A Novel Layered Niobium Oxychloride Compound Based on Nb₂ Pairs and Nb₆ Octahedral Clusters: Synthesis and Crystal and Electronic Structures of Nb₁₀Cl₁₆O₇

The synthesis, single crystal structure determination, and electronic structure of Nb10Cl16O7, the first Nb6 oxychloride stabilized without countercation, are reported in this work. The crystal structure is very original since it consists of layers built up from both Nb6 octahedral clusters and Nb2 pairs. The Nb6Oi6Cli6Cla6 and Nb2(μ2-Cl)2Cl4O4 units form [Nb6Cli6Oi4Oi-i2/2Cla-a4/2Cla2]∞ infinite chains and [{Nb2(μ2-Cl)2O2/2Cl4/2O2}2]∞ double chains, respectively, that are interconnected by shared oxygen and chlorine ligands leading to layers. The cohesion of the three-dimensional structure (3D) is ensured by van der Waals contacts between layers that are randomly stacked along the [011] direction. Structural correlations between Nb10Cl16O7 and related Nb6 cluster oxyhalides, as well as NbOCl2 and NbCl4 containing Nb2 pairs, are discussed. DFT results show that among the 20 valence electrons involved in the metal−metal bonding states, 14 electrons belong to the octahedral Nb6Cli6Oi6Cla6 unit whereas the 6 others (i.e., 1.5 per Nb atom) participate in the bonding in the distorted [{Nb2(μ2-Cl)2O2/2Cl4/2O2}2]∞ double chains.本工作报道了首个无需抗衡阳离子稳定的六铌氧氯化物Nb10Cl16O7的合成、单晶结构解析与电子结构性质。该晶体结构极具创新性，其由Nb6八面体簇与Nb2二聚体共同构建层状骨架。其中，Nb6Oi6Cli6Cla6与Nb2(μ2-Cl)2Cl4O4单元分别形成[Nb6Cli6Oi4Oi-i2/2Cla-a4/2Cla2]∞无限链与[{Nb2(μ2-Cl)2O2/2Cl4/2O2}2]∞双链，二者通过共享氧与氯配体相互连接，最终形成层状结构。三维（3D）结构的内聚性依靠层间范德华接触维持，各层沿[011]方向随机堆叠。本文还讨论了Nb10Cl16O7与相关六铌簇氧卤化物，以及含Nb2二聚体的NbOCl2和NbCl4之间的结构相关性。密度泛函理论（Density Functional Theory）结果表明，在参与金属-金属成键态的20个价电子中，有14个属于八面体Nb6Cli6Oi6Cla6单元，剩余6个（即每个Nb原子分摊1.5个价电子）则参与畸变的[{Nb2(μ2-Cl)2O2/2Cl4/2O2}2]∞双链的成键作用。