The ternary stannides PrZnSn and NdZnSn were synthesized by induction-melting of the elements in sealed tantalum tubes. They were characterized by powder and single-crystal X-ray diffraction: YPtAs-type structure, P63=mmc, a = 455:4(1) and c = 1650:3(2) pm, wR2=0.0266, 297 F2 for PrZnSn and a = 453:7(1) and c = 1637:0(4) pm, wR2=0.1558, 234 F2 for NdZnSn with 12 variables per refinement. PrZnSn and NdZnSn are AlB2 superstructures with slightly puckered and ordered [Zn3Sn3] hexagons in AA0BB0 stacking sequence along the crystallographic c axis. Hydrogenation results in the new hexagonal hydrides PrZnSnH1:5 (a = 447:98(8) and c = 1707:5(5) pm) and NdZnSnH1:5 (a = 448:28(8) and c = 1689:8(2) pm). Filling of RE3Zn tetrahedra by hydrogen leads to anisotropic changes of the lattice parameters and a drastic flattening of the [Zn3Sn3] layers. Temperature-dependent magnetic susceptibility measurements show Curie-Weiss behavior for PrZnSn and NdZnSn with experimental magnetic moments close to the free-ion values of RE3+. Magnetic ordering is detected at 4.7 (PrZnSn) and 6:5 K (NdZnSn). Hydrogenation induces ferromagnetism with increased ordering temperatures of 12.0 (PrZnSnH1:5) and 14:5 K (NdZnSnH1:5).Read less <