Chemical bonding topology of ternary transition metal-centered bismuth cluster halides: from molecules to metals.

The bismuth polyhedra in ternary transition metal-centered bismuth cluster halides may form discrete molecules or ions, infinite chains, and/or infinite layers. The chemical bonding in many of these diverse structures is related to that in deltahedral boranes exhibiting three-dimensional aromaticity by replacing the multicenter core bond in the boranes with two-center two-electron (2c-2e) bonds from the central transition metal to the nearest neighbor bismuth vertices. Examples of discrete molecules or ions include octahedral MBi(6)(micro-X)(12)(z)()(-) (X = Br, I; M = Rh, Ir, z = 3; M = Ru, z = 4) with exclusively 2c-2e bonds and pentagonal bipyramidal RhBi(7)Br(8) with a 5c-4e bond in the equatorial pentagonal plane indicative of Möbius aromaticity. The compound Ru(3)Bi(24)Br(20) contains a more complicated discrete bismuth cluster ion Ru(2)Bi(17)(micro-Br)(4)(5+), which can be dissected into a RuBi(5) closo octahedron and a RuBi(8) nido capped square antiprism bridged by a Ru(2)Bi(4)(micro-Br)(4) structural unit. In RuBi(4)X(2) (X = Br, I), the same Ru(2)Bi(4)(micro-Br)(4) structural unit bridges Bi(4) squares similar to those found in the known Zintl ion Bi(4)(2)(-) to give infinite chains of Ru(2)Bi(4) octahedra. The electron counts of the RuBi(5), RuBi(8), and Ru(2)Bi(4) polyhedra in these structures follow the Wade-Mingos rules. A different infinite chain structure is constructed from fused RhBi(7/2)Bi bicapped trigonal prisms in Rh(2)Bi(9)Br(3). This Rh(2)Bi(9)Br(3) structure can alternatively be derived from alternating Rh(2/2)Bi(4) octahedra and Rh(2/)(2)Bi(5) pentagonal bipyramids with electron counts obeying the Wade-Mingos rules. Related chemical bonding principles appear to apply to more complicated layer structures such as Pt(3)Bi(13)I(7) containing Kagomé nets of PtBi(8/2) cubes and Ni(4)Bi(12)X(3) containing linked chains of NiBi(6/3)Bi capped trigonal prisms.