1. Identify the point group for each of the following: a) CO32–; b) PCl3; c) MnO4–; d) HCN.
a) CO32– has the structure
that belongs to the D3h point group.
b) PCl3 has the structure
that belongs to the C3v point group.
c) MnO4– has the structure
that belongs to the Td point group.
d) HCN has the structure
that belongs to the C∞v point group.
2. Name the following transition metal complexes: a) Mo(CO)6; b) Mn(NO)(CN)5; c) Ru(bpy)(CN)4; d) Co(η5-cp)2.
a) Mo(CO)6: hexacarbonylmolybdenum(0)
b) Mn(NO)(CN)5: pentacyanonitrosylmanganese(V)
c) Ru(bpy)(CN)4: 2,2'-bipyridinetetracyanoruthenium(IV)
d) Co(η5-cp)2: bis-η5-cyclopentadienylcobalt(II)
3. The ligand, [2,4-ditert-butyl-6-{[(2-pyridyl)ethyl](2-hydroxybenzyl)-aminomethyl}-phenol when complexed to Co2+, Ni2+, and Cu2+ gives the data shown below. Is the ligand a weak field or strong field? Are the data internally consistent? Explain your reasoning.
Ionλmax (nm) ε (M–1cm–1)μeff (BM)
Co2+750 304.4
Ni2+680 702.9
Cu2+770 4001.3
Co2+ is d7, which can be either high spin (t2g5eg2 with 3 unpaired spins and a spin-only magnetic moment of about [3(3+2)]½ = 3.87 μB) or low spin (t2g6eg1 with 1 unpaired spin and a spin-only magnetic moment of about [1(1+2)]½ = 1.73 μB). The observed magnetic moment indicates the high spin configuration. Ni2+ and Cu2+ only have one spin-state: Ni2+, d8, t2g6eg2 with 2 unpaired spins and a spin-only magnetic moment of about [2(2+2)]½ = 2.83 μB and Cu2+, d9, t2g6eg3 with 1 unpaired spin and a spin-only magnetic moment of about [1(1+2)]½ = 1.73 μB, both consistent with the experimental data. The magnetic moments would imply a weak ligand. The spectral data predict 10Dq values of 107/750 = 13000 cm–1 for Co2+, (107/680)×(10/8) = 18000 cm–1 for Ni2+, and 107/770 = 13000 cm–1 for Cu2+. These are all small values, which are consistent with the magnetic moment data indicating a weak ligand.
4. Predict if the following will be Jahn-Teller active. For those that are J-T active, predict whether the distortion will be elongation or compression. a) Mo(CO)6; b) Fe(CN)64–; c) Fe(CN)63–; d) CoF64–.
a) Mo(CO)6: Mo0 is d6 and CO is a strong ligand so the electron configuration is t2g6, which is not Jahn-Teller active.
b) Fe(CN)64–: Fe2+ is d6 and CN– is a strong ligand so the electron configuration is t2g6, which is not Jahn-Teller active.
b) Fe(CN)63–: Fe3+ is d5 and CN– is a strong ligand so the electron configuration is t2g5, which is Jahn-Teller active. Elongation stabilizes the dxz and dyz orbitals and destabilizes the dxy, which removes the degeneracy.
d) CoF64–: Co2+ is d7 and F– is a weak ligand so the electron configuration is t2g5eg2, which is Jahn-Teller active. Elongation stabilizes the dxz and dyz orbitals and destabilizes the dxy, which removes the degeneracy.
5. Use the EAN rule to determine if the following are stable or not: a) Mo(CO)6; b) Ni(PF3)4; c) V(CO)6; d) Co(η5-cp)2.
a) Mo(CO)6: Mo0 is d6, contributing 6 e–, and each CO contributes 2 e– so the total is 6 + 2×6 = 18, so this complex is predicted to be stable.
b) Ni(PF3)4: Ni0 is d10, contributing 10 e–, and each PF3 contributes 2 e– so the total is 10 + 2×4 = 18, so this complex is predicted to be stable.
c) V(CO)6: V0 is d5, contributing 5 e–, and each CO contributes 2 e– so the total is 5 + 2×6 = 17, so this complex is not predicted to be stable.
d) Co(η5-cp)2: Co2+ is d7, contributing 7 e–, and each η5-cp contributes 6 e– so the total is 7 + 2×6 = 19, so this complex is not predicted to be stable.