Until the discoveries of Alfred Werner, it was thought that...

Until the discoveries of Alfred Werner, it was thought that carbon had to be present in a compound for it to be optically active. Werner prepared the following compound containing $\mathrm{OH}^{-}$ ions as bridging groups and separated the optical isomers. a. Draw structures of the two optically active isomers of this compound. b. What are the oxidation states of the cobalt ions? c. How many unpaired electrons are present if the complex is the low-spin case?

Until the discoveries of Alfred Werner, it was thought that carbon had to be present in a compound for it to be optically active. Werner prepared the following compound containing $\mathrm{OH}^{-}$ ions as bridging groups and separated the optical isomers.
a. Draw structures of the two optically active isomers of this compound.
b. What are the oxidation states of the cobalt ions?
c. How many unpaired electrons are present if the complex is the low-spin case?

Key Concepts

Low-Spin Complexes

Low-spin complexes are characterized by electron configurations in which electrons are paired in the lower-energy d orbitals due to a large crystal field splitting induced by strong-field ligands. This results in fewer unpaired electrons, lower magnetic moments, and influences the spectroscopic properties of the complex.

Oxidation States

The oxidation state in coordination chemistry refers to the formal charge on the metal ion after accounting for the charges contributed by the ligands. Determining the oxidation state is crucial for understanding the complex’s electronic structure, reactivity, and overall stability.

Crystal Field Theory

Crystal field theory models the electronic structure of coordination complexes by considering the electrostatic interactions between the metal ion and the surrounding ligands. It explains how the d orbitals split into different energy levels, which in turn affects the optical and magnetic properties of the compound.

Coordination Compounds

Coordination compounds consist of a central metal ion bonded to a set of surrounding molecules or ions known as ligands. Their geometric arrangements and bonding interactions influence properties such as reactivity, color, magnetism, and the ability to form stereoisomers.

Optical Isomerism

Optical isomerism arises when a coordination compound exists as two non-superimposable mirror images, called enantiomers, due to an asymmetric arrangement of ligands around the metal center. This chirality leads to distinct interactions with plane-polarized light, a fundamental aspect in stereochemistry.

Transcript

00:01 This problem is great practice to build our intuition of coordination chemistry, isomerism, and crystal field splitting.

00:10 The first thing that we need to do is draw to optically active isomers.

00:16 And these are what the isomers are going to look like.

00:19 These are the exact same compound, but they're essentially mirror images of one another.

00:24 We essentially reflect them across this line to see if they are actually near images, if they're superimposable is what we say.

00:36 And again, these are what our two isomers are going to look like.

00:41 And now what we need to do is find the charge of our cobalt in each of these isomers.

00:49 What we have to do in order to find that is determine the charge of each of the ligands.

00:55 Each ammonia ligand is neutral.

00:57 That would be nh3, where we see here.

01:01 Nh3 is neutral.

01:02 H -o -minus is negative 1.

01:08 Chlorine has a negative 1 charge, which means that our cobalt has to have a plus 3 charge.

01:16 So we're dealing with cobalt 3 in this case.

01:19 And because we know that we have cobalt 3, we can find the electron configuration of cobalt.

01:26 So we have cobalt 3.

01:28 We would look at the periodic table...

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