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Crystal field theory (CFT) . Crystal field effects in complexes of square planar . Groups exist at the four-coordinated ( xy ) only. The generated square planar complex if progress distortion in the octahydral to move away ligand end along an axis (z) to infinity.

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## Crystal field theory (CFT)

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**Crystal field theory (CFT)**Dr-Najlaa AL-Radadi**Crystal field effects in complexes of square planar**Groups exist at the four-coordinated (xy) only. The generated square planar complex if progress distortion in the octahydralto move away ligand end along an axis (z) to infinity. Dr-Najlaa AL-Radadi**Therefore, the crystal field theory is not a square planar**complexes are a new type of complexes coordination , but considers a special case of the maximum distortion octahedral. Dr-Najlaa AL-Radadi**Imagine that we have begun complexe octahedral (and**different configuration square planar, the existence of two groups on the axis z) and then we try to keep the two groups on the z axis to infinity and the process of removal of the two groups on the z axis will affect the equal in energy the two groups (t2g), (eg) and thus occurs the separation of as in the following figure: - Dr-Najlaa AL-Radadi**(xy) level in the level of the paper And the (z) axis**perpendicular to the (xy) level Dr-Najlaa AL-Radadi**Application of the theory of crystal field on the system**Five coordinate : Can have five groups coordination in (Squar Pyramidal)and in the (TriagonalBipyramidal) as in the following forms: Dr-Najlaa AL-Radadi**This type of consistency is not common, such as 4 , 6.**does not differ much in these two figures their energy, and can switch to one of the other. Dr-Najlaa AL-Radadi**complex [Ni(CN)5]3- has crystallized in :two forms**splitting energy levels in (Squar Pyramidal) splitting energy levels in (TriagonalBipyramidal) Dr-Najlaa AL-Radadi**The Quartet distortions that occur depend on the metal ion**as well as on coordination groups in the presence of four groups coordination with a very strong field, we find that metal ions such as ion Cu complexes are usually the same type of geometric shape (square planar) Dr-Najlaa AL-Radadi**In this case, the density of electronic orbital (dz2) expel**ion strongly not happen correlation at both ends of the axis (z), while linked to the four groups strongly along the orbit (dx2-y2) and be close to the metal ion of the stairs they expel electrons metal that are in orbit ( dxy),raising the capacity of each of the (dxz) and (dyz) They are less affected by the electronic density of the groups coordination the strong field. Dr-Najlaa AL-Radadi**As a result of the presence of four ligand around the**central atom is divided into orbits (d) into four equal sections, a (dx2-y2) & (dxy) & (dz2) & (dxz) (dyz) as follows: Dr-Najlaa AL-Radadi**The influence of (Jahn - teller) and study**the distortion complexes: For example, Cu (II) binary, we find that the three electrons in orbits under the group (eg) will arise by either of the :following 1(dx2-y2) 2(dz2) 2(dx2-y2) 1(dz2) Dr-Najlaa AL-Radadi**In the first :**case would we expect the power of expulsion is higher among electrons the metal ion and the group-giving in the direction of the axis (dz2) than in the direction (dx2-y2) and this will be the links in the direction (dz2) longer than the links of the four directions (dx2-y2) - elongated - Dr-Najlaa AL-Radadi**In the other case:**would be exactly the opposite sense of direction made by two shorter (dz2) and four links in the longest direction (dx2-y2) - compressed - . In practice, the latter type is rarely a result, groups (eg) and (t2g) no longer have the same energy (degenerate), but separated as in the following figure: Dr-Najlaa AL-Radadi**Distortion for the octahedral or tetrahedral is what is**known as the impact of (Jahn- teller) , which states, "If found under the orbit (Sub shell) (eg or t2g) is unsaturated or half saturated or empty, the distortions of the previous types occur and result in separation at levels that have the same energy. Dr-Najlaa AL-Radadi**In the previous case was the difference in the number of**electrons is set (eg) the difference if the number of electrons in a orbitals(t2g) in the octahedral. Happen distortion simple because the orbits (dyz, dxz, dxy) components