Question

Name the following complex ions. a. \(\mathrm{Ni}(\mathrm{CN})_{4}^{2-}\) c. \(\mathrm{Fe}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)_{5}{ }^{3-}\) b. \(\mathrm{Cr}\left(\mathrm{NH}_{3}\right)_{4} \mathrm{Cl}_{2}^{+}\) d. \(\mathrm{Co}(\mathrm{SCN})_{2}\left(\mathrm{H}_{2} \mathrm{O}\right)_{4}^{+}\)

Short answer

The names of the complex ions are: a. Tetracyanonickelate(II) b. Tetraamminedichlorochromium(III) c. Trioxalatoferrate(III) d. Aqua(4)thiocyanato(2)cobalt(III)

Step-by-step solution

Identify the Ligands and Metal

The ligands in this complex ion are CN^-, and the metal is Ni.

Name the Ligands and the Metal

The name for the CN^- ligand is Cyanide. The metal is Nickel, and since it's an anionic complex ion, we will use the "-ate" suffix, resulting in Nickelate.

Determine the Oxidation State and Name the Complex Ion

The Cyanide ligand has a charge of -1, and since there are 4 of them and the overall charge is -2, the oxidation state of Ni is 2. Thus, the name of the complex ion is Tetracyanonickelate(II). b. Cr(NH_{3})_{4} Cl_{2}^{+}

Identify the Ligands and Metal

The ligands in this complex ion are NH_3 and Cl^-, and the metal is Cr.

Name the Ligands and the Metal

The name for the NH_3 ligand is Ammine (not ammonia), and the name for Cl^- is Chloro. The metal is Chromium.

Determine the Oxidation State and Name the Complex Ion

The Chloro ligand has a charge of -1, and since there are 2 of them and the overall charge is +1, the oxidation state of Cr is 3. Therefore, the name of the complex ion is Tetraamminedichlorochromium(III). c. Fe(C_{2}O_{4})_{3}^{3-}

Identify the Ligands and Metal

The ligands in this complex ion are C_{2}O_{4}^{2-}, and the metal is Fe.

Name the Ligands and the Metal

The name for the C_{2}O_{4}^{2-} ligand is Oxalate. The metal is Iron, and since it's an anionic complex ion, we will use the "-ate" suffix, resulting in Ferrate.

Determine the Oxidation State and Name the Complex Ion

The Oxalate ligand has a charge of -2, and since there are 3 of them and the overall charge is -3, the oxidation state of Fe is 6. Thus, the name of the complex ion is Trioxalatoferrate(III). d. Co(SCN)_{2}(H_{2}O)_{4}^{+}

Identify the Ligands and Metal

The ligands in this complex ion are SCN^- and H_2O, and the metal is Co.

Name the Ligands and the Metal

The name for the SCN^- ligand is Thiocyanate, and the name for H_2O is Aqua. The metal is Cobalt.

Determine the Oxidation State and Name the Complex Ion

The Thiocyanate ligand has a charge of -1, and since there are 2 of them and the overall charge is +1, the oxidation state of Co is 3. Therefore, the name of the complex ion is Aqua(4)thiocyanato(2)cobalt(III).

Key concepts

Ligands Nomenclature

In coordination chemistry, ligands are ions or molecules that can donate pairs of electrons to a metal ion, forming a coordination complex. The nomenclature for naming ligands is systematic, helping to avoid ambiguity.

For negatively charged ligands, the names often end in '-o', like 'cyanido' for CN^-, 'chloro' for Cl^-, and 'oxalato' for C₂O₄^2-. Neutral ligands are named after their molecular names, with some exceptions, such as 'NH₃' being called 'ammine' (with double 'm') and 'H₂O' known as 'aqua'. Importantly, ligands' prefixes denote the number of each type present: 'di-' for two, 'tri-' for three, and so on. Complex ion names start with ligands in alphabetical order followed by the metal ion.

When multiple identical ligands are present, prefixes such as 'bis-', 'tris-', and 'tetrakis-' are used to avoid confusion with the numerical prefixes that are part of the ligand's name, like in the case of 'ethylene diamine' which becomes 'bis(ethylene diamine)'.

Oxidation States

The oxidation state of a metal in a coordination compound is crucial for the correct naming of the complex ion. It is represented by a Roman numeral in parentheses after the metal's name. To determine the oxidation state, identify the overall charge of the complex and the charges of the ligands, then calculate the net charge that must be present on the metal to result in the overall charge of the complex.

For instance, in \(\mathrm{Ni}(\mathrm{CN})_{4}^{2-}\), the four cyanido ligands each bring a charge of \(-1\), totaling \(-4\). Since the overall charge of the complex is \(-2\), the oxidation state of Nickel (Ni) is \(+2\). Thus, the correct naming would include 'Nickel(II)', indicating the oxidation state. It is this systematic approach that allows chemists to accurately convey the composition and structure of coordination compounds.

Transition Metal Chemistry

Transition metals possess unique properties that are essential to the formation and properties of coordination compounds. These metals can exhibit multiple oxidation states and have unfilled d-orbitals that allow the formation of coordinate bonds with ligands. Such versatility explains their widespread use in diverse applications, ranging from pigments and catalysts to biological systems.

The chemistry of transition metals is dominated by their capacity to form stable complexes and the color changes associated with different ligand arrangements. For example, the different colors of the hydrated and anhydrous forms of transition metal salts can be attributed to these electronic transitions within their d-orbitals, which can be influenced by the type of ligands attached to the metal ion.

Coordination Compounds

Coordination compounds are compounds in which a central metal ion is surrounded by molecules or ions called ligands. The metal and its surrounding ligands form what's called a 'coordination sphere'. The overall charge of a coordination compound can be neutral, positive, or negative, and they are written in a specific format, with the ligands named before the metal center.

Coordination compounds are widely researched for their roles in biology and technology. They are used in medicinal chemistry, such as in chemotherapy drugs and in the synthesis of materials with specific electronic and magnetic properties. The correct naming and understanding of coordination compounds can thus provide insights into their behavior and potential applications.