Electronic Structure of Face- and Edge-Shared Bioctahedral Systems:  A Comparison of M₂Cl₉^3- and M₂Cl₁₀^4-, M = Cr, Mo, W

Abstract

Potential energy curves for the broken-symmetry states of the edge-shared bimetallic systems, M(2)Cl(10)(4-) (M = Cr, Mo, W), are analyzed using approximate density functional theory. The potential energy curves are made up of distinct sections, depending on which subsets of metal-based electrons are localized or delocalized. Starting from the fully delocalized limit, the metal-based electrons localize in the order delta before pi before sigma as the metal-metal separation is progressively increased. As a result there are four distinct regions of the potential energy curve, corresponding to (a) sigma + pi + delta delocalized; (b) sigma + pi delocalized, delta localized; (c) sigma delocalized, pi + delta localized; and (d) sigma + pi + delta localized. Localization of the delta subset of electrons is particularly facile, because interactions with the bridging ligands destabilize the delta orbital relative to delta. As a result, at metal-metal separations greater than approximately 2.30 Å, delocalization of the delta electrons would result in formation of a M-M antibond rather than a bond. For Cr(2)Cl(10)(4-), the fully localized region of the curve lies much lower than the others, but for the molybdenum and tungsten congeners, all four regions lie within 1.0 eV of each other, giving rise to complex and relatively flat potential energy curves. The decahalides of the chromium triad therefore exhibit the well-established trend toward greater delocalization in complexes of the heavier transition metals. This trend is, however, found to be far less prominent than in the face-shared analogues, M(2)Cl(9)(3-), and the difference between the two structural types is traced to the inability of the edge-shared bridge to support the short metal-metal separations necessary for complete electron delocalization.

Periodic trends in metal–metal bonding in edge-shared [M2Cl10]4− systems

“…The success of this procedure can be exemplified by noting that our broken-symmetry density functional calculations have accurately reproduced experimentally observed properties in a large number of [M 2 X 9 ] zÀ dimers with electronic configurations ranging from d 1 d 1 through to d 5 d 5 [7][8][9][10][11][12][13][14] as well as mixed-valence [15,16]. We have also used this methodology to successfully investigate metal-metal interactions in a variety of other dimer systems, including edge-shared [M 2 X 10 ] zÀ and phosphinebridged [M 2 X 6 (P-P) 4 ] zÀ systems [17,18], indicating that this theoretical approach is broadly applicable across many dinuclear transition metal complexes.…”

A Non‐Radical Mechanism for Methane Hydroxylation at the Diiron Active Site of Soluble Methane Monooxygenase

“…Siegbahn,14e Friesner et al,16 and Noodleman et al26f,26g,26i used the broken‐symmetry approach to describe the electronic structures of the weakly coupled diiron active site of MMOH. If the active site of MMOH Q involves a kind of edge‐shared six‐coordinate diiron( IV ) complex, this electronic feature is basically as described in Scheme 24e–24g. When an iron atom is octahedrally coordinated, the relevant d orbitals are split into three low‐lying t 2g orbitals and two high‐lying e g orbitals.…”

Simple Preparations of Pd6Cl12, Pt6Cl12, and Qn[Pt2Cl8+n], n = 1, 2 (Q = TBA+, PPN+) and Structural Characterization of [TBA][Pt2Cl9] and [PPN]2[Pt2Cl10]·C7H8

“…Edge-shared systems like [M 2 Cl 10 ] n-have been the subject of theoretical studies aimed at correlating the electronic configuration of the metal centers with the presence of metal-metal interactions and comparisons with the faceshared [M 2 Cl 9 ] n-anions have also been made. 34 The reactivity of the two types of salts toward [Q]Cl has been studied: Pt 2 Cl 9 -reacts rapidly with 1 equiv of Clproducing [Pt 2 Cl 10 ] 2-, while [Pt 2 Cl 10 ] 2-reacts slowly yielding [PtCl 6 ] 2-. These results show that for the doubly bridged [Pt 2 Cl 10 ] 2-anion, the typical inertness of platinum(IV) is observed, while [Pt 2 Cl 9 ] -behaves anomalously.…”