Thinking about metal-metal quadruple bonding in extended structures: a hypothetical A2M6E8 network

Abstract

The electronic and structural possibilities of a recently conceived, as-yet unsynthesized, AM₆E₈ (or A₂M₆E₈) structural type are explored. With A an alkaline earth metal, M a transition metal, and E a main group element, a range of geometries containing M–M pairs with very short separations is feasible. Density functional theory geometry optimizations and an extended Hückel analysis of the bonding in a representative Ca₂W₆O₈ realization support the qualitative picture of quadruple metal-metal bonding in these hypothetical phases. The MM pairs interact moderately (metallic behavior is anticipated) through linking atoms. Geometry optimizations of a wide range of hypothetical compounds show that the M–M separation in these will be in the range of realistic quadruple metal-metal bonding, 2.20–2.30 Å.