Influence of hydrogen bonding on the second harmonic generation effect: neutron diffraction study of 4-nitro-4′-methylbenzylidene aniline

A neutron diffraction study of the non-linear optical (NLO) material 4-nitro-4′-methylbenzylidene aniline (NMBA) is presented. NMBA exhibits a large macroscopic second-order NLO susceptibility, χ⁽²⁾, and this study shows that hydrogen bonding is, in part, responsible for this. No hydrogen bonding was reported in the X-ray study [Ponomarev et al. (1977). Sov. Phys. Crystallogr. 22, 223–225], whereas the present work shows that C—H...X hydrogen bonds (where X = N, O or π) direct the nature of the three-dimensional lattice. C—H...X (X = N or O) hydrogen bonds are common; however, C—H...π hydrogen-bond motifs are relatively rare. Such intermolecular interactions help extend the molecular charge transfer into the supramolecular realm, the charge transfer originating as a consequence of the high level of molecular planarity and strong donor-to-acceptor interactions. Molecular planarity, coupled with the favourable nature of the hydrogen bonds, results in parallel stacking of molecules in both the a and c crystallographic directions with extremely close interplanar spacings. Such a combination of influential hydrogen-bonding characteristics accounts, in part, for the large second-order NLO output of the material since the phenomenon is so critically dependent upon the nature of the charge transfer.

S1. Refinement

Alert A: < 85% complete (theta max?) revealed: given that this is a neutron structure, completeness is much more resources demanding and is not necessary since monochromatic neutron diffraction is intrinsically much more precise than analogous XRD measurements. The completeness given here for this experiment is satisfactory.

Computing details

Data collection: MAD (Barthelemy, 1984); cell refinement: RAFIN (Fihol, 198?); data reduction: COLL5N (Lehmann & Wilson, 198?); program(s) used to solve structure: SHELXS86 (Sheldrick, 1990); program(s) used to refine structure: SHELXL93 (Sheldrick, 1993); molecular graphics: SHELXTL-Plus (Sheldrick, 1995); software used to prepare material for publication: SHELXL93 (Sheldrick, 1993).

Figures

(NMBA)

Crystal data

C14H12N2O2	F(000) = 184
Mr = 240.00	Dx = 1.393 Mg m^−3
Monoclinic, Pc	Neutrons radiation, λ = 1.26170 Å
a = 7.305 (4) Å	Cell parameters from 1349 reflections
b = 11.495 (5) Å	θ = 15.4–70.4°
c = 7.240 (3) Å	µ = 0.18 mm^−1
β = 109.71 (5)°	T = 20 K
V = 572.3 (5) Å^3	Block, yellow
Z = 2	5.3 × 2.1 × 1.2 mm

Data collection

The single-crystal diffractometer, D10	1304 reflections with I > 2σ(I)
Radiation source: Institut Laue Langevin Reactor, Grenoble, France	Rint = 0.017
Cu (200) monochromator	θmax = 70.4°, θmin = 15.5°
ω–x–θ scans	h = −4→10
Absorption correction: integration DATAP (Coppens, 1970)	k = −16→16
Tmin = 0.618, Tmax = 0.806	l = −10→10
1877 measured reflections	1 standard reflections every 50 reflections
1349 independent reflections	intensity decay: none

Refinement

Refinement on F^2	Hydrogen site location: inferred from neighbouring sites
Least-squares matrix: full	All H-atom parameters refined
R[F^2 > 2σ(F^2)] = 0.031	Calculated w = 1/[σ^2(Fo^2) + (0.P)^2] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.047	(Δ/σ)max = −0.002
S = 1.96	Δρmax = 0.52 e Å^−3
1349 reflections	Δρmin = −0.50 e Å^−3
272 parameters	Extinction correction: SHELXL, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
2 restraints	Extinction coefficient: 0.0071 (6)
Primary atom site location: structure-invariant direct methods	Absolute structure: Flack H D (1983), Acta Cryst. A39, 876-881
Secondary atom site location: difference Fourier map

