Coordination Chemistry and Photoreactivity of the Dinitramide Ion

Full text of DOI:10.1021/ic951332l

Inorg. Chem. 1996, 35, 1421-1422
1421
Coordination Chemistry and Photoreactivity of the Dinitramide Ion
Scott Trammell, Patricia A. Goodson, and B. Patrick Sullivan*
Department of Chemistry, University of Wyoming, Laramie, Wyoming 82071-3838
ReceiVed October 18, 1995
The dinitramide ion (N3O4-) is a relatively new simple
nitrogen oxyanion of theoretical1 and practical interest.2 Despite
its potential as a non-chlorine containing, high energy density
material, its chemistry is not well understood.3 Such studies
-
are of importance since possible environmental effects of N3O4
include its ability to act as a potent oxidant and/or nitrating
agent.4 From a published description of X-ray structural studies
I
II
III
-
of several dinitramide salts,5 it is apparent that N3O4 can act
Here we report the first demonstrated metal complex of
N3O4-, the first published X-ray structure of the coordinated
ion, and an unusual example of an intramolecular photosensi-
tized reaction of a coordinated ligand (N3O4-) via a metal-to-
ligand charge transfer excited state.
Reaction of KN3O4 with the reactive precursor fac-Re(bpy)-
(CO)3OSO2CF3 at room temperature in water gives a yellow
microcrystalline solid which when recrystallized slowly from
hexanes/CH2Cl2 gives thin yellow plates of fac-Re(bpy)-
(CO)3N3O4 in 75% yield.7 The replacement of triflate by
dinitramide is suggested by their relative acidity i.e., -14.68
versus -5.6,1b respectively.
as a ligand to transition metals.6 For example, three of the
possible coordination modes to a single metal are depicted by
structures I-III where only the skeletal atoms are shown, and
M represents a transition metal complex fragment. It should
be noted that structures I and III are similar to bonding modes
known for the acetylacetonate ion. Prediction of the dominant
bonding mode of N3O4- should be facilitated by knowledge of
the site of protonation in dinitraminic acid (HN3O4); unfortu-
nately this is the subject of debate with structures analogous to
I and III being suggested.1a,f,2b,d,h,3d
(1) (a) Politzer, P.; Seminario, J. M. Chem. Phys. Lett. 1993, 216, 348.
(b) Brinck, T.; Murray, J. S.; Politzer, P. J. Org. Chem. 1991, 56,
5012. (c) Politzer, P.; Seminario, J. M.; Concha, M. C.; Redfern, P.
C. J. Mol. Struct. (THEOCHEM) 1993, 287, 235. (d) Leroy, G.; Sana,
M.; Wilante, C.; Peeters, D.; Dogimont, C. J. Mol. Struct. (THEOCHEM)
1987, 153, 249. (e) Leroy, G.; Sana, M.; Wilante, C.; Peeters, D. J.
Mol. Struct. (THEOCHEM) 1989, 187, 251. (f) Redfern, P. C.;
Politzer, P. Computational Analyses of Structural Properties of the
Dinitramide Ion, N(NO2)2-, and Related Molecules; Dinitramine and
Trinitroamide. ONR Technical Report AD-A288 139; 1990. (g)
Mebel, A. M.; Lin, M. C.; Morokuma, K.; Melius, C. F. J. Phys. Chem.
1995, 99, 6842.
The X-ray crystal structure9a (Figure 1) of fac-Re(bpy)-
(CO)3N3O4 clearly shows that coordination occurs at the central
nitrogen of the dinitramide skeleton with the rest of the complex
possessing the typical facial geometry exhibited by Re(bpy)-
(CO)3X complexes. The Re-N bond lengths for the bpy ligand
are 2.166(10) Å (Re(1)-N(4)) and 2.160(10) Å (Re(1)-N(5)).
The Re-bpy bond lengths are typical of those in similar
9c
complexes of the type fac-Re(bpy)(CO)3X (for X ) OSO2CF3
and PO2F29d bond lengths are between 2.140 and 2.150 Å). The
Re-N3O4 (Re(1)-N(2)) bond length is considerably longer,
2.223(10) Å, consistent with its being a weaker donor than
pyridine type ligands. A structurally interesting feature is the
“tilting” of the planar nitro groups away from each other along
the Re(1)-N(2) axis.
(2) (a) Bottaro, J. C.; Penwell, P. E.; Schmitt, R. J. Synth. Commun. 1991,
21, 945. (b) Michels, H. H.; Montgomery, Jr., J. A. J. Phys. Chem.
1993, 97, 6602. (c) Doyle, R. J. Org. Mass Spectrom. 1993, 28, 83.
