Synthetic control and empirical prediction of redox potentials for Co₄O₄ cubanes over a 1.4 V range: implications for catalyst design and evaluation of high-valent intermediates in water oxidation

Abstract

The oxo-cobalt cubane unit [Co4O4] is of interest as a homogeneous oxygen-evolution reaction (OER) catalyst, and as a functional mimic of heterogeneous cobalt oxide OER catalysts.

Stabilization of reactive Co 4 O 4 cubane oxygen-evolution catalysts within porous frameworks

“…An alternative method found to provide material of similar purity was Soxhlet extraction of the materials with boiling methanol over 16 h. This method is significantly faster than the chelation method and also produces material that is free of Co(II), as evidenced by the absence of any pink color in a chelating membrane when the Soxhlet-treated solids were stirred for 5 d together with the membrane. (17,19,22), which has a characteristic electron paramagnetic resonance (EPR) signal at g = 2.33 (43). After oxidation with aqueous ceric ammonium nitrate for 1 h (SI Appendix, Scheme S1), each of the networks exhibited an EPR spectrum that is consistent with that reported for 1 + (SI Appendix, Fig.…”

“…A notable exception is the cobalt(III)oxo "cubane" cluster Co 4 O 4 (OAc) 4 (py) 4 (1), which emulates the OEC's oxo-bridged arrangement of four metal centers and is unique among tetrametallic clusters in being demonstrated, in thorough mechanistic detail, as a functional OER catalyst (17,18). The Co(III) centers in this cubane impart short-term stability, and the cluster is highly tunable by synthetic manipulation, making it an attractive starting point for mechanistic and structure-function relationship studies (19)(20)(21). Since the carboxylate ligand lability that is required for its water oxidation activity also causes eventual aggregation (and deactivation) of the cluster units (Scheme 1A) (17), a critical goal is the stabilization of the catalytic [Co 4 O 4 ] core to allow for more in-depth studies of its reactivity over a broader range of potentials, pHs, and timescales.…”

Artificial Metalloproteins Containing Co4O4 Cubane Active Sites

“…35 Thus, the selection of Mn ions for biological water oxidation, and the optimum pH for enzymatic activity of 6.5, 36 coincide with Y-driven PCET events. 37 If WOCs are to incorporate PCET relays playing a similar role to that of Y Z , either a stronger oxidant than phenol, or WOCs requiring lower oxidation potentials 13 are needed. Notwithstanding, we have successfully installed a PCET mediator within the secondary coordination sphere of a “substrate”- bound multinuclear metal complex.…”

Structural Diversity of Nickel and Manganese Chloride Complexes with Pyridin-2-One

“…Platinum complexes were widely studied to elucidate interactions of cis-[PtCl 2 (NH 3 ) 2 ] and nucleic acid bases or their analogues [47]. This type of coordination was detected in a complex of the first-row transition-metal-in a tetranuclear cobalt complex-only few years ago [53]. The tetranuclear complex of cobalt has been of interest as a catalyst in an oxygen-evolution reaction [53].…”

“…This type of coordination was detected in a complex of the first-row transition-metal-in a tetranuclear cobalt complex-only few years ago [53]. The tetranuclear complex of cobalt has been of interest as a catalyst in an oxygen-evolution reaction [53].…”