Special details

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

Refinement. Refinement on F² for ALL reflections except for 0 with very negative F² or flagged by the user for potential systematic errors. Weighted R-factors wR and all goodnesses of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The observed criterion of F² > σ(F²) is used only for calculating R factor obs 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
O1	1.1583 (4)	0.9665 (2)	0.6238 (3)	0.0110 (4)
O2	1.2740 (4)	0.8444 (2)	0.4654 (3)	0.0119 (4)
N1	0.3211 (2)	0.70490 (12)	−0.1104 (2)	0.0094 (3)
N2	1.1386 (2)	0.89530 (12)	0.4911 (2)	0.0088 (2)
C1	0.6025 (3)	0.9190 (2)	0.2429 (2)	0.0092 (4)
H1	0.4839 (10)	0.9739 (5)	0.2458 (7)	0.0252 (10)
C2	0.5666 (3)	0.8224 (2)	0.1178 (2)	0.0080 (4)
C3	0.7216 (3)	0.7515 (2)	0.1144 (2)	0.0086 (4)
H3	0.6917 (9)	0.6769 (4)	0.0175 (6)	0.0238 (10)
C4	0.9103 (3)	0.7756 (2)	0.2343 (2)	0.0098 (4)
H4	1.0315 (9)	0.7204 (5)	0.2348 (7)	0.0234 (10)
C5	0.9411 (3)	0.8711 (2)	0.3590 (2)	0.0080 (3)
C6	0.7914 (3)	0.9435 (2)	0.3662 (2)	0.0089 (4)
H6	0.8204 (10)	1.0171 (5)	0.4679 (7)	0.0245 (10)
C7	0.3647 (3)	0.7962 (2)	−0.0035 (2)	0.0095 (4)
H7	0.2563 (8)	0.8591 (5)	0.0066 (7)	0.0317 (11)
C8	0.1248 (3)	0.6796 (2)	−0.2231 (2)	0.0083 (4)
C9	−0.0368 (3)	0.7430 (2)	−0.2187 (2)	0.0089 (4)
H9	−0.0191 (10)	0.8193 (5)	−0.1247 (7)	0.0260 (10)
C10	−0.2240 (3)	0.7103 (2)	−0.3347 (2)	0.0089 (4)
H10	−0.3498 (9)	0.7602 (5)	−0.3301 (7)	0.0241 (10)
C11	−0.2561 (3)	0.6131 (2)	−0.4583 (2)	0.0082 (3)
C12	−0.0932 (3)	0.5502 (2)	−0.4630 (2)	0.0086 (4)
H12	−0.1130 (9)	0.4759 (5)	−0.5613 (7)	0.0243 (10)
C13	0.0939 (3)	0.5823 (2)	−0.3474 (2)	0.0092 (4)
H13	0.2202 (9)	0.5336 (5)	−0.3523 (7)	0.0256 (10)
C14	−0.4582 (4)	0.5789 (2)	−0.5840 (2)	0.0108 (4)
H14A	−0.4956 (11)	0.4918 (5)	−0.5537 (8)	0.0388 (14)
H14B	−0.4754 (12)	0.5801 (7)	−0.7399 (6)	0.041 (2)
H14C	−0.5674 (11)	0.6380 (7)	−0.5675 (9)	0.041 (2)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0123 (11)	0.0075 (10)	0.0127 (7)	−0.0009 (9)	0.0035 (7)	−0.0027 (6)
O2	0.0091 (12)	0.0123 (10)	0.0142 (7)	0.0002 (9)	0.0036 (7)	−0.0008 (6)
N1	0.0086 (8)	0.0075 (6)	0.0114 (5)	−0.0004 (6)	0.0027 (5)	−0.0016 (4)
N2	0.0098 (7)	0.0061 (6)	0.0113 (4)	−0.0009 (5)	0.0045 (4)	−0.0001 (4)
C1	0.0102 (11)	0.0046 (8)	0.0125 (6)	0.0009 (8)	0.0037 (7)	−0.0017 (5)
H1	0.019 (3)	0.022 (2)	0.033 (2)	0.008 (2)	0.007 (2)	−0.0071 (15)
C2	0.0088 (11)	0.0047 (7)	0.0103 (6)	−0.0005 (7)	0.0030 (7)	−0.0008 (5)
C3	0.0093 (11)	0.0049 (9)	0.0119 (6)	−0.0004 (8)	0.0039 (7)	−0.0015 (5)
H3	0.025 (3)	0.018 (2)	0.026 (2)	0.001 (2)	0.005 (2)	−0.0089 (14)
C4	0.0109 (11)	0.0081 (9)	0.0114 (6)	−0.0004 (8)	0.0051 (7)	−0.0011 (5)
H4	0.018 (3)	0.021 (2)	0.031 (2)	0.003 (2)	0.008 (2)	−0.0051 (14)
C5	0.0084 (10)	0.0053 (8)	0.0109 (6)	−0.0007 (7)	0.0040 (6)	0.0001 (5)
C6	0.0091 (11)	0.0058 (8)	0.0119 (6)	0.0010 (7)	0.0037 (7)	−0.0006 (5)
H6	0.025 (3)	0.016 (2)	0.032 (2)	−0.001 (2)	0.010 (2)	−0.0091 (14)
C7	0.0093 (11)	0.0053 (8)	0.0123 (6)	−0.0006 (8)	0.0016 (7)	−0.0022 (5)
H7	0.014 (3)	0.027 (3)	0.049 (2)	0.004 (2)	0.003 (2)	−0.015 (2)
C8	0.0088 (11)	0.0061 (8)	0.0102 (6)	0.0000 (8)	0.0032 (6)	−0.0003 (5)
C9	0.0081 (10)	0.0067 (9)	0.0119 (6)	0.0005 (7)	0.0035 (6)	−0.0014 (5)
H9	0.024 (3)	0.023 (2)	0.031 (2)	0.002 (2)	0.008 (2)	−0.010 (2)
C10	0.0089 (11)	0.0051 (8)	0.0124 (6)	−0.0003 (7)	0.0033 (6)	−0.0001 (5)
H10	0.022 (3)	0.017 (2)	0.034 (2)	0.004 (2)	0.010 (2)	−0.0054 (13)
C11	0.0083 (10)	0.0059 (7)	0.0103 (6)	−0.0001 (7)	0.0027 (6)	−0.0003 (5)
C12	0.0091 (11)	0.0055 (9)	0.0109 (6)	−0.0003 (8)	0.0028 (6)	−0.0018 (5)
H12	0.023 (3)	0.018 (2)	0.028 (2)	−0.002 (2)	0.005 (2)	−0.0118 (13)
C13	0.0095 (11)	0.0066 (8)	0.0114 (6)	0.0004 (7)	0.0032 (7)	−0.0012 (5)
H13	0.023 (3)	0.023 (2)	0.033 (2)	0.004 (2)	0.011 (2)	−0.0072 (15)
C14	0.0104 (11)	0.0082 (9)	0.0124 (6)	−0.0019 (8)	0.0019 (6)	0.0003 (5)
H14A	0.028 (4)	0.025 (3)	0.051 (2)	−0.013 (3)	−0.002 (2)	0.012 (2)
H14B	0.043 (4)	0.062 (4)	0.0186 (15)	−0.015 (3)	0.009 (2)	−0.001 (2)
H14C	0.015 (3)	0.039 (4)	0.059 (3)	0.009 (3)	0.001 (2)	−0.022 (2)

