N,N′-Dibenzyldithiooxamide

The title compound, alternatively known as N,N′-di­benzyl­ethane­di­thioamide, C₁₆H₁₆N₂S₂, lies about an inversion centre and contains a planar trans-di­thiooxamide fragment characterized by a strong intramolecular hydrogen bond between the S atom and the adjacent amide H atom in the solid state, with an S...N distance of 2.926 (1) Å. The aryl substituent is oriented orthogonal to the mean plane of the trans-di­thiooxamide fragment due to steric hindrance and this effect is discussed.

S1. Comment

We are interested in the building of polymetallic complexes through the combined use of both bi- and monofunctionalized metal complexes of the type (I) and (II). In both classes of compound, the ═N—H···N═moiety splits the [L'_nM'Cl]₂ Cl-bridged dimers and gives rise to the heterobimetallic fragment, (III). \sch

To date, we have prepared and fully characterized a number heterobimetallic complexes (Lanza et al., 1996, 2000; Bruno et al., 2002). The synthesis of trimetallic and tetrametallic species is at an advanced stage. In this context, we have found that steric hindrance on N and nitrogen basicity are important factors in determining the reactivity of secondary dithioxamides in the stepwise construction of our polymetallic systems (Lanza et al., 2002). For this reason, it is useful to collect structural information on the R substituents of secondary dithioxamides, both free and coordinated, with regard to both their steric congestion and their electronic influence over the N—C—S fragment. Hence, the title compound, (IV), has been crystallized and its structure is presented here.

Compound (IV) lies on a crystallographic centre and consists of a central N—CS—CS—N moiety and two benzyl substituents linked through the N atoms. A detailed analysis of the bond distances reveals a strong double-bond character for C1—S and C1—N [1.660 (1) and 1.316 (2) Å, respectively], confirming that the important electronic π-delocalization on the N—C—S system does not affect the central C—C single bond [1.533 (2) Å].

The central dithioxamide (DTO) fragment is perfectly planar, with a maximum deviation of -0.003 (1) Å for atom C1. The bond parameters for C1—N show the typical slightly distorted trigonal geometry, the sums of their valence bond angles being 360.0 (1) and 360 (1)°, respectively. The planarity of the trans-thioxamide, as required by the intermediate inversion centre, allows the formation of a significant intramolecular interaction between the H atom on N and the S(-x, -y, -z) atom. The intermolecular hydrogen bond detected in the solid state has also been observed in solution; the ¹H NMR spectrum of (IV) in CDCl₃ shows the N—H resonance at 10.55 p.p.m. Chemical shift (Emsley, 1980), line-broadening and dilution experiments also indicate that the N—H group is involved in a strong intramolecular –RN—H···S═interaction in solution.

The tetrahedral atom C2 of the benzyl N-substituent is almost in the same plane as the DTO fragment [deviation 0.020 (1) Å], with respect to which the phenyl ring forms a dihedral angle of 82.91 (6)°. This orthogonal arrangement, and the enlargement of the C1—N—C2 and N—C2—C3 endo angles with respect to the idealized values [126.1 (1) and 113.4 (1)°, respectively], might be related to steric hindrance between the H atoms linked to atoms N and C8. This is confirmed by the complete planarity observed for the molecule of N,N'-bis(2-pyridylmethyl)dithioxamide (Bermejo et al., 1998), where atom C8 is formally replaced by an N atom carrying no H atom. In such a case, the N H atom interacts either with the S atom or with the pyridine N atom on the same plane, like a three-atom/four-electron bond, which gives a further stabilization of the coplanar arrangement.

The same situation is observed in the analogous N,N'-bis(pyridylmethyl)dioxamides reported in the literature. The two 4-pyridyl structures reported by Nguyen et al. (1998) have the ortho position occupied by the hindering CH group, which causes the same orthogonal disposition; their OC—NH—CH₂—C_py torsion angles are 97.4 (2) and 100.9 (2)°, comparable with the corresponding value of 99.6 (1)° in (IV). On the other hand, the 4-pyridyl isomer reported by Liu et al. (1999) shows the planar conformation, with the N H atom interacting with both the adjacent O and pyridine N atoms.

