Crystal structure of 13-phenyl-2,3,4,13-tetra­hydro-1H-indazolo[1,2-b]phthalazine-1,6,11-trione

The title compound, C21H16N2O3, consists of an indazolone moiety, bearing a phenyl group, fused to a phthalazine ring system (r.m.s. deviation = 0.018 A). The phenyl ring is almost normal to the mean plane of the five-membered ring of the indazolone moiety, making a dihedral angle of 89.64 (7)°. The six-membered ring of the indazolone moiety has an envelope conformation, with the central methyl­ene C atom as the flap. In the crystal, mol­ecules are linked via C—H⋯O hydrogen bonds, forming slabs parallel to the bc plane. The slabs are linked via C—H⋯π and π–π inter­actions [the shortest inter-centroid distance involving rings of pyrazolo­phthalazine moieties is 3.6430 (8) A], forming a three-dimensional structure.