Ba(3)BiPbREO(BO(3))(4) RE = Pr, Nd, Gd, and Dy: two-dimensional rare-earth antiferromagnets with a geometrically-perfect triangular lattice directed by a triangular BO(3) unit.

The synthesis of novel two-dimensional (2D) triangular frustrated compounds is important for providing various platforms to investigate exotic quantum magnetism. Here, we successfully synthesised a series of RE-based magnetic compounds BaBiPbREO(BO) RE = Pr, Nd, Gd, and Dy with a geometrically-perfect 2D triangular lattice directed by the triangular BO unit. These compounds stabilise 2D layered structures in the hexagonal (6/) crystal system, where magnetic ions are linked by BO to form a perfect triangular frustrated lattice. The magnetisation susceptibility results show that all synthesised compounds BaBiPbREO(BO) exhibit dominant antiferromagnetic (AFM) interactions, with no long-range order (LRO) down to 2 K, which is further confirmed by specific heat measurements. Additionally, their thermal stability and attenuated total reflectance Fourier-transform infrared (ATR-FTIR) and ultraviolet-visible-near-infrared (UV-Vis-NIR) diffuse reflectance spectra are also reported. This work provides a series of RE-based magnetic compounds with a two-dimensional triangular frustrated lattice, offering novel model materials for further investigation on rare-earth-based frustrated magnetism.