Synthesis of Alkaline Earth Diazenides MAEN2 (MAE = Ca, Sr, Ba) by Controlled Thermal Decomposition of Azides under High Pressure

The alkaline earth diazenides MAEN2 with MAE = Ca, Sr and Ba were synthesized by a novel synthetic approach, namely, a controlled decomposition of the corresponding azides in a multianvil press at highpressure/ high-temperature conditions. The crystal structure of hitherto unknown calcium diazenide (space group I4/mmm (no. 139), a = 3.5747(6) Å, c = 5.9844(9) Å, Z = 2, wRp = 0.078) was solved and refined on the basis of powder X-ray diffraction data as well as that of SrN2 and BaN2. Accordingly, CaN2 is isotypic with SrN2 (space group I4/mmm (no. 139), a = 3.8054(2) Å, c = 6.8961(4) Å, Z = 2, wRp = 0.057) and the corresponding alkaline earth acetylenides (MAEC2) crystallizing in a tetragonally distorted NaCl structure type. In accordance with literature data, BaN2 adopts a more distorted structure in space group C2/c (no. 15) with a = 7.1608(4) Å, b = 4.3776(3) Å, c = 7.2188(4) Å, β = 104.9679(33)°, Z = 4 and wRp = 0.049). The N−N bond lengths of 1.202(4) Å in CaN2 (SrN2 1.239(4) Å, BaN2 1.23(2) Å) correspond well with a double-bonded dinitrogen unit confirming a diazenide ion [N2]2−. Temperature-dependent in situ powder X-ray diffractometry of the three alkaline earth diazenides resulted in formation of the corresponding subnitrides MAE2N (MAE = Ca, Sr, Ba) at higher temperatures. FTIR spectroscopy revealed a band at about 1380 cm−1 assigned to the N−N stretching vibration of the diazenide unit. Electronic structure calculations support the metallic character of alkaline earth diazenides

Synthesis of Alkaline Earth Diazenides M_AEN₂ (M_AE = Ca, Sr, Ba) by Controlled Thermal Decomposition of Azides under High Pressure

The alkaline earth diazenides M_AEN₂ with M_AE = Ca, Sr and Ba were synthesized by a novel synthetic approach, namely, a controlled decomposition of the corresponding azides in a multianvil press at high-pressure/high-temperature conditions. The crystal structure of hitherto unknown calcium diazenide (space group <i>I</i>4/<i>mmm</i> (no. 139), <i>a</i> = 3.5747(6) Å, <i>c</i> = 5.9844(9) Å, <i>Z</i> = 2, <i>wR</i>_p = 0.078) was solved and refined on the basis of powder X-ray diffraction data as well as that of SrN₂ and BaN₂. Accordingly, CaN₂ is isotypic with SrN₂ (space group <i>I</i>4/<i>mmm</i> (no. 139), <i>a</i> = 3.8054(2) Å, <i>c</i> = 6.8961(4) Å, <i>Z</i> = 2, <i>wR</i>_p = 0.057) and the corresponding alkaline earth acetylenides (M_AEC₂) crystallizing in a tetragonally distorted NaCl structure type. In accordance with literature data, BaN₂ adopts a more distorted structure in space group <i>C</i>2<i>/c</i> (no. 15) with <i>a</i> = 7.1608(4) Å, <i>b</i> = 4.3776(3) Å, <i>c</i> = 7.2188(4) Å, β = 104.9679(33)°, <i>Z</i> = 4 and <i>wR</i>_p = 0.049). The N–N bond lengths of 1.202(4) Å in CaN₂ (SrN₂ 1.239(4) Å, BaN₂ 1.23(2) Å) correspond well with a double-bonded dinitrogen unit confirming a diazenide ion [N₂]^2–. Temperature-dependent <i>in situ</i> powder X-ray diffractometry of the three alkaline earth diazenides resulted in formation of the corresponding subnitrides M_AE₂N (M_AE = Ca, Sr, Ba) at higher temperatures. FTIR spectroscopy revealed a band at about 1380 cm^–1 assigned to the N–N stretching vibration of the diazenide unit. Electronic structure calculations support the metallic character of alkaline earth diazenides