Textbook Question
In octahedral complexes, the choice between high-spin and low-spin electron configurations arises only for d4 - d7 complexes. Explain.
Ch.21 - Transition Elements and Coordination Chemistry
Chapter 21, Problem 123c
For each of the following, (i) give the systematic name of the compound and specify the oxidation state of the transition metal, (ii) draw a crystal field energy-level diagram and assign the d electrons to orbitals, (iii) indicate whether the complex is high-spin or low-spin (for d4 - d7 complexes), and (iv) specify the number of unpaired electrons.
(c) [Ni(NH3)4(H2O)2](NO3)2
Verified step by step guidance1
**Step 1:** Determine the systematic name of the compound. The complex ion is [Ni(NH_3)_4(H_2O)_2]^(2+). Nickel is the transition metal, and it is coordinated with four ammonia (NH_3) ligands and two water (H_2O) ligands. Ammonia and water are neutral ligands, so they do not affect the oxidation state of nickel. The overall charge of the complex ion is +2, and the nitrate ions (NO_3^-) are counterions. Therefore, the systematic name is tetraamminediaquanickel(II) nitrate.
**Step 2:** Determine the oxidation state of the transition metal. Since the complex ion has a charge of +2 and all ligands are neutral, the oxidation state of nickel is +2.
**Step 3:** Draw the crystal field energy-level diagram for the d orbitals. Nickel(II) has a d^8 electron configuration. In an octahedral field, the d orbitals split into two sets: the lower energy t_{2g} orbitals (d_{xy}, d_{xz}, d_{yz}) and the higher energy e_g orbitals (d_{x^2-y^2}, d_{z^2}).
**Step 4:** Assign the d electrons to the orbitals. For Ni(II) with a d^8 configuration, fill the t_{2g} orbitals first, then the e_g orbitals. The electron configuration in the crystal field is t_{2g}^6 e_g^2.
**Step 5:** Determine if the complex is high-spin or low-spin and specify the number of unpaired electrons. Since NH_3 is a weak field ligand, the complex is high-spin. In a high-spin d^8 configuration, there are two unpaired electrons in the e_g orbitals.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Coordination Compounds
Coordination compounds consist of a central metal atom bonded to surrounding molecules or ions called ligands. The nature of these ligands and their arrangement around the metal ion significantly influence the properties of the complex, including its geometry and electronic structure. Understanding the coordination number and the types of ligands is essential for naming the compound and determining the oxidation state of the metal.
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Coordination Compound Naming
Crystal Field Theory
Crystal Field Theory (CFT) explains the electronic structure of transition metal complexes by considering the effect of ligands on the d orbitals of the metal ion. According to CFT, the presence of ligands causes the degenerate d orbitals to split into different energy levels, which can be represented in a crystal field energy-level diagram. This theory helps predict the electronic configuration of the metal ion and the resulting magnetic properties of the complex.
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01:18The study of ligand-metal interactions helped to form Ligand Field Theory which combines CFT with MO Theory.
Spin States in Transition Metal Complexes
The spin state of a transition metal complex refers to the arrangement of electrons in the d orbitals, which can be either high-spin or low-spin. High-spin complexes have more unpaired electrons due to a weaker field strength of the ligands, while low-spin complexes have fewer unpaired electrons as a result of stronger field ligands causing greater splitting of the d orbitals. Determining the spin state is crucial for understanding the magnetic properties and reactivity of the complex.
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Related Practice
Textbook Question
For each of the following, (i) give the systematic name of the compound and specify the oxidation state of the transition metal, (ii) draw a crystal field energy-level diagram and assign the d electrons to orbitals, (iii) indicate whether the complex is high-spin or low-spin (for d4 - d7 complexes), and (iv) specify the number of unpaired electrons.
(a) (NH4)[Cr(H2O)6](SO4)2
Textbook Question
For each of the following, (i) give the systematic name of the compound and specify the oxidation state of the transition metal, (ii) draw a crystal field energy-level diagram and assign the d electrons to orbitals, (iii) indicate whether the complex is high-spin or low-spin (for d4 - d7 complexes), and (iv) specify the number of unpaired electrons. (d) K4[Os(CN)6]
Textbook Question
For each of the following, (i) give the systematic name of the compound and specify the oxidation state of the transition metal, (ii) draw a crystal field energy-level diagram and assign the d electrons to orbitals, (iii) indicate whether the complex is high-spin or low-spin (for d4 - d7 complexes), and (iv) specify the number of unpaired electrons.
(e) [Pt(NH3)4](ClO4)2
Textbook Question
For each of the following, (i) give the systematic name of the compound and specify the oxidation state of the transition metal, (ii) draw a crystal field energy-level diagram and assign the d electrons to orbitals, (iii) indicate whether the complex is high-spin or low-spin (for d4 - d7 complexes), and (iv) specify the number of unpaired electrons.
(f) Na2[Fe(CO)4]