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The title compound, C32H42N4O6, is a novel nitroxide radical used for pulsed electron-electron double resonance (PELDOR) spectroscopy. Its crystal structure was determined from laboratory X-ray powder diffraction data. The attractive forces between the mol­ecules in the crystal structure are mainly of dispersive nature. A special inter­action of the nitroxide radicals was not observed.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270113029211/sk3514sup1.cif
Contains datablock I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270113029211/sk3514Isup2.hkl
Contains datablock I

CCDC reference: 968242

Crystal structure top

The compound (Fig. 2) crystallizes in the monoclinic space group P21/c. The molecules are situated on crystallographic inversion centres, located at the mid-point of the central –NN– bond. The OOC—Ph—NN—Ph—COO fragment is almost planar. The N—O bond length [1.308 (5) Å] is within the range of distribution in comparison to 325 known N—O bond lengths [1.28 (4) Å] for nitroxide radicals (Allen, 2002). The molecules are arranged in thick layers parallel to (100) (i.e. in the bc plane). The –NN– group is in the centre of this layer, whereas the piperidine N-oxide fragments are positioned at the surfaces of the layers (see Fig. 3). In the b direction, neighbouring molecules are parallel, but in the c direction, the central units of neighbouring molecules form an angle of about 58°. Each molecule is surrounded by 14 neighbouring molecules. The molecules are mainly connected by dispersive inter­actions supported by polarisation and weak Coulombic inter­actions. The intra­molecular distance between the two oxygen radicals of the N-oxyl centres in each molecule is 23.658 (6) Å. The closest inter­molecular O···O distance is 4.886 (6) Å, which indicates that inter­actions between the radicals do not play a role in the molecular packing.

Experimental top

Synthesis and crystallisation top

The title compound was synthesised by the addition of 4-hy­droxy-2,2,6,6-tetra­methyl­piperidine­oxyl (TEMPOL) to azo­benzene-4,4'-di­carbonyl dichloride. The crude product was recrystallised from ethanol as an orange powder. Elemental analysis calculated: C 66.39, H 7.31, N 9.72%; found: C 66.17, H 7.42, N 9.47%.

Thermal analysis top

Differential thermal and thermogravimetrical analysis (DTA/TGA) were performed on a SETARAM (TGA 92) device. Approximately 10–15 mg of the sample was filled into corundum crucibles and measured from 293 to 773 K at a rate of 3 K min-1 under a nitro­gen atmosphere.

X-ray powder diffraction top

For the crystal structure determination from laboratory X-ray powder diffraction data, the diffractogram was recorded in transmission mode on aa Stoe STADI-P diffractometer with a Ge(111) monochromator and a linear position-sensitive detector using Cu Kα1 radiation. The sample was measured for 26 h in a 0.7 mm capillary. The software WinXPOW (Stoe & Cie, 2004) was used for data acquisition.

Indexing and structure solution top

For indexing and structure solution, the powder pattern was truncated to a real-space resolution of approximately 2.58 Å, which for Cu Kα1 radiation corresponds to the range 3.0–34.8° in 2θ. The background was subtracted with a Bayesian high-pass filter (David & Sivia, 2001). The indexing was performed with the program DICVOL91 (Boultif & Louër, 1991). For the structure solution, DASH (David et al., 2006) was used. The starting molecular geometry, including H atoms, was generated using the force field CHARMM (Brooks et al.,1983). The asymmetric unit contains only half a molecule, thus half a molecule was used for the structure solution.

Refinement top

The structure was refined by the Rietveld method using the program TOPAS (Coelho, 2007) and the full 2θ range. Initially a Pawley refinement was carried out, refining the background, unit-cell parameters, zero-point error, peak-width and peak-asymmetry parameters. To allow the peak profiles to be described as accurately as possible, anisotropic peak broadening was included in a second Pawley refinement step, which improved the fit noticeably. The refinement converged with Rexp = 2.198%, Rexp' = 4.870%, Rwp = 2.345%, Rwp' = 5.196 %, Rp = 1.785%, Rp' = 5.356 % and a goodness-of-fit (gof) = 1.067 (the values with a prime denote the background-subtracted values). 89 restraints were used.

