The 1,3-phosphaazaallene DippTerP = C=NtBu (DippTer = 2,6-(2,6-iPr2C6H3)2-C6H3) is thermally labile towards iso-butene elimination and formation of the corresponding cyanophosphine DippTerP(H)CN (1). In previous work we have shown facile deprotonation of 1 with K[N(SiMe3)2 and formation of cyanophosphide [(DippTerPCN)K]. We now present the alkali metal tethered cyanophosphides [(DippTerPCN)M(crown)] (M = Na, K; crown = 15-c-5, 18-c-6) and their structural diversity in the solid state depending on the metal (M) and the crown ether. Facile oxidation of [DippTerPCN][M(crown)] with O2 yields the formal cyanide adducts of dioxophosphoranes [DippTerPO2(CN)]-. Surprisingly, [DippTerPO2(CN)]- is obtained as a mixture of the cyanide and isocyanide isomers, indicating a coordination isomerism. This phenomenon is corroborated by experimental and theoretical studies revealing the cyanide isomer to be thermodynamically more stable. The oxidation with elemental sulphur gave the corresponding dithiophosphorane cyanide adduct [DippTerPS2(CN)]-, in which no isomerism was observed. This points to a crucial role of triplet oxygen in the isomerisation process. Monooxidation occurs when [DippTerPO2(CN)]- salts were treated with N2O, giving formal anionic phoshinidene monoxide adducts.
Photoelectrochemical (PEC) water splitting offers a promising route to sustainable green hydrogen production by directly converting solar energy into hydrogen without consuming fossil fuels. However, inefficient charge separation and sluggish interfacial charge transfer remain major limitations in photoanode development. Herein, fibrous silica iron oxide (FSFe) was synthesized as a photoanode and modified with CuO, ZnO, and NiO to regulate heterojunction pathways for enhanced PEC water splitting. Characterization results confirmed the formation of high-surface-area spherical fibrous structures with well-dispersed metal oxide species, while the primary FSFe framework was preserved after metal loading. The electrochemical characterization revealed that transition-metal oxide modification increased the charge carrier density and reduced charge transfer resistance, indicating efficient charge separation and interfacial charge transport. Among the prepared photoanodes, Cu/FSFe exhibited the highest photocurrent density of 4.14 mA cm-2 at 1.23 VRHE and an applied bias photon-to-current efficiency of 0.78%, compared with 2.70 mA cm-2 and 0.54% for pristine FSFe. The superior performance of Cu/FSFe was attributed to the combined effects of Z-scheme heterojunction formation and the strong visible-light response of CuO. Compared with the Type-II pathways proposed for Ni/FSFe and Zn/FSFe, the Z-scheme pathway in Cu/FSFe promoted efficient charge separation while preserving strong redox potentials, leading to a higher charge carrier density of 1.92 × 1021 cm-3, improved interfacial charge transfer, and enhanced PEC water splitting performance. This work provides insight into how the selection of transition-metal oxide modifiers governs heterojunction formation and charge transfer pathways in FSFe-based photoanodes for PEC water splitting.