A comparison of structure and stability between the group 11 halide tetramers M4X4 (M= Cu, Ag, or Au; X = F, Cl, Br, or I) and the group 11 chloride and bromide phosphanes (XMPH3)4

The tetramers of the group 11 (I) halides, M4X4 (M = Cu, Ag, or Au; X = F, Cl, Br, or I), and corresponding group 11 (1) phosphanes, chloride and bromide (XMPH3)(4) (X = Cl or Br), are investigated by the density functional theory. All coinage metal(l) halide tetramers adopt squarelike ring structures with an out-of-plane distorted (butterfly) D-2d symmetry. These structures are much lower in energy than the more compact cubelike T-d arrangements, which maximize dipole-dipole interactions and more closely resemble the solid-state structures of the copper and silver halides. Phosphine coordination completely changes the structures of these M4X4 clusters. The copper(l) and silver(l) phosphane chloride and bromide tetramers adopt a heterocubane structure, slightly preferred over a step (ladder-type)-cluster structure well-known in the coordination chemistry of such compounds. In stark contrast, gold(l) phosphane chloride and bromide tetramers prefer assemblies of linear XAuPH3 units with direct gold-gold contacts, resulting in a square planar, centered trigonal planar, or tetrahedral gold core.