In the Rietveld refinement, the profile parameters, the cell parameters, the scale parameter, the background parameters and the atomic positions were allowed to refine. The molecule is situated on a crystallographic inversion center located on the midpoint of its NN double bond. To fix the molecule at the inversion centre, the two N atoms of the –NN– group were both included, but with occupancies of 0.5. Suitable chemical restraints were added for bond lengths, valence angles and the planarity of the benzene rings. A common isotropic displacement parameter for C, N and O atoms was refined. The isotropic displacement parameter of the H atoms was constrained at 1.2 times the global isotropic displacement parameter. The C—H bond lengths were set at the standard value of 0.96 Å, as obtained from the Cambridge Structural Database (Allen, 2002) for single-crystal studies at room temperature. Crystal data, data collection and structure refinement details are summarized in Table 1.

Results and discussion top

Thermal analysis top

The DTA/TGA shows no mass loss or gain up to about 498 K. This indicates that the crystals do not contain water or solvent molecules in the lattice. The DTA exhibits a sharp endothermic signal at 498 K (melting point), followed by a broad exothermic signal at 502 K with a large weight loss resulting from decomposition.

Structure determination top

The powder pattern could be indexed without ambiguity, resulting in a monoclinic unit cell with corresponding figures of merit M(20) = 28.4 (de Wolff, 1968) and F(20) = 52.8 (Smith & Snyder, 1979) as indices for the quality of indexing. A comparison of the unit-cell volume (V = 1574 Å3) with Hofmann's volume increments (Hofmann, 2002) led to the estimation that Z = 2. Subsequently, a Pawley (1981) refinement was carried out to extract integrated intensities and their correlations, converging with a Pawley χ2 value of 1.916. The space group was determined as P21/c from the refinement using Bayesian statistical analysis (Markvardsen et al., 2001). The crystal structure was solved without problems from the powder pattern in direct space with simulated annealing. The number of simulated annealing runs was increased from 10 to 50 in order to obtain better statistics regarding reproducibility. The subsequently Rietveld refinement converged with an excellent fit (Rexp = 2.330%, Rexp' = 6.774%, Rwp = 3.096%, Rwp' = 8.999%, Rp = 2.352%, Rp' = 9.287% and a gof = 1.329); the difference curve is almost a straight line (Fig. 1).

Crystal structure top

The compound (Fig. 2) crystallizes in the monoclinic space group P21/c. The molecules are situated on crystallographic inversion centres, located at the mid-point of the central –NN– bond. The OOC—Ph—NN—Ph—COO fragment is almost planar. The N—O bond length [1.308 (5) Å] is within the range of distribution in comparison to 325 known N—O bond lengths [1.28 (4) Å] for nitroxide radicals (Allen, 2002). The molecules are arranged in thick layers parallel to (100) (i.e. in the bc plane). The –NN– group is in the centre of this layer, whereas the piperidine N-oxide fragments are positioned at the surfaces of the layers (see Fig. 3). In the b direction, neighbouring molecules are parallel, but in the c direction, the central units of neighbouring molecules form an angle of about 58°. Each molecule is surrounded by 14 neighbouring molecules. The molecules are mainly connected by dispersive inter­actions supported by polarisation and weak Coulombic inter­actions. The intra­molecular distance between the two oxygen radicals of the N-oxyl centres in each molecule is 23.658 (6) Å. The closest inter­molecular O···O distance is 4.886 (6) Å, which indicates that inter­actions between the radicals do not play a role in the molecular packing.

Related literature top

For related literature, see: Allen (2002); Bode et al. (2007); Boultif & Louër (1991); Brooks et al. (1983); Coelho (2007); David & Sivia (2001); David et al. (2006); Herget et al. (2011); Hofmann (2002); Jeschke (2002); Krstic et al. (2010); Markvardsen et al. (2001); Pawley (1981); Smith & Snyder (1979); Stoe & Cie (2004); de Wolff (1968).

