6-Amino-5-(1-amino-2,2-dicyanovinyl)-3,3a,4,5-tetrahydro-2H-indene-4-spiro-1′-cyclopentane-3a,7-dicarbonitrile–thiophene-2-carbaldehyde (1/0.5)

In each of the two independent indene-4-spiropentane molecules in the asymmetric unit of the title 2:1 adduct, C19H18N6·0.5C5H4OS, the cyclohexene ring adopts a half-chair conformation and the cyclopentene and cyclopentane rings adopt envelope conformations. The mean plane through the cyclohexene/cyclopentene fused system is aligned at a dihedral angle of 77.9 (1)° with respect to the mean plane through the cyclopentane ring in one molecule and 87.0 (1)° in the other. In the crystal, adjacent indene-4-spiropentane molecules are linked by N—H⋯N hydrogen bonds into a three-dimensional network. The spaces within the network are occupied by the thiophene-2-carbaldehyde molecules. The thiophene-2-carbaldehyde unit is disordered over two positions of equal occupancy. The crystal studied was found to be a non-morohedral twin with two minor twin components of 18.4 and 9.7%.

In each of the two independent indene-4-spiropentane molecules in the asymmetric unit of the title 2:1 adduct, C 19 H 18 N 6 Á0.5C 5 H 4 OS, the cyclohexene ring adopts a half-chair conformation and the cyclopentene and cyclopentane rings adopt envelope conformations. The mean plane through the cyclohexene/cyclopentene fused system is aligned at a dihedral angle of 77.9 (1) with respect to the mean plane through the cyclopentane ring in one molecule and 87.0 (1) in the other. In the crystal, adjacent indene-4-spiropentane molecules are linked by N-HÁ Á ÁN hydrogen bonds into a three-dimensional network. The spaces within the network are occupied by the thiophene-2-carbaldehyde molecules. The thiophene-2-carbaldehyde unit is disordered over two positions of equal occupancy. The crystal studied was found to be a non-morohedral twin with two minor twin components of 18.4 and 9.7%.

Comment
We have previously reported the condensation of cyclopentylidenemalononitrile and thiophene-2-carbaldehyde to form 2,5-bis(thienylidene)-1-dicyanomethylene-cyclopentane, a purple-colored compound suitable for application as a dye (Asiri, 2003). For reasons that we are not clear of, our attempted synthesis gave only colorless crystals. We examined a plate-like specimen and identified it as 6-amino-5,5,7-tricyano-3,3a,4,5-tetrahydro-2H-indene-4-spirocyclo-pentane, whose structure has already been reported (Nesterov & Viltchinskaia, 2000). We identified a prismatic specimen as the title 1: 0.5 co-crystal (Scheme I, Fig. 1); the second component is unchanged thiophene-2-carbaldehyde. The first component differs from the reported compound in having an aminodicyanovinyl group (along with a methine hydrogen) in place of the two cyano groups in the 5-position. Additionally, the compound has another cyano group in the 3a position.
Experimental Cyclopentylidenemalononitrile (0.13 g, 1 mmol) and thiophene-2-carbaldehyde (0.22 g, 2 mmol) were heated in an oil bath for 6 h. Ethanol was added to break up the solid material. The product was collected and recrystallized from acetic acid.

Refinement
Carbon-bound H-atoms were placed in calculated positions (C-H 0.95 to 0.99 Å) and were included in the refinement in the riding model approximation, with U(H) set to 1.2U(C). The amino H-atoms were similarly positioned (N-H 0.86 Å) by rotating them; their temperature factors were tied by a factor of 1.2. Modeling the amino group as if it was a methyl group but setting the occupancy factor of one of the three H-atoms to zero gave a satisfactory hydrogen bond scheme except for the H2n2 and H3n2 atoms, which were 1.82 Å apart.
The thiophene-2-carbaldehyde molecule is disordered over two positions; as the disorder refined to nearly 1:1, the occupancy of each component was set to 0.5. The sulfur-carbon distances were restrained to 1.70±0.01 Å and the oxygen-carbon distances to 1.25±0.01 Å. The excyclic carbon-carbon distances were restrained to 1.50±0.01 Å and the endocyclic ones to 1.35±0.01 Å. All atoms of each component were restrained to lie on a plane. The temperature factors of C41' were set to those of S1, and that of S1' to those of C41 as the pair of atoms are close to each other. The anisotropic temperature factors of the disordered atoms were restrained to be nearly isotropic. The primed carbon atoms were set to those of the unprimed ones; the anisotropic temperature factors of these carbon atoms were restrained to be nearly isotropic.
The structure is a non-meohedrally twinned structure with two minor twin components of 18.5 and 9.7%. The twin domains were identified by the use of PLATON (Spek, 2009 Fig. 1. Thermal ellipsoid plot (Barbour, 2001) of the asymmetric unit of the C 19 H 18 N 6 . 0.5C 5 H 4 OS co-crystal at the 70% probability level; hydrogen atoms are drawn as spheres of arbitrary radius.