Chłopek Krzysztof, Muresan Nicoleta, Neese Frank, Wieghardt Karl
Max-Planck-Institut für Bioanorganische Chemie, Stiftstrasse 34-36, 45470 Mülheim an der Ruhr, Germany.
Chemistry. 2007;13(30):8390-403. doi: 10.1002/chem.200700897.
The electronic structures of a series of five-coordinate complexes of iron containing zero, one, or two bidentate, organic pi-radical ligands and a monodentate ligand (pyridine, iodide) have been studied by broken-symmetry (BS) density functional theoretical (DFT) methods. By analyzing the set of corresponding orbitals[5] (CO) a convenient division of the spin-up and spin-down orbitals into 1) essentially doubly-occupied molecular orbitals (MO), 2) exactly singly-occupied MOs, 3) spin-coupled pairs, and 4) virtual orbitals can be achieved and a clear picture of the spin coupling between the ligands (non-innocence vs. innocence) and the central metal ion (dN configuration) can be generated. We have identified three classes of complexes which all contain a ferric ion (d5) with an intrinsic intermediate spin (SFe= 3/2) that yield 1) an St=3/2 ground spin state if the two bidentate ligands are closed-shell species (innocent ligands); 2) if one pi-radical ligand is present, an St=1 ground state is obtained through intramolecular antiferromagnetic coupling; 3) if two such radicals are present, an St=1/2 ground state is obtained. We show unambiguously for the first time that the pentane-2,4-dione-bis(S-alkylisothiosemicarbazonato) ligand can bind as pi-radical dianion (L.TSC)2- in [FeIII(L.TSC)I] (St=1) (6); the description as [Fe IV(L TSC(3-))I] is incorrect. Similarly, the diamagnetic monoanion in 14 must be described as FeIII(CN)2(L.TSC) (St=0) with a low-spin ferric ion (d5, SFe=1/2) coupled antiferromagnetically to a pi-radical ligand; [FeII(CN)2(L TSC-]- is an incorrect description.
采用破缺对称性（BS）密度泛函理论（DFT）方法研究了一系列含零个、一个或两个双齿有机π-自由基配体以及一个单齿配体（吡啶、碘离子）的五配位铁配合物的电子结构。通过分析相应的轨道集[5]（CO），可以方便地将自旋向上和自旋向下的轨道划分为：1）基本双重占据的分子轨道（MO），2）恰好单占据的MO，3）自旋耦合对，4）虚轨道，并且可以清晰地描绘配体（非无辜与无辜）与中心金属离子（dN构型）之间的自旋耦合情况。我们确定了三类配合物，它们都含有具有固有中间自旋（SFe = 3/2）的铁离子（d5），如果两个双齿配体是闭壳层物种（无辜配体），则产生1）St = 3/2的基态自旋态；2）如果存在一个π-自由基配体，则通过分子内反铁磁耦合获得St = 1的基态；3）如果存在两个这样的自由基，则获得St = 1/2的基态。我们首次明确表明，戊烷-2,4-二酮-双（S-烷基异硫代半卡巴腙基）配体在[FeIII（L.TSC）I]（St = 1）（6）中可以作为π-自由基二价阴离子（L.TSC）2-结合；将其描述为[FeIV（L TSC（3-））I]是不正确的。同样，14中的抗磁性单阴离子必须描述为FeIII（CN）2（L.TSC）（St = 0），其中低自旋铁离子（d5，SFe = 1/2）与π-自由基配体反铁磁耦合；[FeII（CN）2（L TSC-]是不正确的描述。
