Question

Carbon monoxide, \(\mathrm{CO}\), is an important ligand in coordination chemistry. When \(\mathrm{CO}\) is reacted with nickel metal the product is \(\left[\mathrm{Ni}(\mathrm{CO})_{4}\right]\), which is a toxic, pale yellow liquid. (a) What is the oxidation number for nickel in this compound? (b) Given that \(\left[\mathrm{Ni}(\mathrm{CO})_{4}\right]\) is diamagnetic molecule with a tetrahedral geometry, what is the electron configuration of nickel in this compound? (c) Write the name for \(\left[\mathrm{Nu}(\mathrm{CO})_{4}\right]\) using the nomenclature rules for coordination compounds.

Short answer

The oxidation number of Nickel in the compound \(\left[\mathrm{Ni}(\mathrm{CO})_{4}\right]\) is 0. The electron configuration of Nickel in the complex is Ni in \([\mathrm{Ar}]\ 3d^8(\mathrm{sp^3-d^4})^4\ 4s^0\). The name of the coordination compound is Tetracarbonylnickel.

Step-by-step solution

(a) Oxidation number of Nickel

To determine the oxidation number of Nickel in the compound, we must look at the individual components of the complex. Carbon monoxide (CO) acts as a neutral ligand, meaning it doesn't contribute to the charge of the coordination compound or change the overall oxidation state of the metal. Since the overall charge of the complex \(\left[\mathrm{Ni}(\mathrm{CO})_{4}\right]\) is neutral (no charge), this implies that the oxidation number of Nickel in this compound is 0.

(b) Electron configuration of Nickel

Now we need to figure out the electron configuration of the nickel in the coordination complex. In its natural state, the electron configuration of nickel is \([\mathrm{Ar}]\ 3d^8\ 4s^2\). The coordination of the ligands to the metal (in this case, CO to Ni) results in the rearrangement of electrons within the d- and s-orbitals. According to the problem, the geometry of the complex is tetrahedral and the molecular description is provided as diamagnetic. The provided molecule consists of nickel and four carbon monoxide ligands, hinting at the need for 4 d-orbitals to accommodate the bonding interactions. In a tetrahedral geometry, these orbitals are characterized as \(3d_{z^2}, 3d_{x^2-y^2}, 3d_{xy},\) and \(3d_{xz}\). Since the complex is diamagnetic, meaning there are no unpaired electrons, the electron configuration of nickel can be written as: Ni in \([\mathrm{Ar}]\ 3d^8(\mathrm{sp^3-d^4})^4\ 4s^0\)

(C) Name of the coordination compound

To name the given complex, \(\left[\mathrm{Ni}(\mathrm{CO})_{4}\right]\), we first consider the rules of nomenclature for coordination compounds: 1. Ligands are named before the central metal. 2. The ligand names are arranged in alphabetical order. 3. Numerical prefixes (e.g., di-, tri-, etc.) are used to indicate the number of ligands, but are omitted if there is only one ligand of that type. 4. For the central metal, we use the Latin name of the element and add the suffix "-ate" if the complex is negatively charged. In this case, there is no charge, and we simply use the Latin name. In this complex, there are four carbon monoxide ligands, which are named carbonyl. Following the nomenclature rules, the name of the coordination compound \(\left[\mathrm{Ni}(\mathrm{CO})_{4}\right]\) is: Tetracarbonylnickel

Key concepts

Oxidation State

In coordination chemistry, determining the oxidation state of the metal center within a coordination compound is an essential step. This involves understanding how different ligands contribute to the overall charge of the compound. For the coordination compound \([\text{Ni}( ext{CO})_4]\), one must consider the properties of the ligand, carbon monoxide (CO). Carbon monoxide acts as a neutral ligand, meaning it does not have a charge and does not affect the oxidation state of the nickel center.

The entire complex \([\text{Ni}( ext{CO})_4]\) is neutral, implying there is no net charge on the compound. Therefore, the oxidation state of nickel in this compound is 0. This conclusion is particularly straightforward in this case, as nickel doesn’t gain or lose electrons when bonded to neutral CO ligands, maintaining its elemental oxidation state.

Electron Configuration

Electron configurations give insight into the electron distribution in an atom or ion's orbitals. For transition metals like nickel, coordination in complexes can adjust their electron configuration. In its ground state, the electron configuration for nickel is \([\text{Ar}]\ 3d^8\ 4s^2\).

When forming a coordination compound with carbon monoxide, the electron distribution alters. The complex \([\text{Ni}( ext{CO})_4]\) has a tetrahedral geometry, where the energies of the d-orbitals are affected by the ligand field created by the CO ligands. Given this coordination environment and the nature of the ligands, the electron configuration remains close to \(3d^{10}\ 4s^0\) after rearrangement. Since the complex is diamagnetic, meaning there are no unpaired electrons, electrons pair up within these orbitals.

• Configuration becomes \([\text{Ar}]\ 3d^{10}\ 4s^0\).
• All the d-orbitals accommodate paired electrons.

This specific electron arrangement is influenced by the tetrahedral coordination and results in paired electrons, explaining the observed diamagnetism of the compound.

Coordination Compound Nomenclature

Naming coordination compounds can seem daunting, but following standard nomenclature rules simplifies the process. These rules are critical in correctly identifying the structure and constituents of a coordination complex like \([\text{Ni}( ext{CO})_4]\).

The first rule in naming such compounds is to list the ligand names before the central metal atom. For our compound, the ligand is carbon monoxide, referred to as carbonyl in the nomenclature of coordination chemistry. The number of identical ligands present is indicated by prefixes such as mono-, di-, tri-, etc. However, these are omitted if only one type is present multiple times, and numeral prefixes like 'tetra-' indicate the number of carbonyls.

• Ligand: Carbon monoxide (CO), called carbonyl.
• Indicate four carbonyl ligands with 'tetra'.

The next part of the name reflects the central metal. Since the complex is not an anion, the metal's Latin-based name, nickel, is used directly. Thus, the full name of \([\text{Ni}( ext{CO})_4]\) becomes Tetracarbonylnickel, accurately describing the complex's structure.