Crown compounds for anions. Sandwich complexes of cyclic trimeric perfluoro-o-phenylenemercury with hexacyanoferrate(III) and nitroprusside anions

Cyclic trimeric perfluoro-o-phenylenemercury (o-C6F4Hg)3 (1) is able to bind hexacyanoferrate(III) and nitroprusside anions to form complexes {[(o-C6F4Hg)3]2[Fe(CN)6]}3− and {[(o-C6F4Hg)3]2[Fe(CN)5NO]}2−, respectively, which contain one anionic species per two macrocycles. According to X-ray diffraction data, the complexes have unusual sandwich structures wherein the anionic guest is located between the planes of two molecules of 1 and is coordinated to each of these through two types of Fe–C–N–Hg bridges. One type is the simultaneous coordination of a cyanide ligand to all three Hg centres of the cycle. The other type is the coordination of a cyanide group to a single Hg atom of the macrocycle. In both types, the bonding of the anionic guest with the macrocyclic host is accomplished with the participation of π-electrons of the cyanide ligands. The synthesized compounds are the first examples of host–guest complexes of a macrocyclic multidentate Lewis acid with anionic metal complexes.