For each of the following compounds or ions: 1) draw the structure and give the point group; 2) indicate the appropriate bonding theory to predict if the compound or ion will be stable or not, briefly explaining your prediction (hint: quantitative predictions are the best); 3) if the compound or ion is paramagnetic, predict the spin-only magnetic moment in units of Bohr-Magnetons; 4) determine if the compound or ion will be Jahn-Teller active and, if so, predict the nature of the distortion.
1. hexacyanoferrate(III) ion
1) structure =
Point group = Oh
2) Ligand field theory predicts a stable compound for this d5, t2g5 ion in a strong field with LFSE = 20Dq – 2P
3) There is one unpaired spin so the predicted magnetic moment is μ = [1(1+2)]½ = 1.73 μB.
4) The electronic state is degenerate so is Jahn-Teller active. An axial elongation is predicted.
2. bichlorobiaquacobalt(II) (hint: this is a deep blue color)
1) structure =
Point group = C2v. Both the lack of cis or trans designation and the hint about the color (a blue color means a small Δt) indicate a tetrahedral distribution of the ligands about the metal ion.
2) Ligand field theory predicts a stable compound for this d7, e4t23 ion in a weak field with LFSE = 12Dqt
3) There are three unpaired spins so the predicted magnetic moment is μ = [3(3+2)]½ = 3.87 μB.
4) The electronic state is nondegenerate so is not Jahn-Teller active.
3. hexacarbonylchromium(0)
1) structure =
Point group = Oh.
2) Valence bond theory predicts a stable compound: for this d6 metal the EAN count is 6 e– from Cr and 2 × 6 = 12 e– from the ligands for a total of 18 e–.
3) There are no unpaired spins.
4) The electronic state is nondegenerate so is not Jahn-Teller active.
4. trans-chlorobis(hydrido)tris(triphenylphosphine)rhodium(III) (hint: the PPh3 ligand freely rotates)
1) structure =
Point group = C2v.
2) Ligand field theory predicts a stable compound for this d6, t2g6 compound in a strong field with LFSE = 24Dq – 2P
3) There are no unpaired spins.
4) The electronic state is nondegenerate so is not Jahn-Teller active.
5. cis-tetraamminebinitritonickel(II)
1) structure =
Point group = C2v.
2) Ligand field theory predicts a stable compound for this d8, t2g6eg2 compound in a strong field with LFSE = 12Dq
3) There are two unpaired spins so the predicted magnetic moment is μ = [2(2+2)]½ = 2.83 μB.
4) The electronic state is nondegenerate so is not Jahn-Teller active.
6. bis(η1-cyclopentadienyl)bis(η5-cyclopentadienyl)titanium(IV)
1) structure =
Point group = C2v.
2) Valence bond theory predicts that this compound is probably stable: for this d0 metal the EAN count is 0 e– from Ti, 2 × 2 = 4 e– from the η1-cp ligands, and 2 × 6 = 12 e– from the η5-cp ligands for a total of 16 e–.
3) There are no unpaired spins.
4) The electronic state is nondegenerate so is not Jahn-Teller active.
7. pentacyanonitrosylmanganate(III) ion
1) structure =
Point group = C4v.
2) Ligand field theory predicts a stable compound for this d4, t2g4 compound in a strong field with LFSE = 16Dq – P
3) There are two unpaired spins so the predicted magnetic moment is μ = [2(2+2)]½ = 2.83 μB.
4) The electronic state is degenerate so is Jahn-Teller active. An axial compression is predicted.
8. cis-bibromobichlorocuprate(II) ion
1) structure =
Point group = C2v.
2) Ligand field theory predicts a stable compound for this d9, t2g6eg3 ion in a weak field with LFSE = 6Dq
3) There is one unpaired spin so the predicted magnetic moment is μ = [1(1+2)]½ = 1.73 μB.
4) The electronic state is degenerate so is Jahn-Teller active. An axial elongation is predicted, hence the ion is square planar.
9. fac-triamminetriaquachromium(III) ion
1) structure =
Point group = C3v.
2) Ligand field theory predicts a stable compound for this d3, t2g3 ion in a weak field with LFSE = 12Dq
3) There are three unpaired spins so the predicted magnetic moment is μ = [3(3+2)]½ = 3.87 μB.
4) The electronic state is not degenerate so is not Jahn-Teller active.
10. bi(η6-benzene)molybdenum(0)
1) structure =
Point group = D6h if the benzene rings are eclipsed and D6d if the benzene rings are staggered.
2) Valence bond theory predicts that this compound is stable: for this d6 metal the EAN count is 6 e– from Mo and 2 × 6 = 12 e– from the η6-benzene ligands for a total of 18 e–.
3) There are no unpaired spins.
4) The electronic state is nondegenerate so is not Jahn-Teller active.