1.* (1997 F 5) A. Indicate the oxidation state, d-electron count, and number of unpaired electrons in each of the following isostructural complexes: K4[Fe(CN) 6] and [Et4N]4[V(CN) 6]. B. How many unpaired electrons, if any, are in each of the following complexes? Indicate whether either complex would be an oxidizing or a reducing agent.
2.* (1997 2 4) Following are classifications of organometallic reactions. Next to each type of reaction put letters which correspond to the nature of this reaction. (a) This reaction is also known for
d0 complexes.
3.* (1996 2 2) For each of the following diamagnetic, coordinatively saturated ("18 electron") complexes: 1. Identify the metal, Note that the nature of the metal (3d, 4d, or 5d) is specified. A. M(CO)4 (3d) B. (C6H6)2M+ (5d) C. [Cp2M] (3d)
4.* (1995 3 1) One can make "educated guesses" about the rates of outer sphere electron transfer reactions. For each of the following suggest whether the "self-exchange" is either very fast or not very fast. Briefly indicate the basis for your guess. B. Fe(CN)63- and Fe(CN)64- (do not worry about like charges
repelling on another).
5.* (1995 3 2) Below are electrode potentials for conventional half-cell reactions (reduction potentials) versus the "normal hydrogen electrode."
A. Which substance among all of these components is the strongest reducing agent? B. Which substance is the strongest oxidizing agent? C. Is it feasible to find a catalyst to make H2O2 by bubbling O2 into water according to the following equation? O2 + 2H2O --> 2H2O2
6.* (1995 2 2) A. Draw all possible stereoisomers of [CoCl2(en)(NH3)2]+. Which are chiral? (en = H2NCH2CH2NH2) B. Which of the following complexes obey the 18-electron rule: Cr(CO)6, Fe(CN)64-, Co(en)32+.
7.* (1995 2 3) Paramagnetic complexes of Pd are quite rare whereas Ni complexes are often paramagnetic. It is also true that octahedral complexes of Pd(II) are virtually unknown whereas four-coordinate complexes of Pd(II) are common. A. What is the electron count in 4-coordinate Pd(II) complexes? Are these complexes "coordinately" saturated? B. What is the typical coordination geometry manifest by four-coordinate Pd(II) complexes? C. Propose a d orbital splitting pattern for an octahedral complex; mark each orbital by the usual Cartesian coordinates X, Y, Z assuming that the ligands lie on the X, Y, and Z axes. Show patterns of orbital degeneracies. Fill in the correct number of electrons derived from the oxidation state Pd(II). How many electrons are unpaired? D. What accounts for the difference between the diamagnetism of Pd(II) complexes and the paramagnetism of Ni(II) complexes?
8.* (1994 F 6) Anhydrous chromium trichloride (CrCl3) is insoluble; in the solid state CrCl3 exists as a three-dimentsional polymeric bridging chloride structure. By contrast, the hydrate, CrCl3(H2O)3 is soluble in water; it does not exchange with radioactive chloride anions over a period of many days in solution. Chromium dichloride (CrCl2) is also soluble in H2O; the chloride ligands in CrCl2 are rapidly exchanged by H2O forming Cr(H2O) x2+. A. Propose a mechanism for this process by writing equations for the steps which may occur. (Hint: Eo for Zn2+/Zn- is -0.7 V vs. NHE.) B. Give a rationale for the difference in the rates of chloride exchange comparing Cr(III) and Cr(II). C. Discuss the number and nature of isomers formed by CrCl3(L)3. Draw structural formulas depicting these stereoisomers.
9.* (1994 3 1) A. Which is the stronger oxidizing agent? KReO4 vs. KMnO4 B. Which is the better reducing agent? CrCl2 vs. MnCl2
10.* (1994 3 2) Which of the following redox reactions (A or B) do you expect to be faster? Explain your answer. A. Ru(en)32+ + Ru(en)33+ --> Ru(en)33+ + Ru(en)32+ B. Co(en)32+ + Co(en)33+ --> Co(en)33+ + Co(en)32+
11.* (1994 2 4) The following is a list of reaction classes which encompasses the majority of the transformations of organometallic compounds: (a) ligand substitution or dissociation, (b) oxidative addition, (c) reductive elimination, (d) migratory insertion, (e) electrocyclization. Now consider the catalytic cycle of reactions which are known to occur in the Monsanto acetic acid process in which methanol combines with CO to form acetic acid: CH3OH + CO ---(Rh catalyst, I-)--> CH3CO2H
The steps in this cycle are labeled (1), (2), (3), and (4); the intermediate complexes are labeled I, II, III, and IV. Over the arrow for each step put the letter from the above list indicating the nature of that step. Under each intermediate complex put the formal oxidation state and d electron configuration of the central metal (i.e. Mo(II) d4). Place an asterisk beside each coordinatively unsaturated ("16-electron") complex.
12.* (1993 F 6) A. Will an inner sphere reaction in which water is the bridging ligand occur more rapidly in strong acid or in strong base? Explain your answer with a mechanism. B. Other than self exchange rates, what additional factors must be taken into account to predict the approximate rates of inner sphere redox reaction between two different complexes?
13.* (1993 3 1) Explain each of the following. A. Metal containers corrode more rapidly in dilute HCl than in aqueous H2SO4 solutions having the same pH. B. The anion [IrCl6]2- is a strong oxidizing agent whereas the cation Cr2+ aqueous is a strong reducing agent. C. At the time Stanford was founded, aluminum metal dinner plates were more expensive than solid silver plates whereas today the opposite is true. D. A sample of [Co(dipy)3](ClO4)3, A, in aqueous solution has been resolved and is optically active. The optical isomer is stable for prolonged periods at room temperature. All attempts to resolve [Co(dipy)3](ClO4)2, B, failed to yield an optically active product. When a trace of B was added to a solution of optically active A, the optical activity of the latter slowly fell to a value of zero. Discuss both the mechanism and the thermodynamic driving force for this reaction.
14.* (1993 3 2) Which of the following reactions do you expect to be the fastest; which the slowest. Explain your answer. (1) [Ru(dipy)3]2+ + [Ru(phen)3]3+ --> B. Copper(I) disproportionates into copper(II) and Cuo (Eo Cu+/Cuo = +0.52 V; Eo Cu2+/Cu+ = +0.15 V). Given the following Eo values for Ag, calculate the feasibility of Ag+ disproportionating into Ag2+ and Ago. (Eo Ag+/Ago = +0.799 V; Eo Ag2+/Ag+ = +1.98 V).
15.* (1993 2 3) A. Which of the following is rouge and which is colorless? TiO2 and Fe2O3 B. Which of the following is more stable towards thermal decomposition? trans-Pt(PPh3)2R2: R= -CH2-C(CH3)3 or R = -CH2-CH(CH3)2
16.* (1992 F 24) Which would make a better oxidizing agent: [IrCl6]2- or [PtCl6]2-?
17.* (1992 F 25) Consider the diamagnetic complex [M(en)3(ClO4) 3] where M is a 3d metal. A. What is M? B. What is the oxidation state of M? C. How many d electrons? D. Will this complex be a strong oxidizing agent? E. Sketch a picture of all stereoisomers of this complex. F. What features would the 13C NMR spectrum exhibit?
18.* (1992 2 5) For each of the following, A. Which compounds could dimerize? B. Which compounds are not coordinatively saturated? C. For which compounds is cis-trans isomerism possible? D. Which compounds have more than 18 electrons?
19.* (1991 F 6A) In a complex M(OH2) 6Cl3, what is the oxidation state of M?
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