Molecular Orbitals in Inorganic Chemistry

Transcription

1 Outlin olcular Orbitals in Inorganic Chmistry Dr. P. Hunt Rm 167 (Chmistry) octahdral complxs forming th O diagram for Oh colour, slction ruls Δoct, spctrochmical sris forming th O diagram for C4v 1 Octahdral Complxs vry larg and important class of transition mtal complxs T complxs act as catalysts to control and improv catalysts w nd to undrstand th undrlying lctronic structur magntic proprtis, colour! Rmovd du Imag from p16 of tal igand Bonding by R. Jans and E. oor RSC, Cambridg, work through for an octahdral molcul 2 O chcklist Stps to construct a O diagram dtrmin th molcular shap and idntify th point group of th molcul dfin th axial systm and find all of th symmtry oprations on th molcul idntify th chmical fragmnts, and put thm along th bottom of th diagram dtrmin th nrgy lvls and symmtry labls of th fragmnt orbitals (us H1s as a rfrnc) combin fragmnt orbitals of th sam symmtry, stimat th splitting nrgy and draw in th O nrgy lvls and Os (in pncil!) dtrmin th numbr of lctrons in ach fragmnt and hnc th cntral O rgion, add thm to th diagram idntify if any O mixing occurs, dtrmin th mixd orbitals and rdraw th O diagram with shiftd nrgy lvls and th mixd Os annotat your diagram us th O diagram to undrstand th structur, bonding and chmistry of th molcul 3 4 6_Slids_wb.ky - 1 Dcmbr 2017

2 Stps 1-2: Point Group dtrmin molcular shap: octahdral dtrmin th point group of th molcul find Oh in your charactr tabls dfin th axial systm find all of th symmtry oprations covrd last lctur Fig. 3 C 3 σ d C 4 Fig. 1 E 8C 3 6C 3σ 2 6C 4 3 i 6S 4 8S 6 h 6σ d A 1g A 2g Eg T 1g T 2g A 1u A 2u Eu T 1u T 2u y z x (x 2 +y 2 +z 2 ) (2z 2 -x 2 -y 2, x 2 -y 2 ) (xy, xz, yz) (T x, T y,t x) Fig. 2 Stps 3-4: Fragmnt Orbitals dtrmin th fragmnts cntral mtal and th symmtry adaptd fragmnt orbitals for 6 dtrmin th nrgy lvls and symmtry labls of th fragmnts covrd last lctur => tricks to hlp rmmbr Fig. 4 ligands C 4,C 4 σ v = σ h, C 4 mtal,c 4,C 4, C 4, C 4 Fig.5 Fig St up O Diagram St up O Diagram draw th fragmnts and chmical structur us plac holdrs! add th fragmnt orbitals mtal is lctropositiv daos ar highr in nrgy ligand orbitals ar bonding FOs li dpr in nrgy Fig 7 Pag 3 colour th plac holdrs in on your nots! 7 8 6_Slids_wb.ky - 1 Dcmbr 2017

3 Enrgy Diagram Combin Orbitals combin orbitals of th sam symmtry stimat th xtnt of nrgy splitting g ar s-σ =>strong splitting nrgy g ar far apart in nrgy =>rducs splitting stimat th xtnt of nrgy splitting t1u intraction is p-σ => mdium t1u nrgy diffrnc is vry larg => dcrass splitting siz mattrs! siz mattrs! antibonding =>larg bonding =>larg Fig.8 Fig Combin Orbitals Combin Orbitals stimat th xtnt of nrgy splitting g intraction is d-σ => small g clos in nrgy => incrass splitting stimat th xtnt of nrgy splitting mtal rmain non-bonding as thr ar no ligand orbitals of this symmtry siz mattrs! Fig _Slids_wb.ky - 1 Dcmbr 2017

4 Stps: 6-8 lctronic configuration six 2 donor ligands =12 numbr d lctrons dpnds on th mtal and oxidation stat I v usd six hr Enrgy Diagram Th full O diagram! dtrmin if thr is mixing no mixing occurs us O diagram chcklist! Fig.9 y z x Stp 9: Analysis Stp 9: Analysis thr lowst nrgy sts of orbitals ar ligand basd thr lowst nrgy sts of orbitals ar ligand basd highr nrgy Os ar mtal basd tal basd Os Fig.8 for xampl th Os igand basd Os Fig.8 for xampl th Os _Slids_wb.ky - 1 Dcmbr 2017

