Possible Peierls Distortion through Re2 Dimer Formation in the LaNiO2-type Nitrides LnReN2 (Ln = Pr, Nd)

Nitride perovskites are a recently opened class of materials with a limited number of stable compounds. Notably anion-vacancy ordered materials such as LaNiO2-type nitrides are rare despite useful properties such as superconductivity reported for analogous oxides. Here, we report the preparation of two LnReN2 (Ln = Pr, Nd) materials with a distorted LaNiO2-type structure at high-pressure high-temperature conditions of a large volume press. Powder X-ray and neutron diffraction show an orthorhombic distortion (o-LnReN2) of the LaNiO2-aristotype structure is caused by buckling of the ReN4/2 layers through Re dimerization. Electronic structure analysis reveals that the o-LnReN2 materials are composed of classic nitridometallate anions and a cationic intermetallic framework. Moreover, the driving force of the Re dimerization likely stems from an electronic instability re-lated to a Peierls-type distortion. We further characterize the magnetic ground state of both materials with magnetization measurements as well as magnetic neutron scattering uncovering a long-range antiferromagnetic order of Nd3+ moments in NdReN2 at TN = 15.5 K. The stability of the compounds are investigated by temperature-dependent powder X-ray diffraction showing decomposition of NdReN2 at ca. 750 °C. The o-LnReN2 materials represent a curious class of nitrides at the border of classic nitridometallates, intermetallics, and low-dimensional complex chemistry. DOI of Publication: 10.1002/anie.202519710