DFT Investigation of the Tri(amino)amine N(NH 2 ) 3 2+ and the Tri(azido)amine N(N 3 ) 3 2+ Dications and Related Mixed Amino(azido)ammonium Ions (N 3 ) x N(NH 2 ) 4-x + (x ) 0-4) 1 Golam Rasul, G. K. Surya Prakash, and George. A. Olah* Loker Hydrocarbon Research Institute and Department of Chemistry, UniVersity of Southern California, UniVersity Park, Los Angeles, California 90089-1661 Received May 20, 2002 Structures of the tri(amino)amine N(NH 2 ) 3 2+ and the tri(azido)amine N(N 3 ) 3 2+ dications were calculated at the density functional theory (DFT) B3LYP/6-311+ G* level. The tri(amino)amine dication (NH 2 ) 3 N 2+ (1) was found to be highly resonance stabilized with a high kinetic barrier for deprotonation. The structures of diamino(azido)amine dication (NH 2 ) 2 N(N 3 ) 2+ (2), amino(diazido)amine dication (NH 2 )N(N 3 ) 2 2+ (3), and tri(azido)amine dication (N 3 ) 3 N 2+ (4) were also found to be highly resonance stabilized. The structures and energetics of the related mixed amino(azido)- ammonium ions (N 3 ) x N(NH 2 ) 4-x + (x ) 0-4) were also calculated. Introduction The guanidinium ion (NH 2 ) 3 C + and the triazidocarbenium ion (N 3 ) 3 C + are highly resonance stabilized ions. These ions owe their thermodynamic stability to the efficient p-p interaction between the positively charged carbon atom and the nonbonded electron pairs on the three adjacent nitrogen atoms (Scheme 1). The guanidinium ion is so stable that it is inert in boiling water. 2 The guanidinium ion can be easily further protonated 3 in superacids to give the N,N-diprotonated guanidinium dication. 4 The triazidocarbenium ion was first prepared in 1966 by Mu ¨ller and Dehnicke. 5 The ion was characterized by crystal structure determination 6 and NMR and vibrational spectroscopy. 7,8 Skancke calculated 9 the structure of the tri(amino)amine dication (NH 2 ) 3 N 2+ , the isoelectronic analogue of the guani- dinium ion, focusing on the concept of Y-aromaticity. The structure was calculated at the ab initio MP2/6-31G* level to be a minimum with D 3 symmetry with a planar nitrogen framework. We report now the investigation of the tri- (amino)amine (NH 2 ) 3 N 2+ and the tri(azido)amine (N 3 ) 3 N 2+ dications as well as the mixed amino-azido dications (N 3 ) x N(NH 2 ) 3-x 2+ (x ) 0-3) by the density functional theory (DFT) method. The corresponding azido derivatives, amino- (azido)ammonium ions (N 3 ) x N(NH 2 ) 4-x + (x ) 0-4), were also investigated. Calculations Calculations were performed with the Gaussian 98 program system. 10 The geometry optimizations were performed using the density functional theory (DFT) 11 method at the B3LYP/6-31G* level. 12,13 Vibrational frequencies at the B3LYP/6-31G*//B3LYP/ 6-31G* level were used to characterize stationary points as minima (number of imaginary frequencies (NIMAG) ) 0) or transition state structures (NIMAG ) 1) and to evaluate zero point vibrational energies (ZPEs), which were scaled by a factor of 0.98. Further optimizations were carried out at the higher B3LYP/6-311+G* level. Final energies were calculated at the B3LYP/6-311+G*// B3LYP/6-311+G* + ZPE level. Atomic charges were obtained using the natural bond orbital analysis (NBO) method. 14 * To whom correspondence should be addressed. E-mail: olah@usc.edu. (1) Onium Ions. Part 60. For Part 59 see: Rasul, G.; Prakash, G. K. S.; Olah, G. A. Proc. Natl. Acad. Sci., submitted. (2) Gund, P. J. Chem. Educ. 1972, 49, 100. (3) Rasul, G.; Prakash, G. K. S.; Olah, G. A. J. Org. Chem. 1994, 59, 2552. (4) Olah, G. A.; Prakash, G. K. S.; Sommer, J. Superacids; Wiley- Interscience: New York, 1985. (5) Mu ¨ller, U.; Dehnicke, K. Angew. Chem., Int. Ed. Engl. 1966, 5, 841. (6) Kolitsch, W.; Mu ¨ller, U. Z. Anorg. Allg. Chem. 1974, 410, 21. (7) Mu ¨ller, U.; Kolitsch, W. Spectrchim. Acta 1975, 31A, 1455. (8) Petrie, M. A.; Sheehy, J. A.; Boatz, J. A.; Rasul, G.; Prakash, G. K. S.; Olah. G. A.; Christe, K. O. J. Am. Chem. Soc. 1997, 119, 8802. (9) (a) Skancke, A. J. Phys. Chem. 1994, 98, 5234. (b) Bernhard, H.; Skancke, A. J. Am. Chem. Soc. 1993, 115, 7465. Scheme 1 Inorg. Chem. 2002, 41, 5589-5592 10.1021/ic020358r CCC: $22.00 © 2002 American Chemical Society Inorganic Chemistry, Vol. 41, No. 21, 2002 5589 Published on Web 09/21/2002