Synthesis and crystal structures of (2E)-1,4-bis­(4-chloro­phen­yl)but-2-ene-1,4-dione and (2E)-1,4-bis­(4-bromo­phen­yl)but-2-ene-1,4-dione

The mol­ecular structure of (2E)-1,4-bis­(4-chloro­phen­yl)but-2-ene-1,4-dione [C(16)H(10)Cl(2)O(2), (1)] is composed of two p-chlorophenyl rings, each bonded on opposite ends to a near planar 1,4-trans enedione moiety [–C(=O)—CH=CH—(C=O)–] [r.m.s. deviation = 0.003 (1) Å]. (2E)-1,4-Bis(4-bromo­phen­yl)but-2-ene-1,4-dione [C(16)H(10)Br(2)O(2), (2)] has a similar structure to (1), but with two p-bromophenyl rings and a less planar enedione group [r.m.s. deviation = 0.011 (1) Å]. Both mol­ecules sit on a center of inversion, thus Z′ = 0.5. The dihedral angles between the ring and the enedione group are 16.61 (8) and 15.58 (11)° for (1) and (2), respectively. In the crystal, mol­ecules of (1) exhibit C—Cl⋯Cl type I inter­actions, whereas mol­ecules of (2) present C—Br⋯Br type II inter­actions. van der Waals-type inter­actions contribute to the packing of both mol­ecules, and the packing reveals face-to-face ring stacking with similar inter­planar distances of approximately 3.53 Å.