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Key indicatorsSingle-crystal X-ray study T = 293 K Mean '(Er±Si) = 0.004 A Ê Disorder in main residue R factor = 0.049 wR factor = 0.135 Data-to-parameter ratio = 27.5For details of how these key indicators were automatically derived from the article, see http://journals.iucr.org/e. # 2004 International Union of Crystallography Printed in Great Britain ± all rights reservedThe title erbium platinum silicide compound represents a new structure type of intermetallic silicide with platinum and a heavy rare earth element (Tb±Tm). Four atoms exhibit disorder. Coordination polyhedra of most of the Pt atoms are distorted cuboctahedra; coordination polyhedra of the silicon atoms are distorted trigonal prisms with three additional atoms capping the square faces. CommentWe have shown that intermetallic compounds RPt 3 Si of the light rare earths (R = La, Ce, Nd, Sm) crystallize with the CePt 3 B structure type (Sologub et al., 2002) et al., 2003). The compounds with approximate composition RPt 3 Si, where R is a heavy rare earth element (R = Tb±Tm), are found to belong to a new structure type. The present work reports the results of a crystal structure investigation of the ®rst member of this new structural family of ternary intermetallic silicides. A view of the structure is shown in Fig. 1. In the structure of the title compound, atoms Si1, Pt4 and Pt10 deviate from the ideal positions on the symmetry elements. To account for the

The crystal structure of a new low-temperature modification of CePdAl was determined from single-crystal x-ray data: CePdAl-type; space group Pmmn (No. 59), Z = 14, oP42, a = 0.426 07 nm, b = 2.887 58 nm, c = 0.721 90 nm; R F = 0.048. Physical properties of orthorhombic CePdAl are governed by a mutual balance of the RKKY interaction, the Kondo effect and crystalline electric field splitting, resulting in antiferromagnetic ordering below ≈2.5 K. Electronic transport is reminiscent of a textbook-like Kondo lattice, which comes along with a significant negative magnetoresistance of more than 50% at low temperatures. Although geometrical frustration is absent when compared to the hexagonal modification of CePdAl, the ordering temperature T N is even smaller. A possible cause is enhanced Kondo interactions.

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