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Ch.23 - Transition Metals and Coordination Chemistry
All textbooksBrown 14th EditionCh.23 - Transition Metals and Coordination ChemistryProblem 91a,d
Chapter 23, Problem 91a,d

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.

Verified step by step guidance
1
Identify the ligands in the coordination complex. In [Cr(CO)6], the ligand is carbon monoxide (CO), which is a neutral ligand.
Determine the charge of the ligands. Since CO is a neutral ligand, it contributes a charge of 0 to the complex.
Calculate the overall charge of the complex. [Cr(CO)6] is a neutral complex, meaning the sum of the oxidation state of chromium and the charges of the ligands is zero.
Set up the equation for the oxidation state of chromium. Let x be the oxidation state of chromium. Since the complex is neutral and CO is neutral, the equation is x + 6(0) = 0.
Solve for x to find the oxidation state of chromium. Since the equation simplifies to x = 0, the oxidation state of chromium in [Cr(CO)6] is 0. The name of the compound is hexacarbonylchromium(0).

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Key Concepts

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

Oxidation Number

The oxidation number is a measure of the degree of oxidation of an atom in a compound. It indicates the number of electrons that an atom can gain, lose, or share when forming chemical bonds. In coordination complexes, the oxidation state of the central metal ion can be determined by considering the charges of the ligands and the overall charge of the complex.
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Coordination Complex

A coordination complex consists of a central metal atom or ion bonded to surrounding molecules or ions known as ligands. The ligands can be neutral or charged and donate electron pairs to the metal, forming coordinate covalent bonds. The geometry and properties of the complex depend on the metal's oxidation state and the nature of the ligands.
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Nomenclature of Coordination Compounds

The nomenclature of coordination compounds follows specific rules established by the International Union of Pure and Applied Chemistry (IUPAC). The name typically starts with the ligands listed in alphabetical order, followed by the name of the metal with its oxidation state indicated in Roman numerals. For example, in [Cr(CO)6], 'carbonyl' is the ligand, and the name would be 'hexacarbonylchromium(0)' indicating the oxidation state of chromium.
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Related Practice
Open Question
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.
Open Question
Complete the exercises below. When Alfred Werner was developing the field of coordination chemistry, it was argued by some that the optical activity he observed in the chiral complexes he had prepared was due to the presence of carbon atoms in the molecule. To disprove this argument, Werner synthesized a chiral complex of cobalt that had no carbon atoms in it, and he was able to resolve it into its enantiomers. Design a cobalt(III) complex that would be chiral if it could be synthesized and that contains no carbon atoms. (It may not be possible to synthesize the complex you design, but we will not worry about that for now.)
Open Question
Complete the exercises below. Generally speaking, for a given metal and ligand, the stability of a coordination compound is greater for the metal in the +3 oxidation state rather than in the +2 oxidation state (for metals that form stable +3 ions in the first place). Suggest an explanation, keeping in mind the Lewis acid–base nature of the metal–ligand bond.
Textbook Question

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

c. Given that [Cr(CO)6] is colorless, would you expect CO to be a weak-field or strong-field ligand?

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