Vibrational Circular Dichroism (VCD)#
Vibrational Circular Dichroism (VCD) is a powerful and cheap spectroscopic method to gain information on the three-dimensional structure of any compound.
In ORCA, VCD spectra can be easily requested via the %FREQ block
! FREQ B3LYP D4 def2-TZVP
%FREQ
DOVCD true
END
Note
Note that VCD cannot be computed with NUMFREQ.
Example: VCD Spectra of Ansa-Metallocenes#
In this example, we will compute the VCD spectra of the ansa-metallocene complex en(thind)2ZrCl2. Ansa-metallocenes are best known for their application as polymerization catalysts (cf. Ziegler-Natta catalysis). Due to the structure of the ethylenebis(4,5,6,7-tetrahydro-1-indenyl) ligands connected by the ansa bridge, distinct enantiomers of this complex are accessible. Here, we will compare the (S,S) and (R,R) enantiomers.
Figure: (S,S) and (R,R) enantiomers of en(thind)2ZrCl2.#
We will now compute the VCD spectra in chloroform solution for both enantiomers at the B3LYP-D4/def2-TZVPP[C-PCM(CHCl3)] level:
! FREQ B3LYP D4 def2-TZVPP CPCM(chloroform)
%FREQ
DOVCD true
END
*XYZFILE 0 1 structure.xyz
After a successful calculation, the VCD spectrum can be found in the output:
------------------------
VCD SPECTRUM CALCULATION
------------------------
Calculating the atomic axial tensor (analytic) ... done ( 0.151 sec)
---------------------------------
Mode Freq VCD-Intensity
(1/cm) (1E-44*esu^2*cm^2)
---------------------------------
6 5.8 -3.66
7 74.7 3.09
8 90.5 13.12
[...]
Important
To avoid imaginary frequencies, the VCD calculation should be performed on geometries that were optimized at the same level.
If we now plot the IR and VCD spectra for both compounds, we see that while the IR spectra are identical for both enantiomers, the VCD spectra are exactly inverted and allow a clear distinction of the (S,S) and the (R,R) enantiomers.
Figure: IR (top) and VCD (bottom) spectra of (S,S)- and (R,R)-en(thind)2ZrCl2.#
Important
For a reasonable comparison to experimental data, A Boltzmann-weighted spectrum may be necessary for a reasonable comparison to experimental data. The respective conformer ensembles can be generated with the GOAT algorithm available in ORCA.
Structures#
(S,S)-en(thind)2ZrCl2
47
C 2.1742581678898598 -0.2445844120182100 0.0446091234872100
C 1.6154841777462501 -1.4976078340452299 -0.6336477249081500
C 0.4678430596774400 -2.1103038388773299 0.1815466920423200
C -0.5619063759860100 -1.0560542982915799 0.4727325198560900
C 1.1236920945913600 0.8695454613127800 0.1809762903584500
C -0.2428541847048000 0.3321324991342400 0.4914462883090400
C -1.9636428631709599 -1.1965269423246900 0.6312436458244400
C -1.4405982013668199 1.0450914898481500 0.6885943517151700
C -2.5031691166377699 0.1096871555872400 0.7911376199599600
H 2.5438641351029698 -0.5164778729500100 1.0338529360910900
H 2.4083047594010800 -2.2368781301448299 -0.7613701065143700
H 0.8699588345188100 -2.5321329780628998 1.1070637455013199
H -3.5443766990624099 0.3499255475529800 0.9428035438116900
H 1.2500470976467499 -1.2456076689939299 -1.6342778677240599
H 0.0112275687850600 -2.9378457183847502 -0.3639276498152700
H -1.5346782841505999 2.1159153360942300 0.7595362119718300
H 1.4383731341169399 1.5938108219204199 0.9342790543835300
H 1.0528783830442601 1.4196993781035001 -0.7629242544785700
H 3.0271116983124702 0.1369715267215600 -0.5195790536371701
C -2.7427912980150899 -2.4795713358849700 0.6640229626184601
C -3.6515583603848900 -2.5147899113865200 1.9002146426382800
H -3.3370908046764001 -2.5903312870566002 -0.2464734411828100
H -2.0505128568850699 -3.3210854158662602 0.6901837806392700
H -4.4888279720406201 -1.8298547432781000 1.7639078110995601
H -4.0813424703970700 -3.5116341682427699 2.0287155800280501
Cl -1.7515648287175600 1.9495941162672099 3.7728286542864700
C -4.6234433837531803 0.5057853439889500 5.4175907654132400
C -3.9062538879398798 -0.0626639931202600 6.6456824730135100
C -2.4171051940022799 -0.3061458200530100 6.3612389063918098