5 Not! lav off som of th lins for th mtal dominatd (s & p FOs) and th ligand dominatd (low nrgy) FOs kp all th lins for th daos! lav off som of th lins! paramtr Δoct nrgy span of th dao dominatd Os σ-ligands is non-bonding g is antibonding! Δoct dpnds on strngth of intraction: Δε nrgy btwn and FOs Sij strngth/dnsity of ovrlap of FOs Hij which is hard to stimat! total charg on complx oxidation stat of th (charg on ) 17 paramtr 18 Colour and d-d Transitions highr in nrgy th ligand FOs th bttr th intraction larg small g colour molcul absorbs light lctron is xcitd d-d transition right wavlngth for colour [Ti(OH2)6] 3+ absorbs in yllow/ grn and appars rd/violt Rmovd du rmindr Fig.10 => largr intraction => highr orbital => a largr Δoct Rmovd du Fig.11 Coordination Chmistry imi Hi ( ) Fig _Slids_wb.ky - 1 Dcmbr 2017

6 Colour and d-d Transitions Colour and d-d Transitions Slction Ruls d-d transitions ar forbiddn aport slction rul : only ±1 for angular quantum numbr s->p or p->d NOT d->d anothr form rul : must hav a chang of parity u->g or g->u NOT g->g (d->d transition involvs ->g) spin slction rul : cannot chang spin stat d->d transitions rmindr rul is brokn! wak transitions du to vibronic coupling vibrations and lctronic structur coupl low intnsity broad du to vibrations (mov nrgy lvls slightly) dx 2 -y 2 basd O Fig.12 Stats or configurations dz 2 basd O dxy dyz dxz start d 2 ground stat 21 Colour and d-d Transitions 22 Colour and d-d Transitions Stats or configurations ach stat has slightly diffrnt nrgy diffrnt lctron distribution diffrnt Coulomb intractions diffrnt lctron corrlation dx 2 -y 2 basd O dz 2 basd O multipl stats = multipl paks in spctra Trm symbols: dfin symmtry, multiplicity, total angular momntum of th stat nxt trm! dxy dyz dxz any initial and final stats! important for lcturs nxt yar! Rmovd du Fig.12 Absorption spctrum of [n(h2o)6] 2+, downloadd from Tanab Sugano_diagram, Dc [n(h 2O) 6] 2+ Fig _Slids_wb.ky - 1 Dcmbr 2017

7 Spctrochmical Sris Spctrochmical Sris uv-vis xprimntally masurs Δoct ordr ligands according to siz Δoct rmindr strong fild ligand larg Δoct for xampl CO wak fild ligand small Δoct for xampl Clwak fild Spctrochmical sris I- <Br- <Cl- <F- < OH- <O 2- <H 2O < py < NR 3 <NH 3 < n < NO 2 - < CH 3 - < C 6H 5 - < CN- < CO < NO + strong fild 25 xampl! rplac Ni6 ligands from strongr fild to wakr fild chang Δoct and th colour [Ni(H2O)6] 2+ has low nrgy, small Δoct absorbs in th rd and is grn Fig.14 Colour of various Ni(II) complxs in aquous solution. Rmovd du [Ni(NH 3) 6] 2+, [Ni(n) 3] 2+, [NiCl 4] 2-, [Ni(H 2O) 6] Spctrochmical sris I- <Br- <Cl- <F- <OH- <O 2 - <H 2O <NH 3 < n < NO 2 - <CH 3 - <C 6H 5 - <CN- <CO Rmovd du Imag from Inorganic_Chmistry/Crystal_Fild_Thory/ Colors_of_Coordination_Complxs, downloadd 1 Dc 2014 Imag from Nickl(II)_chlorid, Hch, downloadd 1 Dc 2014 Fig.15 T-Colour! Info-graphics from Rmovd du Rmovd du Othr Factors not only th ligands ffct th siz of Δoct ovrall charg on th th complx oxidation stat mtal charg on th mtal / ligands dnsity of ovrlapping orbitals radius of mtal (row) stric congstion ligands rmindr high charg on draws ligands in incrass ovrlap incrass intraction incrass Δoct Rmovd du Rmovd du Rmovd du larg ligand cannot approach mtal poor ovrlap rducd intraction dcrass Δoct Fig.16 Coordination Chmistry imi Hi ( ) _Slids_wb.ky - 1 Dcmbr 2017

