\\([NiCl_4]^{2-}\\) is paramagnetic while \\(Ni(CO)_4]\\) diamagnetic though both are tetrahedral. Why? (Atomic no. of \\(Ni = 28\\))

In \\(Ni{\left( CO \right)}_{4}\\), the oxidation state of \\(Ni\\) is zero whereas in \\({\left[ Ni{Cl}_{4} \right]}^{2-}\\), the oxidation state of \\(Ni\\) is \\(+2\\).The presence of \\(CO\\) ligand, which is a strong ligand, can pair all electrons in \\(Ni{\left( CO \right)}_{4}\\) and thus it is diamagnetic in nature but \\({Cl}^{-}\\) is a weak ligand and is unable to pair up the unpaired electrons and thus \\({\left[ Ni{Cl}_{4} \right]}^{2-}\\) is paramagnetic in nature.

Draw figure to show the splitting of d orbitals in an octahedral crystal field.

The splitting of \\(d-\\) orbitals in an octahedral crystal field is as shown.

The crystal field splitting energy for octahedral \\((\Delta_0)\\) and tetrahedral \\((\Delta_t)\\) complexes are related as:

Since splitting in tetrahedral complex is \\(\cfrac{2}{3}\\)rd of octahedral complex ,so for one legand splitting in \\(OH =\cfrac { \Delta _0 }{ 6 } \\),then for one legend splitting in tetrahedral is \\(\cfrac { 2 }{ 3 } \left( \cfrac { \Delta _0 }{ 6 } \right) \\), so for \\(4\\) legand ,\\(\Delta t=4\times \cfrac { 2 }{ 3 } \times \cfrac { \Delta _0 }{ 6 } \\ \quad \quad \quad =\cfrac { 4 }{ 9 } \Delta _0\\)

Crystal field stabilization energy for high spin \\(d^4\\) octahedral complex is:

For high spin \\(d^4\\) Octahedral complex the splitting is given by(Refer to Image)\\(CFSE=[-0.4\times 3+0.6\times 1]\triangle_0\\)\\(=[-1.2+0.6]\triangle_0\\)\\(=-0.6\triangle_0\\)\\(\therefore\\) Answer is option D.

Explain the violet colour of \\([Ti(H_2O)_6]^{3+}\\) complex on basis of the crystal field theory?

In the complex \\(\displaystyle [Ti(H_2O)_6]^{3+}\\), the Ti atom has oxidation state of \\(\displaystyle+3\\). Its outer electronic configuration is \\(\displaystyle 3d^1\\). It has one unpaired electron. This unpaired electron is excited from \\(\displaystyle t_{2g}\\) level to \\(\displaystyle e_g\\) level by absorbing yellow light and hence appears violet coloured.

What is crystal field splitting energy? How does the magnitude of \\(\Delta_{0}\\) decide the actual configuration of d orbitals in a coordination entity?

The crystal field stabilisation energy (CFSE) is the gain in the energy achieved by preferential filling up of orbitals by electrons. It is usually less than or equal to 0. When it is equal to 0, the complex is unstable. The magnitude of CFSE depends on the number and nature of ligands and the geometry of the complex.Consider octahedral \\(\displaystyle d^4\\) system. Three electrons are in lower \\(\displaystyle t_{2g}\\) level. Fourth electron will enter into higher \\(\displaystyle e_g\\) level if \\(\displaystyle \Delta _o P\\). Here, P is the pairing energy. It is the energy required to pair two electrons against electron electron repulsion in the same orbital.

What is the correct electronic configuration of the central atom is \\(K_4(Fe(CN)_6]\\) on crystal field theory?

\\(K_4[Fe(CN)_6]\\)Fe ground state \\([Ar]3d^64s^2\\)\\(Fe^{2+}:3d^64s^0\\)So, B is the correct option.

Explain the following:\\(Co^{2+}\\) is easily oxidised to \\(Co^{3+}\\) in the presence of a strong ligand.

With the electronic configuration \\(3d^2 4s^0, Co^{2+}\\) has three unpaired electrons. \\(H_2O\\) being a weak ligand, the unpaired electrons present in \\(3d\\) orbital of \\(Co\ (II)\\) do not pair up. In the presence of strong ligands, two unpaired electrons in \\(3d\\) orbitals pair up and the third unpaired \\(e^-\\) shifts to higher energy orbital from where it can be easily lost and hence show an oxidation state of \\(III\\).

The hexaaquomanganese (II) ion contains five unpaired electrons while the hexacyano ion contains only one unpaired electron. Explain using Crystal Field Theory.

