Schmolke Christian, Oeckler Oliver, Bichler Daniel, Johrendt Dirk, Schnick Wolfgang
Department Chemie und Biochemie, Lehrstuhl für Anorganische Festkörperchemie, Ludwig-Maximilians-Universität München, Butenandtstr. 5-13, 81377 München, Germany.
Chemistry. 2009 Sep 14;15(36):9215-22. doi: 10.1002/chem.200900703.
A new structure type of nitridosilicates with an interrupted framework has been identified for M(7)Si(6)N(15) with M = La, Ce, and Pr. The materials have been synthesized in a radio-frequency furnace at temperatures between 1550-1625 degrees C, starting from the respective metals, metal nitrides, and silicon diimide. The crystal structure of Ce(7)Si(6)N(15) has been determined by using single-crystal X-ray diffraction. Besides ordered crystals 1 with a complicated triclinic superstructure and multiple twinning (P1, no. 2; a = 13.009(3), b = 25.483(5), c = 25.508(10) A; alpha = 117.35(3), beta = 99.59(3), gamma = 99.63(3) degrees; V = 7114(2) A(3); Z = 18; R1 = 0.0411), disordered crystals 2 with identical composition exhibiting a trigonal average structure (R3, no. 148) have also been observed (a = 43.420(6), c = 6.506(2) A; V = 10 623(3) A(3); Z = 27; R1 = 0.0309). Pr(7)Si(6)N(15) (3) and La(7)Si(6)N(15) (4) are isostructural with 1 as evidenced by twinned single-crystal data for 3 (P1, no. 2; a = 12.966(3), b = 25.449(10), c = 25.459(10) A; alpha = 117.28(3), beta = 99.70(4), gamma = 99.60(4) degrees; V = 7068(4) A(3); Z = 18; R1 = 0.0526) and powder diffraction data for 4 (P1, no. 2; a = 13.109(9), b = 25.606(18), c = 25.609(18) A; V = 7223(12) A(3); Z = 18; R(P) = 0.0194; R(F)(2) = 0.0936). The crystal structure of M(7)Si(6)N(15) (M = La, Ce, Pr) is built up exclusively of corner-sharing tetrahedrons that appear as Q(2)-, Q(3)-, and Q(4)-type tetrahedrons forming different ring sizes within a less condensed three-dimensional network. Among the characteristic structural motifs are saw-blade-shaped 12-rings and finite chains consisting of four corner-sharing SiN(4) tetrahedrons. High-resolution transmission electron micrographs indicate both ordered and disordered crystallites. In the diffraction patterns of disordered rhombohedral crystals, diffuse maxima appear in reciprocal space at those positions in which sharp superstructure reflections are found in the case of the respective ordered crystallites. Magnetic susceptibility measurements of Ce(7)Si(6)N(15) show paramagnetic behavior with an experimental magnetic moment of 2.29 mu(B) per Ce, thereby corroborating the existence of Ce(3+).
已确定具有间断骨架的新型氮硅化物结构类型，适用于M(7)Si(6)N(15)，其中M = 镧、铈和镨。这些材料是在射频炉中于1550 - 1625摄氏度的温度下合成的，起始原料为相应的金属、金属氮化物和硅二亚胺。通过单晶X射线衍射确定了Ce(7)Si(6)N(15)的晶体结构。除了具有复杂三斜超结构和多重孪晶的有序晶体1（P1，编号2；a = 13.009(3)，b = 25.483(5)，c = 25.508(10) Å；α = 117.35(3)，β = 99.59(3)，γ = 99.63(3)度；V = 7114(2) ų；Z = 18；R1 = 0.0411）外，还观察到了具有相同组成且呈现三角平均结构的无序晶体2（R3，编号148）（a = 43.420(6)，c = 6.506(2) Å；V = 10 623(3) ų；Z = 27；R1 = 0.0309）。孪晶单晶数据表明Pr(7)Si(6)N(15)（3）和La(7)Si(6)N(15)（4）与1同构，3的数据为（P1，编号2；a = 12.966(3)，b = 25.449(10)，c = 25.459(10) Å；α = 117.28(3)，β = 99.70(4)，γ = 99.60(4)度；V = 7068(4) ų；Z = 18；R1 = 0.0526），4的粉末衍射数据为（P1，编号2；a = 13.109(9)，b = 25.606(18)，c = 25.609(18) Å；V = 7223(12) ų；Z = 18；R(P) = 0.0194；R(F)(2) = 0.0936）。M(7)Si(6)N(15)（M = 镧、铈、镨）的晶体结构完全由共享顶点的四面体构成，这些四面体表现为Q(2)-、Q(3)-和Q(4)-型四面体，在一个不太致密的三维网络中形成不同的环大小。其特征结构单元包括锯片状的12元环和由四个共享顶点的SiN(4)四面体组成的有限链。高分辨率透射电子显微镜图像显示了有序和无序的微晶。在无序菱面体晶体的衍射图谱中，在倒易空间中出现漫射最大值的位置，在相应有序微晶的情况下会出现尖锐的超结构反射。Ce(7)Si(6)N(15)的磁化率测量显示出顺磁行为，每个铈的实验磁矩为2.29 μB，从而证实了Ce(3+)的存在。