8 Rduc th Symmtry rplac 1 ligand with a diffrnt σ-ligand loss of symmtry Oh -> C4v C 4 σ ' σ σ v σ σ σ σ σ d σ σ σ σ dtrmin nw symmtry labls for mtal AOs dtrmin th nw symmtry labls for th ligand FOs VERY Fig.19 dz 2, dx 2 -y 2 dxy, dyz, dxz dgnrat lvls rmain dgnrat, I v split thm for as of intrprtation σ σ procss simpl: Os rmain th sam just nd to work out rducd symmtry labls! watch for dgnracy braking Fig.18 us short-cuts and your charactr tabl for Fig dtrmin nw symmtry labls for mtal AOs dtrmin th nw symmtry labls for th ligand FOs VERY dz 2, dx 2 -y 2 dxy, dyz, dxz rad off charactr tabl for Fig.19 b1 b2 dtrmin nw symmtry labls for mtal AOs dtrmin th nw symmtry labls for th ligand FOs VERY dz 2, dx 2 -y 2 dxy, dyz, dxz Fig.19 b1 b2 Fig.20 Fig.20 totally symmtric _Slids_wb.ky - 1 Dcmbr 2017

9 dtrmin nw symmtry labls for mtal AOs dtrmin th nw symmtry labls for th ligand FOs VERY dz 2, dx 2 -y 2 dxy, dyz, dxz Fig.19 b1 b2 dtrmin nw symmtry labls for mtal AOs dtrmin th nw symmtry labls for th ligand FOs VERY dz 2, dx 2 -y 2 dxy, dyz, dxz Fig.19 b1 b2 b1 lik dz 2 and dx 2 -y 2 lik paos -> T x,t y,t z Fig.20 Fig now combin th T daos and th ligand FO to form th nrgy lvl diagram for a C4v T complx now combin th T daos and th ligand FO to form th nrgy lvl diagram for a C4v T complx hint 1 add th fragmnt orbital nrgy lvls ' σ ' σ σ σ σ σ σ σ σ σ Fig.21 σ σ _Slids_wb.ky - 1 Dcmbr 2017

10 Diagram now combin th T daos and th ligand FO to form th nrgy lvl diagram for a C4v T complx hint 1 add th fragmnt orbital nrgy lvls dgnrat sprad out to illustrat diffrnt symmtris compltd! hint 2 combin lvls of th sam symmtry ' σ ' σ ' σ ' σ σ σ σ σ σ σ σ σ σ σ σ σ σ σ σ σ Fig.21 σ σ Fig.22 σ σ Diagram Diagram compltd! compltd! was dgnracy is brokn was dgnracy is rducd ' σ ' σ ' σ ' σ σ σ σ σ σ σ σ σ σ σ σ σ σ σ σ σ Fig.22 σ σ Fig.22 σ σ _Slids_wb.ky - 1 Dcmbr 2017

11 Diagram T Diagram compltd! ligand Os T daobasd Os primary ffct of th rduction in symmtry => split th g nrgy lvls ordring of and b1 will dpnd on th ligands Δoct is splitting of dao manifold (group of orbitals!) bonding ligand-basd Os dx 2 -y 2 and dz 2 antibonding mtal-basd Os non-bonding mtal-basd Os dxy, dxz and dyz ' σ ' σ Fig.22 σ σ σ σ σ σ σ σ σ σ Fig Ky Points b abl to draw nrgy lvl diagrams for octahdral T complxs with σ b abl to draw and dscrib th important Os b abl to discuss ky faturs of th diagrams, spcially faturs rlating to th charactr of th Os b abl to dfin th octahdral splitting paramtr and b abl to discuss ky proprtis that impact on or ffct Δoct b abl to draw th nrgy diagram for a lowr symmtry T complx with σ-bonding ligands, including squar planar S my wb-sit 42 Finally nots AND slids link to panopto whn it bcoms availabl optional background support for bginnrs optional matrial to tak you a littl furthr links to intrsting popl and wb-sits links to rlvant rsarch paprs on Os modl answrs!! _Slids_wb.ky - 1 Dcmbr 2017