Novel Ternary Intermetallic Compounds R₄Ru₂Ga₃ (R = Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er)

A number of new isostructural ternary intermetallic compounds of the composition R₄Ru₂Ga₃ (R = Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er) were found in ternary R–Ru–Ga systems. The single-crystal X-ray diffraction study of Nd₄Ru₂Ga₃ showed that this compound crystallizes in the monoclinic system and it is a representative of a new structure type (a = 10 Å, b = 4.0533(11) Å, c = 9.720(3) Å, β = 111.080(7)°, space group С2, Z = 2, R1 = 0.043, wR2 = 0.077 for 1518 reflections). The specific structural feature of this compound is the presence of distorted RuNd₆ (AlB₂ type) and GaNd₈ (CsCl type) units. The shortest Nd–Ru distance in the polyhedron is 2.8463(16) Å, which is significantly smaller than the sum of the corresponding atomic radii. The unit cell parameters and volumes in the R₄Ru₂Ga₃ series (R = Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er) decrease in accordance with lanthanide compression, while their melting points increase.