(1E,2E)-1,2-Bis(2,3-dihydro-1H-inden-1-ylidene)hydrazine

In the title compound, C18H16N2, there are two independent half-molecules (A and B) in the asymmetric unit, each molecule being completed by an inversion center situated in the mid-point of the central N—N bond. The molecules themselves therefore are essentially planar with r.m.s. deviations of 0.015 (1) and 0.020 (1) Å, respectively. In the crystal, molecules are connected via C—H⋯π interactions in which only type B molecules are donors, while both A and B molecules act as acceptors. As a result, type B molecules are linked into infinite chains along b, which are interconnected by molecules of type A.

In the title compound, C 18 H 16 N 2 , there are two independent half-molecules (A and B) in the asymmetric unit, each molecule being completed by an inversion center situated in the mid-point of the central N-N bond. The molecules themselves therefore are essentially planar with r.m.s. deviations of 0.015 (1) and 0.020 (1) Å , respectively. In the crystal, molecules are connected via C-HÁ Á Á interactions in which only type B molecules are donors, while both A and B molecules act as acceptors. As a result, type B molecules are linked into infinite chains along b, which are interconnected by molecules of type A.
Cg1 and Cg2 are the centroids of the C1-C6 and C10-C15 rings, respectively.  In the course of a study concerning the reactivity of azines towards Fe 2 (CO) 9 we became interested in the structual properties of several substituted aromatic azine derivatives (Dönnecke et al., 2004a(Dönnecke et al., , 2004b. Azines derived from indanone derivatives have been investigated concerning their structural and physical properties due to the fact that some of them exhibit NLO properties (Choytun et al., 2004).

D-HÁ
In the asymmetric unit of the crystal structure two independent halves of the molecules of the title compound, C 18 H 16 N 2 , are observed (fIG. 1). Each fragment is expanded to a complete molecule by crystallographic inversion centers that are situated in the middle of the central N-N bonds of both molecules. The molecules themselves therefore are essentially planar with Rms deviations of 0.015 (1) (molecule A: N1, C1 to C9) and 0.020 (1) (molecule B: N2, C10 to C18) Å, respectively. The central N-N bonds are 1.412 (2) (N1-N1 i ) and 1.415 (3) The planes of the two molecules form an angle of 5.77 (7)° with respect to each other. In the crystal structure molecules are connected via C-H···π interactions (Cg···Cg distances: 2.76 and 2.79 Å). Molecules B are linked by mutual C-H···π contacts in which the molecules act as hydrogen bond donors and acceptors resulting in infinite chains.
These chains are interconnected by molecules A which only act as acceptor sites for C-H···π interactions ( Figure 2).

Experimental
2,3-Dihydro-1H-inden-1-one (2 g, 1.8 ml, 15.15 mmol) is dissolved in 30 ml ethanol and mixed with hydrazine hydrate (379 mg, 0.37 ml, 7.58 mmol) in the presence of a catalytic amount of p-toluene sulfonic acid. The resulting orange colored mixture is stirred at room temperature for 3 h. Evaporation of the solvent at room temperature for 3 d leads to the formation of the crystalline title compound (yield: 78%).

Refinement
Hydrogen atoms have been placed in idealized positions and were refined using the riding model approximation with C-H distances of 0.95 and 0.99 Å for aromatic and methylene groups, respectively, with U iso (H) = 1.2 U eq (C).  Molecular structure of the independent molecules of the title compounds with displacement ellipsoids at the 50% probability level (i = -x, 1-y, 2 -z; ii = -x, -y, 1-z).

Figure 2
Packing diagram of the title compound. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.