Conradie Jeanet, Wondimagegn Tebikie, Ghosh Abhik
Department of Chemistry and Center for Theoretical and Computational Chemistry, University of Tromsø, N-9037 Tromsø, Norway.
J Phys Chem B. 2008 Jan 31;112(4):1053-6. doi: 10.1021/jp709980y. Epub 2008 Jan 5.
Density functional theory (DFT) calculations, regardless of the exchange-correlation functional, have long failed to reproduce the observed dz2(1) ground state of the [NiIII(TtBuP)(CN)2]- anion (where TtBuP is the strongly ruffled tetra(tbutyl)porphyrin ligand), predicting instead a dx2-y2(1) ground state. Normally, such failures are associated with DFT calculations on spin states of different multiplicity, which is not the case here. The calculations reported here strongly suggest that the problem does not lie with DFT. Instead environmental factors need to be taken into account, such as counterions and solvents. Counterions such as K+ placed against the cyanide nitrogens and polar solvents both result in a dz2(1) ground state, thus finally reconciling theory and experiment.
密度泛函理论（DFT）计算，无论采用何种交换关联泛函，长期以来都无法重现观察到的[NiIII(TtBuP)(CN)2]-阴离子的dz2(1)基态（其中TtBuP是高度褶皱的四（叔丁基）卟啉配体），反而预测其基态为dx2-y2(1)。通常，这种失败与对不同多重度自旋态的DFT计算有关，但此处并非如此。本文报道的计算结果有力地表明问题不在于DFT。相反，需要考虑环境因素，如抗衡离子和溶剂。诸如K+等抗衡离子靠近氰基氮原子以及极性溶剂都会导致dz2(1)基态，从而最终使理论与实验结果相符。
