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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >DFT-UX3LYP Studies on the Coordination Chemistry of Ni2+. Part 1: Six Coordinate [Ni(NH3)(n)(H2O)(6-n)](2+) Complexes
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DFT-UX3LYP Studies on the Coordination Chemistry of Ni2+. Part 1: Six Coordinate [Ni(NH3)(n)(H2O)(6-n)](2+) Complexes

机译：DFT-UX3LYP关于Ni2 +配位化学的研究。第1部分：六坐标[Ni（NH3）（n）（H2O）（6-n）]（2+）配合物

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摘要

DFT calculations with the UX3LYP hybrid functional and a medium-sized 6-311++G(d,p) basis set were performed to examine the gas-phase structure of paramagnetic (S = 1) six-coordinate complexes [Ni(NH3)(n)(H2O)(6-n)](2+) 0 <= 17 <= 6. Significant interligand hydrogen bonding was found in [Ni(H2O)(6)](2+), but this becomes much less significant as NH3 replaces H2O in the coordination sphere of the metal. Bond angles and bond lengths obtained from these calculations compare reasonably well with available crystallographic data. The mean calculated Ni-O bond length in [Ni(H2O)(6)](2+) is 2.093 angstrom, which is 0.038 angstrom longer than the mean of the crystallographically observed values (2.056(22) angstrom, 108 structures) but within 2 sigma of the experimental values. The mean calculated Ni-N bond length in [Ni(NH3)(6)](2+) is 2.205(3) angstrom, also longer (by 0.070 angstrom) than the crystallographically observed mean (2.135(18) angstrom, 7 structures). Valence bond angles are reproduced within 1 degrees. The successive replacement of H2O by NH3 as ligands results in an increase in the stabilization energy by 7 +/- 2 kcal mol(-1) per additional NH3 ligand. The experimentally observed increase in the lability of H2O in Ni(II) as NH3 replaces H2O in the coordination sphere is explained by an increase in the Ni-OH, bond length. It was found from a natural population analysis that complexes with the highest stabilization energies are associated with the greatest extent of ligand-to-metal charge transfer, and the transferred electron density is largely accommodated in the metal 4s and 3d orbitals. An examination of the charge density rho(bcp) and the Laplacian of the charge density del(2)rho(bcp) at the metal-ligand bond critical points (bcp) in the series show a linear correlation with the charge transferred to the metal. Values of del(2)rho(bcp) are positive, indicative of a predominantly closed-shell interaction. The charge transferred to the metal increases as it, the number of NH3 ligands in the complex, increases. This lowers the polarizing ability of the metal on the ligand donors and the average metal-ligand bond length increases, resulting in a direct correlation between the dissociation energy of the complexes and the reciprocal of the average metal-ligand bond length. There is a strong correlation between the charge transferred to the metal and experimental Delta H values for successive replacement of H2O by NH3, but a correlation with stability constants (log beta values) breaks when n = 5 and 6, probably because of entropic effects in solution. Nevertheless, DFT calculations may be a useful way of estimating the stability constants of metal-ligand systems.
机译：使用UX3LYP混合函数和中型6-311 ++ G（d，p）基集进行DFT计算，以检验顺磁性（S = 1）六坐标配合物[Ni（NH3） （n）（H2O）（6-n）]（2+）0 <= 17 <=6。在[Ni（H2O）（6）]（2+）中发现了显着的配位体氢键，但这种结合变少了NH3在金属的配位范围内替代了H2O，因此意义重大。从这些计算中获得的键角和键长与现有的晶体学数据相当合理地比较。 [Ni（H2O）（6）]（2+）中计算得出的Ni-O键平均长度为2.093埃，比晶体学观察值的平均值（2.056（22）埃，108个结构）长0.038埃，但在实验值的2 sigma之内。 [Ni（NH3）（6）]（2+）中计算得出的平均Ni-N键长为2.205（3）埃，也比晶体学上观察到的平均值（2.135（18）埃）长（0.070埃），有7种结构）。价键角在1度内复制。 NH3连续取代H2O作为配体导致每个额外的NH3配体稳定能量增加7 +/- 2 kcal mol（-1）。通过实验观察到的Ni（II）中NH 2取代配位球中H 2 O引起的H 2 O在Ni（II）中的不稳定性的增加可以通过Ni-OH键长的增加来解释。从自然种群分析中发现，具有最高稳定能的络合物与最大程度的配体到金属的电荷转移有关，并且转移的电子密度很大程度上容纳在金属4s和3d轨道中。在系列中的金属-配体键临界点（bcp）处检查电荷密度rho（bcp）和电荷密度del（2）rho（bcp）的拉普拉斯算子，表明与转移到金属上的电荷呈线性关系。 del（2）rho（bcp）的值为正，表示主要为闭壳相互作用。随着金属（配合物中NH3配体的数量）增加，转移到金属上的电荷也会增加。这降低了金属在配体供体上的极化能力，并且平均金属-配体键长增加，导致络合物的解离能与平均金属-配体键长的倒数之间具有直接相关性。连续被NH3取代H2O时，转移到金属上的电荷与实验Delta H值之间有很强的相关性，但是当n = 5和6时，与稳定性常数（对数beta值）的相关性会破坏，可能是由于解。但是，DFT计算可能是估算金属配体系统稳定性常数的有用方法。

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