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Research Paper

Carbonyl versus Dinitrogen Bonding to Nickel(0) and Iron(0)

Douglas L. Strout

Department of Physical Sciences, Alabama State University, Montgomery, Alabama 36101, USA,

*Corresponding author, Douglas L. Strout, Email; dstrout@alasu.edu

Received April 15, 2017, revised September 21, 2017, accepted September 23, 2017

Publication Date (Web): September 23, 2017

Abstract

Complex nitrogen-containing molecules are of interest for their potential as energetic materials, because reactions such as Nx à (x/2) N2 are highly exothermic. Synthetic routes to high-energy nitrogen are important reaction pathways. Transition metals are well-known as reaction catalysts, but can they participate in the production of large nitrogen molecules? A significant step in answering questions of that kind would be understanding the bonding between dinitrogen (N2) and transition metal atoms. In this study, N2bonding to nickel(0) and iron(0) is compared with a much more widely known counterpart, carbonyl (CO). Theoretical calculations are carried out using density functional theory (DFT) to determine the relative strength of N2 and CO bonds to the transition metal centers. Trends in bonding to both nickel and iron are calculated and discussed.

Keywords

Computational chemistry, Nitrogen, High-energy materials, Transition metals, Catalysis, Iron, Nickel

Introduction

Since chemical reactions of the general type Nx à (x/2) N2 are highly exothermic, owing to the stability of the nitrogen triple bond, molecules of nitrogen (or predominantly of nitrogen) are of interest as high-energy materials. The N5 cation and anion (Christe et al. 1999, Vij et al. 2002, Dixon et al. 2004) have been produced in the laboratory. Other laboratory successes include various azido compounds (Knapp et al. 2004, Haiges et al. 2004, Huynh et al. 2004, Klapotke et al. 2003), a network polymer of nitrogen (Eremets et al. 2004), the N7O+ and CN7_ ions (Christe et al. 2010, Klapotke et al. 2009), and a hexamer of diazomethane (Klapotke et al. 2004). High-energy nitrogen has also been the subject of much theoretical research, including cyclic and acyclic molecules (Chung et al. 2000, Strout 2002, Thompson et al. 2002, Li and Liu 2002, Li and Zhao 2002, Gagliardi et al. 2000, Law et al. 2002) and nitrogen cages (Gagliardi et al. 1997, Schmidt et al. 2000, Zhao et al. 2006, Zhao et al. 2006, Bruney et al. 2003, Sturdivant et al. 2004, Strout 2004). Calculations have been carried out on all-nitrogen systems with as many as seventy-two atoms.

Many such high-energy nitrogen systems are challenging synthetic targets. As transitional metals have well-known catalytic properties, it is reasonable to ask whether a transition metal center can catalyze the synthesis of high-energy nitrogen molecules. An exploration of this chemistry begins with an understanding of N2 bonding to transition metal centers. In this study, eighteen-electron complexes of iron(0) and nickel(0) are calculated to compare the properties of N2 as a ligand with the more well-known carbonyl ligand CO.

Computational Methods

Geometries of the molecules N2 and CO, as well as all transition metal complexes in this study have been optimized using the PBE1PBE density functional method (Perdew et al. 1996). All calculations have been carried out in the singlet electronic state. Vibrational frequencies of all molecules have been calculated, and all energies include zero-point energy (ZPE) corrections. The correlation-consistent cc-pVDZ basis set of Dunning has been used (Dunning 1989). All calculations have been carried out using the Gaussian16 computational chemistry software (Frisch et al. 2016).

Table 1. Energetic comparison between carbonyl and dinitrogen bonding to nickel(0). Energies calculated by PBE1PBE/cc-pVDZ with ZPE corrections. Energies in kJ/mole.

Results and Discussion

Nickel(0) complexes calculated in this study are shown in Figure 1. Ligands are either CO2 or N2, and each complex is an eighteen-electron complex with four ligands. The nickel complexes are tetrahedral in geometry and have a singlet ground state. Iron(0) complexes calculated in this study are shown in Figure 2. Each complex is an eighteen-electron complex with five ligands. The iron complexes are trigonal bipyramidal in geometry and have a singlet ground state. For iron complexes in which variations of axial-versus-equatorial ligand placement are applicable, only the most stable isomer of the complex is shown.

Table 2. Energetic comparison between carbonyl and dinitrogen bonding to iron(0). Energies calculated by PBE1PBE/cc-pVDZ with ZPE corrections. Energies in kJ/mole.

