Question

Write the formula for each of the following compounds, being sure to use brackets to indicate the coordination sphere: (a) tetraaquadibromomanganese(III) perchlorate (b) bis(bipyridyl) cadmium(II) chloride (c) potassium tetrabromo(ortho-phenanthroline)cobaltate (III) (d) cesium diamminetetracyanochromate(III) (e) tris(ethylenediammine)rhodium(III) tris(oxalato)cobaltate(III)

Short answer

The short version of the answer is: (a) Tetraaquadibromomanganese(III) perchlorate: \[Mn(H_2O)_4Br_2(ClO_4)_3\] (b) Bis(bipyridyl)cadmium(II) chloride: \[Cd(bipy)_2Cl_2\] (c) Potassium tetrabromo(ortho-phenanthroline)cobaltate (III): \[K_3[Co(o-phen)Br_4]\] (d) Cesium diamminetetracyanochromate(III) : \[Cs_3[Cr(NH_3)_2(CN)_4]\] (e) Tris(ethylenediammine)rhodium(III) tris(oxalato)cobaltate(III): \[[Rh(en)_3]_3[Co(C_2O_4)_3]_2\]

Step-by-step solution

(a) Tetraaquadibromomanganese(III) perchlorate

For this coordination compound, the name gives us the following information: - Central metal ion: Manganese (III), Mn³⁺ - Ligands: Four aqua ligands (H₂O) and two bromo ligands (Br⁻) - Anion: Perchlorate (ClO₄⁻) Hence, the formula becomes \[Mn(H_2O)_4Br_2(ClO_4)_3\]

(b) Bis(bipyridyl)cadmium(II) chloride

For this coordination compound, the name gives us the following information: - Central metal ion: Cadmium (II), Cd²⁺ - Ligand: Two bipyridyl ligands (bipy) - Anion: Chloride (Cl⁻) Hence, the formula becomes \[Cd(bipy)_2Cl_2\]

(c) Potassium tetrabromo(ortho-phenanthroline)cobaltate (III)

For this coordination compound, the name gives us the following information: - Central metal ion: Cobalt (III), Co³⁺ - Ligands: Four bromo ligands (Br⁻) and one ortho-phenanthroline ligand (o-phen) - Anion: Potassium (K⁺) Hence, the formula becomes \[K_3[Co(o-phen)Br_4]\]

(d) Cesium diamminetetracyanochromate(III)

For this coordination compound, the name gives us the following information: - Central metal ion: Chromium (III), Cr³⁺ - Ligands: Two ammine ligands (NH₃) and four cyano ligands (CN⁻) - Anion: Cesium(Cs⁺) Hence, the formula becomes \[Cs_3[Cr(NH_3)_2(CN)_4]\]

(e) Tris(ethylenediammine)rhodium(III) tris(oxalato)cobaltate(III)

This coordination compound is a complex ion containing two coordination compounds. The name gives us the following information: - First coordination compound: - Central metal ion: Rhodium(III), Rh³⁺ - Ligand: Three ethylenediammine ligands (en) - Second coordination compound: - Central metal ion: Cobalt (III), Co³⁺ - Ligand: Three oxalato ligands (C₂O₄²⁻) Hence, the formula becomes \[[Rh(en)_3]_3[Co(C_2O_4)_3]_2\]

Key concepts

Complex Compounds

In coordination chemistry, complex compounds are fascinating structures formed by the combination of central metal atoms or ions with surrounding ligands. The interactions between the central atom and ligands create a coordination sphere, which is often depicted in a chemical formula using brackets. Complex compounds play a significant role in various chemical reactions and are essential in fields like catalysis and materials science. To understand these compounds, one must comprehend how the central ion and ligands form specific geometries and how this affects the overall properties of the complex. Coordination compounds can vary widely in appearance, stability, and function based on the types and number of ligands as well as the oxidation state of the central metal ion.

Ligands

Ligands are molecules or ions that bind to a central metal ion in complex compounds, forming a coordination sphere. They can be single, double, or even multi-bonded to the metal through donor atoms containing lone pairs of electrons. Ligands play a critical role in defining the stability, reactivity, and color of complex compounds.

• Aqua Ligands: These are simple as they refer to water molecules ( H_2O aqua) bound to the metal ion. They are neutral ligands and participate in many biological systems.
• Bromo Ligands: Consisting of bromide ions ( Br^- ), they provide a single point of attachment with the metal, carrying a negative charge. These can influence the electronic properties of the metal.
• Ammin Ligands: These consist of ammonia molecules ( NH_3 ) that attach to metals through donate electrons from nitrogen atoms, frequently used in coordination chemistry due to their stability.

The number and types of ligands can change the whole structure and function of the coordination compound.

Chemical Formulas

Chemical formulas of complex compounds convey essential information, such as the composition and structure of the compound. By following specific naming conventions, chemists can deduce the formula from the name and vice versa. A name like "tetraaquadibromo" provides a concise description of the ligands involved and their numbers.

• Ligands are often written in brackets, which distinguish them within the coordination sphere.
• The central metal usually has its oxidation state denoted in parentheses.
• The charge of the overall complex can be deduced by balancing the charges from the metal ion and ligands.

Knowing how to write and interpret these formulas is key to understanding and predicting the properties and reactions of coordination compounds.

Transition Metals

Transition metals are the backbone of complex compounds due to their unique ability to form stable complexes with a variety of ligands. They belong to the d-block of the periodic table and include elements like manganese, cobalt, rhodium, cadmium, and chromium. These metals can exhibit multiple oxidation states and are known for their vibrant colors in compounds.

• They have partially filled d-orbitals, allowing complex bonding and providing room for ligands to attach.
• Their compounds often have significant magnetic, electronic, and catalytic capabilities.
• Transition metals in coordination chemistry allow the formation of compounds with varied geometries, like octahedral, tetrahedral, and square planar.

Understanding transition metals and their chemistry is fundamental in synthesizing new compounds and materials with desired properties.