Intercalation of ferrocene into vanadyl phosphate by density functional theory

Abstract

Vanadyl phosphate (VOPO₄) is often studied as an intercalation host with both atomic and molecular guests as battery electrodes and for related energy storage applications. Among redox active guests, metallocenes, primarily ferrocene, are frequently employed. Here, a systematic investigation of 17 possible configurations of the intercalation of ferrocene into VOPO₄ revealed the existence of 14 structurally distinct configurations. Among these configurations, the most stable was determined to be that of ferrocene intercalated between a vanadium and oxygen–vanadium site, with the carbon–hydrogen apex from the cyclopentadienyl rings facing the vanadium atom, and the axis of ferrocene rotated by 45° with respect to the [100] direction of the (001) plane of the VOPO₄. Analysis of charge density distributions indicated a charge transfer between iron and vanadium, supporting the preference for ferrocene to intercalate between vanadium and oxygen–vanadium site rather than on a phosphorus site. When intercalated on the vanadium site, the cyclopentadienyl ring adopts an eclipsed arrangement, while it exhibited a gauche arrangement when intercalated on a phosphorus. Additionally, when the apical hydrogen was oriented towards the vanadium atom, there was a noticeable bend in the ferrocene. This bend can be attributed to both van der Waals interactions and the polarizable ion interaction between the ferrocene and the VOPO₄ layer, supported by the electron localized function and the Hirshfeld surface analysis, respectively. Results provide new atomic level insights into how metallocene guest molecules interact with the layered VOPO₄ host.