Solution:
To determine which species exhibits both Ligand-to-Metal Charge Transfer (LMCT) and paramagnetism, we need to examine the electronic structure and bonding characteristics of each species.
Ligand-to-Metal Charge Transfer (LMCT): This occurs when an electron is transferred from a ligand orbital (usually nonbonding or occupied π orbitals) to an empty or partially filled metal d-orbital. For LMCT to occur, the metal should have accessible empty d-orbitals and the ligands must be capable of donating electrons.
Paramagnetism: A species is paramagnetic if it has one or more unpaired electrons. This can be determined using the electronic configuration of the metal center.
Let's analyze each given species:
Option A: MnO42−
In MnO42−, the oxidation state of Mn is +6 . The electron configuration of Mn in the +6 oxidation state is [Ar]3d^1. It has one unpaired electron, so it is paramagnetic. However, LMCT typically involves the transfer of electrons from ligands to the metal's empty d-orbitals. Since MnO42− is already in a high oxidation state, it is less likely to exhibit LMCT.
Option B: MnO4−
In MnO4−, the oxidation state of Mn is +7 . The electron configuration of Mn in +7 oxidation state is [Ar]3d∧0, which means there are no unpaired electrons. Therefore, it is diamagnetic. Additionally, it has empty d-orbitals, making it capable of exhibiting LMCT.
Option C: Cr2O72−
In Cr2O72−, each Cr is in the +6 oxidation state. The electron configuration of Cr in the +6 oxidation state is [Ar]3d∧0. Like MnO4−, there are no unpaired electrons, so it is diamagnetic. However, it can exhibit LMCT due to the presence of empty d-orbitals.
Option D: CrO42−
In CrO42−, the oxidation state of Cr is +6 . The electron configuration of Cr in the +6 oxidation state is also [Ar] 3d∧0. Therefore, it is diamagnetic. Similar to Cr2O72−, it can exhibit LMCT due to empty d-orbitals.
From the analysis, only MnO42− exhibits paramagnetism (due to one unpaired electron) while also being capable of LMCT. Thus, the correct answer is:
Option A: MnO42−.
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