Crystal structures and Hirshfeld surface analyses of 4-benzyl-6-phenyl-4,5-di-hydro-pyridazin-3(2H)-one and methyl 2-[5-(2,6-di-chloro-benz-yl)-6-oxo-3-phenyl-1,4,5,6-tetra-hydropyridazin-1-yl]acetate.

The asymmetric units of the title compounds both contain one nonplanar mol-ecule. In 4-benzyl-6-phenyl-4,5-di-hydro-pyridazin-3(2H)-one, C(17)H(14)N(2)O, (I), the phenyl and pyridazine rings are twisted with respect to each other, making a dihedral angle of 46.69†(9)°; the phenyl ring of the benzyl group is nearly perpendicular to the plane of the pyridazine ring, the dihedral angle being 78.31†(10)°. In methyl 2-[5-(2,6-di-chloro-benz-yl)-6-oxo-3-phenyl-1,4,5,6-tetra-hydropyridazin-1-yl]acetate, C(20)H(16)Cl(2)N(2)O(3), (II), the phenyl and pyridazine rings are twisted with respect to each other, making a dihedral angle of 21.76†(18)°, whereas the phenyl ring of the di-chloro-benzyl group is inclined to the pyridazine ring by 79.61†(19)°. In the crystal structure of (I), pairs of N-H⋯O hydrogen bonds link the mol-ecules into inversion dimers with an R (2) (2)(8) ring motif. In the crystal structure of (II), C-H⋯O hydrogen bonds generate dimers with R (1) (2)(7), R (2) (2)(16) and R (2) (2)(18) ring motifs. The Hirshfeld surface analyses of compound (I) suggests that the most significant contributions to the crystal packing are by H⋯H (48.2%), C⋯H/H⋯C (29.9%) and O⋯H/H⋯O (8.9%) contacts. For compound (II), H⋯H (34.4%), C⋯H/H⋯C (21.3%) and O⋯H/H⋯O (16.5%) inter-actions are the most important contributions.