On europium digallides

The europium gallide Eu${}_{1-x}$Ga${}_{2+3x}$ (x is between 0.06 and 0.07) has been synthesized and its crystal structure has been refined from single crystal X-ray diffraction data. Eu${}_{1-x}$Ga${}_{2+3x}$ crystallizes with hexagonal structure related to the AlB${}_2$-type (space group P6/mmm, a=4.354 Å, c=4.485 Å). The structure refinement finished with R(F)=0.015 for 1603 reflections revealing a defect occupation of the Eu position (93 %) and additional Ga position, yielding the non-integer element ratio. From magnetic susceptibility measurements, EuGa${}_2$ and Eu${}_{1-x}$Ga${}_{2+3x}$ phases show the 4f${}^7$ (Eu${}^{+2}$) oxidation state. The analysis of effective atomic charges within the Quantum Theory of Atoms in Molecules reveals the formation of four-bonded Ga species with low electron demand (in comparison to the three-bonded in AlB${}_2$-type and four-bonded in the KHg${}_2$-type structures) and shows, that Eu${}_{1-x}$Ga${}_{2+3x}$ represents a new way of stabilizing intermetallic structures formed at valence electron concentration, which does not allow to apply Zintl-like electron counting. (© 2023 The Authors. Zeitschrift für anorganische und allgemeine Chemie published by Wiley-VCH GmbH)