Mel­amine (1,3,5-triazine-2,4,6-tri­amine): a neutron diffraction study at 14 K

The single-crystal neutron diffraction technique was used to determine the crystal structure of mel­amine, C₃H₆H₆, at 14 K. The mol­ecule is nearly planar. There are three crystallographically inequivalent amine groups with different geometries, the asymmetric unit being the complete molecule.

Key indicators

• Single-crystal neutron study
• T = 14 K
• Mean [sigma](N-C) = 0.001 Å
• R factor = 0.047
• wR factor = 0.043
• Data-to-parameter ratio = 13.3

checkCIF/PLATON results

No syntax errors found



Alert level A
DIFMN02_ALERT_2_A  The minimum difference density is < -0.1*ZMAX*2.00
            _refine_diff_density_min given =     -1.670
            Test value =     -1.400

Author Response: The corresponding peak Q1 has been located in the center of the melamine ring. this is nonsensical

DIFMX01_ALERT_2_A  The maximum difference density is > 0.1*ZMAX*2.00
            _refine_diff_density_max given =      1.810
            Test value =      1.400

Author Response: The corresponding peak Q2 has been located Q2 - C3 = 0.768\%A , Q2 - N4 = 1.3287\%A , Q2 - N3 = 1.052\%A , this is nonsensical

PLAT097_ALERT_2_A Maximum (Positive) Residual Density ............       1.81 e/A   3

Author Response: we are working with neutrons. The nuclear scattering density unity is fm/A   3

PLAT098_ALERT_2_A Minimum (Negative) Residual Density ............      -1.67 e/A   3

Author Response: The nuclear scattering density unity is fm/A   3

Alert level C
CELLK01_ALERT_1_C  Check that the cell measurement temperature is in Kelvin.
            Value of measurement temperature given =    14.000

Author Response: the temperature is in kelvin

DIFMN03_ALERT_1_C  The minimum difference density is < -0.1*ZMAX*0.75
            The relevant atom site should be identified.

Author Response: The corresponding peak QN3 has been located QN3 - N3 = 0.5787 \%A , QN3 - Q2 = 1.1975 \%A , this is nonsensical

DIFMX02_ALERT_1_C  The minimum difference density is > 0.1*ZMAX*0.75
            The relevant atom site should be identified.
PLAT125_ALERT_4_C No _symmetry_space_group_name_Hall Given .......          ?
PLAT128_ALERT_4_C Non-standard setting of Space group P21/c   ....    P21/a
PLAT250_ALERT_2_C Large U3/U1 Ratio for Average U(i,j) Tensor ....       2.29
PLAT353_ALERT_3_C Long    N-H Bond (0.87A)   N1     -   H1     ...       1.02 Ang.
PLAT353_ALERT_3_C Long    N-H Bond (0.87A)   N1     -   H2     ...       1.01 Ang.
PLAT353_ALERT_3_C Long    N-H Bond (0.87A)   N2     -   H4     ...       1.02 Ang.
PLAT353_ALERT_3_C Long    N-H Bond (0.87A)   N3     -   H5     ...       1.02 Ang.
PLAT353_ALERT_3_C Long    N-H Bond (0.87A)   N3     -   H6     ...       1.01 Ang.

   4 ALERT level A = In general: serious problem
   0 ALERT level B = Potentially serious problem
  11 ALERT level C = Check and explain
   0 ALERT level G = General alerts; check

   3 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   5 ALERT type 2 Indicator that the structure model may be wrong or deficient
   5 ALERT type 3 Indicator that the structure quality may be low
   2 ALERT type 4 Improvement, methodology, query or suggestion

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Computing details

Data collection: DIF4N (modified linux version of DIF4; Stoe & Cie, 2000); cell refinement: DIF4N (modified linux version of DIF4; Stoe & Cie, 2000); data reduction: PRON (modified version of REDU4; Stoe & Cie, 2000); program(s) used to solve structure: CRYSTALS (Watkin et al., 2001); program(s) used to refine structure: CRYSTALS (Watkin et al., 2001); molecular graphics: CAMERON (Watkin et al., 1996); software used to prepare material for publication: CRYSTALS (Watkin et al., 2001).

