3. Assign these molecules to point groups a. (9) All of the dichlorobenzene isomers Cl

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1 CE 610 Spring 2007 Problem Set 1 key Total points = (10 points) What distinguishes transition metals from the other elements in the periodic table? List five physical or chemical features that are distinctive properties of transition metals. Many possibilities: Partially filled d orbitals Multiple oxidation states Magnetic behavior (esp. ferromagnetism) Brightly colored complexes orm complexes with a variety of geometries orm kinetically both labile and inert complexes orm a variety of homogenous and heterogeneous catalysts 2. (15) What group is obtained by adding or deleting from each of the following groups the indicated symmetry operation? a. C 3v plus i = D 3d b. S 6 minus i = C 3 c. C 5v plus σ h = D 5h 3. Assign these molecules to point groups a. (9) All of the dichlorobenzene isomers C 2v C 2v D 2h b. (3) cis-[pt 2 (N 3 ) 2 ] (ignore positions) c. (3) trans-[pt 2 (N 3 ) 2 ] (ignore positions) N 3 Pt Pt N 3 N 3 N 3 D 2h C 2v 1

2 d. (39) All isomers of tetrafluorocyclooctatetraene (C in a tub conformation) I found 13 unique isomers. Did I miss any? 1,2,3,4-C ,2,3,5-C C 2 C 1 1,2,3,6-C C 1 1,2,3,7-C C 1 1,2,3,8-C C s 1,2,4,5-C ,2,4,6-C 4 4 C 1 C 1 C s 1,2,5,6-C ,3,5,7-C ,3,5,8-C ,3,6,8-C ,4,5,8-C C 2v S 4 C 1 C 2 D 2 Picture each isomer in a tub conformation. ere are four examples. 1,2,3,4-C ,2,3,5-C C 2 C 1 1,2,3,8-C C s 1,3,5,7-C S 4 2

3 e. (3) S 4 f. (3) P 3 g. (3) N 4 + h. (3) [B ] 2- B 2- S P N B B B B B B B B B B C 2v i. (3) C 3v T d I h Zr D 4 Tetra(acetylacetonato)zirconium(IV) (ignore symmetry of acac) 3

4 j. (18) e 1,1'-dichloroferrocene, all eclipsed and staggered rotamers C 2 C 2 C 2h C 2v C 2 C 2 4

5 k. (9) [Re 2 8 ] 2-, eclipsed (shown), staggered (45 ) and gauche (any other angle) Re Re Re Re Re Re D 4h D4d has 4 σ d D 4 lacks 4 σ d 4. (20 points) The interaction of [Mo() 6 ] with triphenylphosphite gives two complexes with the formula [Mo() 4 {P(Ph) 3 } 2 ]. Assign the isomers to point groups (treat the phosphites as point ligands i.e., ignore their symmetry). The carbonyl stretching frequencies at about 2000 cm - 1 are well isolated from other vibrations in the molecules. Derive the symmetry (Mulliken label) of each stretching frequency, and tell whether it is IR and/or Raman active. PR 3 C PR 3 Mo C PR 3 C C Mo PR 3 cis, C 2v trans, D 4h C 2v E C 2 (z) σ v (xz) σ v (yz) linear, rotations quadratic 5

6 A z x 2, y 2, z 2 A R z xy B x, R y xz B y, R x yz Γ() Γ() reduction: Number of A 1 = [(4)(1)(1) (2)(1)(1) + (2)(-1)(1)]/4 = 2 Number of B 1 = [(4)(1)(1) (2)(1)(1) + (2)(1)(1)]/4 = 1 Number of B 2 = [(4)(1)(1) (2)(-1)(1) + (2)(1)(1)]/4 = 1 The cis isomer has 4 ν() absorptions, all IR and Raman active D 4h E 2C 4 (z) C 2 2C' 2 2C'' 2 i 2S 4 σ h 2σ v 2σ d linear, quadratic rotations A 1g x 2 +y 2, z 2 A 2g R z B 1g x 2 -y 2 B 2g xy E g (R x, R y ) (xz, yz) A 1u A 2u z B 1u B 2u E u (x, y) Γ() Γ() reduction: Number of A 1g = [(4)(1)(1) (2)(2)(1) (4)(1)(1) + (2)(2)(1) + 0]/16 = 1 Number of B 1g = [(4)(1)(1) (2)(2)(1) (4)(1)(1) + (2)(2)(1) + 0]/16 = 1 Number of E u = [(4)(2)(1) (4)(2)(1) ]/16 = 1 The trans isomer has 3 ν() absorptions: E u is IR active; A 1g and B 1g are Raman active, 5. (24 points) The interaction of trigonal bipyramidal [e() 5 ] with P 3 gives several products with the formula [e() 3 (P 3 )} 2 ]. Sketch each isomer and assign its point group. The carbonyl stretching frequencies at about 2000 cm - 1 are well isolated from other vibrations in the molecules. Derive the symmetry (Mulliken label) of each stretching frequency, and tell whether it is IR and/or Raman active. 6

