Water splitting is considered to be one of the most promising sources of sustainable energy, as it can produce hydrogen (H₂) fuel. To have successful water splitting in a sustained manner, it is necessary to develop efficient and robust catalysts that can perform water oxidation, the bottleneck process of water splitting either electrochemically or photochemically. Here, we have presented a brief descriptive analysis of different aspects of designing such catalysts in connection with our recent works on the same field. The focus of the article is to discuss contemporary works in the field of designing cobalt-based heterogeneous water oxidation electrocatalysts. To the best of our knowledge, although cobalt is the most extensively studied 1st row transition metal for water oxidation catalysis reaction, no such report has been found where the simplest cobalt complex, [Co(H₂O₆]²⁺ , has been employed as a water oxidation catalyst. Not only that, reports of cobalt-based simple and small molecular catalysts are also not very frequent. With the help of our recent works, we have tried to detail here a wide aspect of the study on cobalt-based simple and small molecular catalysts, starting from the reasons behind the scarcity of such water oxidation catalysts, to development of new ideas addressing the challenges in utilization of such small cobalt complexes for water oxidation catalyst. Here, we have addressed the scope of encapsulation chemistry in designing robust and efficient heterogeneous water oxidation catalysts using cobalt-based small molecular guest species. With the help of structural insight, gained from the recent results, we published in the field of water oxidation catalysis; here, we try to formulate a general approach that can help to prepare water oxidation catalyst based on host-guest chemistry. The article critically evaluates our recent results in connection with the approach of addressing the problem.

Functional inorganic materials are very important today to meet the needs of our society. The most demanding needs are sustainable and clean energy (it would be nice if that can be achieved from water splitting), smart materials for sensing toxic volatile as well as water-soluble substances (health care) andefficient catalysts that can cycle multiple times without deterioration for useful chemical reactions. Supramolecular chemistry, that plays a vital role to design and synthesize such functional molecules, controls over the intermolecular interactions, thereby the molecular recognition processes leading to molecularfunctions, e.g., sensing, catalysis, etc. This article deals with inorganic supramolecular chemistry of a number of mono-nuclear coordination complexes to selected di-nuclear systems through trinuclear metal basic carboxylates,mostly in their solid-state, leading to the functional inorganic materials. We have demonstrated that some of the very old inorganic systems can be explored in the light of supramolecular chemistry to describe them as functional materials, which have potential in serving our society to some extent