Computing details top

Data collection: WinXPOW (Stoe & Cie, 2004); cell refinement: TOPAS Academic (Coelho, 2007); data reduction: DASH (David et al., 2006); program(s) used to solve structure: DASH (David et al., 2006); program(s) used to refine structure: TOPAS Academic (Coelho, 2007); molecular graphics: Mercury (Macrae et al., 2008).

Figures top
[Figure 1] Fig. 1. Final Rietveld plot: observed (black dots), calculated (red line) and difference (blue line) profiles and tick marks (green vertical lines) for the Rietveld refinement of the title compound. The change of scale at 36° in 2θ is a factor of 5.
[Figure 2] Fig. 2. A view of the molecule of (I), located on an inversion centre, showing the atom-numbering scheme.
[Figure 3] Fig. 3. Packing diagram of (I), viewed along the b axis. Two layers of molecules (horizontally) are shown.
4,4'-{Diazenediylbis[(1,4-phenylene)bis(carbonyloxy)]}bis(2,2,6,6-tetramethylpiperidinyloxidanyl) top
Crystal data top
C32H42N4O6F(000) = 620.0
Mr = 578.7standard setting
Monoclinic, P21/cDx = 1.222 Mg m3
Hall symbol: -P 2ybcMelting point: 498.38 K
a = 19.3355 (5) ÅCu Kα1 radiation, λ = 1.54056 Å
b = 5.9277 (2) ŵ = 0.69 mm1
c = 14.5264 (4) ÅT = 293 K
β = 109.222 (1)°Particle morphology: needles
V = 1572.12 (8) Å3cylinder, 30 × 0.7 mm
Z = 2
Data collection top
Stoe Stadi-P
diffractometer
Data collection mode: transmission
Radiation source: sealed x-ray tubeScan method: step
Primary focussing Ge 111 monochromator2θmin = 2.0°, 2θmax = 79.99°, 2θstep = 0.01°
Specimen mounting: 0.7 mm glass capillary
Refinement top
Least-squares matrix: full with fixed elements per cycle114 parameters
Rp = 9.33659 restraints
Rwp = 8.99767 constraints
Rexp = 6.772H-atom parameters not refined
RBragg = 0.929Weighting scheme based on measured s.u.'s w = 1/σ[Yõbs~]2
χ2 = 1.329(Δ/σ)max = 0.001
7700 data pointsBackground function: Chebyshev polynomials with 20 refinable coefficients
Excluded region(s): nonePreferred orientation correction: none
Profile function: Fundamental Parameters Line Profile Fitting Approach (Cheary et al., 2004)
Crystal data top
C32H42N4O6V = 1572.12 (8) Å3
Mr = 578.7Z = 2
Monoclinic, P21/cCu Kα1 radiation, λ = 1.54056 Å
a = 19.3355 (5) ŵ = 0.69 mm1
b = 5.9277 (2) ÅT = 293 K
c = 14.5264 (4) Åcylinder, 30 × 0.7 mm
β = 109.222 (1)°
Data collection top
Stoe Stadi-P
diffractometer
Scan method: step