Mn(II) has an electronic configuration of \\(3d^54s^0\\). In the case of hexaaquomanganese (II) ion the ligand attached to metal is water which is a weak field ligand and is not able to pair up the electrons of 3d subshell and the configuration is \\(t_2g^3\\) and \\(eg^2\\). whereas in the case of hexacyano ion the \\(CN^-\\) is a strong field ligand and it causes pairing of electrons in the d orbitals and hence thee exist only one unpaired electron in \\(t_2g^5\\)\\(eg^0\\).

Crystal Field Theory | Definition, Examples, Diagrams

definition

Crystal field theory

The crystal field theory (CFT) is an electrostatic model which considers the metal-ligand bond to be ionic arising purely from electrostatic interactions between the metal ion and the ligand. Ligands are treated as point charges in case of anions or dipoles in case of neutral molecules.

definition

Features of CFT

Crystal field theory (CFT) describes the breaking of orbital degeneracy in transition metal complexes due to the presence of ligands. CFT qualitatively describes the strength of the metal-ligand bonds. Based on the strength of the metal-ligand bonds, the energy of the system is altered. This may lead to a change in magnetic properties as well as color.

definition

Crystal field for octahedral complexes

In an octahedral complex, there are six ligands attached to the central transition metal. The d-orbital splits into two different levels. The bottom three energy levels are named

d_{x y}, d_{y z}, d_{x z}

(collectively referred to as

t_{2 g}

). The two upper energy levels are named

d_{x^{2} - y^{2}}, d z^{2}

(collectively referred to as

e_{g}

). The reason they split is because of the electrostatic interactions between the electrons of the ligand and the lobes of the d-orbital. In an octahedral, the electrons are attracted to the axes. Any orbital that has a lobe on the axes moves to a higher energy level. This means that in an octahedral, the energy levels of

e_{g}

are higher

(0.6 Δ_{o})

while

t_{2 g}

is lower (0.4

Δ_{o}

definition

Crystal field stabilisation energy

The Crystal Field Stabilization Energy is defined as the energy of the electronic configuration in the ligand field minus the energy of the electronic configuration in the isotropic field.
CFSE=

Δ E = E_{l i g a n d f i e l d} - E_{i s o t r o p i c f i e l d}

definition

Spectrochemical series

A spectrochemical series is a list of ligands ordered on ligand strength and a list of metal ions based on oxidation number, group and its identity.

definition

Weak field ligands

Ligands that produce a small

Δ

are called weak-field ligands and lie at the left end of the spectrochemical series. Weak field ligands cannot make pairing of electrons to the metal atoms. They are

π

donor ligands, e.g., halide ions are weak field ligands.

definition

Strong field ligands

Strong field ligands have large

Δ

. They are

π

-acceptor ligands. They have the tendency of pairing of electrons of the metal ions.

definition

Properties of octahedral

High spin state and low spin state
Magnetism
Colour

definition

High spin and low spin states on the basis of CFT

As the electrons first enter the lower energy three

t_{2 g}

orbitals with parallel spin, hence for complexes with

d^{1}, d^{2}, d^{3}

ions, the orbital occupancy is certain. For

d^{4}, d^{5}, d^{6}, d^{7}

etc. ions, three electrons first enter

t_{2 g}

orbitals with parallel spin but the remaining may pair up in the

t_{2 g}

orbital or may enter

e_{g}

orbital, giving rise to low-spin complex in the former case or high-spin complex in the later case.

definition

Crystal field theory for tetrahedral complexes

In a tetrahedral complex, there are four ligands attached to the central metal. The d orbitals also split into two different energy levels. The top three consist of the

d_{x y}, d_{y z}, d_{x z}

orbitals. The bottom two consist of the

d_{x^{2} - y^{2}}

and

d_{z^{2}}

orbitals. The reason for this is due to poor orbital overlap between the metal and the ligand orbitals. The orbitals are directed on the axes, while the ligands are not.

Δ_{t}

is typically smaller than the spin pairing energy, so tetrahedral complexes are usually high spin.

definition

Factors affecting orbital splitting energy

Oxidation state of the metal
Nature of the metal
Geometry of the coordination entity
Nature of the ligand

definition

Limitation of crystal field theory

As ligands are regarded as point charges, the anionic ligands should exert greater splitting effect.
It treats the metal-ligand bond as purely ionic and does not take into the account the covalent character of the bond.

definition

Weak field ligands

The ligand which on splitting goes in low energy field is called as weak field ligand.
Examples :

I, B r, N O^{3 -}

etc.

definition

Advantages of crystal field theory over valence bond theory

CFT predicts a gradual change in magnetic properties of complexes rather than the abrupt change predicted by VBT. According to VBT, the bond between the metal and the ligand is covalent,,while according to CFT it is purely ionic. The bond is now considered to have both ionic and covalent charachter. Unlike valence bond theory.

