 A degrees C from oxalate and acetate precursors. The morphology consists of nanometric particles (about 25 nm) with a narrow particle size distribution. HRTEM and electron paramagnetic resonance (EPR) spectroscopy of Mn(4+) are employed for local structure analysis. The HRTEM images recorded on nano-domains in Li(4)Mn(5)O(12) reveal its complex structure. HRTEM shows one-dimensional structure images, which are compatible with the (111) plane of the cubic spinel structure and the (001) plane of monoclinic Li(2)MnO(3). For Li(4)Mn(5)O(12) compositions annealed between 400 and 800 A degrees C, EPR spectroscopy shows the appearance of two types of Mn(4+) ions having different metal environments: (i) Mn(4+) ions surrounded by Li(+) and Mn(4+) and (ii) Mn(4+) ions in Mn(4+)-rich environment. The composition of the Li(+), Mn(4+)-shell around Mn(4+) mimics the local environment of Mn(4+) in monoclinic Li(2)MnO(3), while the Mn(4+)-rich environment is related with that of the spinel phase. The structure of XRD-pure Li(4)Mn(5)O(12) comprises nano-domains with a Li(2)MnO(3)-like and a Li(4/3-x) Mn(5/3+x) O(4) composition rather than a single spinel phase with Li in tetrahedral and Li(1/3)Mn(5/3) in octahedral spinel sites. The annealing of Li(4)Mn(5)O(12) at temperature higher than 600 A degrees C leads to its decomposition into monoclinic Li(2)MnO(3) and spinel Li(4/3-x) Mn(5/3+x) O(4).