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首页> 外文期刊>Dalton transactions: An international journal of inorganic chemistry >A DFT based investigation into the electronic structure and properties of hydride rich rhodium clusters
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A DFT based investigation into the electronic structure and properties of hydride rich rhodium clusters

机译：基于DFT的富氢铑簇簇电子结构和性能研究

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摘要

Density functional theory has been used to investigate the structures, bonding and properties of a family of hydride rich late transition metal clusters of the type [Rh-6(PH3)(6)H-12](x)(x=0,+1,+2,+3 or +4), [Rh-6(PH3)(6)H-16](x)(x=+1or+2) and [Rh-6(PH3)(6)H-14](x)(x=0,+1or+2). The positions of the hydrogen atoms around the pseudo-octahedral Rh-6 core in the optimized structures of [Rh-6(PH3)(6)H-12](x) (x=0,+1,+2,+3 or +4) varied depending on the overall charge on the cluster. The number of semi-bridging hydrides increased (semi-bridging hydrides have two different Rh-H bond distances) as the charge on the cluster increased and simultaneously the number of perfectly bridging hydrides ( equidistant between two Rh centers) decreased. This distortion maximized the bonding between the hydrides and the metal centers and resulted in the stabilization of orbitals related to the 2T(2g) set in a perfectly octahedral cluster. In contrast, the optimized structures of the 16-hydride clusters [Rh-6(PH3)(6)H-12](x)(x=+1 or +2) were similar and both clusters contained an interstitial hydride, along with one terminal hydride, ten bridging hydrides and two coordinated H-2 molecules which were bound to two rhodium centers in an eta(2): eta(1)-fashion. All the hydrides were on the outside of the Rh-6 core in the lowest energy structures of the 14-hydride clusters [Rh-6(PH3)(6)H-14] and [Rh-6(PH3)(6)H-14](+), which both contained eleven bridging hydrides, one terminal hydride and one coordinated H-2 molecule. Unfortunately, the precise structure of [Rh-6(PH3)(6)H-14](2+) could not be determined as structures both with and without an interstitial hydride were of similar energy. The reaction energetics for the uptake and release of two molecule of H-2 by a cycle consisting of [ Rh-6(PH3)(6)H-12](2+), [ Rh6( PH3) 6H16](2+), [ Rh-6(PH3)(6)H-14](+), [Rh-6(PH3)(6)H-12](+) and [ Rh-6( PH3)(6)H-14](2+) were modelled, and, in general, good agreement was observed between experimental and theoretical results. The electronic reasons for selected steps in the cycle were investigated. The 12-hydride cluster [Rh-6(PH3)(6)H-12](2+) readily picks up two molecules of H-2 to form [Rh-6(PH3)(6)H-16](2+) because it has a small HOMO-LUMO gap (0.50 eV) and a degenerate pair of LUMO orbitals available for the uptake of four electrons (which are provided by two molecules of H-2). The reverse process, the spontaneous release of a molecule of H-2 from [ Rh-6( PH3)(6)H-16](+) to form [Rh-6(PH3)(6)H-14](+) occurs because the energy gap between the anti-bonding SOMO and the next highest energy occupied orbital in [Rh-6(PH3)(6)H-16](+) is 0. 9 eV, whereas in Rh-6(PH3)(6)H-14](+) the energy gap between the anti-bonding SOMO and the next highest energy occupied orbital is only 0.3 eV. At this stage the factors driving the conversion of [Rh-6(PH3)(6)H-14](+) to [Rh-6(PH3)(6)H-12](2+) are still unclear.
机译：密度泛函理论已用于研究[Rh-6（PH3）（6）H-12]（x）（x = 0，+）类型的一类富含氢化物的后期过渡金属簇的结构，键合和性质1，+ 2，+ 3或+4），[Rh-6（PH3）（6）H-16]（x）（x = + 1或+2）和[Rh-6（PH3）（6）H- 14]（x）（x = 0，+ 1or + 2）。 [Rh-6（PH3）（6）H-12]（x）（x = 0，+ 1，+ 2，+ 3）的优化结构中伪八面体Rh-6核周围的氢原子位置或+4）取决于集群上的总费用。随着团簇上电荷的增加，半桥氢化物的数量增加（半桥氢化物具有两个不同的Rh-H键距），同时完全桥连氢化物的数量（两个Rh中心之间等距）减少。这种变形使氢化物和金属中心之间的键合最大化，并导致与设置在完美八面体簇中的2T（2g）相关的轨道的稳定性。相反，16个氢化物簇[Rh-6（PH3）（6）H-12]（x）（x = + 1或+2）的优化结构相似，并且两个簇都包含间隙氢化物，以及一个末端氢化物，十个桥联氢化物和两个配位的H-2分子，它们结合到eta（2）：eta（1）-时尚中的两个铑中心上。所有氢化物都位于14氢化物簇[Rh-6（PH3）（6）H-14]和[Rh-6（PH3）（6）H]的最低能级结构中Rh-6核的外侧-14]（+），它们都包含11个桥联氢化物，1个末端氢化物和1个配位的H-2分子。不幸的是，[Rh-6（PH3）（6）H-14]（2+）的精确结构无法确定，因为有和没有间隙氢化物的结构都具有相似的能量。通过[Rh-6（PH3）（6）H-12]（2 +），[Rh6（PH3）6H16]（2+）组成的循环吸收和释放两个分子的H-2的反应能，[Rh-6（PH3）（6）H-14]（+），[Rh-6（PH3）（6）H-12]（+）和[Rh-6（PH3）（6）H-14对]（2+）进行了建模，总体而言，实验和理论结果之间观察到了很好的一致性。调查了循环中选定步骤的电子原因。 12个氢化物簇[Rh-6（PH3）（6）H-12]（2+）容易拾取两个H-2分子以形成[Rh-6（PH3）（6）H-16]（2 +），因为它具有较小的HOMO-LUMO间隙（0.50 eV）和一对简并的LUMO轨道，可用于吸收四个电子（由两个H-2分子提供）。相反的过程是，从[Rh-6（PH3）（6）H-16]（+）自发释放H-2分子以形成[Rh-6（PH3）（6）H-14]（+ ）的出现是因为[Rh-6（PH3）（6）H-16]（+）中反键SOMO与次高能量占据轨道之间的能隙为0. 9 eV，而在Rh-6（PH3）中）（6）H-14]（+），反键SOMO与次高的能量占据轨道之间的能隙仅为0.3 eV。在此阶段，驱动[Rh-6（PH3）（6）H-14]（+）转换为[Rh-6（PH3）（6）H-12]（2+）的因素尚不清楚。

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