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21.1-21.4, 22 Ch Assigned Reading: 21.1-21.4, 22 Ch 102 – Problem Set 6 Due : Thursday, May 20 – Before Class Problem 1 (20 pts) For the following molecules, (i) Determine the oxidation state and d electron count of the metal (ii) Identify the compound as high spin or low spin (iii) Calculate the spin-only magnetic moment based on the number of unpaired electrons 3- a) [FeBr6] 2+ b) [Co(NH3)6] 3+ c) [Co(NH3)6] 3+ d) [Mn(CO)6] 3- e) [OsBr6] 2- f) [RhF6] g) TiCl4 - h) [TiCl4] Problem 2 (20 pts) For the following transition metal complexes, propose the most reasonable structure. Keep in mind the 18-electron rule. Give the valence shell electron count, the formal oxidation state and the d-electron count. Make sure that the ligand hapticity is clear in your drawings. Indicate clearly whether the NO ligand is bent or linear, if applicable. a. (C6H6)Fe(CO)2PPh3 2+ b. [(C6H6)Fe(CO)2PPh3] c. Fe(NO)2(CO)2 d. (C6Me6)2Ru (C6Me6 = hexamethylbenzene) e. Mn2(CO)10 f. [(C6H6)W(C3H5)]2(µ-Cl)2 + g. [CoCl(en)2(NO)] (en = ethane-1,2-diamine, a.k.a. ethylenediamine) Problem 3 (15 Points) For the following transition metal complexes, give the valence shell electron count, the formal oxidation state, and the d-electron count. a. PR2 Ph B Fe N R = H2C P R 2PR2 b. tBuO OtBu OtBu W W tBuO tBuO OtBu c. (H3C)2HC Cl Cl CH(CH3)2 (H C) HC CH(CH ) 3 2 P Ni Ni P 3 2 d. CO O C Mo Mo P Me2 CO O N N O H Ni H O N N O e. Problem 4 (20 Points) - Permanganate MnO4 is a tetrahedral ion with an intense purple color that is widely used as an oxidizing agent. The figure below shows a convenient coordinate system for a tetrahedral complex that will be useful for generating a molecular orbital diagram for permanganate. a) Give the total electron count and d-electron count for Mn. Note that O2- is a strong π donor and the donated π-lone pairs are considered in electron count. For now do not consider the availability of appropriate orbitals on Mn to accept these electrons and include them in electron count. b) Using the coordinate system shown above, generate the reducible and irreducible representations for the ligand σ-bonding interactions (note that there are two orbitals on oxygen that have σ-symmetry with respect to the Mn-O interaction; for this problem consider only one σ-orbital per oxygen, the second will formally constitute a low energy lone pair on oxygen that should not be included in your analysis). c) Draw an MO diagram incorporating the ligand σ-bonding framework and d, s, and p orbitals on Mn. For full credit, be sure to do all of the following: • Label metal orbitals with the appropriate Mulliken symbol and designate them as d, s, or p • Label ligand orbitals with the appropriate Mulliken symbol • Draw the metal and ligand orbitals at the appropriate relative energies • Label the generated molecular orbitals with the appropriate Mulliken symbols and indicate whether they are σ, σ*, or nb • Fill in the correct number of electrons • Draw the LUMO d) Generate the reducible and irreducible representations for the ligand π-bonding interactions (two π-interactions per ligand) e) Draw a complete MO diagram incorporating both σ- and π-bonding ligand orbitals and d, s, and p orbitals on Mn. For full credit, be sure to do all of the following: • Label metal orbitals with the appropriate Mulliken symbol and designate them as d, s, or p • Label ligand orbitals with the appropriate Mulliken symbol and designate them as σ or π • Draw the metal and ligand orbitals at the appropriate relative energies • Label the generated molecular orbitals with the appropriate Mulliken symbols and indicate whether they are σ, σ*, π, π*, or nb • Fill in the correct number of electrons • Draw the HOMO and LUMO. f) Based on the MO diagram derived at e), what is the correct electron count for Mn? g) Is the electronic transition from the HOMO to the LUMO Laporte allowed? Depict this spin allowed excited state in the terms of a new electron configuration on the above MO diagram (only redraw the levels involved in the transition). Clearly show the spins of the electrons populating the frontier orbitals. Problem 5 (15 Points) Cytochrome P450 is an enzyme that catalyzes the oxygenation of C−H bonds to alcohols. One intermediate in the catalytic cycle, Compound II, is proposed to be a (porphyrin)iron(IV) oxo, also known as a ferryl complex. We will use the simplest porphyrin, porphine (see Fig. 12.9 in the textbook), to model the bonding in this compound. a. Construct the σ-only MO diagram (see 4(c) for general guidelines; no orbital drawings are required) in the D4h point group for (porphine)Fe(II) with no additional ligands and fill in the electrons. In this complex, porphine is a tetradentate dianionic ligand, so consider this complex as Fe2+ with two L- type and two X-type ligands. This complex is high-spin. b. Assign a spin state to high-spin (porphine)Fe(II) and calculate its spin-only magnetic moment. c. Derive the σ-only MO diagram for the (porphine)iron(IV) oxo complex by interacting the frontier orbitals of the MO diagram from (a) with the oxygen 2pz orbital (consider the z-axis as along the iron−oxygen axis). Make the new σ-interaction a very strong one. Note the change in symmetry and reassign the point group. (Do not fill in electrons yet, just show how the splitting changes. See 4(e) for general guidelines; no orbital drawings are required). d. Modify the MO diagram from (c) to include metal-ligand π-interactions. Consider the oxygen 2px and 2py orbitals perpendicular to the iron−oxygen axis and find the symmetry-allowed interactions with the frontier orbitals of (porphine)iron(II) from (a) that were used in (c). These π-interactions are weaker than the σ-interaction. For each MO energy level, indicate whether it is σ, σ*, π, π*, or nb. Now fill in the electrons for (porphine)Fe(IV) oxo. See 4(e) for general guidelines; no orbital drawings are required. e. What is the metal-oxygen bond order? f. What would the metal-oxygen bond order be for the analogous (porphine)CrIV(O)? for (porphine)NiIVO? Problem 6 (10 Points) Using the output from webmo (provided on the ch102 website) analyze the molecular + orbitals of the [C3H3] fragment as drawn below (D3h symmetry). Attach pictures of the frontier molecular orbitals that have carbon pz contributions (they do not have to be HOMO or LUMO). Discuss what type of ligand this fragment is along the z-axis as a function of these orbitals (σ acid/base, π acid/base). H x H y H .
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