Table 2 Intramolecular contact geometry

S2. Experimental

Dibenzyldithioxamide was synthesized by a slight modification of the method of Hurd et al. (1961). Benzylamine (two equivalents, 2.14 g) was mixed with dithioxamide (0.002 mol). The mixture was homogenized in a mortar and after a few minutes the crude dibenzyldithioxamidate solidified. The pure compound was crystallized from ethanol. For the diffraction study, suitable crystals of (IV) were grown by slow evaporation of an ethanol solution at room temperature. The compound was initially identified from the NMR spectra. Spectroscopic analysis: ¹H NMR (300.13 MHz, CDCl₃, δ, p.p.m): 10.55 (bs, 1H, NH), 7.2–7.4 (mm, 5H, phenyl H), 4.93 (d, ³J_HH = 6.10 Hz, 2H, N—CH₂); ¹³C{¹H}NMR (75.47 MHz, CDCl₃, δ, p.p.m.): C_S 184.5, C₁ 131.01, C₂—C₆ 129.00, C₃—C₅ 128.09, C₄ 128.20 (aromatic C), 51.5 (N—CH₂).

S3. Refinement

All H atoms were located in the difference Fourier syntheses and included in the refinement as free isotropic atoms.

Computing details

Data collection: P3/V (Siemens, 1989); cell refinement: P3/V; data reduction: SHELXTL-Plus (Siemens, 1990); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: XPW (Siemens, 1996); software used to prepare material for publication: PARST97 (Nardelli, 1995) and SHELXL97.

Figures

Fig. 1. A perspective molecular view of (I), showing the atomic numbering scheme for the asymmetric unit. Open atoms and bonds represent the equivalent part of the molecule obtained by the symmetry operation (-x, -y, -z). Dotted lines represent intramolecular hydrogen-bond interactions. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii.

N,N'-dibenzyldithioxamide

Crystal data

C16H16N2S2	F(000) = 316
Mr = 300.43	Dx = 1.349 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 34 reflections
a = 7.665 (2) Å	θ = 6.8–12.9°
b = 10.533 (2) Å	µ = 0.35 mm^−1
c = 9.263 (2) Å	T = 293 K
β = 98.57 (2)°	Irregular, orange
V = 739.5 (3) Å^3	0.68 × 0.40 × 0.12 mm
Z = 2

Data collection

Siemens P4 diffractometer	Rint = 0.014
Radiation source: fine-focus sealed tube	θmax = 29.1°, θmin = 2.7°
Graphite monochromator	h = 0→10
ω/2θ scans	k = 0→14
2167 measured reflections	l = −12→12
1986 independent reflections	3 standard reflections every 197 reflections
1568 reflections with I > 2σ(I)	intensity decay: 2%

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)] = 0.034	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.096	All H-atom parameters refined
S = 1.03	w = 1/[σ^2(Fo^2) + (0.0642P)^2] where P = (Fo^2 + 2Fc^2)/3
1986 reflections	(Δ/σ)max < 0.001
124 parameters	Δρmax = 0.29 e Å^−3
0 restraints	Δρmin = −0.27 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.

Reflection intensities were evaluated by profile fitting of a 96-steps peak scan among 2θ shells procedure [Diamond, R. (1969). Acta Cryst. A25, 43–55.] and then corrected for Lorentz polarization effects. Standard deviations σ(I) were estimated from counting statistics. No absorption and extinction corrections were applied. Structure was solved by direct methods and completed by a combination of full-matrix least-squares technique and Fourier map.

All Non hydrogen atoms were refined anisotropically.

In the last Fourier maps the electron density residuals were not significant.

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

	x	y	z	Uiso*/Ueq
S	0.25312 (5)	0.09398 (4)	0.02265 (4)	0.04614 (14)
N	0.00951 (16)	0.03685 (12)	0.18706 (11)	0.0378 (3)
H	−0.085 (3)	0.0055 (18)	0.1892 (18)	0.053 (5)*
C1	0.06465 (15)	0.03320 (11)	0.05916 (12)	0.0307 (3)
C2	0.1038 (2)	0.09188 (13)	0.32036 (13)	0.0389 (3)
H2A	0.014 (2)	0.1365 (16)	0.3634 (17)	0.044 (4)*
H2B	0.182 (2)	0.1543 (14)	0.2915 (14)	0.037 (4)*
C3	0.19910 (16)	−0.00557 (13)	0.42332 (12)	0.0326 (3)
C4	0.28234 (17)	0.03670 (14)	0.55965 (13)	0.0382 (3)
H4	0.273 (2)	0.1240 (17)	0.5888 (18)	0.048 (4)*
C5	0.37622 (19)	−0.04744 (16)	0.65656 (14)	0.0446 (3)
H5	0.439 (2)	−0.0149 (17)	0.749 (2)	0.057 (5)*
C6	0.3868 (2)	−0.17383 (16)	0.62054 (16)	0.0480 (4)
H6	0.449 (3)	−0.2273 (18)	0.6830 (19)	0.061 (5)*
C7	0.3032 (2)	−0.21653 (16)	0.48677 (18)	0.0493 (3)
H7	0.303 (3)	−0.2974 (19)	0.461 (2)	0.068 (6)*
C8	0.2100 (2)	−0.13223 (14)	0.38819 (15)	0.0422 (3)
H8	0.154 (2)	−0.1626 (16)	0.2951 (17)	0.052 (5)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
S	0.0397 (2)	0.0605 (3)	0.0379 (2)	−0.01512 (16)	0.00460 (13)	−0.00389 (15)
N	0.0354 (6)	0.0521 (7)	0.0246 (5)	−0.0046 (5)	−0.0002 (4)	−0.0005 (4)
C1	0.0316 (6)	0.0331 (6)	0.0255 (5)	0.0025 (5)	−0.0019 (4)	0.0051 (4)
C2	0.0458 (7)	0.0440 (7)	0.0251 (5)	−0.0014 (6)	−0.0002 (5)	−0.0023 (5)
C3	0.0298 (6)	0.0436 (7)	0.0244 (5)	−0.0038 (5)	0.0037 (4)	−0.0021 (5)
C4	0.0374 (7)	0.0492 (8)	0.0274 (6)	−0.0029 (6)	0.0026 (5)	−0.0054 (5)
C5	0.0357 (7)	0.0693 (9)	0.0272 (6)	−0.0001 (7)	−0.0002 (5)	0.0014 (6)
C6	0.0384 (7)	0.0626 (10)	0.0427 (7)	0.0056 (7)	0.0050 (6)	0.0162 (7)
C7	0.0520 (8)	0.0413 (8)	0.0543 (8)	0.0010 (6)	0.0069 (7)	0.0015 (6)
C8	0.0456 (8)	0.0449 (7)	0.0348 (6)	−0.0040 (6)	0.0017 (5)	−0.0053 (5)