1,3,5-triazine-2,4,6-triamine

Crystal data

C3H6N6	F(000) = 204.000
Mr = 126.12	Dx = 1.619 Mg m^−3
Monoclinic, P21/a	Neutron radiation, λ = 0.83100 Å
a = 10.433 (1) Å	Cell parameters from 15 reflections
b = 7.458 (1) Å	θ = 32–44°
c = 7.238 (1) Å	µ = 0.12 mm^−1
β = 113.30 (2)°	T = 14 K
V = 517.26 (14) Å^3	Prism, white
Z = 4	3.50 × 3.00 × 3.00 mm

Data collection

Orphεe reactor (Saclay, France): 5-C2 four-circle diffractometer	θmax = 42.6°, θmin = 3.6°
Cu_(220) monochromator	h = −16→16
ω scans	k = −4→12
2714 measured reflections	l = −11→11
2327 independent reflections	450 standard reflections every 0 reflections
1819 reflections with I > 3.00σ(I)	intensity decay: 0.0%
Rint = 0.08

Refinement

Refinement on F	Hydrogen site location: inferred from neighbouring sites
Least-squares matrix: full	All H-atom parameters refined
R[F^2 > 2σ(F^2)] = 0.047	Method Prince modified Chebychev polynomial, (Watkin, 1994) W = [weight] * [1-(deltaF/6*sigmaF)^2]2 1.42 -1.26 0.982 -0.228
wR(F^2) = 0.043	(Δ/σ)max = 0.000257
S = 1.11	Δρmax = 1.81 e Å^−3
1819 reflections	Δρmin = −1.67 e Å^−3
137 parameters	Extinction correction: Larson 1970 Crystallographic Computing eq 22
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 17.2 (5)

Special details

Experimental. Neutron-diffraction measurements were carried out with the four-circle neutron diffractometer 5 C2 at the LLB (Saclay, France). A prismatic crystal (3.5 × 3.0 × 3.0 mm) was glued on a goniometer head and oriented. Measurements in the ω scan mode were performed with an incident wavelength of 0.831 Å selected with the Cu (220) monochromator. The structure was refined with the program CRYSTALS (Watkin et al., 2001). Absorption corrections were ignored.

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

	x	y	z	Uiso*/Ueq
C1	0.1730 (1)	0.65231 (13)	0.07285 (14)	0.0028
C2	0.12101 (9)	0.51341 (13)	0.31363 (14)	0.0029
C3	0.0643 (1)	0.80507 (12)	0.24100 (14)	0.0026
N1	0.22332 (8)	0.6480 (1)	−0.07076 (11)	0.0050
N2	0.12275 (8)	0.3668 (1)	0.42209 (11)	0.0051
N3	0.01348 (7)	0.96283 (9)	0.27868 (11)	0.0048
N4	0.06065 (7)	0.66176 (9)	0.3501 (1)	0.0041
N5	0.11664 (7)	0.80893 (9)	0.0989 (1)	0.0038
N6	0.18120 (7)	0.50207 (9)	0.1804 (1)	0.0041
H1	0.2411 (3)	0.7663 (4)	−0.1263 (4)	0.0185
H2	0.2715 (3)	0.5352 (4)	−0.0883 (4)	0.0183
H3	0.1577 (4)	0.2514 (4)	0.3879 (5)	0.0229
H4	0.0621 (3)	0.3627 (4)	0.5037 (4)	0.0188
H5	−0.0184 (3)	1.0510 (3)	0.1610 (4)	0.0176
H6	−0.0537 (3)	0.9515 (4)	0.3478 (5)	0.0204

