CHE450G Final Exam. CP-109 December 11, :30-12:30 AM

Transcription

1 CH450G Fnal xam CP-09 December, :30-2:30 AM Last name Frst Name Score [ /5] 00 = %

2 () Construct a physcally realstc molecular orbtal dagram for CS. Draw all SALC s, molecular orbtals, and provde the approprate Mullken symbols for each molecular orbtal. Show all work for credt. (0 ponts) 2

3 3 (2) Metal-lgand bondng s a fundamental concept that s useful n predctng both the propertes and reactvty of a transton metal complex. (a) Compare and contrast the dfferences between π-donors and π -acceptor lgands. Gve an example of each lgand type. Show all work for credt. (5 ponts) π-donors (π-bases): lgands wth flled π symmetry orbtals (p or π) and no low energy or vacant p or π * orbtals that can engage n π-bondng wth the transton metal orbtals (t 2g set n O h complexes); decrease Δ o. (e.g. I - ) π-acceptor (π-acds): lgands that do have empty π symmetry orbtals (p or π * ) that can engage n π-bondng wth transton metal orbtals (t 2g set n O h complexes) and no flled π symmetry orbtals that are close n energy to the metal orbtals; ncrease Δ o. (e.g. CO) (b) Use a partal molecular orbtal dagram to show how π-donor and π-acceptor lgands dffer wth respect to metal-lgand bondng (lgand feld splttng). In other words, explan the spectrochemcal seres for an octahedral complex. Show all work for credt. (5 ponts) π bases: haldes (I -, Br -, - ) π acds: CN -, NO +, CO π * π * e g e g Δ O Δ O t 2g t 2g π Metal Complex Lgand Metal Complex Lgand π σ-donors: alter e g orbtal energes and do not alter the t 2g orbtal energes (O h symmetry) n transton metal complexes. e.g. H - and Me - π-donors/acceptors: alter t 2g orbtal energes (O h symmetry) but do not alter the e g orbtal energes n transton metal complexes

4 4 (3) Inspecton of the Spectrochemcal Seres reveals an nterestng but surprsng trend for halde lgands. It s found that for haldes, the lgand feld strengths are: F - > - > Br - > I - xplan why ths s the case. Hnt: It may prove useful to draw a smple molecular orbtal dagram for each M-X. Show all work for credt. (0 ponts) Note: Modfed verson of problem 0-3 n textbook usng Table 0-3 (3 rd d.) lgand feld strengths: F - > - > Br - > I - For a gven [Cr III X 6 ] 3- complex, where X - = F,, Br, I: Lgand F - - Br - I - Δ o (cm - ) 6,600 3,80 2, Decreasng σ and π donaton s found when.n. of X - decreases (see e σ and e π ). The partal M.O. (octahedral M III X 6 3- complex) dagram qualtatvely scales as a functon of X - : F - s a generally thought of as a good onor whle I - s weaker n comparson. F - s generally thought of as a poor π donor whle I - s a better one. F - gves good M-X orbtal overlap whle I - s poor n comparson. So, Δ o s largest for F - and smallest for I - (4) Construct a molecular orbtal dagram for a tetrahedral ML 4 complex where L s a hydrogen atom. Be sure to clearly draw the lgand SALC s, assgn the approprate Mullken symbols, and how each lgand SALC nteracts wth the transton metal s, p, and d orbtals. Show all work for credt. (0 ponts) z x t 2 () t 2 () T d Complex z y 4p (t 2 ) t 2 transton metal orbtals () 4s (a ) a () y x () a t 2 () t 2 t 2 (v) 3d (e + t 2 ) Δ T e e a (v) t 2 (v) a (v) t 2 (v) (v) a (v) Metal Complex Lgands (v)

5 5 (5) Determne the symmetres (Mullken symbols) of the d orbtals under D 4h symmetry. Show all work for full credt. (0 ponts) d orbtals = xz, yz, xy, z 2, and x 2 y 2 D 4h A g x 2 + y 2, z 2 A 2g R z B g x 2 y 2 B 2g xy g (R x, R y ) (xz, yz) A u A 2u z B u B 2u u (x, y) z y x d(xy) d(xz) d(yz) d(x 2 -y 2 ) d(z 2 ) - yz xz yz -xz yz xz - (6) For each molecule and on below gve the approprate () electron par geometry and () molecular geometry/structure names. Show all work for credt. (6 ponts) (a) [I 2 ] - (b) Se 4 (c) P 4 6- I - Se P P P P 6- F F O F F - total # valence electrons: 3(7) + = 22 (6) + 4(7) = 34 4(5) + 6 = 26 5(7) + (6) + = 42

