Question

The IUPAC name of the coordination compound \(\mathrm{K}_{3}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]\) is (a) potassium hexacyanoferrate (II) (b) potassium hexacyanoferrate (III) (c) potassium hexacyanoiron (II) (d) ripotassium acyanoiron (II)

Short answer

The IUPAC name is Potassium Hexacyanoferrate (III) (option b).

Step-by-step solution

Identify the Central Metal and its Oxidation State

First, identify the central metal atom in the complex. In this case, it's iron (Fe). Next, determine the oxidation state of iron. The cyanide ion (CN) has a charge of 6. Since there are six CN 7 ions, they contribute a total charge of 6. The compound has a charge of 3 (from K due, as potassium has a +1 charge and there are three of them). Therefore, the charge on the [Fe(CN) ] complex must be 3, so Fe must be in the +3 oxidation state to balance these out.

Understand the Coordination Complex Naming Rules

When naming coordination compounds, certain rules must be followed. The ligands are named first in alphabetical order regardless of their charge (here, it's 'cyan-', derived from cyanide), followed by the metal ('ferrate' for iron when it is part of an anion complex). An oxidation state is appended in Roman numerals in parentheses, such as Iron(III), because we have Fe^(+3) as found in Step 1.

Determine the Role of Potassium and Finalize the Compound Name

The potassium cation is a spectator ion balancing the charge of the anionic complex. Thus, it is written first in the name. Then, combine these parts for the complete IUPAC name: Potassium Hexacyanoferrate(III).

Key concepts

IUPAC nomenclature

IUPAC nomenclature is a systematic way to name chemical compounds, ensuring clarity and uniformity. In coordination compounds, the nomenclature rules have specific steps to follow. First, one must list the ligands attached to the central metal in alphabetical order. Ligands are named using specific suffixes like 'cyano' for cyanide (CN). Any prefixes indicating the number of ligands, such as 'hexa' for six, precede the ligand's name.
The central metal's name follows the ligands, using its usual name if the complex is cationic or neutral. However, 'ate' is added to the metal name if the complex is anionic. The oxidation state of the metal is specified in Roman numerals in parentheses. So for the compound \( \mathrm{K}_{3}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right] \), following these rules gives us the name: Potassium Hexacyanoferrate (III).

oxidation states

Understanding oxidation states is vital in describing how electrons are distributed around a molecule or ion in coordination compounds. The oxidation state of an element in a compound gives insight into its electron count and how it interacts with other atoms.
To calculate the oxidation state of the central metal in a coordination compound like \[ \mathrm{K}_{3}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right] \], consider the charges on the ligands and the whole molecule. Here, cyanide (CN) carries a \(-1\) charge. With six cyanides and the complex having a \(-3\) charge overall, the iron must have a +3 oxidation state to balance the charges when including the outer potassium ions. Understanding these calculations helps determine how the metal ion and the ligands combine to form a stable structure.

transition metals

Transition metals are fascinating elements located in the central block of the periodic table. They are characterized by their ability to form multiple oxidation states and complex ions. Elements like iron (Fe), which is central in compounds like \( \mathrm{K}_{3}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right] \), are transition metals because their electron configuration includes partially filled \(d\) orbitals.
This unique property allows them to form vibrant colored compounds, crucial industrial catalysts, and significant in biological systems. The variable oxidation states of transition metals enable them to form multiple different compounds with unique properties, adding complexity and versatility to chemical reactions and processes.

ligands and complexes

Ligands are essential components of coordination compounds, consisting of ions or molecules that donate a pair of electrons to a central metal, forming coordinate covalent bonds. They are key to the structure and properties of coordination complexes. Depending on the number of coordination sites available, they can be monodentate (one donor site), bidentate (two donor sites), or even polydentate, like in ethylenediamine (en).
The nature of the ligand affects the geometry, reactivity, and overall stability of the complex. In \( \mathrm{K}_{3}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right] \), cyanide ions, which are monodentate ligands, contribute to a stable complex as they form strong field ligands, leading to low spin states in the Fe(III) ion. This specific arrangement and interaction with the central metal create distinct geometries and properties observable in various applications of coordination chemistry.