Hybrid organic-inorganic perovskites of the type ABX₃, where A and X are molecular moieties (e.g., A = alkylammonium; X = formate) are of interest as ferroic materials. The functional properties can easily be tuned by mixing different constituents at the A or B sites. Mixing at the X‐site presents the greatest challenge due to the smaller range of available anions than cations, and the larger differences between individual anion sizes. Until now, mixing molecular X‐site ions in hybrid perovskites has not been reported.

Yue Wu, Anthony K. Cheetham, University of Cambridge, UK, and National University of Singapore, and colleagues have prepared hybrid perovskites with mixed molecular X‐site linkers. The team has prepared a series of perovskites with a mixture of formate and hypophosphite at the X sites by doping hypophosphite linkers into the well‐known formate perovskite, [GUA]Mn(HCOO)₃ (GUA = guanidinium, HCOO = formate). Mixed X-site formate perovskites of the composition [GUA]Mn(H
COO)_3–x(H₂POO)_x, with two crystallographically distinct, partially ordered intermediate phases with x = 0.84 and 1.53, corresponding to ca. 30 an d 50 mol% hypophosphite (HP30 and HP50), respectively, formed.

The formate ligand directs the overall structure in both mixed phases. The hypophosphite introduces symmetry lowering through supercell formation, suggesting a possible handle for controlled symmetry lowering. The team alsoobserved antiferromagnetic ordering in both the mixed systems, with Néel temperatures close to those of the end‐members.

Accoring to the researchers, this mixed X‐ligand strategy should be broadly applicable, as it is agnostic to the identity of the A and B‐site ions. It, therefore, has the potential to give rise to a large family of new hybrid perovskites.

• Mixed X-Site Formate-Hypophosphite Hybrid Perovskites,
  Yue Wu, David M. Halat, Fengxia Wei, Trevor Binford, Ieuan D. Seymour, Michael W. Gaultois, Sammy Shaker, John Wang, Clare P. Grey, Anthony K. Cheetham,
  Chem. Eur. J. 2018.
  https://doi.org/10.1002/chem.201803061