6 6 # nonbondng pars on central atom: 7-2() + = 3 6-4() + 0 = 5-3(3) + 6 = 7-4() -(2) + = () electron par geometry consders all electron pars around central atom () trgonal bpyramdal trgonal bpyramdal tetrahedral octahedral () molecular geometry consders only bondng electron pars () lnear see-saw trgonal pyramdal square pyramdal (7) The followng regular polyhedra are members of what are known collectvely as the fve Platonc solds. To whch pont group(s) do each belong? (6 ponts) (a) (b) (c) O h O h T d (8) Assgn the proper pont group for the ons below. Assume an dealzed (hghest symmetry) structure whenever possble. (2 ponts) en = H 2 N H 4 NH 2 ; Tp * = HB(3,5-dmethylpyrazol-yl)borate or [HB(Me 2 C 3 HN 2 ) 3 ] - (a) [Nb IV (Ot) 2 (CN) 4 ] 2- (b) [Mn II (en) 3 ] 2+ (c) [Tp * V II (CN) 3 ] 2- (d) [Nb V (O)(CN) 6 ] 3- (lnear CN - lgands) h D 3 C 3v C 5v (9) xplan why the electronc confguraton for T s [Ar]4s 2 3d 2 but for Cr 2+ t s [Ar] 3d 4. (5 ponts) Short answer: 4s electrons have lower energes than 3d electrons n T In ons, 3d levels move to lower energes and electron-electron parng acts to ncrease the energy of the on (gong from left to rght) In Cr, 3d and 4s levels are very close n energy

7 7 Second electron n Cr 2+ goes to 3d shell to mnmze electron-electron repulson Long answer: To answer ths queston you must consder electron-electron repulson and Z eff for the 4s and 3d electrons snce ttanum(0) and Cr II are soelectronc. As Z eff ncreases, electrons become strongly bound to the transton metal center (more negatve energes) and the energy levels decrease n energy. The energy of the d orbtals decrease more rapdly than do the s orbtals as a functon of ncreasng Z snce they are shelded less than the s orbtals. The ntraorbtal repulson nteractons become greater than the subshell energes and consequently Cr II does not have 4s electrons. (0) Determne the number of nfrared actve ν CO stretchng absorptons for fac-mo(co) 3 (NCMe) 3. Use vectors, symmetry labels, and show all work to justfy your answers. Show all work for credt. (2 ponts)

8 () () Draw the nfrared actve stretchng and deformaton modes for ammona. () Assgn each usng the correct termnology and Mullken symbol approprate for the pont group desgnaton. () Use vectors to ndcate apparent moton of atoms where necessary. (20 ponts) 8

9 9 (2) (a) Plot the radal probablty functons for the 3d, 3s, and 3p orbtals. (5 ponts) (b) Arrange the 3d, 3s, and 3p orbtals as a functon of ncreasng energes. (5 ponts) 3d < 3p < 3s (c) Arrange the orbtals as a functon of ncreasng sheldng. (5 ponts) (d) Arrange the orbtals as a functon of ncreasng Z eff. (5 ponts) 3s < 3p < 3d 3d < 3p < 3s (3) Sold CrF 3 contans a Cr III on surrounded by sx F - ons n an octahedral geometry. All of the Cr-F dstances are 90 pm n length. However, MnF 3 adopts a dstorted geometry, wth Mn-F dstances of 79, 9, and 209 pm (two of each), respectvely. Provde an explanaton for these observatons. (0 ponts) Cr III (t 2g 3 ) s not subject to Jahn-Teller dstorton whle Mn III (t 2g 3 e g ) exhbts tetragonal elongaton that s typcal of Jahn-Teller dstorted ons. (4) Complete the mssng portons of the perodc table. (0 ponts)