N¹-(2,6-Di­methyl­phenyl)-N²-hydroxy-α-oxo-α-phenyl­acet­amidine

The structure of the title compound, C₁₆H₁₆N₂O₂, consists of a dimeric arrangement around an inversion centre of acet­amidine mol­ecules linked via O—H...N hydrogen bonds. There are also H...π-ring interactions. All these interactions result in the formation of infinite chains parallel to the (101) axis. The oxime group has an E conformation.

S1. Comment

Intermolecular hydrogen bonding has received considerable attention, as one of the available directional noncovalent intermolecular interactions (Etter et al., 1990) which combine moderate strength and directionality (Karle et al., 1996) in linking molecules to form supramolecular structures. With the aim of investigating the versatility of oximes in coordination chemistry and further researching their involvement in supramolecular polymer chemistry, succesful syntheses with oximate groups have been carried out (Liu et al., 2002). The oxime (C═N—OH) group possesses stronger hydrogen-bonding capabilities than alcohols, phenols and carboxylic acids (Marsman et al., 1999). Hydrogen bonding plays a key role in molecular recognition in chemical engineering (Bertolasi et al., 1982; Gilli et al., 1983; Hökelek et al., 2001).

The crystal structure determination of the title compound, (I), was carried out not only to determine the strength of the hydrogen-bonding capabilities of the oxime groups, as well as π-ring interaction between the molecules, but also to compare the geometry of the oxime moiety with that found in N-(3-chloro-4-methoxyphenyl)-N'-hydroxy-2-oxo-2-phenylaceatmidine, (II) (Soylu et al., 2003), N-hydroxy-2-oxo-2-diphenylacetamidine, (III) (Büyükgüngör et al., 2003) and N-(3,4-dichlorophenyl)-N'-hydroxy-2-oxo-2-phenylacetamidine, (IV) (Hökelek et al., 2003). \sch

Compound (I) consists of two aromatic rings linked through a monoxime group (Fig. 1). The dihedral angles between the oxime plane A (O2/N2/C7) and the benzene rings B (C1—C6) and C (C9—C14) are A/B 73.37 (11), A/C 50.10 (14) and B/C 89.19 (6)°. Rings B and C are nearly perpendicular to each other. Ring C is linked to the oxime group by atom C8(O1), whereas ring B is linked to the same functional group by atom N1. The steric effects of the bulky phenyl substituent bonded to the oxime group may influence the bond lengths and angles of the oxime moiety, as indicated in Table 1. A comparison of bond lengths and angles for (I) and the related compounds (II), (III) and (IV) is shown in Table 3. One can note significant changes in the geometry of the oxime moiety, which are certainly due to the steric effect of the 2,6-dimethylphenyl group.

The oxime moiety has an E conformation, with C8—C7—N2—O2 − 174.6 (2)°, which deviates slightly from the values reported in other studies (Soylu et al., 2003; Hökelek et al., 2001). In this conformation, atom O2 of the oxime group behaves as a donor, resulting in the formation of O—H···N hydrogen bonds which link two molecules related by an inversion centre (Fig. 2). There is also an intramolecular N1—H···O2 hydrogen bond.

Of greater interest are the intermolecular π-ring interactions with the NH group, which contribute to the crystal packing by forming an infinite chain of dimers (Fig. 2). These π-ring interactions with the NH group are characterized by four parameters, as follows. The distance between atom H1 and the centre of the aromatic ring B (C1—C6) is 2.98 Å. The distance between atom H1 and the plane of ring B is 2.643 (3) Å. The angle between the line connecting atom H1 and the centre of ring B, M, and the normal to the B plane is 27.55°. Finally, the angle N1–H1···M is 145.4°.

The results obtained in this study indicate that there are significant differences when comparing the geometry of (I) with that of other oxime groups such as (II), (III) and (IV). In these previously reported studies, the crystal packing is mainly stabilized by intermolecular hydrogen bonds, which are highly effective in forming polymeric chains. From the results presented in this paper, it can be said that O—H···N hydrogen bonds link two molecules through an inversion centre to form a dimers. Besides these hydrogen bonds, there is an interesting π-ring interaction which stabilizes the crystal. Dipole-dipole and van der Waals interactions are also effective in the molecular packing in the crystal structure.

