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Elsevier, Polyhedron, (76), p. 122-127

DOI: 10.1016/j.poly.2014.04.001

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

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This paper is available in a repository.

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Abstract

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]2- bridging unit, affording weakly-coupled CoII dimer units within the polymer chain of (5).