Intermetallic distance

The first set of experiments was conducted in methanol. The substrate concentration was varied from 15 to 50 mM at a 200 pM concentration of 1 for the determination of kinetic parameters for the transformation of 8 into 9. The catalytic rate constant was determined to be 0.04 min and the Michael constant was determined to be 40 mM at 30°C. The rate constant is comparable to those reported for other dinuclear Cu(ll) complexes with a comparable Cu -Cu distance of 3.5 A, but about one magnitude lower than those observed for complexes with a shorter intermetallic distances (12-14), e.g. 2.9 A (kcat = 0.21 min ) (12) or 3.075 A (kcat = 0.32 min (13). The rate constant Aion for the spontaneous (imcatalyzed) oxidation of 8 into 9 was determined to be 6 x 10" min and corresponds to the oxidation without catalyst under otherwise identical conditions. The rate acceleration (Arca/Aion) deduced from these values is 60,000-fold. 

The most straightforward synthesis of compounds (L)AuAr uses the metathesis of (L)AuX precursors with aryllithium reagents, as, for example, executed for the preparation of (Ph3P)AuPh. The crystal structure of this benchmark complex has been determined. The linear coordination geometry is as expected. No aurophilic contacts are discernible in the crystal packing. Short Au- -Au contacts are observed, however, in the dinuclear compound (dppm)(AuPh)2 with an intramolecular intermetallic distance of 3.154(1) A. This complex shows a UV-VIS absorption at 290-300 nm and is luminescent in fluid solution at room temperature.1... 

As seen, they maintain the trend the closer to the middle the Ni atoms, the shorter are the intermetallic distances. 

The oxidation of 8 resulted in the mixed-valence compound 9 [38] which contain the same cation as the complexes 5 and 7 described above and an AumCI4 anion. The main interesting feature is the one-dimensional chain arrangement in the crystal, with alternating cations and anion separated by intermetallic distances of 3.404(2) A (Au -Au111) and 4.658 A (Hgn-Auln) (Figure 4.5). 

Fig. 58. Computed Rjt factors for pairs H3-Hk (k = 1, 2,4,6, 7) in the crystal structure of [Eu2(L14-2H)3] (the intermetallic distance d varies from 8.4 to 9.2 A, adapted from Rigault et al. (2000a)).

Intermetallic distances around 2.80 A have been found in analogous complexes of formula trans- [A2Pt(l-MeCyH-,A(3),N(4))2Hg]X2 (X = Cl-, N03 ) [56], where 1-MeCyH binds Pt through N(3) and Hg through N(4) (II, Fig. 5). They will be indicated as 4 2 type complexes. The crystal structures reveal that pairs of dimers are held together by the counterions, Cl- or N03, in such a way as to form tetranuclear species. 

The poorly defined concept of the metal-metal bond9- sometimes makes it difficult to distinguish between real and false metal-metal bonds. Many metal-metal bonds are only supposed to exist because of intermetallic distances corresponding to those in the metallic state or because magnetic properties or the noble gas rule demand an interaction between neighbouring metal atoms. 

Clear evidence for the close approach of metal atoms in Cdy-metal-lothionein is well established by Cd NMR spectroscopy. Indications of the intermetallic distances involved for cadmium and other metals have been sought from EXAFS. Although some indications of back-scattering of metals bound within metallothioneins have been obtained (31, 47), the principal conclusion is that these metal-metal separations are not coherent. Therefore, the backscattered waves, especially with their high frequency at distances >3 A, engage in destructive interference, which effectively renders them silent in the EXAFS. 

Here the ionic (atomic) radius is one-half of the smallest intermetallic distance in the lattice of the metal. 

Obviously, the intermetallic energy transfer rate 2 obeys Fermi s golden rule (Eq. (7)). The large intermetallic distances in bimetallic lanthanide helicates (>9 A) combined with the minute expansion of... 

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