Question

Write the IUPAC names of the following coordination compounds.
(i) \( [Cr(NH_3)_2Cl_2(en)]Cl \)
(ii) \( [Pt(NH_3)_4Cl_2][PtCl_4] \) (1+1=2)

Hint:

List ligands alphabetically with -o for anions; the outer \( Cl^- \) fixes Cr as +3, and for the platinum salt the anion metal becomes platinate.

Answer 1

Rules used: Name the ligands alphabetically, then the metal. Anionic ligands take suffix -o (chlorido), neutral ligands keep their name (ammine for \( NH_3 \), ethane-1,2-diamine for en). Use Greek prefixes (di, tetra) for simple ligands and bis, tris for complex names. State the metal oxidation number in Roman numerals. Name the cation first, then the anion.

Part (i): \( [Cr(NH_3)_2Cl_2(en)]Cl \)
Step 1: Ligands inside the sphere: 2 \( NH_3 \) (ammine), 2 \( Cl^- \) (chlorido), 1 en (ethane-1,2-diamine).
Step 2: Oxidation state of Cr: the complex ion charge is +1 (one \( Cl^- \) is outside). So \( x + 0(NH_3\times2) + (-1)(Cl\times2) + 0(en) = +1 \Rightarrow x = +3 \).
Step 3: Arrange ligand names alphabetically: ammine, chlorido, ethane-1,2-diamine.
IUPAC name: diamminedichlorido(ethane-1,2-diamine)chromium(III) chloride.

Part (ii): \( [Pt(NH_3)_4Cl_2][PtCl_4] \)
Step 1: This has a complex cation \( [Pt(NH_3)_4Cl_2]^{2+} \) and a complex anion \( [PtCl_4]^{2-} \).
Step 2: Cation Pt oxidation state: \( x + 0(NH_3\times4) + (-1)(Cl\times2) = +2 \Rightarrow x = +4 \). Anion Pt oxidation state: \( y + (-1)(Cl\times4) = -2 \Rightarrow y = +2 \).
Step 3: Name cation first (ammine before chlorido), then the anion with suffix -ate on the metal (platinate).
IUPAC name: tetraamminedichloridoplatinum(IV) tetrachloridoplatinate(II).