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Structural distortion of the secondary coordination sphere driven by the incorporation of an alkali metal in Ce³⁺imidophosphorane complexes tunes the Ce^3+/4+oxidation potential. 

The molecular tetravalent oxidation state for praseodymium is observed in solution via oxidation of the anionic trivalent precursor [K][Pr 3+ (NP(1,2-bis- t Bu-diamidoethane)(NEt 2 )) 4 ] (1-Pr(NP*)) with AgI at −35 °C. The Pr 4+ complex is characterized in solution via cyclic voltammetry, UV-vis-NIR electronic absorption spectroscopy, and EPR spectroscopy. Electrochemical analyses of [K][Ln 3+ (NP(1,2-bis- t Bu-diamidoethane)(NEt 2 )) 4 ] (Ln = Nd and Dy) by cyclic voltammetry are reported and, in conjunction with theoretical modeling of electronic structure and oxidation potential, are indicative of principal ligand oxidations in contrast to the metal-centered oxidation observed for 1-Pr(NP*). The identification of a tetravalent praseodymium complex in in situ UV-vis and EPR experiments is further validated by theoretical modeling of the redox chemistry and the UV-vis spectrum. The latter study was performed by extended multistate pair-density functional theory (XMS-PDFT) and implicates a multiconfigurational ground state for the tetravalent praseodymium complex. 

Redox-active multimetallic platforms with synthetically addressable and hemilabile active sites are attractive synthetic targets for mimicking the reactivity of enzymatic co-factors toward multielectron transformations. To this end, a family of ternary clusters featuring three edge metal sites anchored on a [Co 6 Se 8 ] multimetallic support via amidophosphine ligands are a promising platform. In this report, we explore how small changes in the stereoelectronic properties of these ligands alter [Co 6 Se 8 ] metalloligand formation, but also substrate binding affinity and strength of the edge/support interaction in two new ternary clusters, M 3 Co 6 Se 8 L 6 (M = Zn, Fe; L (−) = Ph 2 PN (−)i Pr). These clusters are characterized extensively using a range of methods, including single crystal X-ray diffraction, electronic absorption spectroscopy and cyclic voltammetry. Substrate binding studies reveal that Fe 3 Co 6 Se 8 L 6 resists coordination of larger ligands like pyridine or tetrahydrofuran, but binds the smaller ligand CN t Bu. Additionally, investigations into the synthesis of new [Co 6 Se 8 ] metalloligands using two aminophosphines, Ph 2 PN(H) i Pr (L H ) and i Pr 2 PN(H) i Pr, led to the synthesis and characterization of Co 6 Se 8 L H 6 , as well as the smaller clusters Co 4 Se 2 (CO) 6 L H 4 , Co 3 Se(μ 2 -PPh 2 )(CO) 4 L H 3 , and [Co(CO) 3 ( i Pr 2 PN(H) i Pr)] 2 . Cumulatively, this study expands our understanding on the effect of the stereoelectronic properties of aminophosphine ligands in the synthesis of cobalt chalcogenide clusters, and, importantly on modulating the push–pull dynamic between the [Co 6 Se 8 ] support, the edge metals and incoming coordinating ligands in ternary M 3 Co 6 Se 8 L 6 clusters.