MRI contrast agents are paramagnetic metal complexes often administered to patie

Question

MRI contrast agents are paramagnetic metal complexes often administered to patients undergoing magnetic resonance imaging (MRI). In order for these complexes to interact strongly with the strong magnetic field, it is important for them to have a very large ml, and therefore, a large number of unpaired electrons.

a. What is the maximum number of unpaired electrons for a transition metal ion?     
b. Which transition metal ion in the 2+ oxidation state has this number of unpaired electrons?     
c. Which transition metal ion in the 3+ oxidation state has this number of unpaired electrons?     
d. What is the maximum number of unpaired electrons for a lanthanide metal ion?     
e. Which lanthanide metal ion in the 3+ oxidation state has this number of unpaired electrons?  

Explanation / Answer

a. Since transition metals have the general electronic configuration of (n-1)d1-10ns2 , so according to the energy content order, the 2 s orbitals first fill up followed by 5 d orbitals. So, maximum unpaired electrons can arrange them in each t2g and eg orbitals without pairing, i.e. 3 t2g and 2 eg orbitals contain maximum 5 unpaired electrons.

b. The transition metal with ground state electronic configuration (n-1)d5 ns2 can let the electrons from outermost ns orbitals leave in order to form 2+ oxidation state. Hence, that gives the electronic configuration of the ion to be (n-1)d5, so that maximum number of unpaired electron remains without pairing in complexes with weak field ligands (with large energy gap between t2g and eg orbitals)

c. The transition metal with ground state electronic configuration (n-1)d6 ns2 can let the 2 electrons from outermost ns orbitals followed by 1 electron from the (n-1)d orbital to leave in order to form 3+ oxidation state. Hence, that gives the electronic configuration of the ion to be (n-1)d5, so that maximum number of unpaired electron remains without pairing in complexes with weak field ligands (with large energy gap between t2g and eg orbitals)

d. The lanthanide metals have the general electronic configuration of (n-2)f1-14 (n-1)d0-1 ns2. Since, there are 7 f orbitals (compared to 5d and 2s obitals) and unless the outer s and d orbitals are completely filled, the f orbitals do not start filling up (due to higher energy content); so, maximum 7 unpaired electrons can remain the the 7f orbitals.

First 4 questions are answered according to regulations of Chegg. Please post rest of the questions separately.

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