Surface-supported arrays of Fe(4)-type Single-Molecule Magnets retain a memory effect and are of current interest in the frame of molecule-based information storage and spintronics. To reveal the spin structure of [Fe(4)(L)(2)(dpm)(6)] (1) on Au, an isomorphous compound [Fe(3)Cr(L)(2)(dpm)(6)] was synthesized and structurally and magnetically characterized (H(3)L is tripodal ligand 11-(acetylthio)-2,2-bis(hydroxymethyl)undecan-1-ol and Hdpm is dipivaloylmethane). The new complex contains a central Cr(3+) ion and has a S = 6 ground state as opposed to S = 5 in 1. Low-temperature X-ray Magnetic Circular Dichroism studies at Fe- and Cr-L(2,3) edges revealed that the antiparallel alignment between Fe and Cr spins is preserved on surfaces. Moreover, the different Fe-L(2,3) spectral features found in the homo- and heterometallic species disclose the opposing contribution of the central Fe(3+) ion in the former compound, proving that its ferrimagnetic spin structure is retained on surfaces.

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The initial channels of thermal decomposition mechanism of 2,6-diamino-3,5-dinitropyrazine-1-oxide (LLM-105) molecule were investigated. The results of quantum chemical calculations revealed four candidates involved in the reaction pathway, including the C–NO2 bond homolysis, nitro–nitrite rearrangement followed by NO elimination, and H transfer from amino to acyl O and to nitro O with the subsequent OH or HONO elimination, respectively. In view of the further kinetic analysis and ab initio molecular dynamics simulations, the C–NO2 bond homolysis was suggested to be the dominant step that triggered the decomposition of LLM-105 at temperatures above 580 K. Below this temperature, two types of H transfer were considered as the primary reactions, which have advantages including lower barrier and high rate compared to the C–NO2 bond dissociation. It could be affirmed that these two types of H transfer are reversible processes, which could buffer against external thermal stimulation. Therefore, the excellent thermal stability of LLM-105, that is nearly identical to that of 1,3,5-triamino-2,4,6-trinitrobenzene, can be attributed to the reversibility of H transfers at relatively low temperatures. However, subsequent OH or HONO elimination reactions occur with difficulty because of their slow rates and extra energy barriers. Although nitro–nitrite rearrangement is theoretically feasible, its rate constant is too small to be observed. This study facilitates the understanding of the essence of thermal stability and detailed decomposition mechanism of LLM-105.

Thermal decomposition kinetic behavior of energetic materials is of substantial importance for safety enhancement in manufacturing, usage, and storage. The thermal decomposition kinetic behavior of 2,6-diamino-3,5-dinitropyrazine-1-oxide (LLM-105) was studied by simultaneous differential scanning calorimetry and thermogravimetric analysis (DSC–TG). The thermal decomposition of LLM-105 is a two-step process in which the overall reaction was deconvoluted into two reaction steps for better analysis through different physical meanings consideration of the kinetic data derived from DSC and TG. Kinetic parameters of the two individual reaction steps were characterized through isoconversional and combined kinetic analysis methods. It was found that the activation energy of the first reaction step was 222.2 ± 0.5 kJ mol–1, whereas that of the second reaction step was 244.5 ± 0.5 kJ mol–1. Both steps mostly obeyed the nucleation and growth models (Avrami–Erofeev (A3)). The validity of the obtained kinetic parameters was tested through the successful reconstruction of the original experimental curves. The nucleation and growth were also confirmed through scanning electronic microscopy observations of the morphology evolution during the LLM-105 decomposition. The obtained kinetic parameters and kinetic models contributed to a comprehensive and in-depth understanding of the thermal decomposition of LLM-105.