7 P 3 P 3 C e P 3 C e P 3 P 3 3 P e D 3h C 2v C s D 3h E 2C 3 3C' 2 σ h 2S 3 3σ v linear, quadratic rotations A' x 2 +y 2, z 2 A' R z E' (x, y) (x 2 -y 2, xy) A'' A'' z E'' (R x, R y ) (xz, yz) Γ() Number of A' 1 = [(3)(1)(1) (1)(3)(1) + (3)(1)(1) (1)(3)(1)]/12 = 1 Number of E' = [(3)(1)(1) (3)(1)(2) ]/12 = 1 The D 3h isomer has 2 ν() absorptions: E' is IR and Raman active A' 1 is only Raman active, C 2v E C 2 (z) σ v (xz) σ v (yz) linear, quadratic rotations A z x 2, y 2, z 2 A R z xy B x, R y xz B y, R x yz Γ() Number of A 1 = [(3)(1)(1) + (1)(1)(1) + (1)(1)(1) + (3)(1)(1)]/4 = 2 Number of B 2 = [(3)(1)(1) + (1)(1)(-1) + (1)(1)(-1) + (3)(1)(1)]/4 = 1 The C 2v isomer has 3 ν() absorptions, all IR and Raman active, C s E σ h linear, rotations quadratic A' 1 1 x, y, Rz x2, y2, z2, xy A'' 1-1 z, Rx, Ry yz, xz Γ() 3 1 7

8 Number of A' = [(3)(1)(1) + (1)(1)(1)]/2 = 2 Number of A'' = [(3)(1)(1) + (1)(1)(-1)]/2 = 1 The C s isomer has 3 ν() absorptions, all IR and Raman active, 6 (5 each = 20) Name these compounds, both a line formula (where not given) and a full name a. K 2 [ebr 4 ] = Potassium tetrabromoferrate(ii) b. Λ-cis- [Co( 2 NC 2 C 2 N 2 ) 2 ( 2 )( κ-n 2 )] 2+ N 2 2 N 2 Co 2 N N N 2 2+ = Λ-cis-aquabis(ethane-1,2-diamine) (nitritoκ)cobalt(iii) ion Many variations are possible. ethylenediamine and 1,2-diaminoethane are widely accepted names in fact, I think the latter is more proper than the version in the IUPAC guide. Nitrito- is in common use. Indicating the 2+ charge on the ion instead of the oxidation state is accepted. c. 3 N 3 N N 3 Co N 3 N 3 Co N 3 N 3 N 3 4+ [Co 2 (N 3 ) 8 ( µ ) 2 ] 4+ or [{Co(N 3 ) 4 } 2 ( µ ) 2 ] 4+ octaamminedi-µ-hydroxodicobalt(4+). Possible variants: drop one a between octa and ammine, use hydroxy instead of hydroxo, indicate oxidation state III instead of the ionic charge. 8

9 d. trans, trans-[mn 2 () 8 (PPh 3 ) 2 ] or trans, trans-[{mn() 4 (PPh 3 )} 2 ] Ph 3 P C Mn C Mn PPh 3 trans, trans-octacarbonylbis(triphenylphosphine- 1κP,2κP)dimanganese (Mn Mn). Possible variants: phosphane instead of phosphine, indicate the distribution of carbonyls as (octacarbonyl-1κ 4 C,2κ 4 C), or trans, transbis(tetracarbonyltriphenylphosphinemanganese) (Mn Mn) would be understandable. 7. (5 each = 15) Draw structures. Draw all isomers if a single isomer is not specified a. carbonylchlorodihydridobis(trimethylphosphane)rhodium C Me 3 P Me 3 P C 2 pairs of enantiomers b. sodium hexafluoromanganate(iv) 4- Na + 2 Mn c. (µ-ethane-1,1-diyl)bis(pentacarbonyltechnetium) C Tc C C 3 C Tc C 9