Question

What is the systematic name for each of the following coordination compounds? (a) \(\mathrm{Cs}\left[\mathrm{FeCl}_{4}\right]\) (b) \(\left[\mathrm{V}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]\left(\mathrm{NO}_{3}\right)_{3}\) (c) \(\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{4} \mathrm{Br}_{2}\right] \mathrm{Br}\) (d) \(\mathrm{Cu}(\mathrm{gly})_{2}\)

Short answer

(a) Cesium tetrachloridoferrate(III) (b) Hexaquavanadium(III) nitrate (c) Tetraamminedibromocobalt(III) bromide (d) Bis(glycinato)copper(II).

Step-by-step solution

Naming Components (a)

First, identify the components in the complex \( \mathrm{Cs}\left[\mathrm{FeCl}_{4}\right] \). The complex anion \([\mathrm{FeCl}_{4}]^{-}\) consists of iron and four chloride ions. Since iron is a metal in a negative complex, the suffix '-ate' is used in its name. The oxidation state of iron can be calculated by setting the overall charge of the complex to match the charge of the Cs cation, which is +1. Therefore, the charge on the complex anion is -1, and since each chloride ion is -1, iron must be +3. The systematic name is thus cesium tetrachloridoferrate(III).

Naming Components (b)

Consider \( \left[\mathrm{V}\left(\mathrm{H}_{2}\mathrm{O}\right)_{6}\right]\left(\mathrm{NO}_{3}\right)_{3} \). The complex cation \([\mathrm{V(H_{2}O})_{6}]^{3+}\) contains vanadium and six water molecules (aqua ligands). Since the complex cation has a charge of +3, the oxidation state of vanadium is +3. The ligands, being water, are neutral. Therefore, the formula has vanadium(III) hexaquo as the name for the cation part, followed by the counter-ion nitrate as simply 'nitrate'. The systematic name is hexaquavanadium(III) nitrate.

Naming Components (c)

Examine \( \left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{4} \mathrm{Br}_{2}\right]\mathrm{Br} \). The complex cation \([\mathrm{Co(NH}_{3})_{4} \mathrm{Br}_{2}]^{+}\) includes cobalt, four ammine ligands, and two bromide ligands. The overall charge +1 indicates cobalt's oxidation state must be +3 (since each ammonia is neutral and each bromine ion is -1). Cyanide uses the prefix 'amine' in IUPAC nomenclature. This gives us tetraammine dibromo cobalt(III) for the cation, followed by the counter-ion bromide. Thus, the systematic name is tetraamminedibromocobalt(III) bromide.

Naming Components (d)

For \( \mathrm{Cu}(\mathrm{gly})_{2} \), the ligand is glycinate (gly), a bidentate ligand derived from glycine, an amino acid. Since \( \mathrm{Cu} \) often forms +2 complexes, it can be assumed that the copper here is in the +2 oxidation state. With two glycinate ligands, the name becomes bis(glycinato)copper(II).

Key concepts

Systematic Naming

Systematic naming in coordination chemistry involves naming complex compounds following a structured set of rules established by the International Union of Pure and Applied Chemistry (IUPAC). This ensures clarity and consistency in chemical communication. To systematically name a coordination compound, you start by identifying the ligands and the central metal atom or ion. Each part of the compound is named systematically: the names of the ligands are stated first, followed by the name of the central metal.

• Ligands are named in alphabetical order, regardless of their charge status (neutral, positive, or negative).
• If a ligand is an anion, its name typically ends with 'o' (e.g., chloride becomes chlorido), while neutral ligands often have specific names (e.g., water is aqua).
• The metal's name in a complex anion ends with '-ate', and in the case of multiple oxidation states, Roman numerals indicate the oxidation state.

Breaking down the naming process helps in understanding how to approach each coordination compound systematically.

Oxidation States

Oxidation states indicate the degree of oxidation of an atom within a compound or ion. In coordination compounds, determining the oxidation state of the central metal is crucial, as it influences the chemical properties and reactivity of the compound. To determine the oxidation state:

• Calculate the overall charge of the complex by summing up the charges of all ligands and the central metal. Generally, the charge of the entire complex is denoted next to it in parentheses.
• For each ligand, use known charges (e.g., \( -1 \) for chloride, neutral for ammonia).
• Deduce the oxidation state of the central metal by balancing the overall charge.

Understanding oxidation states is essential for predicting how coordination compounds will interact in chemical reactions, and it is an important factor in the nomenclature of these compounds.

Coordination Compounds

Coordination compounds form when metal ions bond to ligands through coordination bonds. These compounds are central to coordination chemistry, where the metal atom acts as the coordination center. The ligands, which are ions or molecules capable of donating an electron pair, surround this center. Coordination compounds are characterized by:

• A central metal ion, termed as the coordination center, often a transition metal due to its ability to accommodate multiple bonds.
• Coordination numbers, which refer to the number of bonds formed between the central metal and its ligands. These determine the geometry, which can be octahedral, tetrahedral, or square planar, depending on the number and arrangement of ligands.
• Diverse properties and applications, such as catalysis, biological systems (e.g., hemoglobin), and material science (e.g., pigments).

Gaining a strong understanding of coordination compounds is critical in grasping their wide-ranging applications and functionality in various chemical contexts.

IUPAC Nomenclature

The IUPAC nomenclature provides a systematic way of naming chemical compounds, including coordination compounds, ensuring consistency across the scientific community. This system is essential for clear communication in chemistry. The rules for naming coordination compounds according to IUPAC include:

• List ligands alphabetically before the central metal. Ligands can be anionic, neutral, or cationic, and have corresponding naming conventions, like 'ammine' for ammonia, or 'cyano' for cyanide.
• The name of the metal follows the ligands, and if in a complex anion, it ends in '-ate'. Include the oxidation state in Roman numerals.
• If a compound has a cationic part and an anionic counterpart, the cation is named first.

These rules allow for the construction of a systematic name that reflects the composition and structure of the compound, invaluable for scientists and students in identifying and discussing chemical substances.