S = 1/2 Chain in BiVO 3 F: Spin Dimers versus Photoanodic Properties

BiVO F was prepared, characterized, and identified as a unique example of bismuth vanadyl oxyhalide with paramagnetic V centers. Its crystal structure shows 1D magnetic units with rare alternation of edge-sharing O-O and F-F μ bridges along the octahedral chains. Structural pairing across the O edges induces antiferromagnetic spin dimers ( = 0) with / ≈ 300 K, ∼15 times greater than the exchange across the F bridges, within a non-ordered magnetic ground state. Despite multiple compositional, structural, and electronic analogies with the BiVO scheelite compound, one of the most promising photoanodes for solar water splitting, the photoactivity of BiVO F is relatively modest, partially due to this electronic pairing benefitting fast electron-hole recombination. Similar to monoclinic VO , the V spin dimerization deters the singlet → triplet electronic photoexcitation, but results in potential carrier lifetime benefits. The reduction of the bandgap from an of ∼2.4 eV to ∼1.7 eV after incorporation of d cations in BiVO makes BiVO F an inspiring compound for local modifications toward an enhanced photoactive material. The direct d → d transition provides a significant enhancement of the visible light capture range and opens a prospective route for the chemical design of performant photoanodes with a mixed anionic sublattice.