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Rational Enantioselective Design of Chiral Heterobimetallic Single-Chain Magnets: Synthesis, Crystal Structures and Magnetic Properties of Oxamato-Bridged MIICuII Chains (M=Mn, Co)

Authors

  • Jesús Ferrando-Soria,

    1. Departament de Química Inorgànica, Instituto de Ciencia Molecular (ICMOL), Universitat de València, Paterna, 46980 València (Spain), Fax: (+34) 96-354-4322
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  • Dr. Danielle Cangussu,

    1. Institut Parisien de Chimie Moléculaire, UPMC-Univ. Paris 06, Paris, 75005 (France), Fax:(+33)144273841
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  • Mercedes Eslava,

    1. Departament de Química Inorgànica, Instituto de Ciencia Molecular (ICMOL), Universitat de València, Paterna, 46980 València (Spain), Fax: (+34) 96-354-4322
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  • Dr. Yves Journaux,

    Corresponding author
    1. Institut Parisien de Chimie Moléculaire, UPMC-Univ. Paris 06, Paris, 75005 (France), Fax:(+33)144273841
    2. UMR CNRS 7201, Institut Parisien de Chimie Moléculaire, Paris (France)
    • Institut Parisien de Chimie Moléculaire, UPMC-Univ. Paris 06, Paris, 75005 (France), Fax:(+33)144273841
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  • Rodrigue Lescouëzec,

    1. Institut Parisien de Chimie Moléculaire, UPMC-Univ. Paris 06, Paris, 75005 (France), Fax:(+33)144273841
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  • Prof. Dr. Miguel Julve,

    1. Departament de Química Inorgànica, Instituto de Ciencia Molecular (ICMOL), Universitat de València, Paterna, 46980 València (Spain), Fax: (+34) 96-354-4322
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  • Prof. Dr. Francesc Lloret,

    Corresponding author
    1. Departament de Química Inorgànica, Instituto de Ciencia Molecular (ICMOL), Universitat de València, Paterna, 46980 València (Spain), Fax: (+34) 96-354-4322
    • Departament de Química Inorgànica, Instituto de Ciencia Molecular (ICMOL), Universitat de València, Paterna, 46980 València (Spain), Fax: (+34) 96-354-4322
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  • Dr. Jorge Pasán,

    1. Laboratorio de Rayos X y Materiales Moleculares, Departamento de Física Fundamental II, Universidad de La Laguna, La Laguna, 38201 Tenerife (Spain)
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  • Prof. Dr. Catalina Ruiz-Pérez,

    1. Laboratorio de Rayos X y Materiales Moleculares, Departamento de Física Fundamental II, Universidad de La Laguna, La Laguna, 38201 Tenerife (Spain)
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  • Dr. Elsa Lhotel,

    1. CNRS, Institut Néel, BP166, Grenoble (France)
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  • Dr. Carley Paulsen,

    1. CNRS, Institut Néel, BP166, Grenoble (France)
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  • Dr. Emilio Pardo

    Corresponding author
    1. Institut Parisien de Chimie Moléculaire, UPMC-Univ. Paris 06, Paris, 75005 (France), Fax:(+33)144273841
    • Institut Parisien de Chimie Moléculaire, UPMC-Univ. Paris 06, Paris, 75005 (France), Fax:(+33)144273841
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Abstract

A new series of neutral oxamato-bridged MIICuII chiral chains of general formula [MCuLx(S)m(H2O)n]aSbH2O [L1=(M)-1,1′-binaphthalene-2,2′-bis(oxamate) with M=Mn (1 a) and Co (1 b); L2=(P)-1,1′-binaphthalene-2,2′-bis(oxamate) with M=Mn (2 a) and Co (2 b)] and the analogous racemic chains of formula [MCuL3(S)m(H2O)n]aSbH2O [L3=1,1′-binaphthalene-2,2′-bis(oxamate) with M=Mn (3 a) and Co (3 b)] have been prepared by reaction of the corresponding dianionic oxamatocopper(II) complex [Cu(Lx)]2− with Mn2+ or Co2+ cations in either dimethylformamide (DMF) or dimethyl sulfoxide (DMSO). Solid circular dichroism (CD) spectra of the bimetallic chain compounds were recorded to establish their chiral and enantiomeric nature. They exhibit maximum positive and negative Cotton effects, each pair of enantiomeric chains being non-superimposable mirror images. The crystal structures of the MnIICuII (1 a3 a) and the CoIICuII (1 b and 2 b) chain compounds were solved by single-crystal X-ray diffraction methods. Our attempts to obtain X-ray quality crystals of 3 b were unsuccessful. The values of the shortest interchain Mn⋅⋅⋅Mn and Co⋅⋅⋅Co distances are indicative of a good isolation of neighbouring chains in the crystal lattice, which is caused by the bulky aromatic ligand. Although all the MnIICuII and CoIICuII chains exhibit ferrimagnetic behaviour (−JMnCu=18.9–26.6 cm−1 and −JCoCu=19.5–32.5 cm−1), only the enantiopure CoIICuII chains (1 b and 2 b) show slow magnetic relaxation at low temperatures (TB=0.6–1.8 K), which is a characteristic of single-chain magnets (SCMs) and is related to the magnetic anisotropy of the high-spin CoII ion. Analysis of the SCM behaviour of 1 b and 2 b, based on Glauber’s theory for an Ising one-dimensional system, shows a thermally activated mechanism for the magnetic relaxation (Arrhenius law dependence). The energy barriers (Ea) to reverse the magnetisation direction are 8.2 (1 b) and 8.1 cm−1 (2 b), whereas the pre-exponential factor (τ0) is 1.9×10−8 (1 b) and 6.0×10−9 s (2 b). Interestingly, the racemic CoIICuII chain analogue, 3 b, showed no evidence of SCM behaviour.

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