What are the coordination number and the oxidation state of...

Key Concepts

Ligands

Ligands are atoms, ions, or molecules that donate one or more pairs of electrons to a central metal ion, forming coordinate covalent bonds. Their nature—whether they are neutral or anionic, monodentate or polydentate—plays a key role in determining both the structure (including the coordination number) and the overall charge of the complex.

Coordination number

The coordination number in a coordination complex is defined as the total number of donor atoms from the ligands that are directly bonded to the central metal. This concept is central to understanding the geometry and spatial arrangement of the ligands around the metal ion, as it directly influences the shape and possible stereochemistry of the complex.

Oxidation state determination

The oxidation state of a metal in a complex is the charge that the metal would possess if all the ligands were removed along with the electron pairs that formed the bonds, typically treating these ligands as if they were ionic. This concept is crucial for charge balance calculations, understanding reactivity, and determining electronic configurations in coordination chemistry.

Naming of coordination compounds

Naming coordination compounds involves following standardized IUPAC guidelines. This includes listing the ligands in alphabetical order, using appropriate prefixes to indicate the number of each type of ligand, and appending the name of the metal along with its oxidation state in parentheses in Roman numerals. This systematic approach helps in unequivocal communication of the structure and composition of the coordination complex.

Transcript

00:01 To find the oxidation state of our metal ion, what we need to do is first take a look at our ligands and see what their oxidation states are, because we know that the oxidation state of our metal ion plus the oxidation state of our ligands must add up to our total charge.

00:21 So if we take a look at our ligand, we have our amine as our ligand.

00:26 The oxidation state for amine is zero.

00:32 So to solve for the oxidation state of our cobalt, what we want to do is say our oxidation state for cobalt is x.

00:41 So we have x plus 0, which is from our amine times 6, since we have 6 of our amines, is going to be equal to our overall charge of positive 2.

00:54 So if we solve for x is just a 0, what we're going to be left with is x is going to be equal to 2.

01:01 So that means that our oxidation state for cobal is going to be positive 2.

01:07 Our coordination number is simply going to be the number of ligands that we have in our complex ion.

01:12 And in our case, we have six amine ligands, so our coordination number will be six.

01:17 When we're naming our complex ion, we can notice that it's positively charged.

01:23 So that's going to mean our metal ion is going to keep its ending.

01:29 And the first thing we want to do when naming it is start by identifying our ligands and list them alphabetically.

01:37 So our ligands is going to be amine, and that's the only one we have, and then we're going to use prefixes for the number of ligands we have.

01:46 So we have six amines, so that's going to mean our prefix that we use is hexa.

01:51 So we're going to have hexa amine, and then for our metal, we're going to have our cobalt, and then in roman numerals, we'll write our oxidation state.

02:06 So we'll have hexamine cobalt 2.

02:11 For part b, we're going to approach this in a very similar way.

02:16 So the first thing we're going to do to find our oxidation state is we're going to take a look at our ligands.

02:24 And our ligand in this case is fluorine.

02:27 And so fluorine has an oxidation state of negative 1.

02:31 So if we write out our equation again, we'll have negative 1 for our fluorine times 6 plus our oxidation state of aluminum, which we're going to say is x, is going to be equal to our overall charge of negative 3.

02:50 So if we solve for x, we'll find that x is going to have to equal positive 3.

02:57 So our oxidation state for aluminum is going to be plus three.

03:04 Again, our coordination number is simply going to be the number of ligands we have.

03:07 In this case, we have six fluorines, so our coordination number will be six.

03:11 Now, when naming our complex ion, we'll start with our ligands, start by identifying them.

03:20 And so fluorine is an anion, so it's going to have its ending replaced by o.

03:26 So we'll have floro.

03:27 There's six of them, so the prefix will use as hexa.

03:31 So we'll have hexaflora.

03:33 And then aluminum, since this is a negatively charged complex ion, our aluminum is going to have an eight ending.

03:41 So it'll be illuminate instead of aluminum.

03:45 So it'll be hexaflora illuminate three, since our oxidation state was three.

03:52 Moving on to part c.

03:53 Again, very similar.

03:54 First we'll start by identifying our ligands and their oxidation state.

04:01 So cyanide has an oxidation state of negative 1.

04:05 So if we write out our equation, we have negative 1 times 4, since we have 4 cyanides, plus x, which is representing the oxidation state of our copper, is going to be equal to negative 2.

04:19 And if we solve for x, we'll find that x has to be equal to positive 2.

04:24 So our oxidation state for copper is going to be plus two.

04:31 Our coordination number is going to be four because we have four cyanides.

04:37 We have four ligands, so our coordination number is four.

04:40 And then when naming our complex ion, we're going to start by listing out our ligands and identifying them.

04:48 So again, anions are going to have an ending in o.

04:52 So that's why we have cyan -o instead of cyanide.

04:55 And there's four cyanides.

04:57 So it'll be tetra -siano.

04:59 And then our copper, since this is a negatively charged complex ion, is going to have to have that eight ending.

05:07 So it's going to be cooperate.

05:10 So we'll have tetra -siano -cuperate 2 is our total complex ion name.