New phases RCu5Sn (R = La, Ce, Pr, Nd, Sm, Gd) and Ce2Cu9Sn2.65

Two new phases were identified in the copper-rich region of the Ce-Cu-Sn system with composition CeCu5Sn and Ce2Cu9Sn2.65 and their crystal structures were determined by single crystal diffractometric data. CeCu5Sn, orthorhombic, space group Pnma, Pearson symbol oP28, a = 8.323(1) Angstrom, b = 5.064(1) Angstrom, c = 10.597(1) Angstrom, Z = 4, R = 0.042 for 352 reflections with F-o > 4 sigma(F-o), is isotypic with CeCu5Au, a ternary derivative of the CeCu6 structure. Ce2Cu9Sn2.65, orthorhombic, space group Pnnm, Pearson symbol oP56-1.4, a = 10.669(1) Angstrom, b = 16.734(2) Angstrom, c = 5.066(1) Angstrom, Z = 4, R = 0.040 for 906 reflections with F-o > 4 sigma(F-o), can be derived from the Ce2Cu9In3 type. Different from the parent structure, the copper and tin atoms occupy all the atomic sites in an ordered way, but a Sn position is only partially filled. The crystal structures of CeCu5Sn and Ce2Cu9Sn2.65 are closely related and show very similar coordination polyhedra. Isotypic phases were found in the series RCu5Sn with R = La, Pr, Nd, Sm, Gd. The crystal structure of the already known Ce3Cu4Sn4 (Gd3Cu4Ge4-type) was also refined from single crystal data.