Structural Studies of Radical Reaction Products. II.* 2,4-Bis(4-ehlorophenyl)-5,5-dimethyl-3-pyrazolidinone

C~7H16C12N20, Mr= 335-23, triclinic, PI, a= 12.280(3), b= 10.191(3), c=6.633(2)A, a= 83-93 (7), fl= 100.05 (8), y= 87.70 (8) °, U= 811.3 (5)/~3, Z = 2, D x = 1.37 Mg m -3, 2(Mo Kfi) = 0.71069 A, g(Mo Kfi) = 0.402 mm -I, F(000) = 348, room temperature, R=0.056 for 2285 observed reflections, S = 0.85. The title compound, which shows pharmacological activity in vitro, presents a puckered pyrazolidinone ring [puckering angle 36.0 (2) ° I with an N-N bond [1.445 (4)A] longer than those usually found in hydrazidic moieties. Geometric and electronic features of this part of the molecule have a close similarity with those of antipyrine, a 3H-pyrazol- 3-one derivative used as an antiinflammatory drug.