Synthesis of N3−/SCN− bridged polynuclear complexes of nickel(II) using N,N,N′-trimethylethane-1,2-diamine as a blocking ligand: low temperature magnetic study and single crystal structure of [Ni(μ1, 1-N3)(μ1, 3-N3)(N,N,N′-Me3en)]n

Abstract

Seven new complexes of nickel(II), derived from azido, thiocyanato and nitrito bridging ligands and N,N,N′-trimethylethylenediamine (N,N,N′-Me₃en) as blocking ligand, were synthesised and characterised; four of them are one-dimensional compounds: [Ni(μ_1, 3-N₃)(N,N,N′-Me₃en)₂]_n(ClO₄)_n1, [Ni(μ_1, 3-N₃)(N,N,N′-Me₃en)₂]_n(PF₆)_n2, [Niμ_1, 1-N₃)(μ_1, 3-N₃)(N,N,N′-Me₃en)]_n3, [Ni(μ-SCN)₂(N,N,N′-Me₃en)]_n4, and three mononuclear: [Ni(NCS)₂(N,N,N′-Me₃en)₂] 5, [Ni(NO₂)(N,N,N′-Me₃en)₂]PF₆6, [Ni(NO₂)₂(N,N,N′-Me₃en)] 7. Crystal structures for 3 and 6 were determined by X-ray diffraction methods. Compound 3 may be described as a one-dimensional system with double azido bridging ligands alternately in end-on and end-to-end co-ordination modes. Compound 6 is a mononuclear complex in which a nitrito ligand acts as a chelate. The magnetic properties of all the compounds were studied by susceptibility measurements vs. temperature. The χ_Mvs.T plots for 1 and 2 show the typical shape for moderate antiferromagnetic one-dimensional nickel(II) complexes, while global strong antiferromagnetic behaviour with a maximum at about 200 K is observed for 3 and 4 exhibits a very weak ferromagnetic interaction. Compounds 5, 6, and 7 follow the Curie law, typical behaviour of mononuclear Ni^II compounds. The superexchange parameter J for 1, 2 and 4 was deduced from the spin Hamiltonian −JΣS_iS_i+1 and from −Σ(J_AFS_2iS_2i+1 + J_FS_2iS_2i−1) for 3. J values for 1 and 2 are −15.5 and −16.6 cm⁻¹, respectively, J_AF = −132 cm⁻¹ and J_FM = 99 cm⁻¹ for 3, and 1.34 cm⁻¹ for 4.