Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306, USA.
J Am Chem Soc. 2010 Dec 15;132(49):17523-30. doi: 10.1021/ja107436n. Epub 2010 Nov 22.
The reaction of carbon and CaH2 in a calcium/lithium flux mixture produces crystals of the new compound Ca2LiC3H. This phase forms with a new structure type in tetragonal space group P4/mbm (a = 6.8236(1) Å, c = 3.7518(1) Å, Z = 2, R1 = 0.0151). This is a stuffed variant of the Cs2(NH2)N3 structure, containing hydride anions in octahedral sites; the structure determination by single-crystal X-ray diffraction surprisingly allowed the hydrogen to be detected. The Ca2LiC3H structure also features the rarely seen C3(4-) carbide anion; the protolysis reaction of this compound with ammonium chloride produces C3H4. The electronic properties of Ca2LiC3H were studied by quantum-chemical calculations including band structure and electron localization function (ELF) analysis; the phase is a charge-balanced semiconductor with a calculated band gap of 0.48 eV. This is in agreement with (7)Li, (13)C, and (1)H MAS NMR data, which show resonances in the ionic region instead of the Knight shifted region. ELF analysis of the theoretical nonhydrided Ca2LiC3 structure confirms the ability of these calculations to properly locate hydrides and supports the structural model based on X-ray diffraction data.
碳与 CaH2 在钙/锂通量混合物中的反应生成了新化合物 Ca2LiC3H 的晶体。该相以四方空间群 P4/mbm(a = 6.8236(1) Å, c = 3.7518(1) Å, Z = 2, R1 = 0.0151)的新结构类型形成。这是 Cs2(NH2)N3 结构的填充变体，其中包含八面体位置的氢化物阴离子；通过单晶 X 射线衍射进行的结构测定出人意料地检测到了氢。Ca2LiC3H 的结构还具有罕见的 C3(4-)碳化物阴离子；该化合物与氯化铵的质子化反应产生 C3H4。通过量子化学计算研究了 Ca2LiC3H 的电子性质，包括能带结构和电子定域函数（ELF）分析；该相是一种电荷平衡的半导体，计算出的能带隙为 0.48 eV。这与（7）Li、（13）C 和（1）H MAS NMR 数据一致，这些数据显示出在离子区域而不是 Knight 位移区域的共振。对理论上未氢化的 Ca2LiC3 结构的 ELF 分析证实了这些计算能够正确定位氢化物的能力，并支持基于 X 射线衍射数据的结构模型。
