Pentazolate Anion
Purpose
Recently Vij, Christe et al1 reported the first successful synthesis and characterization of a gas phase cycloN5– anion (Pentaazacyclopentadienide (Pentazolate) Anion). This paper reports the results of our theoretical characterization of this species.
Methods and Calculation Details
pcGAMESS^{2} was used to perform ground state geometry optimization and determine (at that geometry) the predicted IR and RAMAN absorption spectra for the cycloN5– 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. gOpenMol^{3,4} was used to visualize orbitals and animation of vibrational modes.
RHF closed shell molecular orbital calculations were performed on the cycloN5– 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 functions^{5}.
Excited state transition were calculated using the method of CIsingles and analyzed using the methods suggested by Foresman and Frisch^{6}. 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(NN) = 1.2915362 angstroms and Angle(NNN) = 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:
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/amuangstrom**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: 81% NB LP;15% B 28: 24% AB Pi; 71% NB 
(n) > (π*)

7.8786

0.0


E1″

15: 81% NB LP;15% B 27: 46% AB Pi; 51% NB 
(n) > (π*)

7.8786

0.0


E2′

17: 95* B Pi 28: 24% AB Pi; 71% NB 
(π) > (π*)

8.3710

0.0


E2′

17: 95* B Pi 27: 46% AB Pi; 51% NB 
(π) > (π*)

8.3710

0.0


E2″

15: 81% NB LP;15% B 28: 24% AB Pi; 71% NB 
(n) > (π*)

8.5131

0.0


E2″

16: 81% NB LP;15% B 28: 24% AB Pi; 71% NB 
(n) > (π*)

8.5131

0.0


A2″

13: 80% NB LP;20%B 28: 24% AB Pi; 71% NB 
(n) > (π*)

8.7110

0.0613


E1″

17: 95* B Pi 19:100% NB 
(π) > (n*)

8.8043

0.0

where B = bonding, AB = antibonding, NB = nonbonding, and LP = lone pair.
References
 Experimental Detection of the Pentaazacyclopentadienide (Pentazolate) Anion, cycloN5, Angewandte Chemie International Edition, Volume 41, Issue 16, 2002. Pages: 30513054
 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, 13471363 (1993)
 Laaksonen, L. (1992) A graphics program for the analysis and display of molecular dynamics trajectories. J. Mol. Graph. 10: 3334.
 Bergman, D.L., Laaksonen, L., and Laaksonen, A. (1997) Visualization of solvation structures in liquid mixtures. J. Mol. Graph. Model. 15: 301306.
 For basis set details and references, please refer to the GAMESS User’s Guide, Section 4 “Further Information”
 Foresman, J.B. and Frisch, A. Chapter 9 in “Exploring Chemistry with Electronic Structure Methods”, Second Edition, Gaussian Inc, 1996
 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). .