Homochiral SCM Built of Tetrahedral and Pentagonal Bipyramidal Fe(II) Units Bridged by Chlorine

Abstract

Each enantiomer of a chiral pentagonal bipyramidal (PBP) FeII complex ([FeLN5R,RCl(MeOH)]Cl·H2O, 1R, or [FeLN5S,SCl(MeOH)]Cl·H2O, 1S) has been obtained using either the R or the S stereoisomer of the macrocyclic pentadentate ligand formed in a template-condensation reaction of the tetraamine N,N′-Bis-{(1R,2R)-[2-(amino)]cyclohexyl}-1,2-diaminoethane, or its (1S,2S) enantiomer, and 2,5-diacetylpyridine, respectively LN5R,R and LN5S,S. Subsequently, the 1-D coordination polymers [FeLN5R,R{FeCl4}], 2R, and [FeLN5S,S{FeCl4}], 2S, were formed by reacting respectively 1R or 1S with 1 equiv of FeCl2(H2O)4. These chain compounds consist of an alternation of PBP and tetrahedral FeII units sharing a Cl atom. Theoretical calculations reveal large magnetic anisotropy for each Fe center but of different type with axial zero-field splitting parameter D of respectively −30 cm–1 and 15 cm–1. The magnetic behavior for the 1-D compound revealed canted antiferromagnetic Fe–Fe interactions (J = −6 cm–1) and SCM behavior characterized by Δ/kB = 42 K with pre-exponential factor τ0 = 2.17 × 10–10 s. It was noted that this SCM behavior was accompanied by a magnetic order leading to a weak ferromagnet (i.e., canted antiferromagnet). The preparations, crystal structures (CCDC references 2214580–2214583), spectroscopic data, magnetic behaviors, and theoretical investigations are reported.