Periodic trends in metal–metal bonding in cubane clusters, (C5H5)4M4E4 [M = Cr, Mo, E = O, S]

摘要: Trends in structure and bonding a series of metal cubane clusters are examined using broken-symmetry density functional theory. For the metal–sulfur clusters, (C5H5)4Mo4S4 (C5H5)4Cr4S4, twelve cluster valence electrons delocalised six metal–metal single bonds, giving an approximately tetrahedral core. In (C5H5)4Cr4O4, however, no strong Cr–Cr bonds present, three remain localised on each chromium centres. Antiferromagnetic coupling across four edges tetrahedron, ferromagnetic remaining two give rise to spin-singlet ground state distinct rhombic distortion. The driving force for distortion is only 12 kJ mol–1, consequently inter- intra-molecular steric effects may play major role determining solid state. Both have low-lying excited states which pattern completely reversed, with present (C5H5)4Cr4O4 but none (C5H5)4Cr4S4. case lies less than 45 mol–1 above state, despite fact that substantial structural rearrangement involved. Changes bond strength spin polarisation energy found contribute equally periodic trend towards electron localisation clusters.