A novel: O -vanillin Fe(iii) complex catalytically active in C-H oxidation: Exploring the magnetic exchange interactions and spectroscopic properties with different DFT functionals

The novel complex [FeIIICl(L)2(H2O)] (1) was synthesized by interaction of iron(iii) chloride with ethanol solution of o-vanillin (HL) and characterized by IR, UV/Vis spectroscopy, thermogravimetry and single crystal X-ray diffraction analysis. The molecules of 1 in the solid state are joined into supramolecular dimeric units, where a set of strong hydrogen bonds predefines the structure of the dimer according to the "key-lock"principle. From the Hirshfield surface analysis the contribution of π⋯π stacking to the overall stabilization of the dimer was found to be negligible. Broken symmetry DFT calculations suggested the presence of long-range antiferromagnetic interactions (J = -0.12 cm-1 for H = -JS1S2 formalism) occurring through the Fe-O⋯O-Fe pathway, as evidenced by the studies of the model dimers where the water molecules were substituted by acetonitrile and acetone ones. The benchmark studies using a set of literature examples and various DFT functionals revealed the hybrid-GGA B3LYP as the best one for prediction of FeIII⋯FeIII antiferromagnetic exchange couplings of small magnitude. Magnetic susceptibility measurements confirmed antiferromagnetic coupling between the metal atoms in 1 with a coupling constant of -0.35 cm-1. Catalytic studies demonstrated that 1 acts as an efficient catalyst in the oxidation of cyclohexane with hydrogen peroxide in the presence of nitric acid promoter and under mild conditions (yield up to 37% based on the substrate), while tert-butylhydroperoxide (TBHP) and m-chloroperoxybenzoic acid (m-CPBA) as oxidants exhibit less efficiency. Combined UV/TDDFT studies evidence the structural rearrangement of 1 in acetonitrile with the formation of [FeIIICl(L)2(CH3CN)] species. The TDDFT benchmark using nine common DFT functionals and two model compounds (o-vanillin and [FeIII(H2O)6]3+ ion) support the hybrid meta-GGA M06-2X functional as the one most correctly predicting the excited state structure for the Fe(iii) complexes, under the conditions studied. This journal is © The Royal Society of Chemistry.

Nesterova O.V.1 , Vassilyeva O.Y.2 , Skelton B.W.3 , Bieńko A.4 , Pombeiro A.J.L. 1, 5 , Nesterov D.S. 1
Royal Society of Chemistry
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  • 1 Centro de Química Estrutural, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, Lisboa, 1049-001, Portugal
  • 2 Department of Chemistry, Taras Shevchenko National University of Kyiv, 64/13 Volodymyrska str., Kyiv, 01601, Ukraine
  • 3 School of Molecular Sciences, M310, University of Western Australia, Perth, WA 6009, Australia
  • 4 Faculty of Chemistry, University of Wroclaw, F. Joliot-Curie 14, Wroclaw, 50-383, Poland
  • 5 Peoples' Friendship University of Russia (RUDN University), Research Institute of Chemistry, 6 Miklukho-Maklaya st, Moscow, 117198, Russian Federation
Ключевые слова
Acetone; Antiferromagnetism; Catalytic oxidation; Chlorine compounds; Dimers; Excited states; Hydrogen bonds; Infrared spectroscopy; Iron compounds; Magnetic susceptibility; Molecules; Single crystals; Surface analysis; Thermogravimetric analysis; Ultraviolet visible spectroscopy; X ray diffraction analysis; Condition; Ethanol solutions; Functionals; Interaction properties; Iron chlorides; Iron complex; Magnetic exchange interactions; o-Vanillin; Spectroscopic property; Synthesised; Acetonitrile
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