(d) Schmitt, R. J.; Krempp, M.; Bierbaum, V. M. Int. J. Mass
Spectrom. Ion Processes 1992, 117, 621. (e) Rossi, M. J.; Bottaro, J.
C.; McMillen, D. F. Int. J. Chem. Kinet. 1993, 25, 549. (f) Pace, M.
D. J. Phys. Chem. 1994, 98, 6251. (g) Pace, M. D. Mater. Res. Soc.
Symp. Proc. 1993, 296, 53-60. (h) Shlyapochnikov, V. A.; Oleneva,
G. I.; Cherskaya, N. O.; Lukyanov, O. A.; Gorelik, V. P.; Anikin, O.
V.; Tartakovsky, V. A. J. Mol. Struct. 1995, 348, 103. (i) Brill, T.
B.; Brush, P. J.; Patil, D. G. Combust. Flame 1993, 92, 7788. (j)
Yao, D. C. C.; Su, M.; Mill, T. Photolysis Rates and Pathways for
the Dinitramide Ion. Presented at the Joint USAF/Amy Contractor/
Grantee Meeting on Subsurface Contaminant Fate and Transport, Jun
8, 1995, Boulder, CO. It should be noted that a minor amount of
fac-Re(bpy)(CO)3N3O4 is extremely photosensitive in solu-
tion. This is demonstrated in Figure 2 where changes in the
UV-visible spectrum in CH2Cl2 (2.57 × 10-5 M) after
irradiation (436 nm, 1000 W Hg lamp in a one cm cuvette)
demonstrate the formation of a new product. Analysis10 of the
spectral changes (436 nm irradiation; monitoring the spectrum
between 230 and 550 nm) is best approximated as an A f B
f C process (see inset in Figure 2). Preparative photolysis in
CH2Cl2 allows the isolation and characterization of C, which is
-
NO2 is also observed.
(3) There appears to be a large body of work on dinitramide and
dinitraminous acid in the Russian chemical literature. We have only
been able to retrieve part of this; some important references are as
follows: (a) Lukyanov, O. A.; Anikin, O. V.; Gorelik, V. P.;
Tartakovsky, V. A. Russ. Chem. Bull. (Engl. Transl.) 1994, 43, 1457.
(b) Lukyanov, O. A.; Gorelik, V. P.; Tartakovsky, V. A. Russ. Chem.
Bull. (Engl. Transl.) 1994, 43, 89. (c) Lukyanov, O. A.; Konnova,
Yu. V.; Klimova, T. A.; Tartakovsky, V. A. Russ. Chem. Bull. (Engl.
Transl.) 1994, 43, 1200. (d) Lukyanov, O. A.; Shlyapochnikov, V.
A.; Cherskaya, N. O.; Gorelik, V. P.; Tartakovsky, V. A. Russ. Chem.
Bull. (Engl. Transl.) 1994, 43, 1522. (e) Lukyanov, O. A.; Agevnin,
A. R.; Leichenko, A. A.; Seregina, N. M.; Tartakovsky, V. A. Russ.
Chem. Bull. (Engl. Transl.) 1995, 44, 108. (f) Lukyanov, O. A.;
Shlykova, N. I.; Tartakovsky, V. A. Russ. Chem. Bull. (Engl. Transl.)
1994, 43, 1680. (g) Shlyapochnikov, V. A.; Oleneva, G. I.; Tartak-
ovsky, V. A. Russ. Chem. Bull. (Engl. Transl.) 1995, 44, 1449.
(4) Trammell, S.; Sullivan, B. P. Unpublished results.
(7) Synthesis of fac-Re(bpy)(CO)3N3O4. Caution! Dintramide derivatives
are known to be shock sensitive and explosive.3a In 20 mL of
deionized water, 0.1 mmol (57 mg) of Re(bpy)(CO)3OSO2CF3 was
heated to reflux until dissolved in a 100 mL round bottom flask. After
the solution was allowed to cool to room temperature, 1.0 mmol (0.145
mg) of KN(NO2)2 was added and the solution was stirred overnight
in the dark. A yellow microcrystalline solid was collected by vacuum
filtration and washed with 3 × 15 mL of water and then allowed to
air dry. Crystals were grown for X-ray diffraction and elemental
analysis by slow diffusion of hexanes into a concentrated solution of
product in CH2Cl2. Anal. Calcd for ReC13H8N5O7: C, 29.33; H, 1.51;
N, 13.15. Found: C, 29.53; H, 1.59; N, 12.88. 1H NMR (δ/ppm,
CDCl3): 9.15 (m, 2H), 8.18 (m, 4H), 7.62 (m, 2H). 1H NMR (δ/
ppm, CD2Cl2): 9.02 (m, 2H), 8.14 (m, 2H), 8.08 (m, 2H), 7.55 (m,
2H). UV-visible (λ (nm), CH2Cl2) (ꢀ in M-1 cm-1): 246 (19 100),
266 (16 650), 320 (10 700), 370 (3650). IR (CHCl3) (ν (CO) cm-1):
2036, 1940, 1924. IR (CH2Cl2) (ν(CO) cm-1): 2036, 1934, 1925.