Geometric parameters (Å, º)

O1—N2	1.233 (2)	C7—H7	1.093 (6)
O2—N2	1.216 (3)	C8—C9	1.397 (3)
N1—C7	1.278 (2)	C8—C13	1.405 (3)
N1—C8	1.420 (3)	C9—C10	1.394 (3)
N2—C5	1.464 (3)	C9—H9	1.091 (5)
C1—C6	1.396 (3)	C10—C11	1.402 (3)
C1—C2	1.401 (3)	C10—H10	1.093 (6)
C1—H1	1.078 (6)	C11—C12	1.402 (3)
C2—C3	1.402 (3)	C11—C14	1.502 (4)
C2—C7	1.471 (3)	C12—C13	1.390 (3)
C3—C4	1.387 (4)	C12—H12	1.089 (5)
C3—H3	1.083 (4)	C13—H13	1.091 (6)
C4—C5	1.390 (3)	C14—H14A	1.081 (6)
C4—H4	1.088 (6)	C14—H14B	1.093 (4)
C5—C6	1.389 (3)	C14—H14C	1.084 (7)
C6—H6	1.095 (5)
C7—N1—C8	120.9 (1)	C9—C8—C13	118.4 (2)
O2—N2—O1	123.5 (2)	C9—C8—N1	125.3 (2)
O2—N2—C5	118.8 (2)	C13—C8—N1	116.4 (2)
O1—N2—C5	117.7 (2)	C10—C9—C8	120.7 (2)
C6—C1—C2	120.1 (2)	C10—C9—H9	118.6 (4)
C6—C1—H1	119.8 (3)	C8—C9—H9	120.7 (4)
C2—C1—H1	120.0 (4)	C9—C10—C11	121.2 (2)
C1—C2—C3	119.7 (2)	C9—C10—H10	120.3 (3)
C1—C2—C7	118.7 (2)	C11—C10—H10	118.4 (3)
C3—C2—C7	121.6 (2)	C10—C11—C12	117.8 (2)
C4—C3—C2	120.8 (2)	C10—C11—C14	120.9 (2)
C4—C3—H3	120.3 (4)	C12—C11—C14	121.3 (2)
C2—C3—H3	119.0 (4)	C13—C12—C11	121.2 (2)
C3—C4—C5	118.2 (2)	C13—C12—H12	119.2 (4)
C3—C4—H4	121.4 (3)	C11—C12—H12	119.5 (4)
C5—C4—H4	120.3 (4)	C12—C13—C8	120.7 (2)
C6—C5—C4	122.7 (2)	C12—C13—H13	121.0 (3)
C6—C5—N2	118.5 (2)	C8—C13—H13	118.3 (4)
C4—C5—N2	118.8 (2)	C11—C14—H14A	112.5 (4)
C5—C6—C1	118.4 (2)	C11—C14—H14B	111.7 (5)
C5—C6—H6	120.8 (4)	H14A—C14—H14B	105.8 (5)
C1—C6—H6	120.7 (4)	C11—C14—H14C	112.3 (4)
N1—C7—C2	121.6 (2)	H14A—C14—H14C	108.2 (6)
N1—C7—H7	123.0 (3)	H14B—C14—H14C	105.9 (6)
C2—C7—H7	115.3 (3)