Mononuclear Heptacoordinated 3d-Metal Helicates as a New Family of Single Ion Magnets

The series of Co(II), Fe(II), and Ni(II) mononuclear coordination compounds [CoL(NCS)2]·3DMSO (1), [CoL(H2O)2](ClO4)2·DMSO (2), [CoL(H2O)(EtOH)][CoCl4]·2H2O (2a), [FeL(NCS)2]·DMSO (3), [NiL(NCS)2]·CH3CN (4) composition (where L is 2,6-bis(1-(2-(4,6-dimethylpyrimidin-2-yl)hydrazineylidene)ethyl)pyridine), with an [MLA2] unit A a pair apical monodentate ligands), was synthesized. In 1, 2, 2a, 3, the ligand pentadentate, cobalt iron ions are placed in heavily distorted pentagonal pyramidal environment, while 4 ion hexacoordinated. Easy plane-type magnetic anisotropy (D = 13.69, 11.46, 19.5, 6.2 cm−1 for 4, respectively) established nickel compounds, easy axis-type −14.5 cm−1) compound 3. 1 2 show SIM behavior under 1500 Oe external field, effective magnetization reversal barriers 65(1) 60(1) K respectively. combination Orbach Raman relaxation mechanisms shown to adequately describe temperature dependence times 2. CASSCF/NEVPT2 calculations were performed model parameters spin Hamiltonian study.