(8) Jorgensen, C. K. Naturewissenschaften 1980, 67, 189.
(5) Reported as a personal communication in ref 1c.
(6) Colberg, P. J. S.; Buttry, D. A.; Sullivan, B. P. Abiotic and Biotic
Reactions of Quardracyclane and Dinitramide. Presented at the Joint
USAF/Amy Contractor/Grantee Meeting Subsurface Contaminant Fate
and Transport, Jun 8, 1995, Boulder, CO.
0020-1669/96/1335-1421$12.00/0 © 1996 American Chemical Society

1422 Inorganic Chemistry, Vol. 35, No. 6, 1996
Communications
also produced, which is consistent with the reaction written in
eq 1. The mechanism of formation of the minor product is not
yet understood and the fate of NO3- in the minor pathway has
-
yet to be determined. N2O and NO3 have been identified as
-
the dominate photochemical decomposition products of N3O4
,
in aqueous solution.2j
The photoreaction in eq 1 is extraordinary. Since irradiation
at 436 nm predominantly populates Re(I) to bpy MLCT excited
states to the exclusion of dinitramide states (φ366 ) 0.061 for
KN3O4 in water), it is apparently a rare example13,16 of
intramolecular chemistry photosensitized by a MLCT excited
state. This is made more intriguing by the fact that the quantum
yield (φ436) is 0.67 ( 0.0514 (determined with the ferrioxalate
actinometer in air saturated H2O).15 Our current studies are
concentrated on further defining the coordination chemistry and
photochemistry of this new ligand.16
Figure 1. X-ray crystal structure of fac-Re(bpy)(CO)3N3O4.
Acknowledgment. B.P.S. thanks the AFOSR for funding
(Grant 93-NC-193), and we thank Dr. Robert J. Schmitt (SRI
International) for providing the sample of KN3O4 that made this
work possible.
Supporting Information Available: For fac-Re(bpy)(CO)3N3O4,
tables of atomic coordinates and isotropic displacement coefficients
(Table 1), bond lengths (Table 2), bond angles (Table 3), anisotropic
displacement coefficients (Table 4), hydrogen coordinates and isotropic
displacement coefficients (Table 5), crystallographic data collection
parameters (Table 6), and solution and refinement parameters (Table
7) (7 pages). Ordering information is given on any current masthead
page.
Figure 2. UV-visible spectra of (a) fac-Re(bpy)(CO)3N3O4 (A), (b)
the intermediate complex (B) formed during photolysis and, (c) fac-
Re(bpy)(CO)3NO3 plus the minor product (C) (as determined by global
analysis of the kinetic process; 2.57 × 10-5 M in CH2Cl2).
IC951332L
identified as the nitrato complex fac-Re(bpy)(CO)3NO3. We
also observe a minor product which tentatively has been
assigned as the chloro complex fac-Re(bpy)(CO)3Cl. Indepen-
dent verification of the nitrato complex is provided by the
preparation of this new complex by reaction of fac-Re(bpy)-
(CO)3OSO2CF3 with NaNO3 in water.11 The stoichiometry of
the photolysis was determined by IR and NMR spectroscopic
studies of the course of the reaction. After complete consump-
tion of fac-Re(bpy)(CO)3N3O4, the product distribution (with
respect to the metal) is 90% fac-Re(bpy)(CO)3NO3. N2O12 is
(11) (a) Synthesis of fac-Re(bpy)(CO)3NO3. In 20 mL of deionized water,
0.26 mmol (147 mg) of Re(bpy)(CO)3OSO2CF3 was heated to reflux
until dissolved in a 100 mL round bottom flask. After the solution
was allowed to cool to room temperature, 22.6 mmol (220 mg) of
NaNO3 was added and the solution was stirred for 15 min. A yellow
microcrystalline solid was collected by vacuum filtration and washed
with 200 mL of CH2Cl2. The complex is slighly soluble in CH2Cl2;
10 mg/100 mL. Anal. Calcd for ReC13H8N3O6: C, 31.97; H, 1.65;
N, 8.6. Found: C, 32.00; H, 1.67; N, 8.58. 1H NMR (δ/ppm, CD2-
Cl2): 9.02 (m, 2H), 8.17 (m, 2H), 8.09 (m, 2H), 7.54 (m, 2H). UV-
visible (λ (nm), CH2Cl2) (ꢀ in M-1 cm-1): 246 (16 100), 268 (13 700),
368 (3480). IR (CH2Cl2) (ν (CO) cm-1): 2030, 1928, 1902. IR (ATR
Cell) (ν (ONO2) cm-1):17 147611b ν5, 1280 ν1, 1001 ν2. (b) The exact
band energy is somewhat uncertain because it overlaps a nearby bpy-
ligand band.
