Computational, ¹H NMR, and X-ray structural studies on 1-aryl­urazole tetra­zane dimers

Nitro­gen-centered urazole radicals exist in equilibrium with tetra­zane dimers in solution. The equilibrium established typically favors the free-radical form. However, 1-aryl­urazole radicals bearing substituents at the ortho position favor the dimeric form. We were able to determine the structure of one of the dimers (substituted at both ortho positions with methyl groups), namely 1,2-(2,4-di­methyl­phen­yl)-2-[2-(2,4-di­methyl­phen­yl)-4-methyl-3,5-dioxo-1,2,4-triazoli­din-1-yl]-4-methyl-1,2,4-triazolidine-3,5-dione, C₂₄H₂₈N₆O₄, via X-ray crystallography. The experimentally determined structure agreed well with the computationally obtained geometry at the B3LYP/6-311G(d,p) level of theory. The preferred syn conformation of these 1-aryl­urazole dimers results in the two aromatic rings being proximate and nearly parallel, which leads to some inter­esting shielding effects of certain signals in the ¹H NMR spectrum. Armed with this information, we were able to decipher the more complicated ¹H NMR spectrum obtained from a dimer that was monosubstituted at the ortho position with a methyl group.

Computing details

Data collection: APEX2 (Bruker, 2014); cell refinement: SAINT (Bruker, 2015); data reduction: SAINT (Bruker, 2015); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2017 (Sheldrick, 2015); molecular graphics: ShelXle (Hübschle et al., 2011); software used to prepare material for publication: ShelXle (Hübschle et al., 2011).

4-Methyl-1-[4-methyl-3,5-dioxo-2-(2,4,6-trimethylphenyl)-1,2,4-triazolidin-1-yl]-2-(2,4,6-trimethylphenyl)-1,2,4-triazolidine-3,5-dione

Crystal data

C24H28N6O4	Dx = 1.280 Mg m^−3
Mr = 464.52	Melting point: 433 K
Orthorhombic, Pccn	Mo Kα radiation, λ = 0.71073 Å
a = 9.1077 (7) Å	Cell parameters from 9977 reflections
b = 13.5893 (11) Å	θ = 2.6–30.7°
c = 19.4760 (16) Å	µ = 0.09 mm^−1
V = 2410.5 (3) Å^3	T = 100 K
Z = 4	Block, colourless
F(000) = 984	0.84 × 0.50 × 0.34 mm

Data collection

Bruker APEXII CCD diffractometer	3721 independent reflections
Radiation source: fine-focus sealed tube	3323 reflections with I > 2σ(I)
Detector resolution: 8.3333 pixels mm^-1	Rint = 0.025
φ and ω scans	θmax = 30.7°, θmin = 2.6°
Absorption correction: multi-scan (SADABS; Bruker, 2016)	h = −10→13
Tmin = 0.661, Tmax = 0.746	k = −19→19
20363 measured reflections	l = −25→27

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.045	Hydrogen site location: difference Fourier map
wR(F^2) = 0.126	All H-atom parameters refined
S = 1.04	w = 1/[σ^2(Fo^2) + (0.0749P)^2 + 0.8555P] where P = (Fo^2 + 2Fc^2)/3
3721 reflections	(Δ/σ)max = 0.015
223 parameters	Δρmax = 0.47 e Å^−3
72 restraints	Δρmin = −0.22 e Å^−3

