[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 \(P\overline 3 ,\;a = 15.9307\left( 9 \right)\;\acute{\mathring{\mathrm{A}}} ,\;c = 9.9238\left( 6 \right)\;\acute{\mathring{\mathrm{A}}} ,\;V = 2181.1\left( 3 \right)\;{\acute{\mathring{\mathrm{A}}} ^3},\;Z = 6,\;{d_{\rm{x}}} = 1.822\;{\rm{g/c}}{{\rm{m}}^{\rm{3}}}\), Ni-N is \(2.1182\left( {12} \right) - 2.1498\left( {11} \right)\;\acute{\mathring{\mathrm{A}}} ,\) ∠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 \(P\overline 3 \,1c,\;a = 9.2491\left( 4 \right)\;\acute{\mathring{\mathrm{A}}} ,\;c = 9.9713\left( 4 \right)\;\acute{\mathring{\mathrm{A}}} ,\;V = 738.72\left( 7 \right)\;{\acute{\mathring{\mathrm{A}}} ^3},\;Z = 2,\;{d_x} = 1.794\;{\rm{g/c}}{{\rm{m}}^3}\), Ni-N is \(2.1302\left( {14} \right)\;\acute{\mathring{\mathrm{A}}} \), ∠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 \(1.769\;\acute{\mathring{\mathrm{A}}} \) to \(1.725\;\acute{\mathring{\mathrm{A}}} \) 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.