S2. Experimental

The title compound was prepared from a mixture of ω-chloroisonitrosoacetophenone (2.75 g, 0.015 mol) and 2,6-dimethylaniline (1.82 g, 0,015 mol) in ethyl alcohol (20 ml). The precipitate was stirred for 1 h and filtered. The crystallized product was filtered off, washed with ethanol and dried.

S3. Refinement

All non-H atoms were refined with anisotropic atomic displacement parameters. All H atoms were then fixed at localized positions, with C—H distances in the range 0.93–0.96, an N—H distance of 0.86 and an O—H distance of 0.82 Å. A riding isotropic displacement parameter was used for all H atoms, with U_iso(H) = 1.5U_eq(parent atom). Please check added text.

Computing details

Data collection: X-AREA (Stoe & Cie, 2002); cell refinement: X-AREA; data reduction: X-RED32 (Stoe & Cie, 2002); program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEPIII (Burnett & Johnson, 1996; Farrugia, 1997); software used to prepare material for publication: WinGX (Farrugia, 1999).

Figures

	Fig. 1. A view of the molecule of (I), with the atom-numbering scheme. Displacement ellipsoids are drawn at the 30% probability level and H atoms are shown as small spheres of arbitrary radii.
	Fig. 2. Diagram showing the hydrogen-bonding and π-ring interactions in (I). Displacement ellipsoids are drawn at the 20% probability level. [Symmetry codes: (i) −x, 1 − y, 1 − z; (ii) 1 − x, −y, 1 − z.]

N¹-(2,6-Dimethylphenyl)-N²-hydroxy-α-oxo-α-phenylacetamidine

Crystal data

C16H16N2O2	F(000) = 568
Mr = 268.31	Dx = 1.208 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2yn	Cell parameters from 8969 reflections
a = 8.1002 (10) Å	θ = 1.8–23.7°
b = 7.8837 (10) Å	µ = 0.08 mm^−1
c = 23.108 (3) Å	T = 293 K
β = 90.828 (10)°	Prism, colourless
V = 1475.5 (3) Å^3	0.36 × 0.33 × 0.29 mm
Z = 4

Data collection

Stoe IPDS 2 diffractometer	1316 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.060
Graphite monochromator	θmax = 25.0°, θmin = 1.8°
Detector resolution: 6.67 pixels mm^-1	h = −9→9
ϕ scans	k = −9→9
10735 measured reflections	l = −27→27
2566 independent reflections

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)] = 0.042	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.116	H-atom parameters constrained
S = 0.87	w = 1/[σ^2(Fo^2) + (0.0593P)^2] where P = (Fo^2 + 2Fc^2)/3
2566 reflections	(Δ/σ)max < 0.001
184 parameters	Δρmax = 0.14 e Å^−3
0 restraints	Δρmin = −0.11 e Å^−3

