Problem 29
Comment on the observations that octahedral Ni(II) complexes have magnetic moments in the range \(2.9-3.4\) \(\mu_{\mathrm{B}},\) tetrahedral \(\mathrm{Ni}(\mathrm{II})\) complexes have moments up to \(\cong 4.1 \mu_{\mathrm{B}},\) and square planar \(\mathrm{Ni}(\mathrm{II})\) complexes are diamagnetic.
Problem 30
For which of the following ions would you expect the spin-only formula to give reasonable cstimates of the magnetic moment: (a) \(\left[\mathrm{Cr}\left(\mathrm{NH}_{3}\right)_{6}\right]^{3+}\) (b) \(\left[\mathrm{V}\left(\mathrm{OH}_{2}\right)_{6}\right]^{3+}\) (c) \(\left[\mathrm{CoF}_{6}\right]^{3-}\) ? Rationalize your answer.
Problem 33
Values of \(\Delta_{\mathrm{oct}}\) for \(\left[\mathrm{Ni}\left(\mathrm{OH}_{2}\right)_{6}\right]^{2+}\) and high-spin \(\left[\mathrm{Mn}\left(\mathrm{OH}_{2}\right)_{6}\right]^{3+}\) have been evaluated spectroscopically as 8500 and \(21000 \mathrm{cm}^{-1}\) respectively. Assuming that these values also hold for the corresponding oxide lattices, predict whether \(\mathrm{Ni}^{\mathrm{II}} \mathrm{Mn}_{2}^{\mathrm{III}} \mathrm{O}_{4}\) should have the normal or inverse spinel structure. What factors might make your prediction unreliable?
Problem 36
(a) Which of the following complexes would you expect to suffer from a Jahn- Teller distortion: \(\left[\mathrm{CrI}_{6}\right]^{4-}\) \(\left[\mathrm{Cr}(\mathrm{CN})_{6}\right]^{4-},\left[\mathrm{CoF}_{6}\right]^{3-}\) and \(\left[\mathrm{Mn}(\mathrm{ox})_{3}\right]^{3-} ?\) Give reasons for your answers. (b) \(\left[\mathrm{Et}_{4} \mathrm{N}\right]_{2}\left[\mathrm{NiBr}_{4}\right]\) is paramagnetic, but \(\mathrm{K}_{2}\left[\mathrm{PdBr}_{4}\right]\) is diamagnetic. Rationalize these observations. (c) Using a simple MO approach, explain what happens to the energies of the metal \(d\) orbitals on the formation of a \(\sigma\) -bonded complex such as \(\left[\mathrm{Ni}\left(\mathrm{NH}_{3}\right)_{6}\right]^{2+}\).
Problem 38
(a) The values of \(\epsilon_{\max }\) for the most intense absorptions in the electronic spectra of \(\left[\mathrm{CoCl}_{4}\right]^{2-}\) and \(\left[\mathrm{Co}\left(\mathrm{OH}_{2}\right)_{6}\right]^{2+}\) differ by a factor of about \(100 .\) Comment on this observation and state which complex you expect to exhibit the larger value of \(\varepsilon_{\max }\) (b) In the clectronic spectrum of a solution containing \(\left[\mathrm{V}\left(\mathrm{OH}_{2}\right)_{6}\right]^{3+},\) two bands are observed at 17200 and \(25600 \mathrm{cm}^{-1} .\) No absorption for the \(^{3} A_{28} \leftarrow^{3} T_{1 g}(F)\) transition is observed. Suggest a reason for this, and assign the two observed absorptions. (c) Red crystalline \(\left[\mathrm{NiCl}_{2}\left(\mathrm{PPh}_{2} \mathrm{CH}_{2} \mathrm{Ph}\right)_{2}\right]\) is diamagnetic. On heating to \(387 \mathrm{K}\) for 2 hours, a blue-green form of the complex is obtained, which has a magnetic moment of \(3.18 \mu_{\mathrm{B}}\) at \(295 \mathrm{K}\). Suggest an explanation for these observations and draw structures for the complexes, commenting on possible isomerism.
Problem 40
(a) Explain the origins of MLCT and LMCT absorptions in the electronic spectra of \(d\) -block metal complexes. Give examples to illustrate your answer. (b) Explain what information can be obtained from a Tanabe-Sugano diagram.