Specimen mounting: 0.7 mm glass capillary2θmin = 2.0°, 2θmax = 79.99°, 2θstep = 0.01°
Data collection mode: transmission
Refinement top
Rp = 9.3367700 data points
Rwp = 8.997114 parameters
Rexp = 6.77259 restraints
RBragg = 0.929H-atom parameters not refined
χ2 = 1.329
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
N10.0050 (2)0.0500 (6)0.03407 (19)0.05216
N20.35613 (17)0.7331 (7)0.6456 (2)0.05216
O20.1901 (3)0.0374 (8)0.4832 (3)0.05216
O30.2265 (2)0.3401 (7)0.4226 (3)0.05216
O10.3938 (2)0.8778 (8)0.7109 (3)0.05216
C10.04371 (13)0.0071 (5)0.12878 (18)0.05216
C20.04509 (13)0.1392 (4)0.2037 (2)0.05216
H20.016230.274530.190600.06260
C30.08821 (12)0.0846 (4)0.2969 (2)0.05216
H30.088440.186960.348260.06260
C40.12977 (13)0.1144 (5)0.3158 (2)0.05216
C50.12746 (10)0.2574 (5)0.2397 (2)0.05216
H50.155380.394660.251330.06260
C60.08454 (12)0.2057 (4)0.14597 (18)0.05216
H60.083680.308350.094500.06260
C70.1826 (3)0.1614 (7)0.4152 (3)0.05216
C80.28021 (17)0.3874 (5)0.51578 (19)0.05216
H80.297620.242410.543130.06260
C90.24189 (17)0.5243 (5)0.5733 (2)0.05216
H9A0.204770.437660.587650.06260
H9B0.217890.648590.532960.06260
C100.29508 (17)0.6202 (6)0.6673 (2)0.05216
C130.25209 (16)0.7833 (5)0.7061 (2)0.05216
H13A0.225380.884830.655320.06260
H13B0.286860.865550.757760.06260
H13C0.218240.703680.729970.06260
C140.32373 (16)0.4347 (5)0.7437 (2)0.05216
H14A0.347300.315830.720270.06260
H14B0.282040.377460.758180.06260
H14C0.358370.498610.801180.06260
C110.39471 (15)0.6343 (5)0.5841 (2)0.05216
C120.33927 (15)0.5283 (5)0.49453 (16)0.05216
H12A0.316420.648530.450820.06260
H12B0.366720.429880.467000.06260
C160.43204 (16)0.8275 (5)0.5501 (2)0.05216
H16A0.448320.775130.498120.06260
H16B0.474110.875800.602930.06260
H16C0.397740.948990.527770.06260
C150.45579 (16)0.4722 (5)0.6396 (2)0.05216
H15A0.472280.394900.592540.06260
H15B0.439340.364800.677260.06260
H15C0.495560.560580.680830.06260
Geometric parameters (Å, º) top
N1—C11.429 (3)C9—H9B0.960
N2—O11.308 (5)C9—C101.523 (4)
N2—C101.478 (5)C10—C131.500 (5)
N2—C111.462 (5)C10—C141.531 (4)
O2—C71.201 (6)C13—H13A0.960
O3—C71.339 (6)C13—H13B0.960
O3—C81.437 (4)C13—H13C0.960
C1—C21.384 (4)C14—H14A0.960
C1—C61.393 (4)C14—H14B0.960
C2—H20.960C14—H14C0.960
C2—C31.375 (4)C11—C121.523 (3)
C3—H30.960C11—C161.521 (5)
C3—C41.403 (4)C11—C151.530 (4)
C4—C51.382 (4)C12—H12A0.960
C4—C71.495 (4)C12—H12B0.960
C5—H50.960C16—H16A0.960
