Topologic Equivalents of Coronands, Cryptands and Their Inclusion Complexes: Synthesis, Structure and Properties of {2}‐Metallacryptands and {2}‐Metallacryptates

The synthesis and structural characterisation of two dinuclear iron(III) complexes are reported. The compounds of general structure [Fe 2 L   1 3 ] [ 8 ; L 1 = dianion of 2,2′‐dicyano‐2,2′‐isophthaloyldi(isopropyldicarboxylate)] and [K ⊂ Fe 2 L   2 3 ] + (PF 6 ) ‐ [ 10 ; L 2 = dianion of 1,1′‐(2,6‐pyridylene)bis‐1,3‐(4‐dimethyl)‐pentanedione] are formed by the deprotonation of ligands 7 and 9 with triethylamine and potassium hydride respectively, followed by addition of iron(III) chloride and work up with water or aqueous potassium hexafluorophosphate. X‐ray crystallographic studies reveal that 8 is a racemic mixture composed of triple helicates with (Δ,Δ)‐ fac and (Δ,Δ)‐ fac configuration at the two iron bridgeheads. In contrast to racemic 8 , the two iron centres in the meso ‐ 10 [(Δ,Δ)‐ fac ] have opposite configuration. Investigations of the redox‐active iron centres in {2}‐metallacryptand 8 and {2}‐metallacryptate 10 by cyclic voltammetry show slightly different behaviour. The peaks for the two consecutive reductions of the two iron centres of 8 can hardly be resolved, whereas 10 shows two well‐separated peaks. Mössbauer measurements were performed on 8 and 10 between 4.2 and 300 K, with and without a field applied perpendicular or parallel to the γ‐beam. All zero‐field and 20 mT spectra exhibit a broad and unresolved absorption pattern. Application of 5.3 T at 4.2 K results in well‐resolved magnetic hyperfine patterns which are practically the same for 8 and 10.