Intermetallic contacts

Bis[2-(diphenylphosphino)phenyl]phenylphosphine (TP) is a very inflexible ligand with a rigid backbone and gives the trinuclear complex [Au3Cl3(TP)] (452), that has a compact unsymmetrical structure in the solid state which is retained in solution owing to the fixation of the gold atoms through intermetallic contacts.2651... 

As described above, among the several closed-shell metal ions that form luminescent supramolecular entities with gold, thallium(I) forms the most numerous examples. While aurophilic attractions can be considered the upper extreme of the metallophilic interactions (with values up to 46 kJ mol-1), intermetallic contacts involving T1(I) centers appear as the weakest ones (even <20 kJ mol-1),46 which is explained by the enhancement of the Au---Au interactions and the weakening of the Van der Waals attractions between the s2 metal atoms produced by the relativistic effects.47 Nevertheless, the complexes in which this interaction appears are surprisingly stable, with additional electrostatic, packing forces, or the ligand architecture, responsible for this fact. 

These complexes are also luminescent in the solid state both at room temperature and at 77 K but not in solution, where the intermetallic contacts are no longer present, which,... 

Intermetallic contacts are always regarded as unpolarizable, the Galvani potential differences between metals in contact having then the same values under current as in the absence of current. We then have... 

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... 

In some instances to improve solderability, tin is deposited on nickel surfaces. In a short time, however, interdiffusion of the two metals results in the growth of an intermetallic NiSn3 compound that is much less amenable to soldering. In case of tin over electrolessly deposited nickel surfaces, the interdiffusion results in pores in both films. Pores are to be avoided, of course, if conductivity and/or contact resistance is an issue. 

However, the catalytic activity of contact mass is determined not only by copper concentration. Crucially important is also the structure of the crystal lattices of silicon, copper and the intermetallic compound Cn Si, which is formed during the alloying of silicon with copper or in the synthesis, since the structural failure seems to facilitate silicon or copper entering the reaction. The structure of the crystal lattice is largely determined by the way contact mass is prepared. 

It is supposed that the contact mass used in direct synthesis consists of two phases, free silicon and the intermetallic compound CusSi (r -phase). At the initial stage at synthesis temperature methylchloride interacts with the silicon atom from the intermetallic compound ... 

The mechanism of phenylchlorosilane formation has not been fully established either however, similarly to methyl- and ethylchlorosilanes, it is most probable that initially intermetallic compound Cu3Si in contact mass interacts with chlorobenzene. To intensify the reaction and increase the output of the target product, the reaction is fed with hydrogen chloride in addition to chlorobenzene. 

A continuous, coherent intermetallic layer, 1,5 0.5 pm thick, was found to form during the specimen preparation. Hence, this technique ensured an intimate contact between the nickel and bismuth phases, so that the reaction started simultaneously anywhere along the entire Ni-Bi interface. Therefore, both intermetallics, NiBi and NiBi3, had favourable nucleation conditions. 

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