Q3 · CSIR-NET Chemistry, December 2016
Paper: CSIR-NET December 2016 · Subject: Inorganic Chemistry · Chapter: Chemical Bonding · Topic: Chemical Bonding – General · Marks: 2 · Difficulty: Medium
The oxidation state of gold in the following complex is 
(a)0
(b)1
(c)2
(d)3
Answer
Answer: C ✓ checked by 4AB · confidence high
Explanation
Each bridging ligand [Me₂P(CH₂)₂]⁻ is a phosphonium bis-ylide: P⁺ carries two Me groups and two CH₂⁻ carbanions, so the ligand is mono-anionic (−1), not dianionic. Charge balance for the neutral complex [Au₂{(CH₂)₂PMe₂}₂Cl₂]: 2x + 2(−1) + 2(−1) = 0 ⇒ x = +2. The two d⁹ Au(II) centres pair their odd electrons in an Au–Au bond (Schmidbaur's Au(II) ylide dimer; the structure marks each Au as II). Oxidation state = 2 — option (c).
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