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2.
The factor of the size of the split energy of the color ring
(1) The influence of crystal field symmetry
△p>△o>△t
(2) The influence of the charge in the center
.
The center has a high charge, has a strong interaction with the ligand, and has a large splitting energy
Splitting energy [Fe(CN) 6 ] 3- >[Fe(CN) 6 ] 4-
(3) The influence of the number of cycles where the center is located
.
For the same ligand, the period of the center is higher, and the splitting energy is larger
Splitting energy [Hg(CN) 4 ] 2- >[Zn(CN) 4 ] 2-
(4) The influence of the ligand
.
The smaller the electronegativity of the coordination atom in the ligand, the stronger the electron donating ability, the stronger the coordination ability of the ligand, and the greater the splitting energy
The I - <Br - <the SCN - <CI - <F.
- <OH - <-ONO, - <C 2 O .
4 2 - <H 2 O <the NCS - <NH2 .
3 <EN <-NO2 2 - <the CN - ≈CO
This sequence is called the photochemical sequence, because the size of △ directly affects the spectrum of the coordination compound
.
According to the coordination ability of coordinating atoms, the general law of splitting energy change is
Halogen<oxygen<nitrogen<carbon
The above discussion is only general laws, in fact, there are often some examples that do not conform to these laws or even abnormal
.
For example, [HgCl .
3.
Arrangement of electrons in the split d orbital
When arranging electrons in the split d orbital, the three principles of electron arrangement must be observed, namely, the principle of least energy, the principle of Pau-1i incompatibility, and the rule of Hund
.
For example, for a certain transition metal d4 electronic configuration, there are two possibilities for electron arrangement in an octahedral field.
One is a low-spin mode, all electrons are arranged in dε orbitals, and the pairing of electrons must overcome the pairing energy P; the other One is a high-spin method, where one electron is arranged on a high-energy dγ orbit, and the splitting energy △ must be overcome
.
Therefore, if △>P, the electron arrangement adopts the low-spin mode; if △<P, the electron arrangement adopts the high-spin mode
.
The values of △ and P are usually given in the form of wave numbers
.
The wave number refers to how many wavelengths a length of 1 cm is equivalent to
For example, in [Fe(H 2 O) 6 ] 2+ , △=10400cm -1 , P=15000cm -1 ; △<P, d electrons adopt high spin arrangement (dε)4( dγ) 2
.
In [Fe(CN) 6 ] 4- , A=338000cm -1 , P=15000cm -1 ; △>P, d electrons adopt a low-spin arrangement in the split d orbital (dε)6(dγ )0
