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Keywords:

  • Nickel complexes;
  • Macrocyclic ligands;
  • Amine sulfonate donors;
  • Magnetic properties

Abstract

The preparation and characterisation of two new macrocyclic NiII complexes containing N3Ni(μ1,3-SO3R)2(μ-O2CR)NiN3 cores are described. Complexes [Ni2(L2)(O2CMe)]+ (4) and [Ni2(L2)(O2CPh)]+ (5), where (L2)2– represents a macrocyclic hexaaza-bis(phenylsulfonato) ligand, were synthesised by H2O2 oxidation of the respective parent complexes, [Ni2(L1)(O2CMe)]+ (1) and [Ni2(L1)(O2CPh)]+ (2), supported by the corresponding hexaaza-bis(thiophenolate) macrocycle(L1)2–. The compounds were characterised by means of elemental analysis, mass spectrometry, IR and UV/Vis spectroscopy. The crystal structures of the tetraphenylborate salts of 4 and 5 show that the bridging thiophenolato functions in 1 and 2 are in both cases converted to μ1,3-bridging sulfonato groups. The conversion to the sulfonato groups is accompanied by a drastic increase of the Ni···Ni distance from 3.483(1) Å in 1 and 3.491(1) Å in 2 to 4.543(1) Å in 4 and 4.5725(8) Å in 5. The magnetic properties are also affected. In contrast to 1 and 2, which exhibit an intramolecular ferromagnetic exchange interaction (S = 2 ground state), the spins of the nickel(II) (Si = 1 ions) in 4 and 5 are weakly antiferromagnetically coupled, the coupling constants J (H = –2JS1S2) being –2.0 cm–1 (4) and –2.3 cm–1 (5), to produce a diamagnetic (S = 0) ground state. Supporting DFT (density functional theory) calculations substantiate the experimental results.