Question

Write appropriate formulas for the following. (a) potassium hexacyanoferrate(III) (b) bis(ethylenediamine)copper(II) ion (c) pentaaquahydroxoaluminum(III) chloride (d) amminechlorobis(ethylenediamine) chromium(III) sulfate (e) tris(ethylenediamine)iron(III) hexacyanoferrate(II)

Short answer

The chemical formulas for these compounds are (a) \( K_3[Fe(CN)_6] \) (b) \( [Cu(C_2H_8N_2)_2]^{2+} \) (c) \( [Al(H_2O)_5OH]Cl_2 \) (d) \( [Cr(NH_3)(C_2H_8N_2)_2]SO_4 \) (e) \( [Fe(C_2H_8N_2)_3]_2[Fe(CN)_6] \).

Step-by-step solution

Potassium hexacyanoferrate(III)

In potassium hexacyanoferrate(III), 'potassium' indicates the K+. 'Hexacyanoferrate(III)' is ion containing Fe with an oxidation state of +3 and six cyanide ions. Thus, the formula is \( K_3[Fe(CN)_6] \).

bis(ethylenediamine)copper(II) ion

In bis(ethylenediamine)copper(II) ion, 'bis' indicates we have 2 ethylenediamine molecules. Copper(II) means we have a Cu2+. So, the formula is \( [Cu(C_2H_8N_2)_2]^{2+} \).

Pentaaquahydroxoaluminum(III) chloride

In pentaaquahydroxoaluminum(III) chloride, 'pentaaqua' indicates five water molecules. 'Hydroxo' refers to one hydroxide group. 'Aluminum(III)' suggests we have Al in +3 oxidation state. 'chloride' is just Cl-. Hence, the formula is \( [Al(H_2O)_5OH]Cl_2 \).

Amminechlorobis(ethylenediamine)chromium(III) sulfate

In amminechlorobis(ethylenediamine)chromium(III) sulfate, 'ammine' refers to one group of ammonia, while 'chlorobis' refers to two groups of ethylenediamine. 'Chromium(III)' indicates Cr with +3 charge. 'Sulfate' is SO4^2-. So, the resulting formula is \( [Cr(NH_3)(C_2H_8N_2)_2]SO_4 \).

Tris(ethylenediamine)iron(III) hexacyanoferrate(II)

In tris(ethylenediamine)iron(III) hexacyanoferrate(II), 'tris' indicates three molecules of ethylenediamine. 'Iron(III)' means we have Fe3+. 'Hexacyanoferrate(II)' shows an ion with Fe in +2 oxidation state with six cyanide ions. Therefore, the chemical formula for this compound is \( [Fe(C_2H_8N_2)_3]_2[Fe(CN)_6] \).

Key concepts

Chemical Formulas

Understanding chemical formulas in coordination chemistry is crucial as they show how elements combine and interact in coordination complexes. Coordination complexes often consist of central metal atoms attached to molecules or ions called ligands. The overall chemical formula reflects the composition and structure of the compound.
In general terms, a coordination complex formula consists of square brackets to denote the complex unit, where the central metal atom and its attached ligands are specified. For example, in the formula \( K_3[Fe(CN)_6] \), the part within the brackets \([Fe(CN)_6]\) represents the complex, showing iron (Fe) as the central metal ion bound to six cyanide (CN) ligands.
Outside the brackets, we find additional ions that balance the charge of the complex, such as potassium ions (K\(^+\)) in the mentioned formula. Familiarity with interpreting these formulas helps in understanding the complex's structure and how it interacts with other compounds.

Oxidation States

Oxidation states in coordination chemistry play a key role in determining the types of bonds and interactions within a coordination complex. The oxidation state of a central metal ion is indicated in Roman numerals within parentheses, such as Chromium(III) for Cr\(^{3+}\). It reveals how electrons are distributed between the metal and its ligands.
To find the oxidation state, we consider the charges of the ligands and the overall charge of the complex. For example, in \([Cu(C_2H_8N_2)_2]^{2+}\), the bis(ethylenediamine) ligands are neutral, and since the complex carries a \(2+\) charge, the copper ion has to be in the \(2+\) oxidation state.
This concept helps in predicting the chemical reactivity and stability of the complex. Knowing the oxidation state can also indicate potential applications of the compound in areas such as catalysis and biochemistry.

Ligands in Coordination Complexes

Ligands are essential in forming coordination complexes because they donate electron pairs to bind with the central metal ion. They can be ions or neutral molecules and come in various types and numbers.
Common ligands include water (aqua), ammonia (ammine), chloride, and more complex ones like ethylenediamine. Their names often give clues to their coordination action. For example, in pentaaquahydroxoaluminum(III) chloride, the 'pentaaqua' indicates five water molecules attached to aluminum. Understanding ligands is vital as they affect the solubility, reactivity, and color of the coordination complex.
Moreover, the ligand's arrangement around the central ion, its coordination number, and geometry (like octahedral or tetrahedral) significantly influence the properties and behavior of the entire complex. Recognizing the diversity of ligands allows for the synthesis of a wide range of coordination compounds, each with unique features.

Naming Coordination Compounds

Naming coordination compounds follows specific rules to clearly describe the complex components and their relationships. It often involves stating the name of the ligands first, followed by the metal with its oxidation state in Roman numerals in parentheses.
Ligands are named in alphabetical order regardless of their charge. Prefixes like mono-, di-, tri-, etc., indicate the number of each type of ligand. For example, 'tris(ethylenediamine)' in \([Fe(C_2H_8N_2)_3]_2[Fe(CN)_6]\) means three ethylenediamine ligands. Metal names can change if the complex ion is anionic, such as 'ferrate' for anion-containing iron. Additionally, counter-ions are mentioned after the complex ion name, if present.
Following these principles ensures reproducibility in communication. This systematic approach is crucial for the consistent identification and synthesis of coordination compounds, applicable across diverse fields like chemistry, materials science, and pharmacology.