The first 1-D cyanide-bridged complex assembled from a covalently tethered [CoII(N3O2)Cl(OH2)]22+ macrocyclic building block

The metal-templated synthesis of the bimetallic macrocyclic complex {CoII(N3O2)Cl(OH2)}2·2Cl·H2O (2) containing two N3O2 macrocyclic binding pockets was achieved from the metal-templated Schiff-base condensation of 2,2′-6,6′-tetracetyl-4,4′-bipyridine together with 3,6-dioxaoctane-1,8-diamine. Slow diffusion of (2) with K4[Fe(CN)6] in a (1:1) mixture of methanol and water afforded the 1-D coordination polymer [{Co(N3O2)(OH2)}2{Fe(CN)6}]⋅5H2O (5) whose structure was determined by X-ray diffraction. The polymer comprises two covalently tethered pentagonal bipyramidal Co(II) macrocycles both axially coordinated to a single [Fe(CN)6]4− unit in a zig-zag arrangement, highlighting the versatility of this family of dimeric building blocks for the self-assembly of higher order structures. Magnetic studies on (2) reveal that the ions exist as isolated S = 3/2 spin systems with no first-order spin–orbit coupling, but with significant axial zero field splitting (D = 23 cm−1, giso = 2.37), indicating that the back-to-back N3O2 macrocyclic ligand does not offer an efficient magnetic exchange pathway. The magnetic response of (5) in the high temperature region (T > 50 K) is identical to (2) indicating dominant zero field splitting effects. However, on further cooling an upturn in χT is consistent with weak ferromagnetic exchange (J/k = +7.8 K) via the [Fe(CN)6]4− bridging unit, affording weakly-coupled CoII dimer units within the polymer chain of (5).

Graphical abstractThe first cyanide bridged polynuclear 1-D coordination polymer [{Co(N3O2)(OH2)}2{Fe(CN)6}]·5H2O assembled from a dimeric Schiff-base N3O2 macrocyclic building block comprises two covalently tethered pentagonal bipyramidal CoII macrocycles both axially coordinated to a single [Fe(CN)6]4− unit in a zig–zag arrangement. Magnetic susceptibility measurements indicate that the anisotropy associated with the pentagonal bipyramidal CoII complexes of the dimer is successfully transplanted into the more complex 1-D chain.Figure optionsDownload full-size imageDownload as PowerPoint slide