of the group (t2g) indicate between the axles which do not refer to the groups coordination directly so the asymmetry in the electronic density of these orbital's will not affect much in the spatial structure of the complex. The following table shows the electronic configurations that cause distortions Jahn- teller Dr-Najlaa AL-Radadi**Another type of distortions, but does not result from the**influence of Jahn-Teller in the case of nickel(II) complexes hexagonal coordination. If you find two group coordination a weak field and four groups giving a strong field in this case happens distortion does not produce the effects of Jahn–Teller , but results in the unequal field resulting from the groups coordination leading to the separation of both (dx2-y2) enough as :it :is shown in as follows Dr-Najlaa AL-Radadi**Separation of orbits (d) in the complex Ni (П) (d8) under**the influence of two groups coordination a weak field and four groups coordination a strong field. Dr-Najlaa AL-Radadi**The magnitude of Δo depends on:**Factors affecting the value of the separation (Δ0): 1-the size of ligand: Increase the size of the ligand and decrease the value of (Δ). -I< Br -<Cl-<F - Size is becoming increasingly less energy Dr-Najlaa AL-Radadi**2-Number of couples in single:**Increase the number of the individual couples increase non-centralization, and decrease the value of (Δ). Greater the number of individual couples less energy Dr-Najlaa AL-Radadi**:3- The nature of the ligand*** Δoincreases with strong ligandsmore thn with weak ligands 4-The charge (oxidation state)on the metal: Δoincreases as the charge increaes* The more oxidation increased as the power of attraction between the ion central, groups coordination increase and this leads to increase the value of (Δ0), for example [Ru(H2O)6]2+ (Δ0) = (19800 cm-1), [Ru (H2O)6]3+ (Δ0) = (28600 cm-1). [Ru(H2O)6]2+ [Ru(H2O)6]3+ Δoincreases as the oxidation stateincreaes Dr-Najlaa AL-Radadi**The higher oxidation state, the less the size of the central**atomAnd approaching the group-giving to the central atom are larger and so increase the value (Δ). Dr-Najlaa AL-Radadi**5- Whether the metal is in the first, second or third row of**transition elements • Δoincreases between adjacent members down • a group • (3d < 4d < 5d) [Co(NH3)6]3+ 3d6 [Rh(NH3)6]3+4d6 [Ir(NH3)6]3+5d6 Increase the value of the (d) orbital the value of Δoand increase Dr-Najlaa AL-Radadi**What is the reason ?**[Co(NH3)6]2+ paramagnatic while [Co(NH3)6]3+ diamgnatic. Δ0[Co(NH3)6]3+ >[Co(NH3)6]2 because coordination groups can approach more to the metal ion small with high charge and thus can interact more strongly with the orbitals (d). Dr-Najlaa AL-Radadi**Tetrahedral complexes favoured by:**• 1- large and bulky ligands • 2- Where attainment of regular shape is importante d0,d2,d5,d7, and d10 are regular shape • 3- weak field ligands • 4-Where the central metal has alow oxidation state • 5- Where the electronic configuration of the central metal d0,d5, d10 as there is no CFSE • 6- Where the loss of CFSE is small as in d1,d2,d6,d7 Dr-Najlaa AL-Radadi**Found from the (C F T) that the value of (Δ) in the case of**complex tetrahedral less than about (50%) of the value (Δ) in the case of complex octahedral if all other things equal. o∆ t = 4/9∆ Dr-Najlaa AL-Radadi**o∆ t = 4/9∆ Reasons for**• 1- There are 4 ligands instead of 6, the ligand field is 4/6= 2/3 • 2- In tetrahedral, the direction of the orbitals does not coincide with the direction of the ligands. This reduces • the crystal field splitting by roughly a further 2/3 • t = 2/3 X 2/3 = 4/9 ∆ * Thus Dr-Najlaa AL-Radadi**If the size of a large ligandpreferred composition of**complex tetrahedral .If the size of a small ligandpreferred octahedral as shown.. Dr-Najlaa AL-Radadi**How to account in the tetrahedral pyramid ?