This study presents the novel hexacoordinated Co(ii) mononuclear complex with SIM behavior.

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A dinuclear double end-on azido bridged Ni(II) complex [Ni 2 L 2 (μ-1,1 -N 3 ) 2 (N 3 ) 2 ] (1) with the condensation product of 2-quinolinecarboxaldehyde and trimethylammonium acetohydrazide chloride (Girard's T reagent) (HLCl) has been synthesized and characterized by elemental analysis, IR spectroscopy, single-crystal X-ray diffraction, magnetic measurements and DFT studies. In complex 1 intra-dimer ferromagnetic coupling between Ni 2+ ions (J = +12.0(2) cm -1 ) and inter-dimer antiferromagnetic interaction (δ = -0.8(3) cm -1 ) were observed. DFT-BS calculations provided explanation of ferromagnetic exchange coupling in complex 1.

The magnetic anisotropy in pentagonal bipyramidal complexes of Co(II) (1 and 2), Fe(III) (3 and 4) and Ni(II) (5) with 2,2′-[2,6-pyridinediylbis(ethylidyne-1-hydrazinyl-2ylidene)]bis[N,N,N-trimethyl-2-oxoethanaminium] equatorial ligand and isothiocyanato axial ligands has been investigated by magnetic susceptibility measurements, powder X-band EPR spectroscopy, Mössbauer spectroscopy, ab initio, and LFDFT calculations. The studied complexes display three distinct types of magnetic anisotropy. Co(II) complexes (1 and 2)show an easy plane anisotropy with large and positive D values and negligible rhombicity.Ni(II) complex ( 5) has uniaxial magnetic anisotropy with negative D value. Fe(III) complexes (3 and 4) have small ZFS parameters. Theoretical modeling was used to rationalize the magnetic anisotropy in these systems and to identify the most important excited states that are responsible for the zero-field splitting. These excitations are a consequence of the electronic structure of the central metal ion in ideal pentagonal bipyramidal coordination.

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