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 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 > σ(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
C11	−0.2014 (3)	0.4467 (3)	0.31533 (12)	0.0913 (7)
H11	−0.3086	0.4148	0.3242	0.110*
C16	0.2019 (4)	−0.0671 (4)	0.37992 (16)	0.1328 (11)
H16A	0.1397	−0.0411	0.4138	0.199*
H16B	0.1851	−0.1839	0.3696	0.199*
H16C	0.1659	0.0042	0.3485	0.199*
C12	−0.1729 (4)	0.5500 (4)	0.26919 (12)	0.1054 (9)
H12	−0.2612	0.5893	0.2468	0.126*
C10	−0.0703 (3)	0.3900 (3)	0.34865 (10)	0.0791 (6)
H10	−0.0903	0.3199	0.3801	0.095*
O2	0.1117 (2)	0.34282 (19)	0.51940 (6)	0.0839 (5)
H2	0.0446	0.3965	0.5383	0.126*
C6	0.3817 (3)	−0.0369 (3)	0.39211 (11)	0.0897 (7)
N2	0.1069 (2)	0.3994 (2)	0.46136 (7)	0.0718 (5)
C13	−0.0158 (4)	0.5961 (4)	0.25567 (12)	0.1062 (9)
H13	0.0021	0.6669	0.2242	0.127*
C5	0.5015 (5)	−0.1436 (3)	0.36988 (12)	0.1077 (9)
H5	0.4697	−0.2333	0.3461	0.129*
C9	0.0907 (3)	0.4351 (2)	0.33628 (9)	0.0679 (6)
C7	0.2158 (3)	0.3189 (2)	0.43162 (9)	0.0657 (6)
N1	0.3167 (2)	0.2002 (2)	0.45496 (8)	0.0794 (5)
H1	0.3085	0.1851	0.4917	0.095*
C1	0.4345 (3)	0.0970 (3)	0.42672 (9)	0.0717 (6)
C14	0.1165 (3)	0.5384 (3)	0.28824 (10)	0.0858 (7)
H14	0.2233	0.5685	0.2782	0.103*
C8	0.2352 (3)	0.3777 (2)	0.37040 (9)	0.0689 (6)
C4	0.6643 (5)	−0.1196 (4)	0.38224 (13)	0.1096 (10)
H4	0.7422	−0.1937	0.3673	0.132*
C2	0.6001 (3)	0.1248 (3)	0.43946 (10)	0.0769 (6)
O1	0.3731 (2)	0.3817 (2)	0.35085 (7)	0.0971 (5)
C3	0.7146 (3)	0.0128 (4)	0.41663 (12)	0.0983 (8)
H3	0.8264	0.0280	0.4248	0.118*
C15	0.6534 (3)	0.2719 (3)	0.47589 (12)	0.1080 (9)
H15A	0.6311	0.3756	0.4555	0.162*
H15B	0.7697	0.2636	0.4841	0.162*
H15C	0.5939	0.2711	0.5115	0.162*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C11	0.0826 (18)	0.1030 (18)	0.0882 (18)	−0.0015 (14)	−0.0007 (15)	−0.0067 (15)
C16	0.122 (3)	0.107 (2)	0.169 (3)	−0.0062 (19)	−0.010 (2)	−0.031 (2)
C12	0.115 (3)	0.113 (2)	0.0877 (19)	0.0151 (18)	−0.0084 (18)	0.0009 (16)
C10	0.0930 (19)	0.0736 (14)	0.0708 (13)	−0.0041 (13)	0.0078 (14)	−0.0019 (11)
O2	0.0995 (13)	0.0878 (11)	0.0647 (9)	0.0306 (8)	0.0157 (8)	0.0014 (8)
C6	0.098 (2)	0.0726 (15)	0.0984 (18)	0.0117 (14)	0.0148 (15)	−0.0080 (13)
N2	0.0824 (13)	0.0691 (10)	0.0642 (11)	0.0194 (9)	0.0139 (9)	−0.0004 (8)
C13	0.132 (3)	0.107 (2)	0.0798 (17)	0.0040 (19)	0.0044 (19)	0.0223 (14)
C5	0.137 (3)	0.0759 (17)	0.111 (2)	0.0290 (18)	0.023 (2)	−0.0152 (14)
C9	0.0827 (17)	0.0561 (12)	0.0652 (13)	0.0047 (11)	0.0134 (12)	−0.0064 (10)
C7	0.0686 (15)	0.0576 (11)	0.0712 (13)	0.0078 (10)	0.0130 (11)	−0.0052 (10)
N1	0.0870 (14)	0.0767 (11)	0.0752 (11)	0.0289 (10)	0.0218 (10)	0.0043 (9)
C1	0.0793 (17)	0.0606 (12)	0.0760 (14)	0.0196 (11)	0.0235 (12)	0.0049 (11)
C14	0.0993 (19)	0.0826 (15)	0.0760 (16)	−0.0026 (13)	0.0145 (15)	0.0064 (13)
C8	0.0761 (17)	0.0585 (12)	0.0726 (14)	0.0069 (11)	0.0209 (13)	−0.0037 (10)
C4	0.133 (3)	0.092 (2)	0.105 (2)	0.054 (2)	0.044 (2)	0.0117 (17)
C2	0.0761 (18)	0.0705 (14)	0.0846 (15)	0.0126 (12)	0.0221 (14)	0.0147 (12)
O1	0.0859 (13)	0.1038 (12)	0.1026 (12)	0.0139 (9)	0.0336 (10)	0.0168 (9)
C3	0.0855 (19)	0.1014 (19)	0.109 (2)	0.0289 (15)	0.0326 (16)	0.0299 (17)
C15	0.103 (2)	0.107 (2)	0.114 (2)	−0.0091 (16)	0.0039 (17)	−0.0013 (17)

