Conradie Jeanet, Ghosh Abhik
Department of Chemistry and Center for Theoretical and Computational Chemistry, UiT - The Arctic University of Norway , 9037 Tromsø, Norway.
Department of Chemistry, University of the Free State , 9300 Bloemfontein, Republic of South Africa.
J Phys Chem B. 2016 Jun 9;120(22):4972-9. doi: 10.1021/acs.jpcb.6b04983. Epub 2016 Jun 1.
DFT calculations employing the OLYP and B3LYP functionals have been used to map out the low energy states of the metalloporphyrin-nitroxyl adducts "M(Por) + NO(-)" and "M(Por) + HNO", where M = Fe, Co, and Mn and Por(2-) is the dianion of unsubstituted porphyrin. For Fe(Por)(NO), the calculations yield two low-energy solutions, with MS = 0 and 1. The MS = 0 solution is thought to represent the experimentally observed diamagnetic ground states of {FeNO}(8) porphyrins, and both functionals yield FeNO geometrical parameters in excellent agreement with a recent crystal structure. For Co(Por)(NO), the lowest-energy solution for both OLYP and B3LYP is a true {CoNO}(9) state that appears to be best described as a high-spin Co(II) center with a dxy(2)dxz(1)dyz(1)dz2(2)dx2-y2(1) configuration antiferromagnetically coupled to a NO(-) diradical. Such an electronic configuration is expected to lead to diagnostic structural features, including long equatorial Co-N distances (∼2.1 Å), a strong displacement (∼0.4 Å) of the metal from the mean plane of the equatorial nitrogens, and a relatively short Co-N(O) distance (1.8 Å), which should all be experimentally observable. The dx2-y2(1) electronic configuration should also lead to characteristic EPR hyperfine parameters. The calculations also indicate a number of other low-energy states for Co(Por)(NO), including multiple {CoNO}(8) porphyrin anion radical states. For Mn(Por)(NO), both functionals indicate a rather complex electronic state landscape, including multiple {MnNO}(6) porphyrin anion radical states as well as a high-spin S = 3/2 {MnNO}(7) state. Both functionals clearly indicate a low-spin Fe(II) state for [Fe(Por)(HNO)]. On the other hand, two comparably low-energy states are predicted for both [Co(Por)(HNO)] and [Mn(Por)(HNO)]. For [Co(Por)(HNO)], the two states are a low-spin Co(II) state with a dxy(2)dxz(2)dyz(2)dz2(1) configuration and a low-spin Co(III)(HNO)(•-) state. For [Mn(Por)(HNO)], the two states may be described as low- (S = 1/2) and intermediate-spin (S = 3/2) Mn(II). The latter state has a relatively long Mn-N(O) distance of about 2.07 Å, which may be indicative of facile HNO dissociation.
采用OLYP和B3LYP泛函的密度泛函理论（DFT）计算已用于描绘金属卟啉 - 硝酰基加合物“M(Por) + NO⁻”和“M(Por) + HNO”的低能态，其中M = Fe、Co和Mn，Por²⁻是未取代卟啉的二价阴离子。对于[Fe(Por)(NO)]⁻，计算得出两个低能解，MS = 0和1。MS = 0的解被认为代表了实验观察到的{FeNO}₈卟啉的抗磁性基态，并且两种泛函得出的FeNO几何参数与最近的晶体结构非常吻合。对于[Co(Por)(NO)]⁻，OLYP和B3LYP的最低能量解都是真正的{CoNO}₉态，似乎最好描述为具有dxy²dxz¹dyz¹dz²²dx²⁻y²¹构型的高自旋Co(II)中心，与NO⁻双自由基反铁磁耦合。这样的电子构型预计会导致诊断性的结构特征，包括赤道面Co - N距离长（约2.1 Å）、金属相对于赤道面氮原子平均平面的强烈位移（约0.4 Å）以及相对较短的Co - N(O)距离（1.8 Å），这些都应该可以通过实验观察到。dx²⁻y²¹电子构型也应该导致特征性的电子顺磁共振（EPR）超精细参数。计算还表明[Co(Por)(NO)]⁻存在许多其他低能态，包括多个{CoNO}₈卟啉阴离子自由基态。对于[Mn(Por)(NO)]⁻，两种泛函都表明电子态图景相当复杂，包括多个{MnNO}₆卟啉阴离子自由基态以及高自旋S = 3/2的{MnNO}₇态。两种泛函都清楚地表明[Fe(Por)(HNO)]为低自旋Fe(II)态。另一方面，预测[Co(Por)(HNO)]和[Mn(Por)(HNO)]都有两个能量相当低的态。对于[Co(Por)(HNO)]，这两个态是具有dxy²dxz²dyz²dz²¹构型的低自旋Co(II)态和低自旋Co(III)(HNO)⁻态。对于[Mn(Por)(HNO)]，这两个态可以描述为低自旋（S = 1/2）和中间自旋（S = 3/2）的Mn(II)态。后一种态具有约2.07 Å的相对较长的Mn - N(O)距离，这可能表明HNO易于解离。
