화학공학소재연구정보센터
Inorganic Chemistry, Vol.37, No.22, 5881-5886, 1998
Na12K38Tl48Au2 : A metallic zintl phase with naked icosahedral fragments Tl-7(7-) and Tl-9(9-) plus Au-
The title compound is synthesized by direct reaction of the elements at 500 degrees C followed by slow cooling. Na12K38Tl48Au2 crystallizes hexagonal [space group (No. 189), Z = 1, a = 19.343(2) Angstrom, c = 11.498(5) Angstrom] and is constituted tin terms of oxidation states) as (Na+)(12)(K+)(38)(Tl-7(7-))(3)(Tl-9(9-))(3)(AU(-))(2) Both clusters have C-2 upsilon symmetry and can be viewed as fragments of a centered icosahedral Tl-13. The Tl-7(7-) cluster is an oblate pentagonal bipyramid with an apex-apex bond distance of 3.39 Angstrom, and Tl-9(9-) can be best derived from the centered icosahedron by removal of four adjoining vertexes (or as two fused pentagonal bipyramids). The isolated Au- is bound in a trigonal antiprism of potassium. The compound is structurally electron-precise (Zintl phase), but it shows characteristics of a very poor metal (rho(298) similar to 760 mu Omega(cm) with a Pauli-like susceptibility of similar to 1.4 x 10(-3) emu.mol(-1) over 50-300 K after correction for Larmor precession of cluster orbitals. EHMO results for the bonding in Tl-7(7-) and factors that stabilize this compound are presented and discussed.