Geometric parameters (Å, º)

C11—C12	1.364 (4)	C5—H5	0.9300
C11—C10	1.377 (3)	C9—C14	1.395 (3)
C11—H11	0.9300	C9—C8	1.473 (3)
C16—C6	1.498 (3)	C7—N1	1.349 (2)
C16—H16A	0.9600	C7—C8	1.499 (3)
C16—H16B	0.9600	N1—C1	1.420 (2)
C16—H16C	0.9600	N1—H1	0.8600
C12—C13	1.364 (4)	C1—C2	1.386 (3)
C12—H12	0.9300	C14—H14	0.9300
C10—C9	1.386 (3)	C8—O1	1.212 (2)
C10—H10	0.9300	C4—C3	1.371 (4)
O2—N2	1.413 (2)	C4—H4	0.9300
O2—H2	0.8200	C2—C3	1.390 (3)
C6—C1	1.388 (3)	C2—C15	1.494 (3)
C6—C5	1.389 (4)	C3—H3	0.9300
N2—C7	1.292 (2)	C15—H15A	0.9600
C13—C14	1.378 (3)	C15—H15B	0.9600
C13—H13	0.9300	C15—H15C	0.9600
C5—C4	1.358 (4)
C12—C11—C10	119.5 (3)	N2—C7—C8	115.55 (18)
C12—C11—H11	120.2	N1—C7—C8	121.37 (19)
C10—C11—H11	120.2	C7—N1—C1	128.37 (18)
C6—C16—H16A	109.5	C7—N1—H1	115.8
C6—C16—H16B	109.5	C1—N1—H1	115.8
H16A—C16—H16B	109.5	C2—C1—C6	122.1 (2)
C6—C16—H16C	109.5	C2—C1—N1	117.8 (2)
H16A—C16—H16C	109.5	C6—C1—N1	119.8 (2)
H16B—C16—H16C	109.5	C13—C14—C9	120.2 (3)
C13—C12—C11	120.5 (3)	C13—C14—H14	119.9
C13—C12—H12	119.8	C9—C14—H14	119.9
C11—C12—H12	119.8	O1—C8—C9	121.5 (2)
C11—C10—C9	121.5 (2)	O1—C8—C7	118.0 (2)
C11—C10—H10	119.3	C9—C8—C7	120.5 (2)
C9—C10—H10	119.3	C5—C4—C3	120.5 (2)
N2—O2—H2	109.5	C5—C4—H4	119.7
C1—C6—C5	117.5 (3)	C3—C4—H4	119.7
C1—C6—C16	121.3 (2)	C1—C2—C3	117.9 (2)
C5—C6—C16	121.1 (3)	C1—C2—C15	120.9 (2)
C7—N2—O2	109.89 (15)	C3—C2—C15	121.2 (2)
C12—C13—C14	120.5 (3)	C4—C3—C2	120.6 (3)
C12—C13—H13	119.7	C4—C3—H3	119.7
C14—C13—H13	119.7	C2—C3—H3	119.7
C4—C5—C6	121.3 (3)	C2—C15—H15A	109.5
C4—C5—H5	119.3	C2—C15—H15B	109.5
C6—C5—H5	119.3	H15A—C15—H15B	109.5
C10—C9—C14	117.8 (2)	C2—C15—H15C	109.5
C10—C9—C8	123.6 (2)	H15A—C15—H15C	109.5
C14—C9—C8	118.6 (2)	H15B—C15—H15C	109.5
N2—C7—N1	122.81 (19)
O2—N2—C7—C8	−174.53 (17)	C9—C14—C8—O1	164.5 (2)
N2—C7—N1—C1	176.4 (2)	N2—C7—C8—O1	141.4 (2)
C7—N1—C1—C8	5.08 (18)	C7—N1—C8—O1	151.4 (3)
C7—N1—C1—C2	112.4 (2)	N2—C9—C7—C8	−147.8 (2)
C10—C9—C8—O1	160.7 (2)	C9—C7—N1—C8	25.47 (18)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O2—H2···N2^i	0.82	2.02	2.737 (2)	145
N1—H1···O2	0.86	2.13	2.512 (2)	107

Symmetry code: (i) −x, −y+1, −z+1.