Barium-Triel-Mercuride BaMxHg4-x und Ba3MxHg11-x (M=Ga, In, Cd) / Barium Triel Mercurides BaMxHg4-x and Ba3MxHg11-x (M =Ga, In, Cd)

Abstract

The systematic experimental and bond-theoretical study of the phase width of the BaAl4 structure type in the ternary system BaIn4- BaHg4 shows that this structure type is stable up to BaIn1:7Hg2:3 (tetragonal, tI10, space group I4=mmm, a=474.2(3), c=1228.7(9) pm, R1=0.0529). The planar 44 layers (M(2) site) are preferentially formed by In, whereas Hg occupies the tips (M(1) site) of the [M(1)M(2)4] square pyramids. The layers of the pyramids are connected via short M(1)-M(1) dumbbells (bonds a). The analysis of the calculated band structures of BaIn2Hg2 in comparison to BaIn4 and RbIn4 shows that contributions of Ba-d states (which are missing for RbIn4) and Hg-d states (which are missing in the pure indides) are significant. The respective compound with the smaller triel gallium (Hg-richest phase: BaGa1:9Hg2:1, tetragonal, oI40, space group I41=amd, a=671.3(2), c=2220.4(8) pm, Z =8, R1=0.0641) forms a new superstructure of the BaAl4 structure with a partial ordering of three statistically occupied mixed Ga=Hg positions. The 44 nets are formed by an intermediate proportion of Ga=Hg. The tips of the pyramids are alternately formed by a Ga- and an Hg-rich position leading to smaller and larger bond lengths a’ and a”, respectively, between the tip atoms and, consequentely, a puckering of the 44 net. The two Hg-rich 3 : 11 compounds Ba3InHg10 and Ba3CdHg10 (orthorhombic, oI28, space group Immm, a=513.96(8)=511.50(2), b=993.8(2)=991.54(3), c=1500.7(3)=1499.26(5) pm, Z =2, R1=0.0619=0.0482) crystallize in the La3Al11 structure type, which is also observed for K3Hg11 and is closely related to the BaAl4 type: The square pyramidal nets are corrugated leading to a triplication of the BaAl4 unit cell along one of the tetragonal axes. In each third subcell the tips of adjacent pyramids are directly fused, this position being occupied exclusively by In and Cd. With the smaller triel gallium, the 3 : 11 compound Ba3Ga0:2Hg10:8 crystallizes in the Ba3ZnHg10 structure type (orthorhombic, oP28, space group Pmmn, a=709.36(4), b=1707.96(9), c=630.78(4) pm, Z =2, R1=0.0342). The structure contains folded layers of flat rectangular Ga=Hg pyramids, leaving large channels at the folds, in which Ba(1) and Hg(2) atoms alternate. The formation and stability ranges of 1 : 4, 3 : 11 and related 5 : 19 trieles/mercurides are discussed taking geometric, electronic and M13=Hg ,coloring‘ aspects into account.