7of 17 Pairing energy and splitting energy The energy difference between d orbit

Question

7of 17 Pairing energy and splitting energy The energy difference between d orbitals is called the splitting energy, A, and will vary depending on the ligand Ligands that cause largeA values are said to be strong-field ligands, those that cause smaller ? values are said to be weak-field ligands. In an octahedral complex with a large A, the electrons will ll the lower energy d orbitals before any electrons are placed in the higher energy d orbitals, and so the complex is classified as low spin. In an octahedral complex with a small ?, however, the electrons will fill as if the d orbitals are degenerate because the pairing energy exceeds the splitting energy. In this situation, the higher energy d orbitals become populated sooner, and the complex is classified as high spin. The field strength of the ligand, which affects A determines whether an octahedral complex is low spin or high spin. A tetrahedral complex will always be high spin because A is relatively small even with a strong-field ligand Thus, even though the d orbitals are split, electrons will fill as if the d orbitals are degenerate. A square planar complex will almost always be low spin because A is relatively large even with a weak- field ligand Part A Consider a metal ion with the outer electron configuration of d' In a coordination complex, the number of unpaired electrons in that metal ion depends on the orientation and type of ligands that surround it. Classify each description of a complex by the number of unpaired electrons in the d' metal ion Dra? the appropriate items to their respective bins

Explanation / Answer

Part A: When the metal has d4 configuration with the followoing unpaired electrons, it would have the geamoetry as indicated:

No of unpaired Electrons: 4 : Octahedral weak field, Tetrahedral Strong field and weak field

No of unpaired Electrons: 2 : Octahedral string field

No of unpaired Electrons: 0 : Square planar Strong nad weak fields

Part B: [MnCl6]4-, 6 Cl- corresponds to charge of 6-, and sice the total charge is 4- Mn should be+2. Electronic configuration of Mn: 4s23d5, so Mn2+ would be 3d5. Cl- is a weak filled ligand so ?oct is small and cmplx will have a high spin. So the 5 electrons would occupy each of the t2g and eg orbitals in the following manner: t2g (?)(?)(?)??oct? (?)(?) eg, which makes a total of five unpaired electrons.

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