How can you tell if [ MnCl6]4- or [ Mn(CN)6 ] 4- has the longer wavelength of light? and then how do you figure out how many unpaired electrons each has?
To determine which of the two complexes, [MnCl6]4- or [Mn(CN)6]4-, has the longer wavelength of light, you need to consider the nature of the ligands and the field splitting effect.
1. Ligand nature: Ligands like chloride (Cl-) are weak-field ligands, whereas ligands like cyanide (CN-) are strong-field ligands. Strong-field ligands cause a larger splitting of the d-orbitals, resulting in higher energy transitions and shorter wavelength light absorption.
2. Field splitting effect: In a transition metal complex, the d-orbitals split into two sets due to the presence of ligands - one with lower energy (t2g) and one with higher energy (eg). The magnitude of this energy splitting determines the wavelength of light absorbed by the complex.
Using the above information, we can conclude that [MnCl6]4- has the longer wavelength of light because chloride is a weak-field ligand and causes a smaller energy splitting.
To determine the number of unpaired electrons in each complex, we need to examine the electron configuration of the manganese (Mn) ion.
The electronic configuration of a neutral Mn atom is [Ar] 3d5 4s2. In the complexes [MnCl6]4- and [Mn(CN)6]4-, Mn is in the +2 oxidation state, resulting in the loss of two electrons from the 4s orbital.
1. [MnCl6]4- complex: Chloride is a weak-field ligand, which results in a small spin-allowed energy gap between the t2g and eg orbitals. Electrons preferentially occupy the lower-energy t2g orbitals. Since Mn(II) has a d5 electron configuration, all five electrons occupy the t2g orbitals, and there are no unpaired electrons.
2. [Mn(CN)6]4- complex: Cyanide is a strong-field ligand, causing a large spin-forbidden energy gap between the t2g and eg orbitals. Electrons occupy the lower-energy t2g orbitals, while the higher-energy eg orbitals remain vacant. Since Mn(II) has a d5 electron configuration, three of the electrons occupy the t2g orbitals, leaving two unpaired electrons in the eg orbitals.
Therefore, [MnCl6]4- has zero unpaired electrons, while [Mn(CN)6]4- has two unpaired electrons.