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Issue 17, 2012
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Self-assembly, metal binding ability, and magnetic properties of dinickel(II) and dicobalt(II) triple mesocates

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Abstract

Two metallacyclic complexes of general formula Na8[MII2L3xH2O [M = Ni (4) and Co (5) with x = 15 (4) and 17 (5)] have been self-assembled in aqueous solution from N,N′-1,3-phenylenebis(oxamic acid) (H4L) and M2+ ions in a ligand/metal molar ratio of 3 : 2 in the presence of NaOH acting as base. X-Ray structural analyses of 4 and 5 show triple-stranded, dinuclear anions of the meso-helicate-type (so-called mesocates) with C3h molecular symmetry. The two octahedral metal–tris(oxamate) moieties of opposite chiralities (Δ,Λ form) are connected by three m-phenylene spacers at intermetallic distances of 6.822(2) (4) and 6.868(2) Å (5) to give a metallacryptand core. In the crystal lattice, the binding of these heterochiral dinickel(II) and dicobalt(II) triple mesocates to sodium(I) ions leads to oxamato-bridged heterobimetallic three-dimensional open-frameworks with a hexagonal diamond architecture having small pores of 17.566(4) (4) and 17.640(2) Å (5) in diameter where the crystallization water molecules and the sodium(I) countercations are hosted. Variable temperature (2.0–300 K) magnetic susceptibility measurements reveal relatively anisotropic S = 2 NiII2 (4) and S = 3 CoII2 (5) ground states resulting from the moderate to weak intramolecular ferromagnetic coupling between the two high-spin NiII (SNi = 1) or CoII (SCo = 3/2) ions across the m-phenylenediamidate bridges [J = +3.6 (4) and +1.1 cm−1 (5); H = −JS1·S2]. A simple molecular orbital analysis of the electron exchange interaction identifies the π-type pathways of the meta-substituted phenylene spacers involving the dz2 and dx2−y2 pairs of magnetic orbitals of the two trigonally distorted octahedral high-spin MII ions (M = Ni and Co) as responsible for the overall ferromagnetic coupling observed in 4 and 5 in agreement with a spin polarization mechanism. The decrease of the overall ferromagnetic coupling from 4 to 5 is in turn explained by the additional antiferromagnetic exchange contribution involving the dxy pair of magnetic orbitals of the two trigonally distorted octahedral high-spin CoII ions across the σ-type pathway of the meta-substituted phenylene spacers.

Graphical abstract: Self-assembly, metal binding ability, and magnetic properties of dinickel(ii) and dicobalt(ii) triple mesocates

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Publication details

The article was received on 26 Mar 2012, accepted on 21 May 2012 and first published on 30 May 2012


Article type: Paper
DOI: 10.1039/C2CE25434D
Citation: CrystEngComm, 2012,14, 5639-5648

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    Self-assembly, metal binding ability, and magnetic properties of dinickel(II) and dicobalt(II) triple mesocates

    M. Dul, R. Lescouëzec, L. Chamoreau, Y. Journaux, R. Carrasco, M. Castellano, R. Ruiz-García, J. Cano, F. Lloret, M. Julve, C. Ruiz-Pérez, O. Fabelo and E. Pardo, CrystEngComm, 2012, 14, 5639
    DOI: 10.1039/C2CE25434D

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