What is the oxidation number of the copper in [Cu(NH₃)₃Cl]NO₃?

Question

Quizplus · Accepted Answer

In this compound, Cl has an oxidation state of -1, and the total oxidation state of the entire compound must equal 0. Therefore, the oxidation state of Cu can be determined as follows:

Let x be the oxidation state of Cu. 
(-1) + (x) + (-2) + (-2) + (-1) + (0) = 0 
Simplifying: 
x - 6 = 0 
x = +6

However, Cu cannot have an oxidation state of +6 in this compound, as it violates common oxidation state rules. Therefore, we must adjust the oxidation states of the surrounding atoms. The ligand is NH2CSNH2, which is also called thiourea. The two nitrogen atoms in thiourea each have a lone pair of electrons that can form a bond to Cu, making it a strong ligand. Because of this strong bond, the Cu-S bond is considered to be predominantly covalent in nature, and the sulfur atoms carry a partial negative charge. Therefore, we can assign a -1 oxidation state to each sulfur atom, and use this to determine the oxidation state of Cu: 
(-1) + (-1) + (-2) + (-2) + (-1) + (0) + (x) = 0 
Simplifying: 
x - 7 = 0 
x = +7

This value still violates common oxidation state rules, so we must consider yet another adjustment. The Cu-S bond can be considered to have a partial ionic character, with the S atoms carrying a partial negative charge and the Cu carrying a partial positive charge. Therefore, we can consider the sulfur atoms to have a -0.5 oxidation state, and use this to determine the oxidation state of Cu: 
(-0.5) + (-0.5) + (-2) + (-2) + (-1) + (0) + (x) = 0 
Simplifying: 
x - 6 = 0 
x = +6

This oxidation state of +6 is consistent with the known oxidation states of copper.

What Is the Oxidation Number of the Copper in [Cu(NH3)3Cl]NO3

What Is the Oxidation Number of the Copper in [Cu(NH₃)₃Cl]NO₃