Keggin-type polyoxometalate anions [XM O ] are versatile, as their applications in interdisciplinary areas show. The Keggin anion [CoW O ] turns into an efficient and robust electrocatalyst upon its confinement in the well-defined void space of ZIF-8, a metal-organic framework (MOF). [H CoW O ]@ZIF-8 is so stable to water oxidation that it retains its initial activity even after 1000 catalytic cycles. The catalyst has a turnover frequency (TOF) of 10.8 mol O (mol Co) s , one of the highest TOFs for electrocatalytic oxygen evolution at neutral pH. Controlled experiments rule out the chances of formation and participation of CoO in this electrocatalyic water oxidation.

MOF based proton conductors have received immense importance recently. The present study endeavors to design two post-synthetically modified UiO-66 based MOFs and study the effects of their structural differences on their proton conductivity. UiO-66-NH 2 is modified by reaction with sultones to prepare two homologous compounds i.e., PSM 1 and PSM 2, which have SO 3 H groups in comparable extent (Zr:S ≈ 2: 1) in both. But the pendant alkyl chain holding the -SO3H group is of different length. PSM 2 has longer alkyl chain attachment than that of PSM 1. This difference in length of side arm results in huge difference in proton conducting behavior of the two compounds. PSM 1 is observed to have highest MOF based proton conductivity (1.64 × 10 -1 Scm -1 ) at 80 °C, which is comparable to commercially available Nafion while PSM 2 shows significantly lower conductivity. Again, the activation energy for proton conductivity is one of the lowest among all MOF based proton conductors in case of PSM 1 while, PSM 2 requires larger activation energy (almost three times).This profound effect of variation of chain length of side arm by 1 carbon atom in case of PSM 1 and PSM 2 was rather surprising and never documented before. This effect of length of side arm can be very useful to understand proton conduction mechanism of MOF based compounds and also to design better proton conductors. Besides, PSM 1 showed proton conductivity as high as 1.64 × 10 -1 Scm -1 at 80 °C temperature, which is the highest reported value till date among all MOF based systems. The lability of the -SO3H proton of the post synthetically modified UiO-66 MOFs has theoretically been determined by molecular electrostatic potential (MEP) analysis and theoretical pK a calculation of models of functional sites along with relevant NBO analyses.

A polyoxometalate (POM)-supported nickel(II) coordination complex, [Ni(2,2'-bpy)][{Ni(2,2'-bpy)(HO)}{HCoWO}]·3HO (1; 2,2'-bpy = 2,2'-bipyridine), has been synthesized and structurally characterized. We could obtain a relatively better resolved structure from dried crystals of 1, Ni(2,2'-bpy)][{Ni(2,2'-bpy)(HO)}{HCoWO}]·HO (D1). Because the title compound has been characterized with a {Ni(2,2'-bpy)(HO)} fragment coordinated to the surface of the Keggin anion ([H(CoWO]) via a terminal oxo group of tungsten and the [Ni(2,2'-bpy)] coordination complex cation sitting as the lattice component in the concerned crystals, the electronic spectroscopy of compound 1 has been described by comparing its electronic spectral features with those of [Ni(2,2'-bpy)(HO)Cl]Cl, [Ni(2,2'-bpy)]Cl, and K[CoWO]·6HO. Most importantly, compound 1 can function as a heterogeneous and robust electrochemical water oxidation catalyst (WOC). To gain insights into the water oxidation (WO) protocol and to interpret the nature of the active catalyst, diverse electrochemical experiments have been conducted. The mode of action of the WOC during the electrochemical process is accounted for by confirmation that there was no formation/participation of metal oxide during various controlled experiments. It is found that the title compound acts as a true catalyst that has Ni (coordinated to POM surface) acting as the active catalytic center. It is also found to follow a proton-coupled electron-transfer pathway (two electrons and one proton) for WO catalysis with a high turnover frequency of 18.49 (mol of O)(mol of Ni) s.

Keggin-type polyoxometalate anions [XM 12 O 40 ] nÀ are versatile,a st heir applications in interdisciplinary areas show.T he Keggin anion [CoW 12 O 40 ] 6À turns into an efficient and robust electrocatalyst upon its confinement in the welldefined void space of ZIF-8, am etal-organic framework (MOF). [H 6 CoW 12 O 40 ]@ZIF-8 is so stable to water oxidation that it retains its initial activity even after 1000 catalytic cycles. The catalyst has at urnover frequency (TOF) of 10.8 mol O 2 (mol Co) À1 s À1 ,o ne of the highest TOFs for electrocatalytic oxygen evolution at neutral pH. Controlled experiments rule out the chances of formation and participation of CoO x in this electrocatalyic water oxidation.Photosynthesis,one of the most fundamental and essential processes to sustain life on earth, works on the principle of trapping solar energy via electron-hole pair formation. [1,2] This energy is ultimately utilized in splitting of water molecules into H 2 and O 2 .W ater splitting (WS) has emerged as apromising source of clean and sustainable energy. [3] Water oxidation (WO; 2H 2 O!4H + + O 2 + 4e À ; E 0 = 1.23 V), being the bottleneck process of WS owing to its high thermodynamic potential and high overpotential h,requires an efficient and stable WO catalyst (WOC). [4,5] In last few decades, various research groups have contributed towards understanding of the process of WO and designing of robust and efficient WOCs. [1][2][3][4][5][6][7] Recently enormous efforts have been devoted to prepare first-row transition-metal-ion (particularly,c obalt)-based inexpensive WOCs. [8][9][10][11][12][13][14][15][16][17][18] Development of polyoxometalates (POMs) as WOCs came as am ajor breakthrough in this regard. [19][20][21][22][23][24][25][26][27] Thek ey structural features of POMs for POM-WOCs are their complete inorganic skeleton and the scope of fast, reversible electron transfer (resulting into fast WO kinetics). [14,28] In last few years,a long with remarkable progress in this field, questions also arose about the true catalyst species (formation and participation of CoO x as true catalyst). [28][29][30][31][32] Meanwhile,H ill, Geletii, and their coworkers [23] confirmed that their starting Co-POM compound [Co 4 (H 2 O) 2 (a-PW 9 O 34 ) 2 ] 10À was atrue molecular WO catalyst (not CoO x ). Keggin-type POMs have the general formula of [XM 12 O 40 ] nÀ (X = Co 2+ ,P 5+ ,S i 4+ ,e tc.;M= W 6+ ,M o 6+ ,e tc.) and are the most stable structural variant among all POMs. [33][34][35][36] Despite ac onsiderable development in the field of POM-WOC,n ot much attention has been paid to Keggin (as such)-WOC systems as most of them do not possess suitable WOC-active site (unless it has one or more substitution of Mb yaWO-active transition-metal ion). [28,[37][38][39] Recently,S ong et al. [37] showed K 6 [CoW 12 O 40 ]t ob ei nactive to photocatalytic WO,w hile K 7 [Co III Co II (H 2 O)W 11 O 39 ], was found to be active owing to ap eripheral Co III -aqua coordination complex. We thus made an attempt to prepare WOC from [CoW 12 ...

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