UV Visible Spectra of lanthanide complexes can be calculated from Sparkle Model optimized geometries, followed by ZINDO calculations, in which the lanthanide ion is replaced by a +3e point charge.

The required citation, where this procedure has been first described, is:

Theoretical model for the prediction of electronic spectra of lanthanide complexes

Antonio V. M. de Andrade, Ricardo L. Longo, Alfredo M. Simas and Gilberto F. de Sá
J. Chem. Soc., Faraday Trans., 1996, 92, 1835 - 1839.

 

Tutorial

 

• To perform this task you will need the following softwares: MOPAC2009, ZINDO, and a text editor of your preference (Notepad, Textpad, etc.).



• We assume you are familiar with ZINDO and know how to prepare ZINDO input data files. Since all lanthanide complexes to be calculated are closed shell molecules, this tutorial deals with this situation only.



• As an example, let us consider the complex CCSD: BAFWUB [(Diglyme)-tris(hexafluoroacetylacetonato)-terbium(iii)], below:
  
  



• First draw and optimize the geometry of your complex following the instructions in Drawing Complexes. You should now have the corresponding mop file. As an example, we provide the bafwub.mop



• After optimizing the geometry of the complex, you will need to convert the .out file, bafwub.out, generated by MOPAC2009 into the ZINDO input file using your favorite text editor. The .out file is preferred because ZINDO requires geometries in cartesian coordinates, and the .out file always has the cartesian coordinates of the complexes of lanthanides.



• Build the ZINDO input file. It is composed of four parts: $TITLEI, $CONTRL, $DATAIN, and $CIINPU. Let us address each of these parts individually:



• $TITLEI      




    
    $TITLEI
                                                 
     Here you write whatever you want. For example, the CCSD code for this complex is: BAFWUB 

    $END
    
    

• $CONTRL




    
 $CONTRL
 
 SCFTYP=RHF   RUNTYP=CI   ENTTYP=COORD   UNITS=ANGS
 ONAME=        IPRINT=0
 NEL= 284   MULT=1   ITMAX=50
 SCFTOL=0.000001   APX=INDO/1   INTTYP=1
 INTFA(1)= 1.0  1.267  0.585  1.0  1.0  1.0
 CISIZE= 3601   ACTSPC= 202
 
 $END
    
    



In $CONTRL you need to change only ONAME, NEL, CISIZE and ACTSPC.

ONAME is a path of a temporary file. Any valid path will work.

NEL is the number of electrons in the complex. For a closed shell complex, NEL will be twice the number of doubly occupied levels, present in the MOPAC .out file, ex:
RHF CALCULATION, NO. OF DOUBLY OCCUPIED LEVELS = 142

CISIZE is the size of the CI matrix you expect to generate, and may be calculated as: the number of occupied orbitals in the excitation window, times the number of unoccupied orbitals in the excitation window plus one. The number of occupied and unoccupied orbitals of the excitation window will be defined below in the $CIINPU part.

ACTSPC is the last orbital in the CI window.


• $DATAIN

Here you should copy the cartesian coordinates of the atoms in the complex, as they appear in the MOPAC .out file and transform them into ZINDO input (free format) as follows:

MOPAC .out geometry:



      
           1      Tb         -0.13371567  *  -0.19270501  *   0.01427100  *
           2       O          2.25656822  *  -0.35558383  *  -0.11950609  *
           3       O         -1.75839037  *   1.57025431  *  -0.07199136  *
      
   



Which should become:




      
       $DATAIN
       
       -0.133715670   -0.192705010    0.014271000      0   3.00
        2.256568220   -0.355583830   -0.119506090      8
       -1.758390370    1.570254310   -0.071991360      8

       ...

       $END
      
   



Please, notice that we replaced the lanthanide by a +3e point charge. Instead of placing the lanthanide atomic number in the fourth column (after the x,y,z), we typed 0. Then added, a fourth column, 3.00.


