Formation and Reactivity of a Mn<sup>IV</sup>(O)(μ-O)Ce<sup>IV</sup> Species: A Closest Mimic of Photosystem II
Sikha Gupta, Pragya Arora, Zahra Aghaei, Baghendra Singh, Timothy A. Jackson, Apparao Draksharapu
Abstract
Understanding the basic structure of the oxygen-evolving complex (OEC) in photosystem II (PS-II) and the water oxidation mechanism can aid in the discovery of more efficient and sustainable catalysts for water oxidation. In this context, we present evidence of the formation of a [(TPA)Mn IV (O)(μ-O)Ce IV (NO 3 ) 3 ] + ( 2 ) complex (TPA = tris(pyridyl-2-methyl)amine) by adding aqueous ceric ammonium nitrate to an acetonitrile solution of the [(TPA)Mn II ] 2+ ( 1 ) complex. This unique intermediate ( 2 ) was analyzed by using various spectroscopic techniques and electrospray ionization mass spectrometry. Remarkably, 2 closely mimics the structure of Mn V (O)(μ-O)Ca II (OH 2 ) proposed in the OEC of PS-II. Notably, 2 reacts effectively with ferrocene derivatives, indicating that redox-active Ce IV binding enhances the electron transfer efficiency. Additionally, 2 demonstrated the ability to perform oxygen atom transfer and hydrogen atom abstraction reactions. The discovery of this reactive [(TPA)Mn IV (O)(μ-O)Ce IV (NO 3 ) 3 ] + species provides exciting opportunities for investigating the structure of the Mn V (O)(μ-O)Ca II (OH 2 ) unit in the OEC.