Coordination Chemistry

Both R and S have dsp³ hybridisation and trigonal bipyramidal geometry.

Fe³⁺ and Fe²⁺ have d⁵ and d⁶ electronic configurations and both are in high spin ligand system. The term symbol is calculated by the formula- ^2s+1L_J For d⁵, n = 5s = n/2 = 5/2 2s+1 = 6 L = 0 = S J = (L+s) to (L-s) = 5/2 Possible term symbol for Fe³⁺ = ⁶S_5/2 Similarly, possible term symbols for Fe²⁺ = ⁵D₄, ⁵D₃, ⁵D₂, ⁵D₁, ⁵D₀
The ground state term for Fe³⁺ is ⁶S_5/2. The ground state term for Fe²⁺ is ⁵D₄.

V²⁺ has d³ electronic configuration and it is empowered in a weak field ligand.The term symbol is calculated by the formula- ^2s+1L_J For d³, n = 3s = n/2 = 3/2 2s+1 = 4 L = 3 = F J = (L+s) to (L-s) = 2, 1, 0 Possible term symbols = ⁴F_9/2, ⁴F_7/2, ⁴F_5/2, ⁴F_3/2 The ground state term for V²⁺ is ⁴F_^3/2.

In a weak field ligand system the electron filling of splitting of d-orbital is corresponds to Hund’s rule, followed by pairing occur. In strong field ligand system the electron filling of splitting of d-orbital is corresponds to pairing at initial stage.For Fe³⁺ electronic configuration is d⁵. For d⁵ in weak field ligand system, CFSE = 3 (-4) + 2 (6) = -12 + 12 = 0Dq (All electrons is unpaired, 3 in t2g and 2 in eg) For d⁵ in strong field ligand system, CFSE = 5 (-4) + 0 = -20Dq + 2P (two paired electrons and one electron is unpaired in t_2g and 0 electron in _eg orbital) Hence, the CFSE for octahedral complexes of Fe³⁺ in a weak field and strong field ligand systems are 0 and -20 Dq+2P respectively.

(pi-C₅H₅)₂Ti has zero number of unpaired electrons and possesses diamagnetic nature.

(pi-C₅H₅)₂Ni and (pi-C₅H₅)₂V both have paramagnetic nature with 2 unpaired electrons respectively.(pi-C₅H₅)₂Cr has two unpaired electrons and has paramagnetic nature. Hence, these are identical in the number of unpaired electrons.

On the basis of ligand field theory, the spectrochemical series is an empirically-derived list of ligands ordered by the size of the splitting CFSE that they produce. It can be seen that the low-field ligands are all pi-donors, the high field ligands are pi-acceptors, and ligands such as H₂O and NH₃, which are are in the middle. The spectrochemical series is give as: I⁻ < Br⁻ < S²⁻ < SCN⁻ < Cl⁻ < NO₃⁻ < N₃⁻ < F⁻ < OH⁻ < C₂O₄²⁻ < H₂O < NCS⁻ < CH₃CN < py (pyridine) < NH₃ < en (ethylenediamine) < bipy (2,2'-bipyridine) < phen (1,10-phenanthroline) < NO₂⁻ < PPh₃ < CN⁻ < CO. Hence, S^2-, SCN^- and NO₃^- all are weak field ligands.

[FeF₆]^3- and [Mn(H₂O)₆]³⁺ both have sp³d² hybridisation, and hence  are outer orbital or high spin complexes.

The coordination complexes [Mn(H₂O)₆]²⁺, [(Ph₄As)₂Mn(NO₃)₄], [Mn(EDTA)(H₂O)]^2- and [Mn(S₂C₆H₃Me)₂]^- have the coordination numbers of 6, 8, 7 and 4 respectively. Hence, the representation of the codes P-5, Q-2, R-1, S-4 is the correct answer.

CO : 14 electrons CN^- : 14 electrons CO and  CN^-  are  isoelectronic.

In weak field ligand, the filling of electrons are in accordance with Hund’s rule. The CFSE is given by the formula: CFSE = value of t₂g (n) + value of eg (n) Dq, Fe³⁺ corresponds to the d⁵ configuration. Now, CFSE for Fe³⁺ (d⁵) = -4 (3) + 6 (2) = -12 + 12 = 0 Dq CFSE for Fe²⁺ (d⁶) = -4 (4) + 6 (2) = -16 + 12 = -4 Dq CFSE for Cr²⁺ (d⁴) = -4 (3) + 6 (1) = -12 + 6 = -6 Dq CFSE for Mn⁺ (d⁶) = -4 (4) + 6 (2) = -16 + 12 = -4 Dq CFSE for Mn³⁺ (d⁴) = -4 (3) + 6 (1) = -12 + 6 = -6 Dq Hence, the metal ion with zero CFSE is Fe³⁺ when it associated with weak field ligand.

In octahedral complexes, CFSE is given by the formula:  CFSE = value of t₂g (n) + value of eg (n) Dq Now, CFSE for low spin d⁴ = -4 (4) + 6 (0) = -16 + 0 = -16 Dq CFSE for high spin d⁴ = -4 (3) + 6 (1) = -12 + 6 = -6 Dq CFSE for low spin d⁵ = -4 (5) + 6 (0) = -20 + 0 = -20 Dq CFSE for high spin d⁵ = -4 (3) + 6 (2) = -12 + 12 = 0 Dq CFSE for low spin d⁷ = -4 (5) + 6 (2) = -20 + 12 = -8 Dq Hence, low spin d⁵ will give the maximum CFSE in an octahedral complex.

Fe₃O₄ and NiFe₂O₄ : Both are reverse spinels.

d⁸ ions form square planar complexes with strong field ligands. For example, [Ni(CN)₄]^2-
All the complexes of Pt(II) and Au(II) are square planar. For example, [PtCl₄]^2-

The oxidation state and the strength of the ligands determine the extent of crystal field splitting. The higher the oxidation state or the stronger the ligand, the larger will be the splitting. Ligands are classified as strong or weak based on the spectrochemical series: I^- < Br^- < Cl^- < SCN^- < F^- < OH^- < ox^2-< ONO^- < H₂O < SCN^- < EDTA^4- < NH₃ < en < NO₂^- < CN^- CN^-  is among one of the strongest field ligands. Crystal field splitting will be the highest in [Cr(CN)₆]^3-.