Bi65Cu13Ge41O6Br122, a Low‐Valent Compound of High Structural Complexity Featuring the Trigonal Anion [O(GeIIBr2)3]2–with an sp2‐Hybridized μ3‐Oxide Ion

Abstract

AbstractThiny black air‐sensitive crystals of Bi65Cu13Ge41O6Br122= (Bi5)2(Bi9)6[O(GeBr2)3]6[Cu6Ge5Br20][BiCu7Ge18Br66] were obtained by very slow cooling of a melt of bismuth, bismuth tribromide, copper, and partly oxidized germanium. The crystal structure was described in the hexagonal space groupP63(no. 173) witha= 2584.2(4) pm andc= 1277.4(3) pm at 296(1) K. The polarity of the structure is subtle; large parts of the structure show a pseudo mirror plane. The highly diversified structure comprises five distinct structural fragments. For the first time, two polyhedral bismuth polycations, Bi53+(trigonal bipyramid,D3h) and Bi95+(tricapped trigonal prism,D3h), occur in one and the same chemical compound. A hitherto unknown group is theC3h‐symmetric μ3‐oxido‐tris[dibromidogermanate(II)] anion [O(GeBr2)3]2–, in which the germanium atoms of three GeIIBr2units bind to a central oxide ion with sp2hybridization. Density‐functional‐theory‐based calculations on an isolated [O(GeBr2)3]2–anion confirm the stability of the group and its shape. Real‐space chemical bonding analysis supports the polar nature of the Ge–O and Ge–Br bonds as well as the assigned oxidation states. The [O(GeBr2)3]2–anion and the bismuth polycations are embedded between two kinds of one‐dimensional networks, which are running parallel to thecaxis, a bromido‐cuprate(I)‐germanate(II) network1∞[Cu6Ge5Br20]4–and a bromido‐bismuthate(III)‐cuprate(I)‐germanate(II) network1∞[BiCu7Ge18Br66]20–. The latter features pentacoordinate germanium(II) atoms with bond angles close to 90°. The solution of the crystal structure from X‐ray diffraction data was hampered not only by severe pseudo‐symmetry and the similar scattering power of copper, germanium, and bromine atoms, but also by substantial atomic disorder and orientational disorder of the Bi53+polycation. Bi65Cu13Ge41O6Br122may be seen as a link between low‐valent germanium compounds and low‐valent bismuth compounds.