Organometallic Ligands: Carbonyls, Phosphines and Hapticity · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Ligands that tune the metal

Science · Chemistry · ages 20-21
Name ______________________   Date ____________

  1. What makes a chelate ligand different from a monodentate one?

    • It binds through one donor atom only
    • It never forms a real bond to the metal
    • It grips with several donor atoms at once like a claw

  2. What holds a ligand to the metal in a coordination compound?

    • A shared electron pair donated by the ligand
    • Gravity between the heavy metal and the ligand
    • A physical cage with no bonding at all

  3. A more electron rich metal centre gives its carbonyl ligands a higher stretching frequency.

    Circle one:   True   False

  4. An allyl ligand binds a metal through three neighbouring atoms. What is its hapticity contribution to the count?

    • It touches through one atom, since only the middle atom counts
    • It touches through three atoms, so tally it as a three atom donor
    • It touches through no atoms, since chains cannot bind metals

  5. A metal carbonyl and its anion are compared. Which absorbs at lower frequency, and why?

    • The neutral complex, since neutral bonds always vibrate lower
    • The anion, since extra charge means more back donation
    • Both absorb identically, since charge never matters

  6. How does swapping a phosphine substituent change the ligand?

    • It changes both the donor strength and the bulk at the metal
    • It changes nothing, since all phosphines behave identically
    • It changes the colour of the complex but nothing else

  7. A student counts a cyclopentadienyl ligand as a one atom donor like water. What is the error?

    • Water is not a ligand at all
    • Rings can never bind metals through carbon atoms
    • The ring touches through five neighbouring atoms, so the one atom tally misses most of the donation

  8. Two carbonyl centres show different stretching frequencies. The first absorbs lower. What do you conclude?

    • The first metal centre is more electron poor than the second
    • The first metal centre is more electron rich than the second
    • Frequencies say nothing about either centre
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Ligands that tune the metal W1-mt_JXYSQDYlJ--s1

  1. It grips with several donor atoms at once like a claw · Several donor atoms on one ligand each bind the same centre, which is the chelate grip.
  2. A shared electron pair donated by the ligand · Each ligand lends a pair that forms a coordinate covalent bond to the centre.
  3. False · Richer centres back donate more, which weakens the CO bond and lowers the frequency.
  4. It touches through three atoms, so tally it as a three atom donor · Hapticity names the touch count, and every touching atom joins the electron tally.
  5. The anion, since extra charge means more back donation · The anion is the richer centre, so it back donates harder and softens the CO bond more.
  6. It changes both the donor strength and the bulk at the metal · Substituents tune how strongly the phosphine gives and how much room it takes.
  7. The ring touches through five neighbouring atoms, so the one atom tally misses most of the donation · Hapticity exists exactly because chains and rings bind through several atoms at once.
  8. The first metal centre is more electron rich than the second · Lower frequency means more back donation, which means a richer metal behind it.
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