Special details

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > 2sigma(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq	Occ. (<1)
O1	0.14248 (8)	0.15831 (5)	0.25907 (4)	0.01958 (16)
O2	0.56911 (8)	0.04859 (5)	0.35811 (4)	0.02095 (16)
N1	0.26561 (8)	0.20011 (5)	0.35988 (4)	0.01305 (16)
N2	0.35286 (8)	0.07732 (5)	0.29746 (4)	0.01640 (16)
N3	0.41174 (8)	0.17803 (5)	0.38272 (4)	0.01289 (15)
C1	0.24245 (10)	0.14570 (6)	0.29872 (4)	0.01453 (17)
C2	0.36322 (13)	−0.00245 (8)	0.24773 (6)	0.0268 (2)
H2A	0.2665 (17)	−0.0188 (14)	0.2306 (11)	0.018 (7)*	0.59 (4)
H2B	0.421 (3)	0.0219 (16)	0.2080 (9)	0.052 (11)*	0.59 (4)
H2C	0.412 (3)	−0.0587 (12)	0.2677 (10)	0.027 (8)*	0.59 (4)
H2F	0.321 (4)	−0.0626 (13)	0.2681 (12)	0.037 (12)*	0.41 (4)
H2D	0.308 (3)	0.0144 (18)	0.2066 (10)	0.021 (10)*	0.41 (4)
H2E	0.4647 (18)	−0.0156 (19)	0.2365 (13)	0.017 (10)*	0.41 (4)
C3	0.45849 (10)	0.09596 (6)	0.34806 (5)	0.01476 (17)
C4	0.45249 (9)	0.20492 (6)	0.45127 (4)	0.01326 (16)
C5	0.54272 (11)	0.28700 (7)	0.45977 (5)	0.01975 (19)
C6	0.59948 (14)	0.34619 (9)	0.40023 (6)	0.0310 (3)
H6A	0.5857 (19)	0.3145 (12)	0.3563 (7)	0.052 (6)*
H6B	0.7012 (14)	0.3635 (11)	0.4040 (8)	0.040 (4)*
H6C	0.546 (2)	0.4099 (12)	0.3951 (10)	0.086 (8)*
C7	0.57694 (15)	0.31505 (8)	0.52693 (6)	0.0300 (3)
H7	0.6382 (19)	0.3702 (13)	0.5328 (9)	0.039 (4)*
C8	0.52312 (15)	0.26429 (8)	0.58352 (5)	0.0284 (2)
C9	0.5563 (3)	0.29835 (13)	0.65532 (7)	0.0595 (6)
H9A	0.592 (2)	0.2490 (16)	0.6836 (9)	0.089 (8)*
H9B	0.618 (2)	0.3521 (13)	0.6560 (9)	0.059 (6)*
H9C	0.468 (2)	0.3191 (18)	0.6777 (11)	0.132 (13)*
C10	0.43458 (12)	0.18197 (7)	0.57286 (5)	0.0213 (2)
H10	0.3980 (18)	0.1460 (12)	0.6115 (8)	0.032 (4)*
C11	0.39823 (10)	0.15077 (6)	0.50710 (5)	0.01638 (18)
C12	0.30343 (13)	0.06119 (8)	0.49601 (6)	0.0260 (2)
H12A	0.2787 (17)	0.0309 (11)	0.5393 (7)	0.045 (5)*
H12B	0.3582 (18)	0.0119 (11)	0.4697 (8)	0.056 (6)*
H12C	0.2162 (16)	0.0770 (12)	0.4718 (8)	0.052 (5)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0168 (3)	0.0192 (3)	0.0228 (3)	0.0009 (2)	−0.0055 (2)	−0.0024 (2)
O2	0.0162 (3)	0.0188 (3)	0.0279 (4)	0.0057 (2)	−0.0029 (3)	−0.0039 (3)
N1	0.0119 (3)	0.0094 (3)	0.0178 (3)	0.0016 (2)	−0.0024 (2)	−0.0012 (2)
N2	0.0143 (4)	0.0139 (3)	0.0210 (4)	0.0019 (2)	−0.0021 (3)	−0.0053 (3)
N3	0.0113 (3)	0.0124 (3)	0.0150 (3)	0.0021 (2)	−0.0019 (2)	−0.0013 (2)
C1	0.0140 (4)	0.0116 (3)	0.0180 (4)	−0.0008 (3)	0.0000 (3)	−0.0014 (3)
C2	0.0242 (5)	0.0231 (4)	0.0330 (5)	0.0041 (4)	−0.0034 (4)	−0.0161 (4)
C3	0.0135 (4)	0.0123 (3)	0.0185 (4)	−0.0002 (3)	0.0001 (3)	−0.0010 (3)
C4	0.0135 (4)	0.0122 (3)	0.0141 (4)	−0.0008 (3)	0.0002 (3)	0.0001 (3)
C5	0.0254 (5)	0.0179 (4)	0.0159 (4)	−0.0095 (3)	0.0001 (3)	0.0012 (3)
C6	0.0377 (6)	0.0347 (6)	0.0207 (5)	−0.0232 (5)	−0.0017 (4)	0.0076 (4)
C7	0.0483 (7)	0.0235 (5)	0.0181 (4)	−0.0183 (5)	−0.0036 (4)	−0.0012 (4)
C8	0.0450 (7)	0.0245 (5)	0.0158 (4)	−0.0085 (4)	0.0000 (4)	−0.0021 (3)
C9	0.1150 (17)	0.0468 (8)	0.0168 (5)	−0.0332 (10)	−0.0024 (7)	−0.0059 (5)
C10	0.0254 (5)	0.0222 (4)	0.0163 (4)	−0.0016 (3)	0.0023 (3)	0.0043 (3)
C11	0.0153 (4)	0.0153 (4)	0.0185 (4)	−0.0014 (3)	−0.0002 (3)	0.0045 (3)
C12	0.0252 (5)	0.0237 (4)	0.0292 (5)	−0.0120 (4)	−0.0081 (4)	0.0124 (4)

