Coordination Compounds Test - 8

Cation is named first and then the anion separated by a space. In a coordination complex, name of ligand is written first then the central metal atom/ion with its oxidation state in the parenthesis in roman numerals is mentioned. If the complex is an anion then -ate is added to the name of the central metal atom/ion. Here there are 3 K⁺ ions so cations have a charge of +3. So overall charge on the complex anion is -3. Now each oxalate ion carries -2 charge and there are 3 oxalate ligands attached to aluminium. Let oxidation state of Al be x.
x + 3(-2) = -3
x - 6 = -3
x = -3 + 6 = +3

So, oxidation state of Al=+3

So, the name of the complex is Potassium trioxalatoaluminate(III)

Na₂[Fe(CN)₅NO] i.e. Sodium pentacyanonitrosylferrate(II) is also called Sodium nitroprusside.

SCN^{​​​​-} is an ambidentate ligand i.e it can bind through two different donor atoms, either through S in SCN^{​​​​-} or through N in NCS^{​​​​-} . So it shows linkage isomerism which arises when an ambidentate ligand is present in the complex.

This is a confirmatory test to detect Fe⁺³ ion in unknown sample. Ferric chloride combines with potassium ferrocyanide solution to give blue precipitate of potassium ferri ferrocyanide.
FeCl₃(aq) + K₄[Fe(CN)₆] (aq) →→ KFe[Fe(CN)₆](s) + 3KCl(aq)

On getting ionised this complex gives 3 Cl^{​​​​​-} (ions outside the square brackets are ionisable) and a [Pt(NH_{​​​​​3})₃Cl]⁺ i.e. 4 ions are produced per molecule of the compound.

In this complex there are 6 CN^- ligands means a total of -6 charge on ligands. There is a charge of -3 on the complex so oxidation state of Fe is +3. Atomic number of Fe is 26. So the electronic configuration of Fe⁺³ is 1s²2s²2p⁶3s²3p⁶3d³.Coordination number of the metal is 6 so the complex has octahedral geometry and since CN ^- is a strong field ligand so it causes pairing and hence inner orbital complex is formed. So the hybridization is d ² sp ³.

dsp² hybridisation results in a square planar geometry.

The complex of Fe with CO ligand is [Fe(CO)₅] i.e. pentacarbonyliron(0). So the value of x =5.

Iron (Z=26) has an electronic configuration 1s²2s²2p⁶3s²3p⁶3d⁶4s². CO being a strong field ligand, causes pairing of electrons in the d orbital and shifting of 4s electrons to 3d orbital. With a coordination number 5 it results in sp ³ d hybridisation and hence a trigonal bipyramidal geometry.

In given complex, there are 3 K⁺ ions and so the anion has overall -3 charge. In [Fe(CN)₆]^3-, there are 6CN^- ligands and an overall charge of -3 on the complex and hence Fe is in +3 oxidation state so its electronic configuration is 1s²2s²2p⁶3s²3p⁶3d⁵. Since CN ^- is a strong field ligand and it causes pairing of electrons. But there is one unpaired electron which makes this complex paramagnetic.