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10. Most of the time, closed-shell and neutral-ligand counting will give you the

ID: 1039586 • Letter: 1

Question

10. Most of the time, closed-shell and neutral-ligand counting will give you the same answer because the assumptions they make about the nature of the M-L bond ultimately work the same. There is a situation where one of the methods can fail, though. Consider the acid-base reaction below. NH3 NH3 ??. NH3 NH3 H20 NH3 Ir Ir n/a NH3 4-pyridinecarboxylic acid (N-donor) 3+ charge TOTAL NH3 4-pyridinecarboxylate (N-donor) 2+ charge n/a n/a n/a 18 18 TOTAL n/a Which method gave you a different electron count for the two species? Does it make sense for the metal's electron count to change if you modified a completely different part of the molecule? What assumption has led to this counting failure?

Explanation / Answer

ELECTRON COUNT BY CLOSE CELL METHOD

6+2*5+2

6+10+2

18

9+2*5+2-3

9+10+2-3

18

ELECTRON COUNT BY CLOSE CELL METHOD

7+2*5+1

7+10+1

18

9+2*5+2-3

9+10+2-3

18

[Ir(NH3)5(py-COOH)]3+ LIGAND OR METAL

ELECTRON COUNT BY CLOSE CELL METHOD

ELECTRON COUNT BY NUTRAL METHOD Ir METAL 6 9 NH3 LIGAND 2 2 py-COOH LIGAND 2 2 CHARGE 0 +3 TOTAL ELECTRON

6+2*5+2

6+10+2

18

9+2*5+2-3

9+10+2-3

18