Transition Metals and Coordination Compounds

[Zn(en)₂]SO₄

Bis(ethylenediamine)zinc sulfate

• en = ethylenediamine

• there are 2 of them, so use bis(ethylenediamine)

• the complex is cationic, so the metal stays zinc not zincate

• the outside anion is sulfate

Examples of Transition metals

Ti, Fe, Cu

bis(ethylenediamine)dinitroiron(IV) sulfate

[Fe(en)₂(NO₂)₂]SO₄

1. Identify ligands

• bis(ethylenediamine) → 2 en ligands → (en)₂

• dinitro → 2 NO₂⁻ ligands → (NO₂)₂

2. Metal + oxidation state

• iron(IV) → Fe⁴⁺

3. Ligand charges

• en = neutral (0)

• NO₂⁻ = −1 each → total = −2

4. Charge of complex

Total = +4 (Fe) + (−2 from NO₂⁻) = +2

So the complex ion is 2+

5. Counter ion

• sulfate = SO₄²⁻

To balance +2, we need one sulfate

---

Steps + formulas used

• Charge formula:
  total charge = metal + ligands

• Plug in values:
  Fe⁴⁺ + (2 × 0 from en) + (2 × −1 from NO₂⁻) = +2

Counter ion (what it means)

• A counter ion is the ion outside the brackets that balances the charge of the complex.

• Here, SO₄²⁻ is the counter ion.

Why only ONE sulfate (not two)

• Complex = +2

• Sulfate = −2

• +2 + (−2) = 0 → already balanced

Rules for naming and identifying metals

Metals are identified as lustrous, opaque, conductive, and malleable elements that usually form positive ions (cations) in compounds

. Complex compounds list the metal first in the formula and often the beginning of the namebecause it acts as the positive center of coordination, which is named before the surrounding negative or neutral ligands. How to Identify Metals

• Periodic Table Position: Elements located to the left of the staircase line (boron to polonium) are metals.

• Physical Properties: Metals are generally shiny (lustrous), opaque, malleable, ductile, and strong.

• Chemical Behavior: Metals act as reducing agents and typically form cations (positive ions) by losing electrons.

• Coordination Compounds: Within complex ions, the central atom is typically a transition metal that acts as a Lewis acid. 

  Chemistry LibreTexts +4

Why Metals are Named First in Complex Compounds

• Cation/Anion Convention: Complex compounds follow ionic naming conventions where the cation (positively charged ion) is listed before the anion (negatively charged ion).

• Central Metal Structure: The metal serves as the central atom within a complex ion, surrounded by ligands.

• Naming Order: In naming coordination compounds, ligands are listed first in alphabetical order, followed by the metal name with its oxidation state in parentheses.

• Metal Center Importance: The metal acts as the core of the compound, with ligands acting as attachments to it.

• Latin Names: For complex anions, the metal's Latin name is used with an -ate suffix (e.g., ferrate, cuprate) to identify it as part of the anionic complex.

K₃[CoF₆]

Why K comes first:

• K⁺ (potassium) is a positive ion (cation)

• The complex [CoF₆]³⁻ is a negative ion (anion)

👉 In ionic compounds, we ALWAYS name the cation first, then the anion.

Step-by-step (quick + clear):

• K₃ → 3 K⁺ = +3 total

• So the complex ion must be −3

---

Find oxidation state of Co:

• Each F⁻ = −1 → 6 F⁻ = −6

• Let Co = x

x + (−6) = −3 → x = +3

---

Naming rules:

• 6 fluorides → hexafluoro

• Negative complex → metal ends in -ate → cobalt → cobaltate

• Oxidation state = (III)

---

Final name:

Potassium hexafluorocobaltate(III)

tris(ethylenediamine)manganese(II) nitrate

Answer: [Mn(en)₃](NO₃)₂

WHAT YOU NEED TO KNOW
The formula for tris(ethylenediamine)manganese(II) nitrate is [Mn(en)₃](NO₃)₂.

 Follow the steps below to determine the formula of the coordination compound.

 

Identify the cation and anion.	Cation: tris(ethylenediamine)manganese(II) Anion: nitrate (NO3¯)
Write the formula of each ligand in alphabetical order.	ethylenediamine: en
Determine the quantity of each ligand.	(en)3
Identify the metal ion.	manganese
Determine the charge on the metal ion.	Mn2+
Determine the charge on the complex ion.	[Mn(en)3]2+
Write the formula of the coordination compound.	[Mn(en)3](NO3)2

[PtBr₆]^4-

Hexabromoplatinate(II) ion

What is the name for the ligand with the formula OCN¯?

Cyanato

What is the charge on chromium in [Cr(NH3)3Br3]?

+3

+3

What is the name for the complex ion [Fe(NO2)4(H2O)2]2-?

Diaquatetranitroferrate(II) ion

What is the name for the compound [Cr(NH3)6][Co(CN)6]?

Hexaamminechromium(III) hexacyanocobaltate(III)

What is the name for the ligand with the formula OCN¯?

Cyanato

What is charge on cobalt in the complex ion [Co(NH3)6]SO4?`

+2

The charge on cobalt in the complex ion [Co(NH3)6]SO4 is +2. The charge on the metal in the complex compound is determined by the charges on the ligands and any counter ions. The ammine ligand (NH3) is neutral, so only the counter ions will determine the charge. Sulfate (SO42-) has a −2 charge and the only source of negative charge in the compound, so the charge on cobalt must be +2.

What is the formula for the complex ion tetraamminedinitritocuprate(I)?

[Cu(NH3)4(ONO)2]¯

1. Write the formula for each ligand.

ammine: NH3

nitrito: ONO¯

2. Determine the quantity of each ligand based on prefixes.

(NH3)4

(ONO)2

3. Identify the metal ion.

cuprate(I)

4. Determine the charge on the metal ion.

Cu+

5. Determine the charge on the complex ion.

−1

6. Write the formula of the complex ion.

[Cu(NH3)4(ONO)2]¯

Name the compound with the formula [Zn(en)2]SO4.

Bis(ethylenediamine)zinc(II) sulfate

1. Identify the cation and anion.

Cation: [Zn(en)2]2+

Anion: SO42-

2. Name each ligand and list them in alphabetical order.

en: ethylenediamine

3. Use prefixes to indicate the number of each ligand and write them in alphabetical order.

bis(ethylenediamine)

5. Name the metal ion.

zinc(II)

6. Write the complete name of the coordination compound.

bis(ethylenediamine)zinc(II) sulfate

What is the formula for the compound tris(ethylenediamine)manganese(II) nitrate?

[Mn(en)3](NO3)2

What is the charge for iron in the complex ion Fe(CN)64-?

+2

What is the name for the compound with the formula K3[CoF6]?

Potassium hexafluorocobaltate(III)

What is the formula for the compound bis(ethylenediamine)dinitroiron(IV) sulfate?

[Fe(en)2(NO2)2]SO4

What is the formula for the compound pentaamminechlorocobalt(III) chloride?

[Co(NH3)5Cl]Cl2

What is the formula for the compound sodium dicyanobis(oxalato)ferrate(III)?

Na[Fe(CN)2(ox)2]

What is the formula for the ligand known as carbonyl?

CO

What is the name for the compound with the formula [Pt(CO)3H2O]Br2?

Aquatricarbonylplatinum(II) bromide