Metal quadruple bond

Further Studies of Electronic Spectra of Re2Clg and Re2Br - Assignment of Weak Bands in 600-350-nm Region - Estimation of Dissociation Energies of Metal-Metal Quadruple Bonds. 

The octachloroditechnetate ion, Tc2Cl8 , was among the first compounds recognized as containing a metal-metal quadruple bond [32]. The electrochemical data for this and several other metal-metal-bonded Tc2 complexes are represented in Table 2 [32-35]. Ligands bind at the equatorial positions around each metal in the... 

The octachlorodirhenate ion, Re2Cl8 , was the first substance recognized to contain a metal-metal quadruple bond [40],... 

In the requisite DAh geometry the constituents of the metal-metal quadruple bond comprise a a bond of axg symmetry, formed by the linear union of dz j AOs, a it bond of eu symmetry, which results from the end-to-end overlap of dxz and dyz AOs, and the 8 bond of b2g symmetry, which arises from the face-to-face interaction of eclipsed dxy AOs. When the ligands are considered many additional interactions take place and MO calculations must be used to delineate a cogent MO scheme. For the parent tetracarboxylate, Mo2(02CH)4,... 

III. METAL-METAL QUADRUPLE BONDS A. Recognition of a Quadruple Bond... 

Short review U. Radius, and F. Breher, To Boldly Pass the Metal-Metal Quadruple Bond, Angew. Chem. Int. Ed. 45, 3006-3010 (2006). 

Examples of compounds with carbon-carbon, other main group, and metal-metal single, double, and triple bonds, together with a metal-metal quadruple bond, are shown in Figure 15-7. 

Metal-metal multiple bonding can have dramatic effects on bond distances, as measured by X-ray crystallography. One way of describing the shortening of interatomic distances by multiple bonds is by comparing the bond distances in multiple bonds to the distances for single bonds. The ratios of these distances is sometimes called the formal shortness ratio. Values of this ratio are compared below for main group triple bonds and for some of the shortest of the measured transition metal quadruple bonds ... 

Fig. 21.15 (a) The formation of metal-metal quadruple bond by overlap of appropriate metal orbitals. Both the d z and dy atomic orbitals are used to form 7r-bonds, but either the d y or d i yi atomic orbital is used for fi-bond formation, the choice being arbitrary depending on which has been chosen for Cr—O bond formation, (b) Approximate energy levels of the metal-metal bonding and antibonding MOs. 

Mo2] with a metal-metal quadruple bond has shown bis-adenine coordination in a bidentate N7, N6 bridging mode and head-to-head arrangement. The bis-guanine complex has also been prepared, showing coordination to 06 and N7 in head-to-head arrangement as observed for the dirhodium complex (see Figure 19). ... 

Dimeric molybdenum complexes bearing metal-metal quadruple bonds have been prepared in better yield than previously reported conventionally. The tetra-carboxylate complexes Mo2(p-02CR)4 (R = Me, Et, Ph) were synthesized by heating Mo(CO)6 and the corresponding carboxylic acid at 180-200 °C for 15-32 min." The treatment of a MeOH/CH2Cl2 solution of Cu(BF4)2 H20 and 2,2 -dipyridyldisulfide at 140 °C for 2 h led to the formation of the polymeric Cu complex [Cu9(C5H5NS)8(SH)g](BF4) in 55% yield and the Cu complex [ Cu(dps)2)2(p-S)] +, dps = 2,2 -dipyridylsulfide, in 4% yield. In this unusual reaction, C-S and S-S bonds are cleaved simultaneously. 

As already mentioned in the Introduction, Cotton [1,2] stated that the two Re atoms are bonded through a quadruple bond in Re2Clg . The short rhenium-rhenium bond between two ReCl4" moieties was described as one a, one degenerate n, and one 8 bond. This work inspired experimental research that brought about the discovery of homo- and hetero-dinuclear compounds with metal-metal quadruple bonds [16]. 

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