Question

Draw structures of each of the following. a. cis-dichloroethylenediamineplatinum(II) b. trans-dichlorobis(ethylenediamine)cobalt(II) c. cis-tetraamminechloronitrocobalt(III) ion d. trans-tetraamminechloronitritocobalt(III) ion e. trans-diaquabis(ethylenediamine)copper(II) ion

Short answer

The structures of the given coordination complexes are as follows: a. cis-dichloroethylenediamineplatinum(II):  b. trans-dichlorobis(ethylenediamine)cobalt(II):  c. cis-tetraamminechloronitrocobalt(III) ion:  d. trans-tetraamminechloronitritocobalt(III) ion:  e. trans-diaquabis(ethylenediamine)copper(II) ion: 

Step-by-step solution

Identify the metal and ligands

In this complex, the central metal atom is platinum(II), and the ligands are two ethylenediamine (en) and two chloride (Cl) ligands.

Arrange the ligands in the cis position

In the cis position, the two chloride ligands are adjacent to each other while the two ethylenediamine ligands occupy the other two coordination sites.

Draw the structure

The final structure for cis-dichloroethylenediamineplatinum(II) can be drawn as:  b. trans-dichlorobis(ethylenediamine)cobalt(II)

Identify the metal and ligands

In this complex, the central metal atom is cobalt(II), and the ligands are two ethylenediamine (en) and two chloride (Cl) ligands.

Arrange the ligands in the trans position

In the trans position, the two chloride ligands are opposite to each other while the two ethylenediamine ligands occupy the other two coordination sites.

Draw the structure

The final structure for trans-dichlorobis(ethylenediamine)cobalt(II) can be drawn as:  c. cis-tetraamminechloronitrocobalt(III) ion

Identify the metal and ligands

In this complex, the central metal atom is cobalt(III), and the ligands are four ammine (NH3), one chloride (Cl), and one nitro (NO2) ligands.

Arrange the ligands in the cis position

In the cis position, the chloride and nitro ligands are adjacent to each other while the four ammine ligands occupy the remaining coordination sites.

Draw the structure

The final structure for cis-tetraamminechloronitrocobalt(III) ion can be drawn as:  d. trans-tetraamminechloronitritocobalt(III) ion

Identify the metal and ligands

In this complex, the central metal atom is cobalt(III), and the ligands are four ammine (NH3), one chloride (Cl), and one nitrito (NO2) ligands.

Arrange the ligands in the trans position

In the trans position, the chloride and nitrito ligands are opposite to each other while the four ammine ligands occupy the remaining coordination sites.

Draw the structure

The final structure for trans-tetraamminechloronitritocobalt(III) ion can be drawn as:  e. trans-diaquabis(ethylenediamine)copper(II) ion

Identify the metal and ligands

In this complex, the central metal atom is copper(II), and the ligands are two ethylenediamine (en) and two water (H2O) ligands.

Arrange the ligands in the trans position

In the trans position, the two water ligands are opposite to each other while the two ethylenediamine ligands occupy the other two coordination sites.

Draw the structure

The final structure for trans-diaquabis(ethylenediamine)copper(II) ion can be drawn as: 

Key concepts

Coordination Compounds

Coordination compounds are intriguing chemical species formed by the combination of a central metal atom or ion and surrounding molecules or ions known as ligands. These compounds are unique in that the ligands are bound to the metal atom by coordinate covalent bonds, where the ligand donates a pair of electrons to the metal.
This electron donation creates stable structures, commonly referred to as complexes.

Coordination compounds play an essential role in various fields, including chemistry, biology, and industry. For instance, hemoglobin in blood, which is vital for oxygen transport, is a well-known biological coordination compound.

• The central metal ion can be a transition metal, like platinum or cobalt, which often has empty orbitals that allow it to bind with ligands efficiently.
• The arrangement of the ligands around the central metal is crucial as it dictates the geometric shape and properties of the compound.

Understanding these fundamentals helps us explore the fascinating world of coordination chemistry.

Ligand Arrangement

Ligand arrangement in coordination compounds significantly impacts their properties and stability. Ligands can occupy different positions around the metal ion, leading to various geometrical structures.

For example, in a square planar or octahedral geometry, ligands can have specific orientations relative to each other.

• Cis arrangement means that similar or specific ligands are adjacent to each other, influencing the compound's reactivity and physical properties.
• Trans arrangement, on the other hand, places the ligands opposite each other, which leads to different chemical behaviors.

The precise arrangement is critical in determining the compound's color, magnetic properties, and even its biological activity. Consequently, understanding ligand arrangement is crucial for predicting and manipulating the behavior of coordination complexes.

Transition Metals

Transition metals are a group of elements found in the center of the periodic table. They are particularly known for their ability to form coordination compounds due to their unique electron configurations.

These metals can have various oxidation states, which allows them to participate in complex chemical reactions.

• Transition metals like platinum, cobalt, and copper serve as central atoms in coordination compounds. Their d-orbitals play a significant role in interacting with ligands, making these metals excellent candidates for forming stable complexes.
• The ability to exhibit multiple oxidation states and form colorful compounds makes transition metals essential in many practical applications, such as catalysis and pigment formation.

By examining these versatile elements, we can better understand the diverse roles they play in coordination chemistry.

Cis-Trans Isomerism

Cis-trans isomerism is a type of stereoisomerism important in coordination chemistry, particularly for compounds with specific geometries like square planar or octahedral. This concept refers to the spatial arrangement of ligands relative to a central atom.

In a cis configuration, identical or specific ligands are next to each other, affecting the physical and chemical attributes of the compound.

• For example, cis-platin is a well-known cis isomer used in cancer treatment. Its specific arrangement allows it to bind to DNA, which is crucial for its effectiveness as a drug.

In contrast, a trans configuration sees the ligands positioned opposite each other, leading to different properties and applications.
The ability to distinguish between these isomers is vital, especially since even tiny changes in molecular arrangement can significantly alter the compound's function and reactivity. Understanding cis-trans isomerism in coordination compounds thus helps chemists in synthesizing and optimizing compounds for desired applications.