New compounds REBN2 have been synthesized by direct sintering of mixtures of hex-BN and the rare earth metal under nitrogen at 1800°C. The crystal structure of PrBN2 has been determined from single crystal X-ray counter data. PrBN2 crystallizes in a unique structure type with the noncentrosymmetric rhombohedral space group R3c - C63v, No. 161. The hexagonal lattice parameters are a = 1.21144(13) nm and c = 0.70126(15) nm; Z = 18. For 388 reflections (|F0| > 3σ) the residual values are R = Σ|ΔF|Σ|F0‖ = 0.038, Rw = 0.028. The structure type of PrBN2 is a combination of the typical net-type structural units B3N(1)3 of hex-BN and of irregular bipyramidal units ‖Pr5B‖ centered by the N(2) nitrogen atoms. In accordance with the typical arrangement of B and N atoms in hex-BN, there are no direct BB or NN contacts in PrBN2. With respect to the structural chemical building blocks, the crystal structure of PrBN2 is intermediate between the hexagonal BN type and structure types such as Pr3B2N4. Isotypic compounds REBN2 were synthesized with the early rare earth metals Nd, Sm, and Gd. GdBN2 was only observed at temperatures above 1400°C. No REBN2 phase was found with the smaller rare earth members Tb → Lu, Sc, and yttrium.
