Crystal structure determination of rac-11′-(1-acetyl-1H-indazol-3-yl)-11′,11a′-dihydro-10′H,17′H-spiro[indene-2,18′-[5a,16b]methanotriindeno[1,2-b:1′,2′-d:2′′,1′′-g]oxocine]-1,3,10′,12′,17′(10a′H)-pentaone acetonitrile 1.5-solvate

The title molecule contains a central eight-membered ring, which contains an enol–ester, from which five arms extend. The arms exhibit intermolecular interactions within the crystal lattice between molecules of the title compound and with co-crystallized acetonitrile solvent molecules.

The title compound, C 46 H 26 N 2 O 7 Á1.5CH 3 CN, is the aldol condensation product of bindone with indazole-3-carbaldehyde followed by double intermolecular cyclization. The asymmetric unit, which has monoclinic P2 1 /c symmetry, contains two independent molecules of the title compound and three acetonitrile molecules. The title molecule comprises a central eight-membered ring, which contains an enol-ester, from which five arms extend. The arms exhibit intermolecular interactions within the crystal lattice between molecules of the title compound and with co-crystallized solvent molecules (acetonitrile).

Structural commentary
The asymmetric unit of the title compound, shown in Fig. 1, contains two independent molecules and three co-crystallized acetonitrile molecules (Z = 8, Z 0 = 4). The title compound is shown in Fig. 2.
The core of the molecule represented by an eightmembered oxocine ring, which is linked in the center by a carbon atom, C1 bridging between C2 and C6, and includes an ether group as shown in Fig. 3a. Bond lengths, listed in Table 1, clearly indicate the presence of a C C double bond with a bond length of 1.357 (3) Å and also featuring a short C-C bond with a bond length of 1.494 (3) Å ,. Also interesting to note is the stark difference between the C-O bond lengths within the ring, ranging from 1.333 (3) to 1.462 (2) Å . The presence of the double bond, the short C-C bond and the great variation within the C-O bonds is due to the five arms of the structure, which extend from the central ring as shown in Fig. 3b-3f and are described in Table 2.

Supramolecular features
The packing of the crystal structure indicates that the acetonitrile molecules interact with up to three different aromatic systems belonging to arms 1-3; these interactions can be seen in Fig. 4a. The interactions between acetonitrile and arms 2 and 3 also force some rigidity upon the structure, as seen in  Table 2 The various arms extending from the central ring.
Arm designation Carbon atoms shared with central ring IUPAC name ORTEP representation of the asymmetric unit of the crystal, containing two compound molecules and three co-crystallized acetonitrile molecules. Displacement ellipsoids are drawn at the 50% probability level.

Figure 2
View of one of the independent molecules in the title compound showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level.   . It is worth noting that the interaction seen in Fig. 4b is not observed in the asymmetric unit, but in the extended packing of the crystal. These interactions are listed in Table 3. A second interaction, which contributes to the crystal packing, is ainteraction between arms 4 and 5, as seen in Fig. 5a. A third interaction, which contributes to the crystal packing, is ainteraction between arms 1 and 2, as seen in Fig. 5b. These interactions are listed in Table 3.
Finally, a hydrogen-bonding network (Table 4) is observed throughout the crystal, consisting of a C-HÁ Á ÁO C bonding pattern between the molecules of the title compound, and a C-HÁ Á ÁN C bonding pattern between the acetonitrile molecules, as seen in Fig. 6.
Shortest bond distances that were found are shown for the various interactions.

Figure 6
Part of the C-HÁ Á ÁO C bonding pattern between molecules of the title compound and also part of the C-HÁ Á ÁN C bonding pattern between the acetonitrile molecules.

Synthesis and crystallization
The synthetic procedure for the title compound will be published elsewhere. The title compound was crystallized in HPLC/gradient grade acetonitrile (99.9%) obtained from Sigma (CAS 75-05-8) by slow evaporation at a temperature of 277 K over the course of several weeks, resulting in yellow crystals.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 5. Hydrogen atoms were placed at calculated positions (C-H = 0.93-0.98 Å ) and refined in riding mode, with U iso (H) = 1.2U eq (C) for CH and CH 2 groups and 1.5U eq (C) for CH 3 groups.