The nature of the chemical bond in di- and polynuclear metal cluster complexes as depicted by the analysis of the electron localization function

Abstract

The bonding in transition metal complexes is usually rationalized based on molecular orbital schemes. Topological approaches such as the atoms in molecules (AIM) theory or the electron localization function (ELF) analysis provides an alternative interpretation of the bonding relying on a local description. These topological theories give a very convenient framework to achieve the partition of the molecular space in regions with chemical meaning such as atoms, bonds and lone pairs. In this work we review the possibility offered by ELF to investigate the bond in di-tri-and tetranuclear metal complexes containing metal-metal bond. In the case of bimetallic complexes with different nominal bond orders of formula M 2 (formamidinate) 4 , the metal-metal interaction is associated to a large electron fluctuation between the two metallic cores and interpreted in terms of simple resonance arguments. Such fluctuation between metals can not be invoked for the trinuclear Fe 3 (CO) 12 or the incomplete cuboidal [Mo 3 S 4 (PH 3 ) 6 Cl 3 ] 4+ complexes. The metal-metal interaction in these clusters is mostly characterized by multicenter bonding as is the case for the tetranuclear heterodimetallic cubane-type complexes resulting from the insertion of Cu or Ni into the previous Mo 3 S 4 complex.

Electron localization and delocalization indices for solids

“…the large green sphere in Figure 8 Similar situation of metal-metal bonding was found in metal cluster compounds with ELF valence basins of relatively low population (less than 1 electron even for multiple bonds). 48,55 High DI values between metal core-superbasins (i.e., core given by above prescription merged with the surrounding basin set of the atomic shell containing the d electrons) and valence ELF basins, as well as between the metal core-superbasins at short metal-metal distances (≤ 2 Å) were also reported. 48 …”

“…[45][46][47][48] The DI values for homopolar metal-metal bonds range from 0.3 for single up to 4.2 for multiple bonds. Non-negligible pair interactions between distant metal atoms (with δ(M, M) ≈ 0.03), e.g., between two Co atoms at opposite vertexes of the Co 6 octahedron in Co 6 (CO) 6 were also observed.…”

Comparative Analysis of Electron‐Density and Electron‐Localization Function for Dinuclear Manganese Complexes with Bridging Boron‐ and Carbon‐Centered Ligands

“…[18,81]), including questions of metalÀmetal bonding in polynuclear carbonyl and related clusters. [34,[82][83][84][85][86][87] For example, the ELF shows no direct M À M bonding attractors for the triscarbonyl-bridged Fe-Fe interaction in [Fe 2 (CO) 9 ] [34] or for the bridged edge in the C 2v isomer of [Fe 3 (CO) 12 ], [87] in both cases yielding conclusions consistent with the QTAIM results (as another example, no direct Rh À Rh bonding attractors are found on the carbonyl-bridged faces of [Rh 6 (CO) 16 ) [34] ). The topological discussion of the ELF is typically based on the synaptic order of its attractors and the associated basins, [88,89] where monosynaptic valence attractors are assigned to lone pairs, disynaptic attractors to two-center bonds, and attractors of higher synapticity to delocalized multicenter bonding.…”

The Role of π Electrons in the Formation of Benzene‐Containing Lithium‐Bonded Complexes

“…The ELF basins provide a complementary view to the standard valence one. [64] A nucleus is immersed in the basin of interest and the bordering cores are counted instead of the atoms coordinated. Among the different basins, the points of bifurcation can be considered a measure of the interaction and electron delocalization.…”