The gallides YbNi3Ga9 and YbCu3Ga8 were obtained from flux growth reactions of Yb, various transition metals M, and Ga, to test a stability diagram that predicts the formation of ternary intermetallic phases. The structure of YbNi3Ga9 was redetermined to resolve discrepancies in the literature. For an untwinned crystal of YbNi3Ga9, the ErNi3Al9-type structure was confirmed (space group R32, a = 7.2294(7) Å, c = 27.513(3) Å, Z = 6), giving rise to an ordered arrangement of Yb2Ga3 nets in the stacking sequence. Crystals of YbCu3Ga8 were among the minority formed in the flux growth reaction. YbCu3Ga8 adopts the rare BaHg11-type structure (space group Pm3¯m, a = 8.2818(13) Å, Z = 3), with Cu and Ga atoms assumed to be disordered. As examples of polar intermetallics, these compounds exhibit electron transfer from Yb to Ga atoms, which then form multicentre covalent bonding networks, as confirmed by electronic structure calculations.
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