Pentazolate Anion

 

Purpose

Recently Vij, Christe et al1 reported the first successful synthesis and characterization of a gas phase cyclo-N5– anion (Pentaazacyclopentadienide (Pentazolate) Anion). This paper reports the results of our theoretical characterization of this species.

Methods and Calculation Details

pcGAMESS2 was used to perform ground state geometry optimization and determine (at that geometry) the predicted IR and RAMAN absorption spectra for the cyclo-N5– anion. In addition, excitation energies (and associated oscillator strengths) for electronic transitions from the ground state to a variety of excited states were calculated with pcGAMESS at the optimized ground state geometry.  gOpenMol3,4 was used to visualize orbitals and animation of vibrational modes.

RHF closed shell molecular orbital calculations were performed on the cyclo-N5– anion using D5h point group symmetry. As a basis set on each nitrogen atom we used the internal GAMESS TZV triple valence basis set augmented with two D function polarization functions and additional S and P type diffuse functions5.

Excited state transition were calculated using the method of CI-singles and analyzed using the methods suggested by Foresman and Frisch6. Vibrational modes were calculated using the normal mode analysis capabilities of pcGAMESS. NBO calculations were performed using NBO version 5 developed by Weinhold et al.7.

Results

Geometry

Final optimized Cartesian coordinates (in angstroms) were:

Atom
X
Y
Z
N1 0.3395003686 1.0448746952 0.0000000000
N2 -0.8888235041 0.6457680756 0.0000000000
N3 -0.8888235041 -0.6457680756 0.0000000000
N4 0.3395003686 -1.0448746952 0.0000000000
N5 1.0986462710 0.0000000000 0.0000000000

with R(N-N) = 1.2915362 angstroms and Angle(N-N-N) = 108 degrees

Vibrational Analysis

Calculated frequencies and intensities were:

MODE NUMBER
1
2
3
4
5
6
7
8
9
FREQUENCY:
777.8
777.8
1053.2
1053.2
1123.4
1123.4
1223.2
1306.0
1306.0
IR INTENSITY:
0
0
0
0
0
0
0
0.4002
0.4002
RAMAN INTENSITY:
0
0
2.777
2.818
5.433
5.491
33.013
0
0
DEPOLARIZATION:
0.445
0.744
0.75
0.75
0.75
0.75
0.055
0.75
0.004

VISUALIZATION:

 Mode Number: 1

Mode Number: 1

 Mode Number: 5

Mode Number: 5

 Mode Number: 9

Mode Number: 9

 Mode Number: 2

Mode Number: 2

 Mode Number: 6

Mode Number: 6

 Mode Number: 3

Mode Number: 3

 Mode Number: 7

Mode Number: 7

 Mode Number: 4

Mode Number: 4

 Mode Number: 8

Mode Number: 8

where frequencies are scaled by 0.9 (as usual for RHF calculations of this type) and are in cm**-1, IR intensities are in debye**2/amu-angstrom**2, raman intensities are in angstrom**4/amu, and depolarizations are dimensionless. 

Electronic Transitions

Excited State
Symmetry
Orbital
Transition
NBO
Orbital Descriptions
Transition
Type
Excitation
Energy (eV)
Oscillator
Strength
E1″
15 -> 28
15: 81% NB LP;15% B
28: 24% AB Pi; 71% NB
(n) -> (π*)
7.8786
0.0
E1″
15 -> 27
15: 81% NB LP;15% B
27: 46% AB Pi; 51% NB
(n) -> (π*)
7.8786
0.0
E2′
17 -> 28
17: 95* B Pi
28: 24% AB Pi; 71% NB
(π) -> (π*)
8.3710
0.0
E2′
17 -> 27
17: 95* B Pi
27: 46% AB Pi; 51% NB
(π) -> (π*)
8.3710
0.0
E2″
15 -> 28
15: 81% NB LP;15% B
28: 24% AB Pi; 71% NB
(n) -> (π*)
8.5131
0.0
E2″
16 -> 28
16: 81% NB LP;15% B
28: 24% AB Pi; 71% NB
(n) -> (π*)
8.5131
0.0
A2″
13 -> 28
13: 80% NB LP;20%B
28: 24% AB Pi; 71% NB
(n) -> (π*)
8.7110
0.0613
E1″
17 -> 19
17: 95* B Pi
19:100% NB
(π) -> (n*)
8.8043
0.0

where B = bonding, AB = anti-bonding, NB = non-bonding, and LP = lone pair.

 Orbital 13

Orbital 13

 Orbital 17

Orbital 17

 Orbital 28

Orbital 28

 Orbital 15

Orbital 15

 Orbital 19

Orbital 19

 Orbital 16

Orbital 16

 Orbital 27

Orbital 27

 

References

  1. Experimental Detection of the Pentaazacyclopentadienide (Pentazolate) Anion, cyclo-N5-, Angewandte Chemie International Edition, Volume 41, Issue 16, 2002. Pages: 3051-3054
  2. Alex A. Granovsky, www http://classic.chem.msu.su/gran/gamess/index.html as well as M.W.Schmidt, K.K.Baldridge, J.A.Boatz, S.T.Elbert, M.S.Gordon, J.J.Jensen, S.Koseki, N.Matsunaga, K.A.Nguyen, S.Su, T.L.Windus, M.Dupuis, J.A.Montgomery, J.Comput.Chem. 14, 1347-1363 (1993)
  3. Laaksonen, L. (1992) A graphics program for the analysis and display of molecular dynamics trajectories. J. Mol. Graph. 10: 33-34.
  4. Bergman, D.L., Laaksonen, L., and Laaksonen, A. (1997) Visualization of solvation structures in liquid mixtures. J. Mol. Graph. Model. 15: 301-306.
  5. For basis set details and references, please refer to the GAMESS User’s Guide, Section 4 “Further Information”
  6. Foresman, J.B. and Frisch, A. Chapter 9 in “Exploring Chemistry with Electronic Structure Methods”, Second Edition, Gaussian Inc, 1996
  7. NBO 5.0. E. D. Glendening, J, K. Badenhoop, A. E. Reed, J. E. Carpenter, J. A. Bohmann, C. M. Morales, and F. Weinhold, Theoretical Chemistry Institute, University of Wisconsin, Madison (2001). .