Question

The drug Nipride, \(\mathrm{Na}_{2}\left[\mathrm{Fe}(\mathrm{CN})_{5} \mathrm{NO}\right]\), is an inorganic complex used as a source of \(\mathrm{NO}\) to lower blood pressure during surgery. (a) The nitrosyl ligand in this complex is believed to be \(\mathrm{NO}^{+}\) rather than neutral NO. What is the oxidation state of iron, and what is the systematic name for \(\mathrm{Na}_{2}\left[\mathrm{Fe}(\mathrm{CN})_{5} \mathrm{NO}\right] ?\) (b) Draw a crystal field energy-level diagram for \(\left[\mathrm{Fe}(\mathrm{CN})_{5} \mathrm{NO}\right]^{2-}\), assign the electrons to orbitals, and predict the number of unpaired electrons.

Short answer

Fe oxidation state: +2; systematic name: sodium pentacyanonitrosylferrate(II); unpaired electrons: 0.

Step-by-step solution

Determine Oxidation State of Ligands

The ligands present in the complex are cyanide ( CN) and nitrosyl (NO⁺). Cyanide is a monodentate ligand with a charge of -1, and for NO⁺, typically it can be assumed as having a +1 charge as given by the problem.

Calculate Oxidation State of Iron

Consider the charge balance in the complex. The formula given is Na₂[Fe(CN)₅NO]. The nitrate anion complex [Fe(CN)₅NO] will have a 2- charge, as the two Na⁺ ions balance this charge overall. Therefore, the equation for the net charge is: \[ x + 5(-1) + 1 = -2 \] where \( x \) is the oxidation state of Fe. Solving, we find: \[ x - 5 + 1 = -2 \] \[ x - 4 = -2 \] \[ x = +2 \] So, the oxidation state of the iron is +2.

Systematic Naming of the Complex

Now, name the complex. The full name is "sodium pentacyanonitrosylferrate(II)". This name reflects the oxidation state of iron and the ligands present.

Understand Crystal Field Theory Basic Concepts

In crystal field theory, we consider the splitting of the d orbitals in transition metal complexes. For a complex with symmetry similar to [Fe(CN)₅NO]^2-, the CN ligands and NO will cause splitting, and you'll use a simple approach to finding how the d electrons fill these levels.

Construct Crystal Field Diagram

Construct a crystal field diagram which shows the splitting of the d orbitals. In a pentacoordinate complex with low symmetry dt orbitals might split into different energy levels.

Assign Electrons in the Crystal Field Diagram

Fe²⁺ has a configuration of 3d⁶. Place these six electrons into the d orbitals following Hund's rule and the crystal field splitting diagram predicted for square pyramidal symmetry, typically t^2g_x e_y arrangement shows large splitting in magnitude. Assume it forms a low spin configuration:

Determine the Number of Unpaired Electrons

Since CN and NO⁺ are strong field ligands, they will form a low-spin complex where electron pairing will occur (e.g., t^2g4 and e) resulting in all electrons being paired in Fe²⁺ in the low field configuration splitting.

Key concepts

Oxidation State

In transition metal complexes, understanding the oxidation state of the central metal is crucial, as it influences chemical behavior and properties. Let's take a look at the oxidation state of iron in the complex Nipride, \(\mathrm{Na}_{2}[\mathrm{Fe}(\mathrm{CN})_{5}\mathrm{NO}]\). The formula suggests that the complex has two sodium ions which balance out a 2- charge.To determine the oxidation state, we need to know the charges of the ligands.

• Cyanide (\(\mathrm{CN}^{-}\)): Each cyanide has a charge of -1.
• Nitrosyl (\(\mathrm{NO}^{+}\)): The problem specifies this as a \(+1\) charge.

Calculating the oxidation state of iron involves balancing these charges to achieve the overall -2 charge of the complex:\[ x + 5(-1) + 1 = -2 \]Solving this, we find \(x = +2\). Thus, the oxidation state of iron is \(+2\). Understanding the oxidation state helps us in predicting reactivity and systematic naming, which in this case is "sodium pentacyanonitrosylferrate(II)." This signifies we have iron in the +2 oxidation state.

Crystal Field Theory

Crystal field theory is an essential concept for understanding the behavior of metal ions in coordination complexes. It describes how the degenerate (same energy) d orbitals of a metal ion split into different energy levels when ligands, like cyanide and nitrosyl, are coordinated around the metal ion.For a complex like \([\mathrm{Fe}(\mathrm{CN})_{5} \mathrm{NO}]^{2-}\), the strong field ligands \(\mathrm{CN}^{-}\) and \(\mathrm{NO}^{+}\) lead to significant splitting of iron’s d orbitals. Normally, these d orbitals are degenerate, but their interactions with the point charges of the ligands cause them to split. Different arrangements of ligands, profoundly affected by their geometry, impact the exact pattern of splitting. Due to their strong field, \(\mathrm{CN}^{-}\) and \(\mathrm{NO}^{+}\) form a low-spin complex which results in fewer unpaired electrons, a feature that influences the complex's magnetic and electronic properties.

Coordination Chemistry

Coordination chemistry focuses on the structures and properties of complexes formed between ligands and metal ions. These complexes, like \(\mathrm{Na}_{2}[\mathrm{Fe}(\mathrm{CN})_{5}\mathrm{NO}]\), involve a central metal atom surrounded by molecules or ions, termed ligands.In our example, iron is the central metal, and it's coordinated to five \(\mathrm{CN}^{-}\) and one \(\mathrm{NO}^{+}\) ligand. This specific arrangement is crucial because:

• Coordination Number: Refers to the number of ligand atoms bonded directly to the metal, which in this case is six.
• Geometry: The bonding leads to specific spatial arrangements. Here, the geometry appears as square pyramidal—significant for determining the complex’s properties.

Coordination compounds are vital in chemistry because they exhibit unique properties including color, magnetism, and biological activity. Understanding these features and how they emerge from metal-ligand interactions aids in applications ranging from catalytic transformations to medicine.