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0029 (3)	0.0027 (3)	0.0026 (3)	0.0006 (2)	0.0008 (3)	0.0010 (2)
C2	0.0034 (3)	0.0017 (3)	0.0035 (3)	0.0003 (2)	0.0013 (3)	0.0010 (2)
C3	0.0029 (3)	0.0016 (3)	0.0031 (3)	0.0004 (2)	0.0011 (3)	0.0004 (2)
N1	0.0067 (3)	0.0045 (3)	0.0049 (3)	0.0013 (2)	0.0037 (2)	0.00096 (19)
N2	0.0064 (3)	0.0037 (3)	0.0059 (3)	0.00021 (19)	0.0031 (2)	0.0017 (2)
N3	0.0059 (2)	0.0030 (2)	0.0051 (2)	0.00112 (19)	0.0018 (2)	0.00005 (19)
N4	0.0055 (3)	0.0034 (2)	0.0043 (3)	0.00080 (19)	0.0029 (2)	0.00074 (19)
N5	0.0048 (2)	0.0026 (2)	0.0044 (3)	0.00099 (18)	0.0023 (2)	0.00097 (19)
N6	0.0055 (3)	0.0025 (2)	0.0049 (2)	0.00132 (18)	0.0029 (2)	0.00120 (18)
H1	0.0267 (12)	0.0121 (9)	0.0219 (11)	0.0022 (8)	0.0153 (9)	0.0054 (8)
H2	0.0249 (11)	0.0124 (9)	0.022 (1)	0.0054 (8)	0.0146 (9)	−0.0001 (8)
H3	0.0367 (15)	0.0116 (9)	0.0286 (13)	0.0085 (9)	0.0217 (12)	0.0016 (9)
H4	0.022 (1)	0.019 (1)	0.0224 (11)	0.0027 (8)	0.0162 (9)	0.0047 (8)
H5	0.022 (1)	0.0137 (9)	0.0162 (9)	0.0054 (8)	0.0070 (8)	0.0066 (8)
H6	0.0242 (11)	0.018 (1)	0.0260 (12)	0.0035 (9)	0.018 (1)	0.0012 (9)

Geometric parameters (Å, º)

C1—N1	1.3376 (12)	C3—N5	1.3420 (12)
C1—N5	1.3539 (12)	N1—H1	1.017 (3)
C1—N6	1.3475 (12)	N1—H2	1.013 (3)
C2—N2	1.3420 (12)	N2—H3	1.003 (3)
C2—N4	1.3497 (12)	N2—H4	1.022 (3)
C2—N6	1.3457 (12)	N3—H5	1.022 (3)
C3—N3	1.3618 (12)	N3—H6	1.013 (3)
C3—N4	1.3382 (12)
N1—C1—N5	117.02 (8)	H1—N1—H2	119.6 (2)
N1—C1—N6	118.30 (8)	C2—N2—H3	118.49 (18)
N5—C1—N6	124.68 (8)	C2—N2—H4	119.59 (17)
N2—C2—N4	116.94 (8)	H3—N2—H4	119.0 (2)
N2—C2—N6	117.77 (8)	C3—N3—H5	114.42 (17)
N4—C2—N6	125.28 (8)	C3—N3—H6	115.30 (17)
N3—C3—N4	117.88 (8)	H5—N3—H6	113.9 (2)
N3—C3—N5	116.34 (8)	C2—N4—C3	114.53 (7)
N4—C3—N5	125.76 (8)	C1—N5—C3	114.76 (7)
C1—N1—H1	118.42 (17)	C1—N6—C2	114.87 (7)
C1—N1—H2	118.91 (17)
N3—C3—N5—C1	176.64 (8)	H3—N2—C2—N6	−7.47 (17)
C3—N5—C1—N1	178.32 (8)	H4—N2—C2—N4	13.01 (17)
C3—N4—C2—N2	178.66 (8)	H5—N3—C3—N5	25.12 (17)
H1—N1—C1—N1	−94.89 (7)	H6—N3—C3—N4	−21.30 (17)
H2—N1—C1—N5	176.29 (17)