When a transition metal ion (usually) is involved in octahedral complex formation, the five degenerate d-orbitals split into two set of degenerate orbitals (3 + 2). Three degenerate orbitals of lower energy (dxy, dyz, dzx) and a set of degenerate orbitals of higher energy \left(\right. d_{x^{2} - y^{2}} \textrm{ }\textrm{ } and \textrm{ }\textrm{ } d_{z^{2}} \left.\right). The orbitals with lower energy are called t2g orbitals and those with higher energy are called eg orbitals. In octahedral complexes, positive metal ion may be considered to be present at the centre and negative ligands at the corner of a regular octahedron. As lobes of and lie along the axes, i.e., along the ligands the repulsions are more and so high is the energy. The lobes of the remaining three d-orbitals lie between the axes i.e., between the ligands. The repulsion between them are less, so lesser the energy. In the octahedral complexes, if metal ion has electrons more than 3 then for pairing them, the options are (i) Pairing may start with 4th electron in t2g orbitals. (ii) Pairing may start normally with 6th electrons when t2g and eg orbitals are singly filled.

When a transition metal ion (usually) is involved in octahedral complex formation, the five degenerate d-orbitals split into two set of degenerate orbitals (3 + 2). Three degenerate orbitals of lower energy (d_xy, d_yz, d_zx) and a set of degenerate orbitals of higher energy $(d_{x^{2} - y^{2}} and d_{z^{2}})$ . The orbitals with lower energy are called t₂g orbitals and those with higher energy are called eg orbitals.
In octahedral complexes, positive metal ion may be considered to be present at the centre and negative ligands at the corner of a regular octahedron. As lobes of and lie along the axes, i.e., along the ligands the repulsions are more and so high is the energy. The lobes of the remaining three d-orbitals lie between the axes i.e., between the ligands. The repulsion between them are less, so lesser the energy. In the octahedral complexes, if metal ion has electrons more than 3 then for pairing them, the options are
(i) Pairing may start with 4th electron in t₂g orbitals.
(ii) Pairing may start normally with 6^th electrons when t₂g and eg orbitals are singly filled.

Linked Question 1

Which of the following electronic arrangement is / are possible for inner orbital oct complex.
(I) $t_{2 g}^{3} e_{g}^{2}$ (II) $t_{2 g}^{6} e_{g}^{1}$ (III) $t_{2 g}^{3} e_{g}^{0}$ (IV) $t_{2 g}^{4} e_{g}^{2}$
Select the correct code:

II, III

III only

III, IV

I, IV

For given P > $∆$ ₀
Hybridisation : sp³ d²
μ_eff : 5.9 B.M.
Outer orbital complex / high spin complex.

For given P < $∆$ ₀
Hybridisation : d²sp³
μ_eff : 1.732 B.M.
Inner orbital complex / low spin complex / spin paired complex

For P < $∆$ ₀
Hybridisation : d²sp³
Inner orbital complex
μ_eff : 3.89 B.M.

For given P > $∆$ ₀
Hybridisation : sp³d²
Outer orbital / high spin / spin free complex

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Linked Question 2

Select incorrect match for the following complexes.

${[{PdCl}_{2} {(SCN)}_{2}]}^{2 -}$ ( $∆$ > P)

[IrF₆]^3– ( $∆$ > P)

[Co(H₂O)₆]³⁺ ( $∆$ < P)

Fe(CO)₅ $∆$ > P)

(A) Due to high value of Z_eff in Ir⁺³, which belongs to IIIrd transition series (P < $∆$ 0)
(B) Due to higher oxidation state of Cobalt in ${[\overset{III}{Co} {(H_{2} O)}_{6}]}^{3 +}$ , P < $∆$ ₀, also H₂O lies towards stronger ligand side in spectrochemical series.
(C) CO is a strong field ligand hence P < $∆$
(D) Due to high value of Z_eff of Pd²⁺ , which belongs to 2^nd transition series , (P < $∆$ )

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Linked Question 3

In which of the following configurations, hybridisation and magnetic moment of octahedral complexes are independent of nature of ligands.
(I) d³ configuration of any metal cation
(II) d⁶ configuration of III^rd transition series metal cation
(III) d⁸ configuration of I^st transition series metal cation
(IV) d⁷ configuration of any metal cation
Select the correct code:

I, II, III

I, II, IV

I, III, IV

III, IV

For d¹, d², d³ system for octahedral ligand field, electronic distribution of any metal cation does not change, whatever may be ligands.

Due to increased Z_eff value for 3^rd transition series metal cation, $∆$ ₀ value gets increased, and
P < $∆$ ₀ , therefore electronic distribution for d6 will not change, whatever may be the ligands.

Electronic distribution for d⁸ system for any octahedral ligand field does not change, hence, hybridization and M.M. do not change.

Hence for d⁷ system hybridisation and μ_eff value changes according to strong or weak field ligand.

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