C -2.2626125295550801 -1.1062609166640300 5.1027419162485899
C -4.5972172318803199 -0.4670032893788100 4.2286599013544199
C -3.2759739349648100 -1.1703285217410000 4.1032520475770600
C -1.2305730410587099 -1.9850550537681100 4.7247726337318303
C -2.8787434014559801 -2.1125798347282001 3.1227304835072101
C -1.5938683296279299 -2.5973241508562599 3.4975333555442401
H -5.6608563494038497 0.7400672663088900 5.6629193535983502
H -4.3790328207977902 -1.0048266341692900 6.9412543405992704
H -1.9469752293237601 -0.8363293795062600 7.1916223544877402
H -1.0088899964117699 -3.3255656095752300 2.9571418289416900
H -4.0102838143067201 0.6228007049942900 7.4886123866631600
H -1.9068036724548800 0.6558530849489200 6.2720504290409398
H -0.3148118524222700 -2.1529076851973201 5.2667128968072499
H -5.3697197490720301 -1.2311368186153699 4.3680208863684502
H -4.8572150243891397 0.0568857437771900 3.3060903740698500
H -4.1432088203003996 1.4425171386827600 5.1319389089623098
Zr -1.2071901256747799 -0.2637425852592700 2.8451769027785700
Cl 1.1819895941834400 -0.2621157668015100 3.4469314985293300
(R,R)-en(thind)2ZrCl2
47
C -2.1914554215277899 0.2895605281534100 -0.1058945838212000
C -1.6354448990404500 1.5488116625982999 0.5626695705890100
C -0.4529995380189300 2.1241297568433701 -0.2294016906450000
C 0.5673012704932801 1.0472722203320599 -0.4699816282814900
C -1.1556064195290801 -0.8437127577377300 -0.1730934585853200
C 0.2263969539247800 -0.3360550219188800 -0.4624892626472100
C 1.9763334233995000 1.1618733884694299 -0.5917944171627399
C 1.4168313767130500 -1.0719586932066700 -0.6136141903838400
C 2.4974922793981200 -0.1550591863937300 -0.7071593642384200
H -2.5179051603665399 0.5423749913653499 -1.1155479777902899
H -2.4191992954139501 2.3035632648325901 0.6480289388167200
H -0.8222997305010700 2.5348601940346498 -1.1736502702334399
H 3.5378864282625302 -0.4153723950988500 -0.8283129319555100
H -1.3064438733632000 1.3132588713501001 1.5797649466484101
H 0.0017908149911300 2.9551974539101300 0.3121553595803500
H 1.4954775569178400 -2.1455137474007100 -0.6582555892552500
H -1.4592109318568800 -1.5888938303677100 -0.9099834734456600
H -1.1203461016854599 -1.3600454028710001 0.7916978547841700
H -3.0721241132136199 -0.0634044750563800 0.4335620279082300
C 2.7748349933510998 2.4334894011492199 -0.6347233460260000
C 3.6720382973084700 2.4609186073080900 -1.8803995163440299
H 3.3804593632589102 2.5347980647476600 0.2691366338909700
H 2.0945899574240001 3.2849524739536400 -0.6516340667064100
H 4.5023319059409301 1.7655791662235101 -1.7526205517316200
H 4.1130226931328098 3.4528682169118401 -2.0101242036810700
Cl 1.9925351554928901 -1.9977113886498701 -3.6642227250656800
C 4.6426143437406999 -0.4455267742606400 -5.4961647123921598
C 3.8569907704968598 0.1139095720864600 -6.6860488771203999
C 2.3708117734952201 0.2895759346758100 -6.3420260011193896
C 2.2354278511248702 1.0787756769961800 -5.0745690603738600
C 4.6124961242693301 0.4937909844131300 -4.2797834847542298
C 3.2757650619296999 1.1556026077879600 -4.1048103411467096
C 1.1971310611928001 1.9340165137842700 -4.6590705495322000
C 2.8823789576802898 2.0688448385277201 -3.0960032168269098
C 1.5793817915584600 2.5361873861894200 -3.4338624435920200
H 5.6809703762470596 -0.6228601483285500 -5.7819845571453801
H 4.2773224106211600 1.0804753854427001 -6.9820111394240900
H 1.8431586250757801 0.7989498603941600 -7.1503940062834701
H 0.9956140269250100 3.2479436145840501 -2.8713126423587099
H 3.9582816368405398 -0.5526054307064500 -7.5443874313386203
H 1.9092157491140200 -0.6951111481688100 -6.2347951975059903
H 0.2639075561679300 2.0895165946992100 -5.1742368833924104
H 5.3577885155940397 1.2853812187007101 -4.4130190781240604
H 4.9082246249208401 -0.0477550362699300 -3.3785324426294001
H 4.2190242864600496 -1.4112460957612101 -5.2185557557079498
Zr 1.2590641613056399 0.1893579966168900 -2.8030975385233501
Cl -1.1011967102527500 0.0005996751150900 -3.4796167549262900