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Chemistry 1311 Problem Set 9 From text (RC) Chapter 19: problems 5, 6 (compounds are [Co(en)3]Cl3 and [Co(NH3)3Cl3]), 7, 10, 14, 15-17, 23 (contrary to what the problem indicates the more common abbreviation for this tridentate ligand is actually dien), 26, 31 19.5 In addition to cis- and trans-[Pt(NH3)2Cl2], the other compound of the same empirical formula is [Pt(NH3)4][PtCl4]. It is a structural isomer of the other two since it has different atom connectivities. 19.6 As a tris-chelate complex the cation [Co(en)3]3+ exists in non-superimposable mirror-image forms. [Co(NH3)3Cl3] has two diastereoisomeric forms meridonal and facial. 19.7 H2 N Cl H2 N 1+ Co N H2 Cl N H2 NH2 H2N H 2N 1+ Cl Cl Co Co Cl NH2 1+ H 2N Cl NH2 NH2 H 2N 19.10 [Cr(NH3)6]Cl3 [Co(H2NCH2CH2NH2)2(OH2)(NCS)]NO3 K2[Ni(CN)4] [Co(H 2NCH2CH2NH2)3]I3 19.14 [Fe(CN)6]3- will be low spin because cyanide is a strong field ligand which in itself is enough, but this is also a trivalent metal ion, which also serves to increase the crystal field splitting (relative to a divalent ion). [FeCl4]- will be high spin because the crystal field splitting for tetrahedral complexes is always small and they are therefore always high spin. It is worth noting that chloride ion is a weak field ligand and that the complex contains Fe(II) which results in a smaller crystal field splitting than would exist for a higher oxidation state. 19.15 [Co(NH3)6]3+ has the largest crystal field splitting because it contains a +3 ion; this complex is low-spin d6. The analogous +2 ion has a value that is roughly one half as large, which is predicted for a difference in oxidation state of one; it is high-spin d7. The stereochemistry of [Co(NH3)4]2+ is not given, but assuming that it is tetrahedral the crystal field splitting for tetrahedral complexes is only about 4/9 that of octahedral complexes of similar ligands. If tetrahedral it is high-spin. 19.16 [CrF6]3- and [Cr(OH2)6]3+ both contain Cr3+. The difference in their crystal field splitting is due to the difference in ligand field strength for fluoride (smaller) vs water (larger). [CrF6]2- contains Cr4+; the increase in crystal field splitting is due to the increase charge on the metal. [Cr(CN)6]3- contains Cr3+; the large value for the crystal field splitting reflects the large ligand field strength of the cyanide ligand. 19.17 (a) Both [MnF6]2- and [ReF6]2- contain metal ions in the +4 oxidation state. The crystal field splitting will be larger for the latter ion because it is in the third transition series. Metal-ligand interactions increase in strength in a family due to increased orbital overlap between metal and ligand orbitals and increased covalency in the bond. (b) [Fe(CN)6]4- and [Fe(CN)6]3- contain iron in the +2 and +3 oxidation state, respectively. The latter ion will have the larger crystal field due to the increased ion charge. 19.23 [Ni(OH2)6]2+ + 2 dien = [Ni(dien)2]2+ + 6 H2O. This reaction will be strongly favored because of the increase in entropy resulting from the net gain of four free molecules (chelate effect). Note that the problem did not state whether a 1:1 or 1:2 complex was formed. The latter was assumed in writing the balanced reaction; however, the chelate effect would operate if only a 1:1 complex was formed. There is also a very favorable enthalpy change for both reactions. 19.25 The difference in stoichiometry is a result of the difference in size of the ligands. The tricyclohexylphosphine is so large that only one can be accommodated. Probably [FeL3Cl3] would be formed with a sufficiently small phosphorus ligand, perhaps with trimethylphosphine. The difference in sizes is reflected in the spacefilling models of these ligands shown below. P(CH3)3 P(C6H5)3 P(C6H11)3 19.26 Because [Ni(PPh3)2Cl2], a d8 four-coordinate complex, is paramagnetic it must be tetrahedral (recall that all square-planar d8 complexes are low-spin and diamagnetic) and there is only one stereoisomer. Because [Pd(PPh3)2Cl2] is diamagnetic and also contains a d8 ion it must be square-planar. Therefore there are two stereoisomers (diastereoisomers also known as geometrical isomers) cisand trans-. 19.31 The three compounds are [Cr(OH2)6]Cl3, hexaquachromium(III) chloride; [Cr(OH2)5Cl]Cl2, pentaaquachlorochromium(III) chloride; [Cr(OH2)4Cl2]Cl, tetraaquadichlorochromium(III) chloride. 1. Draw structures for the following molecules or ions and identify the potential donor atoms in each. P(CH3)3, H2NCH2CH2SCH2CH2NH2, SO32-, NCS-, oxalate ion (C2O42-), glycinate (H2NCH2CO2-). P H3C CH3 O O C C H2N CH3 O O NH2 S - S - O O - N O C S - O H2 N - O - 2. Covalent interactions of ligands with transition metal ions can have dramatic effects on the energy separation of the two groups of d orbitals in an octahedral complex. All ligands bond more or less strongly through σ interactions but it is the presence, and type, of π interaction that differentiates ligands into weak (π donor), intermediate (often no π interaction), and strong field (π acceptor) types. Specify a ligand of each type and for the π donor and π acceptor ligands indicate what orbital(s) on the ligand are used for π bonding to the metal. Ligand Orbital used for π bonding σ only H- or NH3 Not applicable π acceptor CO or PR3 π*, 3d π donor halide np 3. Draw structures of the diastereoisomers that can exist for the complex ion [Co(H2NCH2CH2NH2)(NH3)2Cl2]+ ? Which of these diastereoisomers is enantiomeric? N N NH3 Co NH3 Cl Cl N Cl N Co Cl NH3 N NH3 N NH3 Co Cl NH3 Cl 4. Draw structures for all of the diastereoisomers of [Co(dien)(Cl)(NO2)2]? dien is H2NCH2CH2NHCH2CH2NH2. Which of these diastereoisomers is enantiomeric? N N O2N N NO2 Cl N N Cl Cl Co N NO2 N N N NO2 Cl Cl N NO2 NO2 N N NO2 Cl Cl NO2 5. Draw structures for all stereoisomers (diastereoisomers and enantiomeric forms) of [Co(H2NCH2CH2O)3]? N O N Co O N N N O O Co N N N O O N Co O O N N O O Co O N O 6. The tetradentate ligand H2NCH2CH2NHCH2CH2NHCH2CH2NH2 forms six-coordinate complexes with Co(III) having the composition [CoLX2]+ where X is a mondentate ligand. Draw structures of all possible diastereoisomers and indicate which are enantiomeric. trans α-cis β-cis