State Key Laboratory of Crystal Materials, Institute of Crystal Materials, Shandong University, Jinan, Shandong 250100, People's Republic of China.
Inorg Chem. 2011 Sep 5;50(17):8020-7. doi: 10.1021/ic200286t. Epub 2011 Jul 25.
A series of ternary Zintl phases, Ca(2)CdP(2), Ca(2)CdAs(2), Sr(2)CdAs(2), Ba(2)CdAs(2), and Eu(2)CdAs(2), have been synthesized through high temperature metal flux reactions, and their structures have been characterized by single-crystal X-ray diffraction. They belong to the Yb(2)CdSb(2) structure type and crystallize in the orthorhombic space group Cmc2(1) (No. 36, Z = 4) with cell dimensions of a = 4.2066(5), 4.3163(5), 4.4459(7), 4.5922(5), 4.4418(9) Å; b = 16.120(2), 16.5063(19), 16.904(3), 17.4047(18), 16.847(4) Å; c = 7.0639(9), 7.1418(8), 7.5885(11), 8.0526(8), 7.4985(16) Å for Ca(2)CdP(2) (R1 = 0.0152, wR2 = 0.0278), Ca(2)CdAs(2) (R1 = 0.0165, wR2 = 0.0290), Sr(2)CdAs(2) (R1 = 0.0238, wR2 = 0.0404), Ba(2)CdAs(2) (R1 = 0.0184, wR2 = 0.0361), and Eu(2)CdAs(2) (R1 = 0.0203, wR2 = 0.0404), respectively. Among these, Ca(2)CdAs(2) was found to form with another closely related structure, depending on the experimental conditions--monoclinic space group Cm (No. 8, Z = 10) with lattice constants a = 21.5152(3) Å, b = 4.30050(10) Å, c = 14.3761(2) Å and β = 110.0170(10)° (R1 = 0.0461, wR2 = 0.0747). UV/vis optical absorption spectra for both forms of Ca(2)CdAs(2) show band gaps on the order of 1.0 eV, suggesting semiconducting properties, which have also been confirmed through electronic band structure calculations based on the density-functional theory. Results from differential scanning calorimetry measurements probing the thermal stability and phase transitions in the two Ca(2)CdAs(2) polymorphs are discussed. Magnetic susceptibility measurements for Eu(2)CdAs(2), indicating divalent Eu(2+) cations, are presented as well.
通过高温金属通量反应合成了一系列三元 Zintl 相 Ca(2)CdP(2)、Ca(2)CdAs(2)、Sr(2)CdAs(2)、Ba(2)CdAs(2)和 Eu(2)CdAs(2)，并通过单晶 X 射线衍射对其结构进行了表征。它们属于 Yb(2)CdSb(2)结构类型，在正交晶系 Cmc2(1) (No. 36, Z = 4)空间群中结晶，晶胞参数为 a = 4.2066(5)、4.3163(5)、4.4459(7)、4.5922(5)、4.4418(9) Å；b = 16.120(2)、16.5063(19)、16.904(3)、17.4047(18)、16.847(4) Å；c = 7.0639(9)、7.1418(8)、7.5885(11)、8.0526(8)、7.4985(16) Å，用于 Ca(2)CdP(2) (R1 = 0.0152, wR2 = 0.0278)、Ca(2)CdAs(2) (R1 = 0.0165, wR2 = 0.0290)、Sr(2)CdAs(2) (R1 = 0.0238, wR2 = 0.0404)、Ba(2)CdAs(2) (R1 = 0.0184, wR2 = 0.0361)和 Eu(2)CdAs(2) (R1 = 0.0203, wR2 = 0.0404)。在这些化合物中，Ca(2)CdAs(2) 被发现与另一种密切相关的结构形成，这取决于实验条件——具有晶格常数 a = 21.5152(3) Å、b = 4.30050(10) Å、c = 14.3761(2) Å 和 β = 110.0170(10)°的单斜晶系 Cm (No. 8, Z = 10) (R1 = 0.0461, wR2 = 0.0747)。两种形式的 Ca(2)CdAs(2) 的紫外/可见吸收光谱都显示出约 1.0 eV 的带隙，表明具有半导体性质，这也通过基于密度泛函理论的电子能带结构计算得到了证实。还讨论了两种 Ca(2)CdAs(2) 多晶型物的热稳定性和相变的差示扫描量热法测量结果。还给出了 Eu(2)CdAs(2) 的磁化率测量结果，表明 Eu(2+) 阳离子为二价。