Crystal Field Theory

definition

Crystal field theory

definition

Features of CFT

definition

Crystal field for octahedral complexes

definition

Crystal field stabilisation energy

definition

Spectrochemical series

definition

Weak field ligands

definition

Strong field ligands

definition

Properties of octahedral

definition

High spin and low spin states on the basis of CFT

definition

Crystal field theory for tetrahedral complexes

definition

Factors affecting orbital splitting energy

definition

Limitation of crystal field theory

definition

Weak field ligands

definition

Advantages of crystal field theory over valence bond theory

$[N i C l_{4}]^{2 -}$ is paramagnetic while $N i (C O)_{4}]$ diamagnetic though both are tetrahedral. Why? (Atomic no. of $N i = 28$ )

Draw figure to show the splitting of d orbitals in an octahedral crystal field.

The crystal field splitting energy for octahedral $(Δ_{0})$ and tetrahedral $(Δ_{t})$ complexes are related as:

Crystal field stabilization energy for high spin $d^{4}$ octahedral complex is:

Explain the violet colour of $[T i (H_{2} O)_{6}]^{3 +}$ complex on basis of the crystal field theory?

What is crystal field splitting energy? How does the magnitude of $Δ_{0}$ decide the actual configuration of d orbitals in a coordination entity?

What is the correct electronic configuration of the central atom is $K_{4} (F e (C N)_{6}]$ on crystal field theory?

On the basis of crystal field theory write the electronic configuration for $d^{4}$ ion, if $Δ_{0} < P$ .

Explain the following:
$C o^{2 +}$ is easily oxidised to $C o^{3 +}$ in the presence of a strong ligand.

The hexaaquomanganese (II) ion contains five unpaired electrons while the hexacyano ion contains only one unpaired electron. Explain using Crystal Field Theory.

definition

Crystal field theory

definition

Features of CFT

definition

Crystal field for octahedral complexes

definition

Crystal field stabilisation energy

definition

Spectrochemical series

definition

Weak field ligands

definition

Strong field ligands

definition

Properties of octahedral

definition

High spin and low spin states on the basis of CFT

definition

Crystal field theory for tetrahedral complexes

definition

Factors affecting orbital splitting energy

definition

Limitation of crystal field theory

definition

Weak field ligands

definition

Advantages of crystal field theory over valence bond theory

[NiCl4​]2− is paramagnetic while Ni(CO)4​] diamagnetic though both are tetrahedral. Why? (Atomic no. of Ni=28)

Draw figure to show the splitting of d orbitals in an octahedral crystal field.

The crystal field splitting energy for octahedral (Δ0​) and tetrahedral (Δt​) complexes are related as:

Crystal field stabilization energy for high spin d4 octahedral complex is:

Explain the violet colour of [Ti(H2​O)6​]3+ complex on basis of the crystal field theory?

What is crystal field splitting energy? How does the magnitude of Δ0​ decide the actual configuration of d orbitals in a coordination entity?

What is the correct electronic configuration of the central atom is K4​(Fe(CN)6​] on crystal field theory?

On the basis of crystal field theory write the electronic configuration for d4 ion, if Δ0​<P.

Explain the following: Co2+ is easily oxidised to Co3+ in the presence of a strong ligand.

The hexaaquomanganese (II) ion contains five unpaired electrons while the hexacyano ion contains only one unpaired electron. Explain using Crystal Field Theory.

$[N i C l_{4}]^{2 -}$ is paramagnetic while $N i (C O)_{4}]$ diamagnetic though both are tetrahedral. Why? (Atomic no. of $N i = 28$ )

The crystal field splitting energy for octahedral $(Δ_{0})$ and tetrahedral $(Δ_{t})$ complexes are related as:

Crystal field stabilization energy for high spin $d^{4}$ octahedral complex is:

Explain the violet colour of $[T i (H_{2} O)_{6}]^{3 +}$ complex on basis of the crystal field theory?

What is crystal field splitting energy? How does the magnitude of $Δ_{0}$ decide the actual configuration of d orbitals in a coordination entity?

What is the correct electronic configuration of the central atom is $K_{4} (F e (C N)_{6}]$ on crystal field theory?

On the basis of crystal field theory write the electronic configuration for $d^{4}$ ion, if $Δ_{0} < P$ .

Explain the following:
$C o^{2 +}$ is easily oxidised to $C o^{3 +}$ in the presence of a strong ligand.