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Abstract:
The Zintl phases K4-xNaxSi4 (1 <= x <= 2.2) and K7NaSi8 are the first representatives of the K-Na-Si system, and both contain tetrahedral [Si-4](4-) clusters and a charge-balancing number of K+ and Na+ cations. All phases of K4-xNaxSi, (1 <= x <= 2.2) crystallize in a new structure type with space group P2(1)/n, as determined by single-crystal X-ray diffraction analysis of the parent phase K3NaSi4. Rietveld refinement of the X-ray diffraction data showed that the solid solutions follow Vegard's rule. K7NaSi8 can only be synthesized by diffusion-controlled reaction of binary precursors and is isostructural with known A(7)A' T-8 (A = Na-Cs; A' = Li, Na; T = Si, Ge) phases. A combination of solid-state NMR investigations and quantum mechanical calculations served to show the anisotropic chemical bonding behavior of all the atoms in K7NaSi8, which is additionally compared with the related phases A(7)NaSi(8) (A = Rb, Cs).
