( 1 Z , 2 Z )-1 , 2-Bis ( 3-methyl-2 , 3-dihydro-1 , 3-benzothiazol-2-ylidene ) hydrazine

The molecular structure of the title compound, (I), examined at 93 K is shown in Fig. 1. Selected bond distances and angles and the torsion angles relating to the >C NÐN C< chain are listed in Table 1. The packing of the molecules is indicated in Fig. 2. The particular crystal studied here proved to be a racemic twin, as suggested by the Flack parameter (Flack, 1983) of 0.41 (2). During the re®nement, the structure was treated as a racemic twin.

Compound (I) was oxidized by air to a cation radical in acetonitrile or on silica gel. The cation radical is blue and stable for weeks. Its visible spectrum shows a broad band with three peaks at 659, 733 and 818 nm (Nakano & Mori, 2005;Sawicki et al., 1963). The spectrum is very similar to that of the cation radical of 2,2 H -azinobis(3-ethylbenzothiazoline-6sulfonic acid) [ABTS; systematic name: 2,2 H -(hydrazine-1,2diylidene)bis(3-ethyl-2,3-dihydrobenzo[d]thiazole-6-sulfonate)] which is a water-soluble analogue of the present compound (Henriquez & Lissi, 2002). Compound (I) was previously described in reaction with oxidants such as nitrite (Sawicki et al., 1963) and potassium ferricyanide (Bartsch et al., 1970). This electron-donating character to form the stable cation radical suggests that compound (I) would be useful for forming charge-transfer complexes with electron acceptors such as TCNQ (Guerin et al., 2002).
A recent point of concern regarding compounds with azine groups has appeared in the term`conjugate stopper' for heteroatoms in 1,3-diene systems including N atoms (Glaser et al., 1993;Zuman & Ludvik, 2000;Choytun et al., 2004). It was thought that the conjugation effect through the azine group was determined by the bond distances of N1ÐN2 and ÐC1 N1Ð (ÐC9 N2Ð) and the torsion angle about the NÐN bond of the >C NÐN C< chain; the single-bond character of NÐN and the double-bond character of C N indicate a lack of delocalization of % electrons, while the planar structure of C NÐN C indicates % conjugation.
The molecular geometry of compound (I) including >C NÐN C< is completely planar (torsion angle of less than 1 ; Table 1). It has a Z,Z con®guration, with angles of 111.0 and 110.2 for C1ÐN1ÐN2 and N1ÐN2ÐC9, respectively ( Fig. 1). On the other hand, the bond distances of N1Ð N2 and C1 N1 (C9 N2) are 1.409 and 1.287 A Ê (1.294 A Ê ), respectively ( Table 1). The former indicates almost a single bond if compared with the value of 1.45 A Ê in NH 2 NH 2 (Liminga & Olovsson, 1964), and the latter almost a double bond if compared with the value of 1.28 A Ê in imines (Allen et al., 1987). Additionally, these data are very similar to those of formaldehyde azine, where the distances for NÐN and C N are 1.418 and 1.277 A Ê , respectively, and the angles for CÐNÐ N and HÐCÐN are 111.4 and 120.7 , respectively (Lide, 1993). These bond distances suggests less delocalization of % electrons, while the molecule is completely¯at, permitting interaction between % bonds of the C N groups.
The packing of the molecules of (I) in the solid state indicates the lack of intra-and intermolecular hydrogen bonds, suggesting no hydrogen-bonding effect on the lone-pair electrons of the azine group.
The concept of the`conjugation stopper' of the azine group relating to distances and geometry has not been convincing to date and the present structural results add to the knowledge in the ®eld. The fact that the cation radical of compound (I) is stable gives additional information about the electronic structure of azine groups.

Experimental
Compound (I) was prepared by the oxidation of 3-methyl-2-benzothiazolinone hydrazone (MBTH; alternative name: 2-hydrazino-3methyl-2,3-dihydrobenzo[d]thiazole), (II), in air, catalyzed by a water-soluble iron porphyrin, FeTMPyPCl 5 {[5,10,15,20-tetrakis(1methyl-4-pyridyl)-21H,23H-porphine]iron(III) pentachloride}, in a phosphate buffer solution (0.1 M; pH 7.0) (Nakano et al., 2005). Through the redox reaction of the iron porphyrin, the superoxide anion radical is released and the porphyrin peripheral eventually decomposes after 30 min. Reagent (II) acts not only as a reducing one-electron donor, but is also oxidized to form compound (I), and dinitrogen is released from the system. In the present study, the reaction was performed under conditions of 7.0 Â 10 À4 M MBTH hydrochloride and a catalytic concentration of hemin (1 Â 10 À5 M). The product, (I), was extracted from the reaction mixture into dichloromethane, puri®ed by column chromatography (silica gel, dichloromethane) and then crystallized from a solution in dichloro-methane±petroleum ether (1:1) by free evaporation of the solvents overnight. Crystals were collected on ®lter paper, washed with petroleum ether and dried. A single crystal was selected and used for the data collection. H atoms were re®ned using a riding model, with CÐH distances in the range 0.95±0.98 A Ê and with U iso (H) = 1.2U eq (C).
Supplementary data for this paper are available from the IUCr electronic archives (Reference: AV3007). Services for accessing these data are described at the back of the journal.