Relative energies for the nickel complexes are shown in Table 1. Each complex has been calculated along with an appropriate number of CO and/or N2 molecules. Table 1 shows the energetic consequences of progressive substitution of N2 for the CO ligands in tetracarbonylnickel(0). The data show an increase in energy of 75-80 kJ/mole per substitution, which indicates that N2 bonds LESS strongly to nickel than does CO. For the first three substitutions, the difference is about 75 kJ/mole but closer to 80 kJ/mole for the fourth N2 ligand. Table 2 shows the same information for pentacarbonyliron(0). The first N2 substitute ligand causes an energy penalty of 97.3 kJ/mole, which means that the N2 binds to iron 97.3 kJ/mole LESS strongly than the CO it replaced. Energy differences for subsequent N2 substitutions fall in the 85-95 kJ/mole range. Since the experimental mean dissociation energies (Skinner et al. 1985) of tetracarbonylnickel(0) and pentacarbonyliron(0) are 144 and 116 kJ/mole, respectively, the N2 binding energies to nickel(0) and iron(0) are approximately 65-70 and 20-30 kJ/mole, respectively. If Trouton’s Rule is used as an approximation for entropic effects, that is, iron-N2 dissociation had _S = +85-90 J/mole K, then _T_S favors dissociation at 298 K by about 25 kJ/mole. This would essentially cancel out the iron-nitrogen binding energy and greatly reduce the nickel-nitrogen binding energy calculated in this study. If the N2 ligand cannot bind strongly to the metal center, how can the metal center catalyze the binding of two of more N2 ligands to each other?

Ni-4CO Ni-3CO-1N2 Ni-2CO-2N2

(a) (b) (c)

Ni-1CO-3N2 Ni-4N2

(d) (e)

Figure 1. Nickel(0) complexes: (a) Ni(CO)4, (b) Ni(CO)3N2, (c) Ni(CO)2(N2)2, (d) Ni(CO)(N2)3, (e) Ni(N2)4. Nickel is shown in blue, carbon in black, oxygen in red, and nitrogen in yellow.

Conclusions

For both transition metals, nickel(0) and iron(0), dinitrogen N2 is a weaker binding ligand than carbonyl CO. The differences are such that metal_N2 binding energies are less than half of the corresponding metal_CO binding energies for these systems. The potential consequence is that N2 binding strength to nickel(0) and iron(0) may be insufficient for any reasonable catalysis of high-energy forms of nitrogen. If leaving the coordination sphere of a transition metal is a low-energy pathway for N2, then any reaction between N2 molecules to a larger nitrogen molecule becomes unlikely.

Fe-5CO Fe-4CO-1N2 Fe-3CO-2N2

(a) (b) (c)

Fe-2CO-3N2 Fe-1CO-4N2 Fe-5N2

(d) (e) (f)

Figure 2. Iron(0) complexes: (a) Fe(CO)5, (b) Fe(CO)4N2, (c) Fe(CO)3(N2)2, (d) Fe(CO)2(N2)3, (e) Fe(CO)(N2)4, (f) Fe(N2)5. Iron is shown in orange, carbon in black, oxygen in red, and nitrogen in yellow.

Acknowledgments

The Alabama Supercomputer Authority is gratefully acknowledged for a grant of computer time on the SGI Ultraviolet in Huntsville, AL. This work was supported by the National Science Foundation (NSF/HBCU-UP grant 0505872). This work was also supported by the National Institutes of Health (NIH/NCMHD 1P20MD000547-01) and the Petroleum Research Fund, administered by the American Chemical Society (PRF 43798-B6). The taxpayers of the state of Alabama in particular and the United States in general are gratefully acknowledged.

References

Bruney LY, Bledson TM, Strout DL (2003) What makes an N12 cage stable? Inorg. Chem. 42, 8117

Christe KO, Haiges R, Wilson WW, Boatz, JA (2010) Synthesis and properties of N7O+. Inorg. Chem. 49, 1245

Christe KO, Wilson WW, Sheehy JA, Boatz, JA (1999) N5+: A novel homoleptic polynitrogen ion as a high energy eensity material. Angew. Chem. Int. Ed. 38, 2004

Chung G, Schmidt MW, Gordon MS (2000) An Ab initio study of potential energy surfaces for N8 isomers. J. Phys. Chem. A 104, 5647

Dixon DA, Feller D, Christe KO, Wilson WW, Vij A, Vij, V, Jenkins HDB, Olson RM, Gordon MS (2004) Enthalpies of formation of gas-phase N3, N3_, N5+, and N5_ from Ab initio molecular orbital theory, stability predictions for N5+N3_ and N5+N5_, and experimental evidence for the Instability of N5+N3_. J. Am. Chem. Soc. 126, 834

Dunning TH Jr (1989) Gaussian basis sets for use in correlated molecular calculations. I. The atoms boron through neon and hydrogen. J. Chem. Phys. 90, 1007

Eremets MI, Gavriliuk AG, Trojan IA, Dzivenko DA, Boehler R (2004) Single-bonded cubic form of nitrogen, Nature Materials 3, 558

Gagliardi L, Evangelisti S, Bernhardsson A, Lindh R, Roos BO (2000) Dissociation reaction of N8 azapentalene to 4 N2: A theoretical study. Int. J. Quantum Chem. 77, 311

Gagliardi L, Evangelisti S, Widmark PO, Roos BO (1997) A theoretical study of the N8 cubane to N8 pentalene isomerization reaction. Theor. Chem. Acc. 97, 136

