BiVO3F was prepared, characterized and identified as the unique example of bismuth vanadyl oxyhalide with paramagnetic V 4+ centres. Its crystal structure shows 1D magnetic units with rare alternation of edge sharing O-O and F-F µ2 bridges along the octahedral chains. Structural pairing across the O2 edges induces antiferromagnetic spin dimers(S=0) with J/Kb300K, ⁓15 times greater than the exchange across the F2 bridges, within a non-ordered magnetic ground state. Despite multiple compositional, structural, and electronic analogies with the BiVO4 scheelite compound, one of the most promising photo-anode for solar water splitting, the photo activity of BiVO3F is relatively modest, partially due to this electronic pairing playing for fast electron-hole recombination. Similar to monoclinic-VO2, the V 4+ spin dimerization plays against the singlet → triplet electronic photo-excitation, but brings potential carrier lifetime benefits. The reduction of the bandgap from Eg 2.4 eV to 1.7 eV after incorporation of d 1 cations in BiVO4 makes BiVO3F an inspiring compound for local modifications toward an enhanced photo-active material. The direct d → d transition provides a significant enhancement of the visible light capture section, and opens a prospective route for the chemical design of performant photoanodes with a mixed anionic sublattice.

The Aurivillius-layered compounds with a predominant fraction of paramagnetic transition metals are an emerging playground for the discovery of magnetoelectric or multiferroic compounds. This aim was recently achieved by incorporating F– anions in the perovskite layer of the (Bi2O2)­(CoF4) compound, only described so far in a disordered model (unit cell: a p, a p, c). Here, we report the investigation on the representative compounds (Bi2O2)­(MF4) (M = Fe and Ni) using single crystal, synchrotron, neutron, and electron diffraction. These reveal that the crystallographic average cell (√2 × a p, √2 × a p, c) is orthorhombic, polar, and accompanied by versatile (in)­commensurate modulations. The supercell model was fully refined for (Bi2–x O2)­(FeF4) [q = (0, 1/2, 0)] in the P2111 polar space group with transverse Fe-displacements relative to q. Bi deficiency is compensated by a mixed Fe∼2.5+ valence, but the ideal stoichiometry is preserved for (Bi2O2)­(NiF4). Both compounds are antiferromagnetic below T N = 89 K (Fe) and 45 K (Ni), with moments lying in the (ac) plane and a weak ferromagnetic component along the b-axis. Density functional theory calculations validate a strongly anisotropic distribution of magnetic exchanges (J ab /J c > 10). A broad anomaly on the dielectric constant at T N and a polarization loop at room temperature were obtained on (Bi2–x O2)­(FeF4) single crystals, revealing multiferroism with magnetoelectric couplings.

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