Chair of Solid-State and Quantum Chemistry, Institute of Inorganic Chemistry, RWTH Aachen University, 52056 Aachen, Germany.
Dalton Trans. 2019 Oct 14;48(40):15029-15035. doi: 10.1039/c9dt03062j.
In this work, we describe the synthesis and structure of the quaternary transition-metal cyanamides Na2MnSn2(NCN)6 and Li2MnSn2(NCN)6. These phases crystallise isotypically in layered structures, with P3[combining macron]1m symmetry, that comprise hexagonal close-packed arrays of NCN2- anions with metal cations in 5/6 of the octahedral holes, thereby reflecting low-symmetry modifications of the hierarchical [NiAs]-type MNCN structure. The distinct coordination requirements of the metal cations template an ordered decoration across the octahedral sites with corundum-like [Sn2(NCN)3]2+ layers alternating with [A2Mn(NCN)3]2- layers which resemble a portion of the Li2Zr(NCN)3 structure. This motif is also mirrored in the form of the NCN2- anions which adopt N-C[triple bond, length as m-dash]N2- cyanamide shapes with clear single- and triple-bond character. Distortion-mode analysis reveals the importance of K1 octahedral twist and K2 cyanamide tilt displacements in stabilising these phases, the latter of which is only accessible because of the extended nature of the NCN2- anion. These are the first examples of non-binary transition-metal cyanamides to be discovered and this study highlights how the additional flexibility of the NCN2- anion affords a novel structure-type not observed in oxide chemistry.
在这项工作中，我们描述了四元过渡金属氰化物 Na2MnSn2(NCN)6 和 Li2MnSn2(NCN)6 的合成和结构。这些相以层状结构同晶结晶，具有 P3[combining macron]1m 对称性，由 NCN2-阴离子的六方密堆积排列组成，其中金属阳离子占据八面体孔的 5/6，从而反映了具有低对称性的 MNCN 型[NiAs]结构的修改。金属阳离子的独特配位要求模板化了在八面体位置上的有序装饰，具有刚玉状[Sn2(NCN)3]2+层与[A2Mn(NCN)3]2-层交替排列，类似于 Li2Zr(NCN)3 结构的一部分。这种模式也反映在 NCN2-阴离子的形式上，它们采用 N-C[三重键，长度为 m-dash]N2- 氰胺形状，具有明显的单键和三键特征。扭曲模式分析表明，K1 八面体扭曲和 K2 氰胺倾斜位移对这些相的稳定至关重要，后者仅因为 NCN2-阴离子的扩展性质而成为可能。这些是非二元过渡金属氰化物的第一个例子，本研究强调了 NCN2-阴离子的额外灵活性如何提供了一种在氧化物化学中未观察到的新型结构类型。