C5—C61.376 (3)C16—H16B0.960
C6—H60.960C16—H16C0.960
C8—H80.960C15—H15A0.960
C8—C91.521 (5)C15—H15B0.960
C8—C121.526 (5)C15—H15C0.960
C9—H9A0.960
O1—N2—C10115.9 (3)C9—C10—C13106.4 (3)
O1—N2—C11115.5 (3)C9—C10—C14111.0 (3)
C10—N2—C11123.6 (3)C13—C10—C14107.7 (3)
C7—O3—C8118.1 (4)C10—C13—H13A109.9
N1—C1—C2116.4 (3)C10—C13—H13B106.8
N1—C1—C6121.8 (3)C10—C13—H13C110.3
C2—C1—C6121.7 (2)H13A—C13—H13B110.1
C1—C2—H2120.5H13A—C13—H13C109.1
C1—C2—C3118.4 (2)H13B—C13—H13C110.6
H2—C2—C3121.1C10—C14—H14A111.8
C2—C3—H3117.6C10—C14—H14B106.5
C2—C3—C4120.8 (2)C10—C14—H14C109.3
H3—C3—C4121.6H14A—C14—H14B110.4
C3—C4—C5119.6 (3)H14A—C14—H14C108.7
C3—C4—C7120.7 (3)H14B—C14—H14C110.1
C5—C4—C7119.3 (3)N2—C11—C12109.3 (3)
C4—C5—H5120.7N2—C11—C16106.8 (3)
C4—C5—C6120.3 (2)N2—C11—C15113.0 (3)
H5—C5—C6119.0C12—C11—C16108.0 (2)
C1—C6—C5119.2 (2)C12—C11—C15113.3 (2)
C1—C6—H6122.2C16—C11—C15106.1 (2)
C5—C6—H6118.6C8—C12—C11114.6 (2)
O2—C7—O3121.1 (4)C8—C12—H12A109.1
O2—C7—C4122.6 (4)C8—C12—H12B107.7
O3—C7—C4116.0 (4)C11—C12—H12A107.5
O3—C8—H8105.2C11—C12—H12B106.1
O3—C8—C9106.9 (3)H12A—C12—H12B111.9
O3—C8—C12105.8 (3)C11—C16—H16A109.0
H8—C8—C9114.7C11—C16—H16B109.4
H8—C8—C12112.9C11—C16—H16C109.0
C9—C8—C12110.6 (2)H16A—C16—H16B108.3
C8—C9—H9A111.6H16A—C16—H16C110.3
C8—C9—H9B107.4H16B—C16—H16C110.8
C8—C9—C10112.6 (3)C11—C15—H15A107.8
H9A—C9—H9B107.3C11—C15—H15B111.9
H9A—C9—C10109.7C11—C15—H15C107.9
H9B—C9—C10108.0H15A—C15—H15B109.8
N2—C10—C9109.2 (3)H15A—C15—H15C108.6
N2—C10—C13111.6 (3)H15B—C15—H15C110.7
N2—C10—C14110.8 (3)
O1—N2—C10—C9160.6 (3)H8—C8—C12—H12B41.5
O1—N2—C10—C1343.2 (4)C9—C8—C12—C1153.8 (3)
O1—N2—C10—C1476.8 (4)C9—C8—C12—H12A66.7
C11—N2—C10—C945.7 (4)C9—C8—C12—H12B171.6
C11—N2—C10—C13163.1 (3)C8—C9—C10—N249.2 (4)
C11—N2—C10—C1476.9 (4)C8—C9—C10—C13169.9 (3)
O1—N2—C11—C12163.1 (3)C8—C9—C10—C1473.2 (3)
O1—N2—C11—C1646.5 (4)H9A—C9—C10—N2174.2
O1—N2—C11—C1569.8 (4)H9A—C9—C10—C1365.2
C10—N2—C11—C1243.1 (4)H9A—C9—C10—C1451.7
C10—N2—C11—C16159.7 (3)H9B—C9—C10—N269.2
C10—N2—C11—C1584.0 (4)H9B—C9—C10—C1351.4
C8—O3—C7—O23.6 (6)H9B—C9—C10—C14168.3
C8—O3—C7—C4177.6 (3)N2—C10—C13—H13A69.4
C7—O3—C8—H837.9N2—C10—C13—H13B49.9
C7—O3—C8—C984.5 (4)N2—C10—C13—H13C170.2
C7—O3—C8—C12157.7 (3)C9—C10—C13—H13A49.6
N1—C1—C2—H22.9C9—C10—C13—H13B169.0
N1—C1—C2—C3176.6 (3)C9—C10—C13—H13C70.7
C6—C1—C2—H2179.4C14—C10—C13—H13A168.7
C6—C1—C2—C30.1 (4)C14—C10—C13—H13B71.9
