[NiEn₃]MoO₄: Features of the Phase Transition and Thermal Decomposition in the Presence of Lithium Hydride

The crystal structural characteristics of the [NiEn₃]MoO₄ complex salt (En is ethylenediamine) at 90 K are as follows: space group P3¯,a=15.9307(9)Å´,c=9.9238(6)Å´,V=2181.1(3)Å´3,Z=6,dx=1.822g/cm3, Ni-N is 2.1182(12)−2.1498(11)Å´, ∠Ni-N-N is 80.76(4)-82.27(4)°. According to the differential scanning calorimetry data in a range from 295 K to 310 K, there is a thermal anomaly with peaks at T₁ = 299.6 K and T₂ = 304.7 K. The crystal structural characteristics at 320 K are as follows: space group P3¯1c,a=9.2491(4)Å´,c=9.9713(4)Å´,V=738.72(7)Å´3,Z=2,dx=1.794g/cm3, Ni-N is 2.1302 (14) Å´, ∠N-Ni-N is 80.96(8)°. With increasing temperature from 90 K to 320 K a decrease in the average Mo-O distance from 1.769 Å´ to 1.725 Å´ is observed in the structure. The comparative analysis of the interionic N-H…O and C-H…O contacts is carried out. The ex situ powder X-ray diffraction study of the formation process of metal and carbide phases by the [NiEn₃]MoO₄ thermal decomposition in the presence of LiH in the He atmosphere is performed. At the temperature of 1323 K a Mo₂C and MoNi₄ phase mixture forms in the first minute. With increasing keeping time the Ni₂Mo₄C_x phase forms.