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Ligand-to-ligand electron transfer and temperature induced valence tautomerism in o-dioxolene chelated manganese complexes |
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| Authors: | Sanchita Goswami Anangamohan Panja Ray J Butcher Pradyot Banerjee |
| Institution: | a Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700 032, India b Department of Chemistry, University of Calcutta, 92 Acharya Prafulla Chandra Road, Kolkata 700 009, India c Department of Chemistry, Panskura Banamali College, Panskura RS, WB 721 152, India d Department of Chemistry, Howard University, Washington, DC 20059, USA |
| Abstract: | Three polymeric o-dioxolene chelated manganese(III) complexes, {MnIII(H2L1)(Cl4Cat)2]MnIII(Cl4Cat)2(H2O)2]}∞ (1) (L1 = N,N′-bis(2-pyridylmethyl)-1,4-butanediamine, Cl4Cat = tetrachlorocatecholate dianion], {MnIII(H2L1)(Br4Cat)2]MnIII(Br4Cat)2(H2O)2]·4DMF}∞, (2) and {MnIII(H2L2)(Br4Cat)2]MnIII(Br4Cat)2(DMF)2]}∞ (3) (L2 = N,N′-bis(2-pyridylmethyl)-1,6-hexanediamine, Br4Cat = tetrabromocatecholate dianion) have been synthesized and structures were determined by X-ray crystallography. All the complexes were fully characterized by various spectroscopic techniques and their electronic properties are described. It was found that the simple protonation or deprotonation of the bridging ligand (L1 or L2) coordinated to metal-dioxolene chromophore induce a change in the oxidation state of the coordinated dioxolene ligand without affecting the metal oxidation state. As a result, drastic change in the optical absorption properties of the complexes is observed in the visible and near-IR region as the transformation involves semiquinone-catecholate ligands. Moreover, all three complexes undergo thermally induced valence tautomerism in solution. For all the complexes, on increasing the temperature, the intensity of the lower energy Inter Valence Charge Transfer (IVCT) band at about 1930 nm increases with corresponding decrease of 600 nm band with an isosbestic point at 1820 nm due to the formation of mixed valence species MnII(X4SQ)(X4Cat)− from  (X = Cl or Br) by the transfer of one electron from Cat2− to MnIII center. |
| Keywords: | Dioxolene ligands Polymeric manganese(III) complexes Thermally induced valence tautomerism Ligand-to-ligand electron transfer Magnetic properties |
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