Gaussian 16, Revision A.03, M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone, G. A. Petersson, H. Nakatsuji, X. Li, M. Caricato, A. V. Marenich, J. Bloino, B. G. Janesko, R. Gomperts, B. Mennucci, H. P. Hratchian, J. V. Ortiz, A. F. Izmaylov, J. L. Sonnenberg, D. Williams-Young, F. Ding, F. Lipparini, F. Egidi, J. Goings, B. Peng, A. Petrone, T. Henderson, D. Ranasinghe, V. G. Zakrzewski, J. Gao, N. Rega, G. Zheng, W. Liang, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, K. Throssell, J. A. Montgomery, Jr., J. E. Peralta, F. Ogliaro, M. J. Bearpark, J. J. Heyd, E. N. Brothers, K. N. Kudin, V. N. Staroverov, T. A. Keith, R. Kobayashi, J. Normand, K. Raghavachari, A. P. Rendell, J. C. Burant, S. S. Iyengar, J. Tomasi, M. Cossi, J. M. Millam, M. Klene, C. Adamo, R. Cammi, J. W. Ochterski, R. L. Martin, K. Morokuma, O. Farkas, J. B. Foresman, and D. J. Fox, Gaussian, Inc., Wallingford CT, 2016.

Haiges R, Schneider S, Schroer T, Christe KO (2004) High-energy-density materials: Synthesis and characterization of N5+[P(N3)6]_, N5+[B(N3)4]_, N5+[HF2]_ . nHF, N5+[PF6]_ and N5+[SO3F]_. Angew. Chem. Int. Ed. 43, 4919

Huynh MV, Hiskey MA, Hartline EL, Montoya DP, Gilardi, R (2004) Polyazido high-nitrogen compounds: Hydrazo- and azo-1,3,5-triazine. Angew. Chem. Int. Ed. 43, 4924

Klapotke TM, Krumm R, Mayer P, Schwab I (2003) Binary tellurium(IV) azides: Te(N3)4 and [Te(N3)5]_. Angew. Chem. Int. Ed. 42, 5843

Klapotke TM, Stierstorfer J (2009) The CN7_ anion. J. Am. Chem. Soc. 131, 1122

Klapotke TM, Mayer P, Schulz A, Weigand, JJ (2004) 1,4-Bis-[1-Methyltetrazol-5-yl]-1,4-dimethyl-2-tetrazene: A stable, highly energetic hexamer of diazomethane (CH2N2)6. Propellants Explosives Pyrotechnics 29, 325

Knapp C, Passmore, J (2004) On the way to “solid nitrogen” at normal temperature and pressure? Binary azides of heavier group 15 and 16 elements. Angew. Chem. Int. Ed. 43, 4834

Law CK, Li WK, Wang X, Tian A, Wong NB (2002) A Gaussian-3 study of N7+ and N7_ isomers. Theochem 617, 121

Li, QS, Liu YD (2002) Structures and stability of N11 cluster. Chem. Phys. Lett. 353, 204

Li QS, Zhao JF (2002) Theoretical study of potential energy surfaces for N12 clusters. J. Phys. Chem. A, 106, 5367

Perdew JP, Burke K, Ernzerhof M (1996) Generalized gradient approximation made simple. Phys. Rev. Lett. 77, 3865

Schmidt MW, Gordon MS, Boatz JA (2000) Cubic fuels? Int. J. Quantum Chem. 76, 434

Skinner HA, Connor JA (1985) Metal-ligand bond-energies in organometallic compounds. Pure & Appl. Chem. 57, 79

Vij A, Pavlovich JG, Wilson WW, Vij V, Christe KO (2002) Experimental detection of the pentaazacyclopentadienide (pentazolate), cyclo-N5_ Angew. Chem. Int. Ed. 41, 3051

Strout DL (2002) Acyclic N10 Fails as a high energy density material. J. Phys. Chem. A, 106, 816

Strout DL (2004) Cage isomer of N14 and N16: Nitrogen molecules that are not a multiple of six. J. Phys. Chem. A, 108, 10911

Sturdivant SE, Nelson FA, Strout DL (2004) Trends in stability for N18 cages. J. Phys. Chem. A, 108, 7087

Thompson MD, Bledson TM, Strout DL (2002) Dissociation barriers for odd-numbered acyclic nitrogen molecules N9 and N11. J. Phys. Chem. A, 106, 6880

Zhou HW, Wong NB, Zhou G, Tian AM (2006) Theoretical studies on “multilayer” nitrogen cages. J. Phys. Chem. A, 110, 3845

Zhou HW, Wong NB, Zhou G, Tian AM (2006) What makes the cylinder-shaped N72 cage stable? J. Phys. Chem. A, 110, 7441

Citation:

Douglas L. Strout (2017) Carbonyl versus dinitrogen bonding to nickel(0) and iron(0), Frontiers in Science, Technology, Engineering and Mathematics, Volume 1, Issue 1, 56-61