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Bi 65 Cu 13 Ge 41 O 6 Br 122 , a Low‐Valent Compound of High Structural Complexity Featuring the Trigonal Anion [O(Ge II Br 2 ) 3 ] 2– with an sp 2 ‐Hybridized μ 3 ‐Oxide Ion

2013; Wiley; Volume: 639; Issue: 15 Linguagem: Inglês

10.1002/zaac.201300306

1521-3749

Alexander Gerisch, Anna Isaeva, Michael Ruck,

High-pressure geophysics and materials

Abstract Thiny black air‐sensitive crystals of Bi 65 Cu 13 Ge 41 O 6 Br 122 = (Bi 5 ) 2 (Bi 9 ) 6 [O(GeBr 2 ) 3 ] 6 [Cu 6 Ge 5 Br 20 ][BiCu 7 Ge 18 Br 66 ] 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 group P 6 3 (no. 173) with a = 2584.2(4) pm and c = 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, Bi 5 3+ (trigonal bipyramid, D 3 h ) and Bi 9 5+ (tricapped trigonal prism, D 3 h ), occur in one and the same chemical compound. A hitherto unknown group is the C 3 h ‐symmetric μ 3 ‐oxido‐tris[dibromidogermanate(II)] anion [O(GeBr 2 ) 3 ] 2– , in which the germanium atoms of three Ge II Br 2 units bind to a central oxide ion with sp 2 hybridization. Density‐functional‐theory‐based calculations on an isolated [O(GeBr 2 ) 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(GeBr 2 ) 3 ] 2– anion and the bismuth polycations are embedded between two kinds of one‐dimensional networks, which are running parallel to the c axis, a bromido‐cuprate(I)‐germanate(II) network 1 ∞ [Cu 6 Ge 5 Br 20 ] 4– and a bromido‐bismuthate(III)‐cuprate(I)‐germanate(II) network 1 ∞ [BiCu 7 Ge 18 Br 66 ] 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 Bi 5 3+ polycation. Bi 65 Cu 13 Ge 41 O 6 Br 122 may be seen as a link between low‐valent germanium compounds and low‐valent bismuth compounds.