The Analogy of C−Br···Br−C, C−Br···Br−Fe, and Fe−Br···Br−Fe Contacts: Crystal Structures of (26DAPH)FeBr₄ and (26DA35DBPH)₂FeBr₄·Br

The role of C−Br1···Br2−Fe and Fe−Br1···Br2−Fe interactions in the iron(III) structures (26DAPH)FeBr4 (I) and (26DA35DBPH)2FeBr4·Br (II) (where 26DAPH is 2,6-diaminopyridinium and 26DA35DBPH is 2,6-diamino-3,5-dibromopyridinium) is investigated. In (I), the ions are arranged inside the crystalline lattice based on the N−H···Br−Fe hydrogen bond, including other types of interaction. The [FeBr4−] anions form a ladder structure with extremely short interbromide distances, 3.618 Å within the rungs and 3.814 Å within the rails. There are two Fe−Br1···Br2−Fe contact types; the first type has a Fe−Br1···Br2 angle = Br1···Br2−Fe angle which is equal to 166.6°. In the second, the Fe−Br1···Br2 angle = 100.5° and Br1···Br2−Fe angle = 159.1°. In contrast, in (II), the supramolecular assembly of cations and anions is dominated by the C−Br1···Br2−Fe interaction and the more traditional N−H···Br− hydrogen bond. Here the [FeBr4−] anions form linear chains with interbromide distances of ca. 3.83 Å. Most interestingly, the geometrical characteristics of the C−Br1···Br2−Fe contacts and the Fe−Br1···Br2−Fe contacts, present in (I) and (II), are similar to the well characterized C−Br1···Br2−C contacts; the C−Br1···Br2 angles are essentially linear (avg = 165.5°, range 160.0−176.3°) and the Br1···Br2−Fe angles are essentially normal to the axis containing C−Br1···Br2 atoms (avg = 90.4°, range 82.1−113.8°).