Na9K16Tl18Cd3: A novel phase containing Tl8Cd310- and Tl57- clusters

Reaction of the elements in tantalum containers at 450 C followed by slow cooling yields the title phase, which crystallizes in the hexagonal space group P63/mmc (Number 194), Z = 2, a = 11.136(6) angstrom, c = 29.352(7) angstrom. The compound contains separate layers of Tl8Cd310- and Tl57- clusters separated by Na+ and K+ cations, viz., (Na+)9(K+)16(Tl57-)2(Tl8Cd310-)e-. The new Tl8Cd310- is a pentacapped trigonal prism (D3h), isosteric and isoelectronic with Tl117-, with Cd substituted in the waist-capping positions, the vertexes with the least negative Mulliken charge in the parent cluster. The compound is semiconducting and Curie-Weiss paramagnetic (-1.50 μB), these evidently reflecting the extra electron trapped in some alkali-metal-bordered cavity. Some energetics of the atom substitution reaction are considered