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1.
Boron trihalide
Both boron and 4 halogens can form trihalide BX 3
.
At room temperature, BF3 and BC1 3 are gases, BBr 3 is liquid, and Bl 3 is solid
Gaseous boron trihalide molecular configuration of flat triangles, the center of B atoms taken SP 2 Hybridized, hybrid orbital and X each have the single p-orbital electrons form σ bonds
.
The unhybridized 2p empty orbital of B is parallel to the three p orbitals of one valence layer of X (providing a pair of electrons), overlapping each other to form a delocalized π bond II 6 4
BX 3 is a typical Lewis acid, which can combine with Lewis bases such as ammonia to form acid-base complexes
.
H[BF 4 ] is a strong acid and its salt is quite stable.
For example, K[BF 4 ] and Na[BF 4 ] are stable chemical reagents
BCI at high temperatures above 1000K 3 NH2 and 3 the reaction may be generated BN
.
BCI 3 +NH 3 =BN+3HCI
The BX 3 molecule is easily hydrolyzed
.
BX 3 is an electron-deficient compound, and the unhybridized 2p empty orbital of B can accept the electron pair of O in the H 2 O molecule to make it easy to undergo hydrolysis reaction
BF 3 is not the same as other BX 3 hydrolysates
.
Due to the small radius of the F, B conducive to the lack of coordination of electrons, it may be further reacted with HF generated by the BF .
Therefore, BF 3 is hydrolyzed to produce two products: B(OH) 3 and H[BF 4 ]
.
4BF 3 +3H 3 O=B(OH) 3 +3H[BF 4 ]
To the BCI .
3 ventilation of water, hydrolysis also occurs but not more generated HCI and the BCl .
BCl 3 +3H 2 O=B(OH) 3 +3HCI
2.
Ming's other valence boron halide
Boron and halogen may also be formed in many different valences of boron halides, boron oxidation number lower than BX .
3 oxidation number of boron, called boron halides low
.
B 2 F 4 is gaseous at room temperature (melting point -56°C, boiling point -34°C), the BB bond is longer (similar to N 2 O 4 ), and has a planar structure
.
B 2 CI .
B 8 F 12 is a yellow solid, and the 8 B atoms in the crystal form a structure similar to diborane , as shown in Figure 13-15
.
Figure 13-15 Structure of B 8 F 12
Many types of boron halides can be obtained from B 2 X 4 , among which the more important is B n X n (boron monohalide polymer)
.
For B n Cl n , n=4, 8~12; for B n Br n , n=7~10
.
Among them, the relatively stable ones are B 4 CL 4 , B 8 Cl 8 and B 9 CL 9
.
B n X n all form a cage-like B n structure, with an X connected to each B end
.
B 4 Cl 4 is a light yellow-green solid, and B in the crystal has a regular tetrahedral structure (Figure 11 3-16)
.
B 8 Cl 8 is a dark red or purple solid, and B 8 in the crystal forms a dodecahedron
.
B 9 Cl 9 is an orange-yellow solid, and B 9 in the crystal forms a three-hat triangular prism (a B-cap is provided on each of the three quadrilaterals of the six regular triangular prisms composed of B)
.
Figure 13-16 Structure of B 4 Cl 4
