The Zintl phase Eu2Si

The Zintl phase Eu2Si was synthesized from elemental europium and silicon in a sealed tantalum tube in a high-frequency furnace at 1270 K and subsequent annealing at 970 K. Investigation of the sample by X-ray powder and single crystal techniques revealed: CO2Si (anti-PbCl2) type, space group Pnma, a = 783.0(1). b = 504.71(9), c = 937.8(1) pm, wR2 = 0.1193, 459 F-2 values and 20 variables. The structure contains two europium and one silicon site. Eu-151 Mossbauer spectroscopic data show a single signal at an isomer shift of -9.63(3) mm/s, compatible with divalent europium. Within the Zintl concept electron counting can be written as (2Eu(2+))Si-4+(4-), in agreement with the absence of Si-Si bonding. Each silicon atom has nine europium neighbors in the form of a tri-capped trigonal prism. The silicon coordinations of the Zintl phases (EuSi)-Si-2, Eu5Si3, EuSi, and EuSi2 are compared.