Geometric parameters (Å, º)

O1—C1	1.2062 (11)	C4—C5	1.3953 (12)
O2—C3	1.2115 (11)	C4—C11	1.4030 (12)
N1—N1^i	1.3854 (13)	C5—C7	1.3975 (14)
N1—C1	1.4178 (11)	C5—C6	1.5030 (14)
N1—N3	1.4349 (10)	C7—C8	1.3896 (15)
N2—C1	1.3694 (11)	C8—C10	1.3945 (14)
N2—C3	1.4003 (11)	C8—C9	1.5035 (17)
N2—C2	1.4567 (12)	C10—C11	1.3891 (13)
N3—C3	1.3714 (11)	C11—C12	1.5080 (13)
N3—C4	1.4331 (11)
N1^i—N1—C1	118.68 (5)	C5—C4—C11	122.33 (8)
N1^i—N1—N3	113.27 (8)	C5—C4—N3	117.84 (8)
C1—N1—N3	106.82 (6)	C11—C4—N3	119.81 (8)
C1—N2—C3	111.66 (7)	C4—C5—C7	117.42 (9)
C1—N2—C2	124.36 (8)	C4—C5—C6	122.60 (9)
C3—N2—C2	123.92 (8)	C7—C5—C6	119.96 (9)
C3—N3—C4	125.83 (7)	C8—C7—C5	121.89 (9)
C3—N3—N1	107.79 (7)	C7—C8—C10	118.95 (9)
C4—N3—N1	118.40 (7)	C7—C8—C9	120.93 (11)
O1—C1—N2	129.74 (8)	C10—C8—C9	120.10 (10)
O1—C1—N1	125.18 (8)	C11—C10—C8	121.33 (9)
N2—C1—N1	105.05 (7)	C10—C11—C4	118.07 (8)
O2—C3—N3	127.65 (8)	C10—C11—C12	121.00 (8)
O2—C3—N2	126.08 (8)	C4—C11—C12	120.93 (8)
N3—C3—N2	106.27 (7)
N1^i—N1—N3—C3	−147.65 (6)	C3—N3—C4—C5	110.61 (10)
C1—N1—N3—C3	−15.15 (9)	N1—N3—C4—C5	−104.43 (10)
N1^i—N1—N3—C4	61.61 (8)	C3—N3—C4—C11	−71.19 (12)
C1—N1—N3—C4	−165.89 (7)	N1—N3—C4—C11	73.77 (10)
C3—N2—C1—O1	171.90 (9)	C11—C4—C5—C7	−0.72 (15)
C2—N2—C1—O1	−5.46 (16)	N3—C4—C5—C7	177.43 (9)
C3—N2—C1—N1	−10.06 (10)	C11—C4—C5—C6	−179.11 (10)
C2—N2—C1—N1	172.58 (9)	N3—C4—C5—C6	−0.96 (15)
N1^i—N1—C1—O1	−37.29 (14)	C4—C5—C7—C8	−0.46 (18)
N3—N1—C1—O1	−166.76 (8)	C6—C5—C7—C8	177.98 (13)
N1^i—N1—C1—N2	144.56 (9)	C5—C7—C8—C10	1.2 (2)
N3—N1—C1—N2	15.09 (9)	C5—C7—C8—C9	−177.41 (15)
C4—N3—C3—O2	−23.65 (15)	C7—C8—C10—C11	−0.72 (18)
N1—N3—C3—O2	−171.62 (9)	C9—C8—C10—C11	177.87 (14)
C4—N3—C3—N2	156.86 (8)	C8—C10—C11—C4	−0.40 (15)
N1—N3—C3—N2	8.89 (9)	C8—C10—C11—C12	179.50 (10)
C1—N2—C3—O2	−178.74 (9)	C5—C4—C11—C10	1.14 (14)
C2—N2—C3—O2	−1.37 (15)	N3—C4—C11—C10	−176.98 (8)
C1—N2—C3—N3	0.76 (10)	C5—C4—C11—C12	−178.75 (9)
C2—N2—C3—N3	178.13 (9)	N3—C4—C11—C12	3.13 (13)

Symmetry code: (i) −x+1/2, −y+1/2, z.