Geometric parameters (Å, º)

S—C1	1.660 (1)	C4—C5	1.384 (2)
N—C1	1.316 (2)	C4—H4	0.964 (18)
N—C2	1.455 (2)	C5—C6	1.378 (2)
N—H	0.802 (19)	C5—H5	0.979 (19)
C1—C1^i	1.533 (2)	C6—C7	1.382 (2)
C2—C3	1.513 (2)	C6—H6	0.892 (19)
C2—H2A	0.967 (16)	C7—C8	1.392 (2)
C2—H2B	0.954 (15)	C7—H7	0.88 (2)
C3—C8	1.379 (2)	C8—H8	0.960 (17)
C3—C4	1.3999 (17)
C1—N—C2	126.1 (1)	C5—C4—C3	120.28 (14)
C1—N—H	115.1 (12)	C5—C4—H4	118.8 (10)
C2—N—H	118.8 (12)	C3—C4—H4	120.9 (10)
N—C1—C1^i	113.4 (1)	C6—C5—C4	120.34 (13)
N—C1—S	125.3 (1)	C6—C5—H5	120.8 (11)
C1^i—C1—S	121.3 (1)	C4—C5—H5	118.8 (11)
N—C2—C3	113.4 (1)	C5—C6—C7	119.69 (14)
N—C2—H2A	104.5 (10)	C5—C6—H6	119.8 (12)
C3—C2—H2A	112.1 (9)	C7—C6—H6	120.5 (12)
N—C2—H2B	106.9 (8)	C6—C7—C8	120.28 (15)
C3—C2—H2B	112.3 (9)	C6—C7—H7	122.4 (13)
H2A—C2—H2B	107.2 (13)	C8—C7—H7	117.3 (13)
C8—C3—C4	119.02 (12)	C3—C8—C7	120.37 (13)
C8—C3—C2	123.25 (11)	C3—C8—H8	120.0 (10)
C4—C3—C2	117.72 (12)	C7—C8—H8	119.6 (10)
C2—N—C1—C1^i	179.2 (1)	C4—C5—C6—C7	0.1 (2)
C2—N—C1—S	−1.4 (2)	C5—C6—C7—C8	0.5 (2)
C1—N—C2—C3	−99.6 (1)	C4—C3—C8—C7	−0.3 (2)
N—C2—C3—C8	6.05 (18)	C2—C3—C8—C7	178.52 (13)
N—C2—C3—C4	−175.11 (11)	C6—C7—C8—C3	−0.4 (2)
C8—C3—C4—C5	0.92 (19)	N—C1—C1^i—N^i	180.0
C2—C3—C4—C5	−177.97 (12)	S—C1—C1^i—S^i	180.0
C3—C4—C5—C6	−0.8 (2)	N—C1—C1^i—S^i	−0.5 (2)

Symmetry code: (i) −x, −y, −z.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N—H···S^i	0.80 (2)	2.42 (2)	2.926 (1)	122 (1)
C8—H8···N	0.96 (2)	2.51 (2)	2.855 (2)	101 (1)

Symmetry code: (i) −x, −y, −z.