DFT investigation onto axial ligand effects on the TPP ligand and its manganese complexes [Mn(TPP)(O)(X)] (X=F-, Cl-, Br
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ORIGINAL PAPER
DFT investigation onto axial ligand effects on the TPP ligand and its manganese complexes [Mn(TPP)(O)(X)] (X=F‑, Cl‑, Br‑) Somayyeh Babaei1 · Mahmood Niad1 · Zahra Solati1 Received: 13 July 2019 / Accepted: 29 May 2020 © Iranian Chemical Society 2020
Abstract A theoretical study on the structure and nature of the Mn-X bond in tetraphenylporphyrin and its manganoporphyrines containing halogen as an axial ligand [Mn(TPP)X] {X=F, Cl and Br} was carried through density functional B3LYP/6-311G and M06/def2TZVP methods. Comparison of length and angle of bonds in the optimized geometry of [Mn(TPP)Cl] to its X-ray single crystal structure revealed that M06/def2TZVP basis set resulted in more realistic outcomes. Furthermore, the Mn–X bond was analyzed using AIM and NBO to obtain its nature and order in the presence of different halogen axial ligands. The results showed that the Mn-X bond has a σ nature with no π-back donation from Mn to X ligand and the bond order decreased from F to Br. In addition, the effect of axial ligands on the global and local chemical reactivity descriptors of manganoporphyrins has been discussed. Keywords DFT · Metalloporphyrines · Chemical hardness · Electrophilicity · Nucleophilicity
Introduction Porphyrin is a naturally occurring macrocyclic compound, which has attracted considerable attention because of its role in life and natural systems [1]. Porphyrins have prospective application in analytical chemistry and their derivatives have been intensively studied for many years because of their importance in the photochemistry and photobiology processes [2–4]. Under the influence of the large planar-conjugated structure, porphyrin derivatives exhibit good thermal stability, strong two-photon absorption [5], efficient electron transfer [6–8], and interesting photo-electrochemical properties [9]. Therefore, porphyrins have been frequently employed in various fields such as biomimetic natural photosynthesis [10–12] chemical and biological sensors [13] organic light-emitting diodes [14] field effect transistors [15] non- linear optical properties [16] and dye-sensitized solar cells [17, 18]. The chemical activity of porphyrins, like other molecules, could be predicted and described by global and local reactivity descriptors [19]. Chemical potential [20], chemical * Mahmood Niad [email protected] 1
hardness [21], electronegativity [22], global softness [23], electrophilicity [24] and nucleophilicity [25] are among the well-known global indicators. Conversely, local descriptors as the Fukui function are able to distinguish the most reactive region in a molecule [26]. Prediction, analysis and interpretation of the outcome of these descriptors are mainly done using the conceptual Density Functional Theory (DFT) [27]. In the case of metalloporphyrin, it is well established that the nature of the axial ligand plays an important role in modifying the reactivity of them [28]. In transition metal complexes, such as manganese complexes, soft ligands increase acidity and decrease nucleophi
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