ИСТИНА

Ternary compound Ce2Ru2Ga3 synthesized in Ce-Ru-Ga system be the reaction of elemental components by arc-melting in argon atmosphere with sunsequent anneling at 600 C. It crystallizes in orthorhombic system, space group P212121, Z=4, unit cell parameters a=4.488(2), b=6.912(4), c=17.092(9) A. The Ce2Ru2Ga3 compound belongs to the structural family, containing Ce2Ru2In3, Ce3Ru2In2, NdRh2Sn4. In the structure of Ce2Ru2Ga3 two alternate networks perpendicular to [100] direction can be distinguished. Every network consists of Ce, Ru and Ga atoms forming five- and eight-member cycles. The adjacent networks are shifted relative to each other. One of two crystallographocally independent Ce atoms (Ce2) is a bulding element of network. The shortest interatomic distances Ce2-Ru1 and Ce2-Ru2 in the networks are equal tp 2.331(4) and 2.434(4) A, respectively. Another Ce atom (Ce1) is sutuated in the center of the eight-member cycle. The Ce1 nearest emvironment consists of 19 atoms with interatomic distances from 2.908(4) to 3.700(4) A. If comparing Ce2Ru2Ga3 and Ce2Ru2In3 strcutures, one can see, that the former contains corrugating networks, and tje latter - flat. In the Ce3Ru2Un2 two of three crystallographically independent cerium atoms together with Ru and I atoms for two-dimensional flat networks. In the structures Ce2Ru2In3 and Ce3Ru2in2, there are extremely short Ce-Ru contacts Ce1-Ru1 - 2.3225(8) A, Ce1-Ru2 - 2.3681(8) A, and Ce1-Ru1 - 2.2345(9) A, Ce3-Ru2 = 2.2811 (9) A, respectively. The presence of very short interatomic distances in the Ce2Ry2Ga3, Ce2Ru2In3, and Ce3Ru2In2 structures is caused by intermediate valence state of some of cerium atoms.