The value of the magnetic moment will be independent of temperature for

(acac = acetylacetonato; OAc = acetate; o-phen = o-phenathroline; Pz = pyrazolyl)

Concept:

• The magnetic moment or magnetic dipole moment is the measure of the tendency of the object to align with a magnetic field. ​The magnetic moment has contributions from spin and orbital angular momentum.
• For a metal complex, the spin-only magnetic moment value can be calculated by using the formula:

​\({\rm{\mu = }}\sqrt {{\rm{n(n + 2)}}} {\rm{ B}}{\rm{.M}}\) , where n is the number of unpaired electrons and B.M is Bohr magneton a unit of the magnetic moment.

• For an octahedral complex, orbital contributions are possible only from the t2g orbital.
• The t_2g orbital will contribute to the magnetic moment only when it is singly or doubly degenerate.
• On raising the temperature ground state electrons goes to exited state and the exited state can contribute to the magnetic mommet.
• The excited state will contribute to the magnetic moment only when,

\(\Delta S=0\)

Explanation:

For the complex [Fe(acac)3], the oxidation state of Fe is +3.

• The ground-state electronic configuration of Fe (III) is

​\({t_{2g}}^3{e_g}^2\) (n = 5)

where, n is the number of unpaired electrons in the system.

• Octahedral complexes with a half-filled configuration will give no orbital contribution in magnetic moment.
• On excitation of the ground state, the electronic configuration will be

​\({t_{2g}}^2{e_g}^3\) (n=3)

• As, on excitation, the spin state changes and does not follow \(\Delta S=0\). It will not contribute to the magnetic moment.
• Thus, the magnetic moment is independent of temperature for [Fe(acac)3].

In the complex [Cu2(OAc)4(H2O)2], the oxidation state of Cu is +2. 

• The electronic configuration of Cu(II) is 

\({t_{2g}}^6{e_g}^3\) (n=1)

• On excitation of the ground state, the electronic configuration will be

\({t_{2g}}^5{e_g}^4\) (n=1)

• As, on excitation, the spin state does not changes and does follows \(\Delta S=0\). It will contribute to the magnetic moment.
• Thus, the magnetic moment is dependent of temperature for [Fe(acac)3].

In the complex [Fe(o-phen)2)(NCS)2] and [Fe{HC(3,5-Me2Pz)3}2]2+, the oxidation state of Fe is +2. The electronic configuration of Fe(II) is 

​\({{e}^3t_{2}^3}\) (n=4)

• On excitation of the ground state, the electronic configuration will be

\({{e}^2t_{2}^4}\) (n=4)

• As, on excitation, the spin state does not change and does follows \(\Delta S=0\). It will contribute to the magnetic moment.
• Thus, the magnetic moment is dependent of temperature for [Fe(o-phen)2)(NCS)2] and [Fe{HC(3,5-Me2Pz)3}2]2+.

​​Conclusion:

• Hence, the value of magnetic moment will be independent of temperature for [Fe(acac)3].