(12) N2O was confirmed as a photolysis product by its corresponding IR
peak at 2222 cm-1 in both CH2Cl2 that was saturated with N2O(g)
and the photolysis (excitation at 436 nm) of fac-Re(bpy)(CO)3N3O4
in CH2Cl2. N2O(g) has an IR absorption at 2223.8 cm-1 ν1.17
(13) Balzani, V.; Scandola, F. Supramolecular Photochemistry; Ellis
Horwood Press: New York, 1991.
(9) (a) Single-crystal X-ray data were collected at 23 °C using a yellow
crystal of dimensions 0.45 × 0.20 × 0.02 mm on a Siemens P3
diffractometer equipped with a molybdenum tube [λ(KR1) ) 0.709 26
Å; λ(KR2) ) 0.713 54 Å] and a graphite monochromator. The
compound crystallized in the centrosymmetric triclinic space group
P1h with two molecules in a cell of dimensions a ) 8.035(2) Å, b )
8.161(2) Å, c ) 12.365 (2) Å, R ) 97.36(3)°, â ) 101.24(3)°, γ )
91.66(3)°, and V ) 787.6(3) Å3. A total of 3091 independent
reflections were gathered (Rint ) 0.023), the octants collected being
+h, (k, (l, using the Wyckoff scan method. Three standard
reflections were measured after every 100 reflections collected. The
structure was solved by direct methods and refined by full-matrix least-
squares techniques using structure solution programs from the
SHELXTL system.9b All nonhydrogen atoms were refined anisotro-
pically. Hydrogen atoms were placed in calculated positions (C-H
) 0.96 Å) and refined with fixed isotropic thermal parameters. The
structure has been refined to conventional R factor values of R )
0.0478 and Rw ) 0.0582 on the basis of 2448 observed reflections
with F < 6σ(F) in the 2θ range 4-52° (R ) 0.0627, Rw ) 0.0617 for
all data), giving a data to parameter ratio of 10.4:1. The maximum
and minimum residual densities remaining were +2.91 and -3.06 e
Å-3, respectively, and located near Re(1). The data were corrected
for absorption using semiempirical techniques. (b) Sheldrick, G. M.;
SHELXTL Crystallographic System, Version 4.2/Iris; Siemens Analyti-
cal X-ray Insts. Inc., Madison, WI, 1991. (c) Calabrese, J. C.; Tam,
T. Chem. Phys. Lett. 1987, 133, 244. (d) Horn, E.; Snow, M. R. Aust.
J. Chem. 1980, 33, 2369.
(14) The quantum yield (φ436) of the photodecomposition of fac-Re(bpy)-
(CO)3N3O4 in CH2Cl2 that has been deoxygenated with N2 is 0.92 (
0.05.
(15) Rabek, J. F. Experimental Methods in Photochemistry and Photo-
physics, Part 2; John Wiley and Sons: New York, 1982; pp 937-
946.
(16) Electrochemical studies of N3O4- in H2O6 show a series of reductive
processes in the range of -0.3 to -0.82 V (vs Ag/AgCl) that give
rise to nitrite but not nitrate. No oxidative processes are observed to
the solvent limit (ca. +1.2 V). Given this, it is very unlikely that
intramolecular reductive quenching can occur in the Re(I) complex
with a significant rate. Thus, the mechanism could be intramolecular
oxidative quenching that yields a coordinated but reduced N3O4- that
fragments in a different fashion than direct electrochemical reduction
at an electrode (back electron transfer would then be required to reduce
Re(II) to Re(I) via a product of N3O4- decomposition). Alternatively,
the mechanism could be energy transfer sensitization which gives the
same state that is responsible for photodecomposition of free dini-
tramide ion.2j
(10) Data analysis was done using the Specfit package of Spectrum
Associates, Chapel Hill, NC 27514.
(17) Nakamoto, K. Infrared Spectra of Inorganic and Coordination
Compounds, 4th ed.; Wiley: New York, 1986; pp 112, 256.