The reaction of the octahedral complex Co(NH3)3(NO2)3 with HCl yields a complex [Co(NH3)3(H2O)Cl2]+ in which the two chloride ligands are trans to one another.
(a) Draw the two possible stereoisomers of the starting material [Co(NH3)3(NO2)3]. (All three NO2- ligands are bonded to Co through the N atom.)
(b) Assuming that the NH3 groups remain in place, which of the two starting isomers could give rise to the observed product?

Verified step by step guidance

1. Identify the coordination geometry of the complex [Co(NH3)3(NO2)3]. Since it is octahedral, the ligands are arranged around the central cobalt ion in an octahedral fashion.
2. Draw the two possible stereoisomers of the complex. In an octahedral complex with three identical ligands, the isomers can be facial (fac) or meridional (mer).
3. For the fac isomer, place the three NO2- ligands adjacent to each other, forming a face of the octahedron. The remaining three NH3 ligands will occupy the other three positions.
4. For the mer isomer, arrange the three NO2- ligands such that they form a meridian, with two NO2- ligands opposite each other and the third one adjacent to one of them. The NH3 ligands will fill the remaining positions.
5. To determine which isomer could give rise to the observed product [Co(NH3)3(H2O)Cl2]+ with trans Cl- ligands, consider the positions of the NO2- ligands that can be replaced by Cl- and H2O. The mer isomer allows for two trans positions to be replaced, leading to the observed product.

Key Concepts

Stereoisomerism

Stereoisomerism refers to the phenomenon where compounds have the same molecular formula and connectivity of atoms but differ in the spatial arrangement of those atoms. In coordination chemistry, this can lead to different geometric isomers, such as cis and trans configurations, which can significantly affect the properties and reactivity of the complexes.

Octahedral Complexes

Octahedral complexes are coordination compounds where a central metal atom is surrounded by six ligands arranged at the corners of an octahedron. The geometry of these complexes can lead to various isomeric forms, depending on the nature and arrangement of the ligands, which is crucial for understanding the reactivity and product formation in reactions involving these complexes.

Ligand Substitution Reactions

Ligand substitution reactions involve the replacement of one ligand in a coordination complex with another ligand. The outcome of these reactions can depend on the geometry of the starting complex and the nature of the incoming ligand, which is essential for predicting the products formed, such as the observed complex [Co(NH3)3(H2O)Cl2]+ in this case.