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

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• 作者：Sebastian B. Schneider ; Rainer Frankovsky ; Wolfgang Schnick
• 刊名：Inorganic Chemistry
• 出版年：2012
• 出版时间：February 20, 2012
• 年：2012
• 卷：51
• 期：4
• 页码：2366-2373
• 全文大小：401K
• 年卷期：v.51,no.4(February 20, 2012)
• ISSN：1520-510X

文摘

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 I4/mmm (no. 139), a = 3.5747(6) 脜, c = 5.9844(9) 脜, Z = 2, wR_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 I4/mmm (no. 139), a = 3.8054(2) 脜, c = 6.8961(4) 脜, Z = 2, wR_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 C2/c (no. 15) with a = 7.1608(4) 脜, b = 4.3776(3) 脜, c = 7.2188(4) 脜, 尾 = 104.9679(33)掳, Z = 4 and wR_p = 0.049). The N鈥揘 bond lengths of 1.202(4) 脜 in CaN₂ (SrN₂ 1.239(4) 脜, BaN₂ 1.23(2) 脜) correspond well with a double-bonded dinitrogen unit confirming a diazenide ion [N₂]^{2鈥?/sup>. Temperature-dependent in situ 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鈥? assigned to the N鈥揘 stretching vibration of the diazenide unit. Electronic structure calculations support the metallic character of alkaline earth diazenides.}