1. Find the point group for the following: a) SF6 b) SeF4 c) pentacyanonitrosylferrate(III).
a) SF6:
, Oh.
b) SeF4:
, C2v.
c) pentacyanonitrosylferrate(III):
, C4v.
2. Find the LFSE (in terms of Dq and P) and the spin-only magnetic moment for the following: a) hexacyanoferrate(II) ion; b) diaquadichlorocobalt(II); c) hexaamminechromium(III) ion.
a) hexacyanoferrate(II) ion
Fe(CN)64–: Fe2+ is d6 and CN– is a strong ligand, so the complex will be low spin. The electron configuration is t2g6, which has LFSE = 24Dq – 2P. There are 0 unpaired spins so μ = 0 μB
b) diaquadichlorocobalt(II)
Co(H2O)2Cl2: Co2+ is d7, H2O and Cl– are both weak ligands, and the complex must be in a tetrahderal geometry (no cis or trans information is given) so the complex will be high spin. The electron configuration is e4t23, which has LFSE = 12Dq. There are 3 unpaired spins so μ = [3(3+2)]½ = 3.87 μB
c) hexaamminechromium(III) ion
Cr(NH3)63+: Cr3+ is d3 so the ligand strength is irrelevant. The electron configuration is t2g3, which has LFSE = 12Dq. There are 3 unpaired spins so μ = [3(3+2)]½ = 3.87 μB
3. Which of the following complexes will be stable by the EAN rule: a) tetracarbonylnickel(0); b) bis(η1-cyclopentadienyl)bis(η5-cyclopentadienyl)titanium(IV); c) trichloro-η2-etheneplatinate(II) ion. Explain your reasoning.
a) tetracarbonylnickel(0)
: Ni0 is d10 and each CO donates 2 e–, so the total count is 10 + 4(2) = 18, stable.
b) bis(η1-cyclopentadienyl)bis(η5-cyclopentadienyl)titanium(IV)
: Ti4+ is d0, each η1-cyclopentadienyl donates 2 e–, and each η5-cyclopentadienyl donates 6 e– so the total count is 0 + 2(2) + 2(6) = 16, probably stable.
c) trichloro-η2-etheneplatinate(II) ion
: Pt2+ is d8, each Cl donates 2 e–, and η2-ethene donates 2 e– so the total count is 8 + 3(2) + 2 = 16, probably stable.
4. Which of the following complexes will be Jahn-Teller active: a) dichloroargentate(I) ion; b) hexaaquamanganese(III) ion c) hexanitritovanadate(III) ion. For those complexes that are Jahn-Teller active, predict the nature of the distortion.
a) dichloroargentate(I) ion: Cl–Ag–Cl, this is a linear ion so is not Jahn-teller active.
b) hexaaquamanganese(III) ion: octahedral Mn3+ with the weak ligand water is t2g3eg1, which is Jahn-Teller active. No prediction on the nature of the distortion can be made.
c) hexanitritovanadate(III) ion: octahedral V3+ with the strong ligand nitrite ion is t2g2, which is Jahn-Teller active. The complex is predicted to exhibit an axial elongation.
5. Explain why four coordinate Cu2+ complexes are never found with pure tetrahedral geometry.
Cu2+ with a pure Td geometry would have an electron configuration of e4t25, which is Jahn-Teller active. Consequently, the complex must distort away from the tetrahedral geometry (probably by twisting to a D2d structure).