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Technetium is the first synthetic element.
Because technetium is rare and radioactive, there is not much research on the chemical properties of technetium
.
Bowl is the last non-synthetic element to be discovered
1.
Elements and compounds of nickel
When smelting molybdenite (MoS 2 ), the trace amount is converted into volatile Re 2 O 7 , and the collected Re 2 O 7 is converted into ammonium salt and then reduced with hydrogen at high temperature to obtain a metal pot
.
Rhenium is a silver-gray metal with metallic luster, high density (21g·cm -3 ), and high melting point (3170°C), second only to the most refractory metal tungsten among metals
.
The alloy made of rhenium and other metals has high hardness, high temperature resistance, good elasticity and wear resistance
.
Metal rhenium can be used as the contact of filament, pen tip, switch, rhenium tungsten thermocouple can measure and control high temperature up to 2500℃; in industry, rhenium is used as a catalyst for the production of certain organic compounds
The chemical properties of rhenium are very stable
.
It is acid and alkali resistant and does not react with hydrofluoric acid
Compared with Mn(Ⅶ), Re(Ⅶ) is more stable and weaker in oxidation
.
HReO4 .
4 is a strong acid, which solution was evaporated and the precipitated yellow crystals was concentrated Re 2 O .
7 · 2H 2 O
The oxides of Re mainly include: Re 2 O 7 , yellow, with a melting point of about 300°C; ReO 3 , red, with metallic luster, and decomposes at 400°C; Re 2 O 5 , blue, unstable, easily disproportionated to Re 2 O 7 and ReO 2 ; ReO 2 , gray, very stable, disproportionate to Re 2 O 7 and elemental Re at 900°C
.
Rhenium halides mainly: ReF7, yellow, m.
p.
deg.
] C 48.
3; ReF of .
6 , a yellow liquid, m.
p.
deg.
] C 18.
5; ReF of .
5 , yellow-green, m.
p.
48 ℃; ReF4, blue, sublimation deg.
] C 300; ReCl .
6 , red and green, The melting point is 29°C
.
2.
The structure and four-fold bond of [ReaCl 8 ] 2-
In the [Re 2 Cl 8 ]2- structure, the distance between Re-Re is much smaller than the Re-Re bond length in metal crystals, and there are multiple Re-Re bonds
.
The structure of [Re 2 C 1 8 ] 2- is shown in Figure 16-4 .
Figure 16-4 The structure of [Re 2 Cl 8 ]2- and the δ bond between metals
The d orbitals involved in the hybridization of the central Re are dx 2 -y 2 , and the remaining 4 d orbitals are used to form a four-fold bond between Re-Re when the two ReCl 4 units are combined
.
The two dz 2 orbitals perpendicular to the plane of the ReCl 4 unit overlap to form a σ bond; the dzy orbitals of two Re overlap side by side to form a π bond; the dxz orbitals of two Re also overlap side by side.
, Form a π bond; the two dxy orbitals are located in two parallel ReCl 4 unit planes, and the overlap between them is "face to face" .
The chemical bond formed between the two dxy orbitals between Re-Re is called a delta bond .
The delta bond is between the x-axis and the y axis.
The two Re 3+ dxy orbitals overlap to form 4 electron clouds.
The delta bond is symmetrical to the plane passing through the midpoint of the Re-Re bond axis and perpendicular to the bond axis
.
