SrAu 0.5 Pt 0.5 and CaAu 0.5 Pt 0.5 , analogues to the respective Ba compound, but featuring purely intermetallic behaviour Vyacheslav Saltykov, Jürgen Nuss, Mitsuharu Konuma, Martin Jansen * Max-Plank-Institut für Festkörperforschung, Heisenbergstr. 1, D-70569, Stuttgart, Germany article info Article history: Received 21 April 2010 Received in revised form 7 July 2010 Accepted 8 July 2010 Available online 15 July 2010 Keywords: Alkaline earth elements Crystal structure Intermetallic phases Physical properties abstract Both, SrAu 0.5 Pt 0.5 and CaAu 0.5 Pt 0.5 , have been synthesized by reaction of corresponding mixtures of the pure elements at 1223 K in an argon atmosphere, and characterized by single-crystal X-ray analysis as well as by magnetic susceptibility and electric resistivity measurements. The new compounds crystallize in the CrB type of structure and thus are isostructural to BaAu 0.5 Pt 0.5 (SrAu 0.5 Pt 0.5 : Cmcm; a ¼ 4.262(1)  A; b ¼ 11.435(3)  A; c ¼ 4.632(1)  A; Z ¼ 4; CaAu 0.5 Pt 0.5 : Cmcm; a ¼ 3.9858(4)  A; b ¼ 10.920(1)  A; c ¼ 4.5249 (5)  A; Z ¼ 4). SrAu 0.5 Pt 0.5 as well as CaAu 0.5 Pt 0.5 are poor metallic conductors with r 300K ¼ 0.95 mU.cm and r 300K ¼ 3.93 mU.cm, respectively, and featuring diamagnetic behaviour. According to ESCA measurements SrAu 0.5 Pt 0.5 and CaAu 0.5 Pt 0.5 both can be formulated as having intermetallic character, showing a negligible electron transfer from alkaline earth metals to the noble metals. Ó 2010 Elsevier Masson SAS. All rights reserved. 1. Introduction The term “relativistic effect” addresses the influence of relativ- istic motion of an electron around its nucleus. The most significant impact can be observed for very heavy elements, in particular for platinum, gold and mercury [1e3]. Since these elements are the first ones that experience f- and d-contractions simultaneously, orbital and relativistic effects are superimposed resulting in a substantial stabilization of the electrons in the 6s orbital. p- electrons are similarly affected, but to a smaller extent. The influ- ence of the “relativistic effects” on the electronic structure of the atoms as well as their physical and chemical properties has been fully reviewed several times [2e7]. One of the most conspicuous features of gold, and also of platinum, is its high electron affinity, the highest for Au and second highest for Pt among all metals [8], enabling theses elements to exist as stable anions [3,7e18]. Further experimental evidence confirming an anionic state of gold atoms was provided by interdiffusion in ionic solids demonstrating the mobility of auride ions as integral entities in the solid state [19,20]. The relativistic contraction of the platinum 6s orbital is smaller than that for gold [2]. Platinum 2 species have been shown to be constitutive for Cs 2 Pt [21] and Ba 2 Pt [22]. Partial charge of (1) can be assigned to platinum in BaPt, featuring PtePt bonds [23,24]. Recently we have been able to realize such species as Au  and Pt 2 in one compound, BaAu 0.5 Pt 0.5 [25]. The presence of both anions simultaneously in one compound was confirmed by Electron Spectroscopy for Chemical Analysis (ESCA). In this article, we report on another two new alkaline earth metal auride platinides, CaAu 0.5 Pt 0.5 and SrAu 0.5 Pt 0.5 , which are isostructural to BaAu 0.5 Pt 0.5 but with a different type of chemical bonding. 2. Experimental section 2.1. Synthesis For synthesis of strontium or calcium auride platinides the cor- responding alkaline earth metal was reacted with platinum sponge as well as gold powder. Strontium, or calcium, respectively (99.99% SigmaeAldrich Chemie GmbH, Steinheim, Germany) was distilled twice at 1100 K in a dynamic vacuum of 10 5 mbar, Pt sponge (99.9%, MaTeck GmbH, Jülich, Germany), which was dried and degassed by heating before use at 673 K in a dynamic vacuum of 10 5 mbar, and Au powder, which was prepared by the procedure described in [25]. The elemental strontium or calcium, gold and platinum were weighted out in the required ratios (Sr or Ca):Au:Pt ¼ 2:1:1 in an argon-filled glovebox (H 2 O, O 2 < 0.1 ppm; MB 150BeGeII, M. Braun GmbH, München, Germany), placed into a tantalum tube which was sealed under argon with an arc welder. Tantalum tubes were cleaned with dilute HF (w5%) acid, thoroughly rinsed with water, and heated at 1373 K in high vacuum for 12 h (final vacuum at the maximum temperature of w2  10 5 mbar). In * Corresponding author. Fax: þ49 (0)711 689 1502. E-mail address: M.Jansen@fkf.mpg.de (M. Jansen). Contents lists available at ScienceDirect Solid State Sciences journal homepage: www.elsevier.com/locate/ssscie 1293-2558/$ e see front matter Ó 2010 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.solidstatesciences.2010.07.011 Solid State Sciences 12 (2010) 1615e1619