The crystal structures of three new intermetallic ternary compounds in the LnNiSb 3 (Ln=Pr, Nd and Sm) family have been characterized by single crystal X-ray diffraction. PrNiSb 3, NdNiSb 3 and SmNiSb 3 all crystallize in an orthorhombic space group, Pbcm (No. 57), Z=12, with a=12.5700(2)Å, b=6.2010(4)Å, c=18.670(6)Å, and V=1431.64(11)Å3; a=12.5090(2)Å, b=6.1940(3)Å, c=18.3350(6)Å, and V=1420.61(9)Å3; and a=12.3900(1)Å, b=6.1760(3)Å, c=18.2650(6)Å, and V=1397.65(8)Å3, for Ln=Pr, Nd and Sm, respectively. These compounds consist of rare-earth atoms located above and below layers of nearly square, buckled Sb nets, along with layers of highly distorted edge- and face-sharing NiSb 6 octahedra. Resistivity data indicate metallic behavior for all three compounds. Magnetization measurements show antiferromagnetic behavior with TN=4.5K (PrNiSb 3), 4.6 K (NdNiSb 3), and 2.9 K (SmNiSb 3). Effective moments of 3.62 μ B, 3.90 μ B and 0.80 μ B are found for PrNiSb 3, NdNiSb 3 and SmNiSb 3, respectively, and are consistent with Pr 3+ (f 2), Nd 3+ (f 3), and Sm 3+ (f 4). Structure of PrNiSb 3 viewed down the b-axis containing Pr atoms (gray circles) located between layers of nearly square Sb nets and highly distorted Ni-centered octahedra. © 2004 Elsevier Inc. All rights reserved.