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Ch.23 - Transition Metals and Coordination Chemistry
All textbooksBrown 14th EditionCh.23 - Transition Metals and Coordination ChemistryProblem 87
Chapter 23, Problem 87

Complete the exercises below. In 2001, chemists at SUNY-Stony Brook succeeded in synthesizing the complex trans-[Fe(CN)₄(CO)₂]²⁻, which could be a model of complexes that may have played a role in the origin of life. a. Sketch the structure of the complex. b. The complex is isolated as a sodium salt. Write the complete name of this salt. c. What is the oxidation state of Fe in this complex? How many d electrons are associated with the Fe in this complex? d. Would you expect this complex to be high spin or low spin? Explain.

Verified step by step guidance
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Step 1: To sketch the structure of the complex trans-[Fe(CN)_4(CO)_2]^2-, start by identifying the central metal atom, which is Fe (iron). The ligands are four cyanide ions (CN^-) and two carbonyl groups (CO). Arrange these ligands around the Fe atom in a trans configuration, meaning the two CO ligands are opposite each other.
Step 2: To name the sodium salt of the complex, recognize that the complex ion is trans-[Fe(CN)_4(CO)_2]^2-. Since it is isolated as a sodium salt, the full name would be sodium trans-tetracyanodicarbonylferrate(II). The 'ferrate' indicates the presence of iron in an anionic complex, and the Roman numeral indicates the oxidation state of iron.
Step 3: Determine the oxidation state of Fe in the complex. The overall charge of the complex is 2-. Each CN^- ligand has a charge of -1, and CO is neutral. Set up the equation: x + 4(-1) + 2(0) = -2, where x is the oxidation state of Fe. Solve for x to find the oxidation state.
Step 4: To find the number of d electrons associated with Fe, use the oxidation state determined in the previous step. Iron's electron configuration is [Ar] 3d^6 4s^2. Subtract the electrons lost due to the oxidation state from the total d electrons in the neutral atom.
Step 5: Determine if the complex is high spin or low spin. Consider the ligands present: CN^- is a strong field ligand, which typically leads to low spin configurations due to the large splitting of d orbitals. Explain how the ligand field strength affects the electron pairing in the d orbitals.

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Coordination Complexes

Coordination complexes consist of a central metal atom or ion bonded to surrounding molecules or ions called ligands. The arrangement and type of ligands influence the properties and reactivity of the complex. In the case of trans-[Fe(CN)₄(CO)₂]²⁻, the ligands CN⁻ and CO are crucial for determining the electronic structure and stability of the complex.
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Oxidation States

The oxidation state of an element in a compound indicates the degree of oxidation of that element, reflecting the number of electrons lost or gained. In the complex trans-[Fe(CN)₄(CO)₂]²⁻, determining the oxidation state of iron (Fe) involves considering the charges of the ligands and the overall charge of the complex, which is essential for understanding its electronic configuration.
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Spin States in Transition Metal Complexes

Spin states refer to the arrangement of electrons in the d-orbitals of transition metal complexes, which can be classified as high spin or low spin. High spin complexes have unpaired electrons in higher energy orbitals, while low spin complexes have paired electrons in lower energy orbitals. The nature of the ligands, such as whether they are strong or weak field ligands, influences whether a complex will be high spin or low spin.
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Related Practice
Textbook Question

The coordination complex [Cr(CO)6] forms colorless, diamagnetic crystals that melt at 90 °C

a. What is the oxidation number of chromium in this compound?

d. Write the name for [Cr(CO)6] using the nomenclature rules for coordination compounds.