•  $CIINPU


This part of the input is formatted. Be careful with the positions of the data




      
       $CIINPU
          4    1  100    1    0    0    0    1    1    1  100
        -60000.0  0.000000  0.000000
          0    0    0    0    0    0    0    0    0
          1  142  142
         21   83  142  143  202
       $END
      
   



Here, only the last two lines need to be changed.

Let us consider the penultimate line: 1 142 142. Do not change the first number 1; the second and third numbers are identical for closed shell molecules, in this case 142. They are the number of the last occupied orbital in the molecule, present in the MOPAC .out file, as: RHF CALCULATION, NO. OF DOUBLY OCCUPIED LEVELS = 142.

Consider now the last line. Five numbers appear, in this case: 21 83 142 143 202. The first number must not be changed. The second number is the lowest occupied orbital in the excitation window. In this case we chose 83. The third number, 142, is the HOMO. The fourth number, 143, is the LUMO. Finally, the fifth number, 202, is the last unoccupied orbital included in the excitation window.

That is it. For your convenience, we provide the ZINDO input file bafwub_sing.inp.

Get the frequencies and the oscillator strengths from the ZINDO output .zin file. For your convenience, we provide  bafwub_sing.zin.



• Frequencies and Intensities


ZINDO output files are long and complex. Fortunately, we only need to find a part of it which looks like:



      
       _____________________________________________________________________________
  
          TRANSITION           ENERGY      OSC. STRENGTH     TRANSITION MOMENT
       -----------------------------------------------------------------------------
       -----------------------------------------------------------------------------
       (    1)-->(    2)    29673.4 CM-1        0.00004      X      0.00189152
                              337.0 NM                       Y     -0.04924651
                                                             Z     -0.02567895
       -----------------------------------------------------------------------------
       (    1)-->(    3)    30675.0 CM-1        0.00003      X      0.02565147
                              326.0 NM                       Y      0.03305940
                                                             Z      0.00754372
       -----------------------------------------------------------------------------
       (    1)-->(    4)    30807.5 CM-1        0.00004      X     -0.03832270
                              324.6 NM                       Y     -0.01901276
                                                             Z     -0.03531046
       -----------------------------------------------------------------------------
       (    1)-->(    5)    34898.0 CM-1        0.00762      X      0.57142851
                              286.5 NM                       Y      0.07436793
                                                             Z     -0.36267691
       -----------------------------------------------------------------------------
       (    1)-->(    6)    35417.2 CM-1        0.38993      X     -3.73408804
                              282.3 NM                       Y      2.98911992
                                                             Z      0.70771650
       -----------------------------------------------------------------------------
       (    1)-->(    7)    36208.1 CM-1        0.81584      X      3.99215648
                              276.2 NM                       Y      4.38325693
                                                             Z      3.56322913
       -----------------------------------------------------------------------------
       (    1)-->(    8)    42477.6 CM-1        0.00010      X     -0.05041154
                              235.4 NM                       Y     -0.03903970
                                                             Z     -0.02857051
       -----------------------------------------------------------------------------
      
   



In this case, in order to generate the UV-Vis spectrum of the complex, we need a table with two columns: the frequencies, in the above case, 337.0 NM, 326.0 NM, etc, and the corresponding intensities: 0.00004, 0.00003, etc.



• Generating the Spectrum
  
  
  The spectrum can be generated assuming a bandwwidth of 25nm, unless you have a more accurate idea of this value, based on experimental data. We recommend using the van Vleck-Weisskopf lineshape, where γ is the bandwidth, ν₀ is the ZINDO computed frequency, and ν is the incident radiation frequency. For each incident frequency, the lineshapes for each ν₀ must be multiplied by the corresponding intensity and summed up. Then, transform the frequencies into wavelength (nanometers). For your convenience, we provide the bafwub_spec.out which lists the wavelengths and the respective spectrum intensities, ready to be plotted.

Below, we present the plotted lanthanide complex calculated UV VIS spectrum of BAFWUB.