Crystal structure of N,N′-bis(4-methylphenyl)dithiooxamide

Two half molecules of the title compound, C16H16N2S2, are present in the asymmetric unit and both molecules are completed by crystallographic inversion centers at the mid-points of the central C—C bonds: the lengths of these bonds [1.538 (5) and 1.533 (5) Å] indicate negligible electronic delocalization. The trans-dithiooxamide fragment in each molecule is characterized by a pair of intramolecular N—H⋯S hydrogen bonds. In the crystal, molecules are linked by weak C—H..π interactions, generating a three-dimensional network.

Supporting information for this paper is available from the IUCr electronic archives (Reference: HB7339).
The title compound has been synthesized for a better understanding of the reactivity of the said mesogenic complexes, in the aim to avoid contingent steric hindrance of long chain substituents and the influence on the acid base equilibria of ether moieties. In fact, both the oxygen lone pairs in ether moieties and the exceedingly long alkyl chains of X substituents prevents the formation of ion pairs in the first step of the reaction of secondary dithioxamides with cis-Pt(Me 2 SO) 2 Cl 2 . A detailed analysis of the bond distances reveals a strong double-bond character for both C-S and C-N [1.662 (3) Å and 1.318 (4) Å, respectively], confirming that the important electronic πdelocalization of the N-C-S system does not affect the central C-C bond. In the title compound the central C-C bond distances are 1.538 (5) Å and 1.533 (5) Å respectively for C1-C1′ and C9-C9′. Going from a secondary dithiooxamide to a tertiary one we observe a large changing in structural parameters:essentially in the planarity loss of the central fragment and to the significant shortening of central C-C bond. The p-tolyl groups are rotated by -36.4° (5) and -35.4° (5) with respect to the central DTO fragments.

S2. Experimental
The title compound was obtained from para-toluidine according to a described two-step strategy based on primary amine reaction with oxalyl chloride followed by P 2 S 5 treatment.  Perspective view of the title molecule with displacement ellipsoids plotted at the 50% probability level, while H atoms are shown as small spheres of arbitrary radius.

Figure 2
Packing diagram of the title compound viewed along the c axis.  Packing diagram of the title compound viewed normal the b axis and showing molecular arrangement on the (402) plane.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ. (