New Ternary Silicide LiRh2Si2 - Structure and Bonding Peculiarities

The silicide LiRh2Si2 was synthesized from the elements in a sealed niobium ampoule and was characterized by X-ray powder and single-crystal diffraction: FeMo2B2 type (ordered version of U3Si2), P4/mbm, a = 698.1(5), c = 274.6(4) pm, wR2 = 0.0842, 186 F-2 values and I I variables. The rhodium and silicon atoms build up a covalently bonded three-dimensional [Rh2Si2] network (244-248 pin Rh-Si), in which the lithium atoms fill larger channels which extend along the c axis. A similar structural arrangement occurs in LiY2Si2, however, the strong difference in size between rhodium and yttrium leads to different distortions. LiRh2Si2 and LiY2Si2 are isopointal rather than isotypic. The crystal chemistry and bonding peculiarities of both silicides are discussed on the basis of ab initio electronic structure calculations. Li-7 solid-state NMR studies on LiRh2Si2 revealed restricted motional narrowing due to lithium atomic diffusion in the temperature range 170-450 K.