organic compounds
In the structure of 1,3-dibromoazulene, C10H6Br2, the planar molecule sits on a crystallographic mirror plane. The Br atoms are attached to the five-membered ring adjacent to the ring fusion. Head-to-tail charge-charge interactions due to partial positive charges on ring H atoms and partial negative charges within the aromatic ring system attract adjacent 1,3-dibromoazulene molecules together. This causes them to arrange themselves in a zigzag pattern that allows close packing of the oppositely charged groups.
organic compounds
In the structure of 1,3-diiodoazulene, C10H6I2, as expected, the molecule is planar. Also observed are short contacts between I atoms and between I and ring C atoms. The crystal structure of this compound exhibits two sets of parallel layers, nearly perpendicular to each other. The layers are formed by charge-charge interactions between some I atoms and nearby seven-membered rings of molecules in an adjacent layer. The packing is also affected by attractive dispersion forces between I atoms in adjacent layers.