新型氧硫代铌（IV）水合离子的制备、性质及反应活性以及(Me2NH2)6[Nb5(μ3-S)2(μ3-O)2(μ2-O)2(NCS)14].3.5H2O的晶体结构

Preparation, properties, and reactivities of unprecedented oxo-sulfido Nb(IV) aqua ions and crystal structure of (Me2NH2)6[Nb5(mu3-S)2(mu3-O)2(mu2-O)2(NCS)14].3.5H2O.

作者信息

Ooi Bee-Lean, Søtofte Inger, Sokolov Maxim N, Kozlova Svetlana G, Rasmussen Søren B, Nielsen Loa C, Henriksen Jonas

机构信息

Department of Chemistry, Technical University of Denmark, Kemitorvet, Building 207, Kongens Lyngby, Denmark.

出版信息

Inorg Chem. 2006 Jun 26;45(13):5008-17. doi: 10.1021/ic052145i.

DOI:10.1021/ic052145i

PMID:16780322

Abstract

By treatment of Zn-reduced ethanolic solutions of NbCl5 with HCl in the presence of sulfide followed by cation-exchange chromatography, two oxo-sulfido niobium aqua ions, the red [Nb4(mu4-S)(mu2-O)5(H2O)10]4+ and the yellow-brown [Nb5(mu3-S)2(mu3-O)2(mu2-O)2(H2O)14]8+, were isolated. Both readily form their respective thiocyanate complexes, for which the structure for the former has been previously reported. Brown crystals of (Me2NH2)6[Nb5S2O4(NCS)14].3.5H2O (1) were isolated in the case of the latter, and the structure was determined by X-ray crystallography (space group: a = 15.4018(5) A, b = 21.1932(8) A, c = 22.0487(8) A, alpha=gamma = 90 degrees , beta = 103.4590(10) degrees , and R(1) = 0.0659). An unprecedented pentanuclear Nb5S2O48+ core is revealed in which short Nb-Nb distances (2.7995(8)-2.9111(8) A) are consistent with metal-metal bonding. A stopped-flow kinetic study of the 1:1 equilibration of NCS- with [Nb4(mu4-S)(mu2-O)5(H2O)10]4+ has been carried out. Equilibration rate constants are independent of [H(+)] in the range investigated (0.5-2.0 M) and at 25 degrees C; kf= 9.5 M(-1) s(-1), kaq = 2.6 x 10(-2) s(-1), and K = 365 M1). Conditions with first NCS- and then [Nb4(mu4-S)(mu2-O)5(H2O)10]4+ in excess revealed a statistical factor of 4, suggesting the presence of four kinetically equivalent Nb atoms. Attempts to study the 1:1 substitution of NCS- with [Nb5(mu3-S)2(mu3-O)2(mu2-O)2(H2O)14]8+ showed signs of saturation kinetics. Quantum chemical calculations using the density functional theory (DFT) approach were performed on both the Nb4O5S4+ and Nb5O4S28+ naked clusters. The highest occupied and lowest unoccupied molecular orbitals have dominant Nb(4d) character. The HOMO for Nb4O5S4+ is a nondegenerate fully filled MO, whereas for Nb5O4S28+, it is a nondegenerate partially filled MO with one unpaired electron. EPR spectroscopy on [Nb5(mu3-S)2(mu3-O)2(mu2-O)2(H2O)14]8+ shows that the molecule has total anisotropy (C2v), with all three tensors, gx= 2.399, gy= 1.975, and gz= 1.531, resolved. No hyperfine interaction expected from the nuclear moment of I = 9/2 for 93Nb was observed.

摘要

通过在硫化物存在下用盐酸处理五氯化铌的锌还原乙醇溶液，然后进行阳离子交换色谱，分离出两种氧代硫代铌水合离子，红色的[Nb4(μ4-S)(μ2-O)5(H2O)10]4+和黄棕色的[Nb5(μ3-S)2(μ3-O)2(μ2-O)2(H2O)14]8+。两者都很容易形成各自的硫氰酸盐配合物，前者的结构此前已有报道。对于后者，分离出了(Me2NH2)6[Nb5S2O4(NCS)14].3.5H2O (1)的棕色晶体，并通过X射线晶体学确定了其结构（空间群：a = 15.4018(5) Å，b = 21.1932(8) Å，c = 22.0487(8) Å，α = γ = 90°，β = 103.4590(10)°，R(1) = 0.0659）。揭示了一个前所未有的五核Nb5S2O48+核心，其中短的Nb-Nb距离（2.7995(8)-2.9111(8) Å）与金属-金属键合一致。对NCS-与[Nb4(μ4-S)(μ2-O)5(H2O)10]4+的1:1平衡进行了停流动力学研究。平衡速率常数在所研究的[H(+)]范围（0.5 - 2.0 M）和25℃下与[H(+)]无关；kf = 9.5 M(-1) s(-1)，kaq = 2.6 x 10(-2) s(-1)，K = 365 M1）。先加入NCS-然后过量加入[Nb4(μ4-S)(μ2-O)5(H2O)10]4+的条件显示出统计因子为4，表明存在四个动力学等价的Nb原子。研究NCS-与[Nb5(μ3-S)2(μ3-O)2(μ2-O)2(H2O)14]8+的1:1取代的尝试显示出饱和动力学的迹象。使用密度泛函理论（DFT）方法对Nb4O5S4+和Nb5O4S28+裸簇进行了量子化学计算。最高占据分子轨道和最低未占据分子轨道具有主要的Nb(4d)特征。Nb4O5S4+的HOMO是一个非简并的全充满分子轨道，而对于Nb5O4S28+，它是一个非简并的部分充满分子轨道，有一个未成对电子。对[Nb5(μ3-S)2(μ3-O)2(μ2-O)2(H2O)14]8+的电子顺磁共振光谱表明该分子具有完全各向异性（C2v），所有三个张量gx = 2.399，gy = 1.975，gz = 1.531都已分辨。未观察到93Nb的I = 9/2核矩预期的超精细相互作用。