**Dr-Najlaa AL-Radadi**Whenever the difference in the value of Δ between the**octahedral and the tetrahedral of largePreferred formation of octahedral shape. )d3) (d8) Dr-Najlaa AL-Radadi**No vehicles finally did not separate until now Cr (III) in**the tetrahedral, but would prefer Cr (III) octahedral of [Cr(H2O)6]3+, because in the case of (d3) the difference in the value of Δ between octahedral and the tetrahedral of a large , while that whenever the distance between the values of Δ a small tetrahedral preferred. In the case of (d0), (d5), (d10), select any of them depending on the circumstances of the experiment. in the case of (Mn)2+, we find when you add a large amount of ligand be an octahedral [Mn(H2O)6]2+. Dr-Najlaa AL-Radadi**Relationship rehydration energy (solubility) with the**stability of complexes: charge(e) rehydration energy = Radius(r) Is the only factor that affects the strength of the association and the stability of complexes . when drawing the relationship between them, we find: Dr-Najlaa AL-Radadi***In theory we get the straight line passing the point**of origin * Δ value of the difference between practice and theory. *If we raised the value of Δ from the practical value we get the theoretical value. practical energy rehydration Δ theoretical Dr-Najlaa AL-Radadi**Factors that affect the stability of complexes (energy**rehydration): charge(e) Radius(r) Δ Note of the image equal to the theoretical value and practical value when (d10, d5, d0) where it = zero. Dr-Najlaa AL-Radadi**Colour in Coordination Compounds**• One of the most distinctive properties of transition metal complexes is their wide range of colours.This means that some of the visible spectrum is being removed from white light as it passes through the sample, so the light that emerges is no longer white. Dr-Najlaa AL-Radadi**The colour of the complex is complementary to that which is**absorbed. The complementary colour is the colour generated from the wavelength left over; if green light is absorbed by the complex, it appears red. The colour in the coordination compounds can be readily explained in terms of the crystal field theory. Dr-Najlaa AL-Radadi**Consider, for example, the complex [Ti(H2O)6]3+, which is**violet in colour. This is an octahedral complex where the single electron (Ti3+ is a 3d1 system) in the metal d orbital is in the t2g level in the ground state of the complex. • The next higher state available for the electron is the empty eg level. Dr-Najlaa AL-Radadi**If light corresponding to the energy of yellow-green region**is absorbed by the complex, it would excite the electron from t2g level to the eg level (t2g1 eg0 → t2g0 eg1 ). • Consequently, the complex appears violet in colour . The crystal field theory attributes the colour of the coordination compounds to d-d transition of the electron. Dr-Najlaa AL-Radadi**example:**aqueous solution of Ti (III) Violet [Ti(H2O)6]3+ is due to absorption of visible light transmission of electrons from a (t2g) to (eg) they absorb yellow light and pass the blue and red. Dr-Najlaa AL-Radadi**Magnetism**The magnetic moment can be measured using a Gouy balance. If we assume that the magnetic moment arises entirely from unpaired electron spins then the (spin only)formula can be used to estimate n, the number of unpaired electrons. This gives reasonable agreement for complexes of the first row of transition metals. Dr-Najlaa AL-Radadi**(spin only )formula**• μs = √n(n+2) • Once the number of unpaired electrons is known, either the (VBT) or the (CFT) can be used to work out the shape of the complex. • Examples: • Co3+ in strong field, no unpaired electrons, • diamagnetic. • Co3+ in weak field, 4 unpaired electrons, • Therefore μs = √4(4+2) = 4.9 BM • Note: BM Bohr magnet Dr-Najlaa AL-Radadi**: Success of crystal field**1-Successful theory in the interpretation of spectral and magnetic properties. 2-It was able to explain the colors of complexes transition elements due to the difference in energy between the orbits of non-equivalent complexes in the transition elements is relatively small it becomes possible to raise the electrons from low levels to high absorption of visible light and this is the reason for the emergence of the colors in the complexes. Dr-Najlaa AL-Radadi**Crystal field theory of defects :**Limitations of Crystal Field Theory • The crystal field model is successful in explaining the formation, structures, colour and magnetic properties of coordination compounds to a large extent. • 1-However, from the assumptions that the ligands are point charges, it follows that anionic ligands should exert the greatest splitting effect. The anionic ligands actually are found at the low end of the spectrochemical series(low field). • 2-Further, it does not take into account the covalent character of bonding between the ligand and the central atom. These are some of the weaknesses of CFT, which are explained by ligand field theory (LFT) and molecular orbital theory. Dr-Najlaa AL-Radadi

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