N1—C1—C6—C5176.5 (3)C14—C10—C13—H13C48.3
N1—C1—C6—H63.4N2—C10—C14—H14A64.0
C2—C1—C6—C50.2 (4)N2—C10—C14—H14B175.3
C2—C1—C6—H6179.7N2—C10—C14—H14C56.4
C1—C2—C3—H3179.6C9—C10—C14—H14A57.5
C1—C2—C3—C40.0 (4)C9—C10—C14—H14B63.1
H2—C2—C3—H30.1C9—C10—C14—H14C178.0
H2—C2—C3—C4179.4C13—C10—C14—H14A173.7
C2—C3—C4—C50.1 (4)C13—C10—C14—H14B53.0
C2—C3—C4—C7173.5 (3)C13—C10—C14—H14C65.9
H3—C3—C4—C5179.6N2—C11—C12—C844.9 (3)
H3—C3—C4—C77.0N2—C11—C12—H12A76.6
C3—C4—C5—H5179.7N2—C11—C12—H12B163.6
C3—C4—C5—C60.2 (4)C16—C11—C12—C8160.7 (2)
C7—C4—C5—H56.8C16—C11—C12—H12A39.3
C7—C4—C5—C6173.6 (3)C16—C11—C12—H12B80.6
C3—C4—C7—O22.6 (6)C15—C11—C12—C882.1 (3)
C3—C4—C7—O3171.4 (3)C15—C11—C12—H12A156.4
C5—C4—C7—O2175.9 (4)C15—C11—C12—H12B36.6
C5—C4—C7—O32.0 (5)N2—C11—C16—H16A166.9
C4—C5—C6—C10.2 (4)N2—C11—C16—H16B74.9
C4—C5—C6—H6179.6N2—C11—C16—H16C46.5
H5—C5—C6—C1179.8C12—C11—C16—H16A49.4
H5—C5—C6—H60.1C12—C11—C16—H16B167.7
O3—C8—C9—H9A65.7C12—C11—C16—H16C71.0
O3—C8—C9—H9B51.7C15—C11—C16—H16A72.3
O3—C8—C9—C10170.4 (3)C15—C11—C16—H16B46.0
H8—C8—C9—H9A50.4C15—C11—C16—H16C167.3
H8—C8—C9—H9B167.8N2—C11—C15—H15A169.8
H8—C8—C9—C1073.4N2—C11—C15—H15B49.0
C12—C8—C9—H9A179.6N2—C11—C15—H15C73.1
C12—C8—C9—H9B63.0C12—C11—C15—H15A44.8
C12—C8—C9—C1055.7 (3)C12—C11—C15—H15B76.0
O3—C8—C12—C11169.2 (3)C12—C11—C15—H15C162.0
O3—C8—C12—H12A48.6C16—C11—C15—H15A73.4
O3—C8—C12—H12B73.1C16—C11—C15—H15B165.7
H8—C8—C12—C1176.3C16—C11—C15—H15C43.7
H8—C8—C12—H12A163.2

Experimental details

Crystal data
Chemical formulaC32H42N4O6
Mr578.7
Crystal system, space groupMonoclinic, P21/c
Temperature (K)293
a, b, c (Å)19.3355 (5), 5.9277 (2), 14.5264 (4)
β (°) 109.222 (1)
V3)1572.12 (8)
Z2
Radiation typeCu Kα1, λ = 1.54056 Å
µ (mm1)0.69
Specimen shape, size (mm)Cylinder, 30 × 0.7
Data collection
DiffractometerStoe Stadi-P
diffractometer
Specimen mounting0.7 mm glass capillary
Data collection modeTransmission
Scan methodStep
2θ values (°)2θmin = 2.0 2θmax = 79.99 2θstep = 0.01
Refinement
R factors and goodness of fitRp = 9.336, Rwp = 8.997, Rexp = 6.772, RBragg = 0.929, χ2 = 1.329
No. of data points7700
No. of parameters114
No. of restraints59
H-atom treatmentH-atom parameters not refined

Computer programs: WinXPOW (Stoe & Cie, 2004), TOPAS Academic (Coelho, 2007), DASH (David et al., 2006), Mercury (Macrae et al., 2008).

 

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