**2. Water Oxidizing Catalysts in artificial photosynthesis**

In past few years, there has been a tremendous surge in research on the synthesis of various metal compounds aimed at simulating water oxidizing complex (WOC) of photosystem II (PSII) (Liu et al., 2008; Kanan, M.W. & Nocera, 2008; Cady et al., 2008; Yagi & Kaneko, 2001; Ruttinger & Dismukes, 1997). Of these materials, the Co, Ru and Ir compounds have been shown to be an effective catalyst for water oxidation. However, most of the compounds are expensive and often relate to potentially carcinogenic salts.

Particular attention has been given to the manganese compounds aimed at simulating the WOC of PSII (Umena et al., 2011) not only because it has been used by *Nature* to oxidize water but also because manganese is cheap and environmentally friendly. In this chapter we consider manganese compounds as structural or (and) functional models for the WOC of PSII
