Following a novel synthetic strategy where the strong uniaxial ligand field generated by the Ph₃SiO⁻ (Ph₃SiO⁻=anion of triphenylsilanol) and the 2,4‐di‐^tBu‐PhO⁻ (2,4‐di‐^tBu‐PhO⁻=anion of 2,4‐di‐tertbutylphenol) ligands combined with the weak equatorial field of the ligand L^N6, leads to [Dy^III(L^N6)(2,4‐di‐^tBu‐PhO)₂](PF₆) (1), [Dy^III(L^N6)(Ph₃SiO)₂](PF₆) (2) and [Dy^III(L^N6)(Ph₃SiO)₂](BPh₄) (3) hexagonal bipyramidal dysprosium(III) single‐molecule magnets (SMMs) with high anisotropy barriers of U_eff=973 K for 1, U_eff=1080 K for 2 and U_eff=1124 K for 3 under zero applied dc field. Ab initio calculations predict that the dominant magnetization reversal barrier of these complexes expands up to the 3rd Kramers doublet, thus revealing for the first time the exceptional uniaxial magnetic anisotropy that even the six equatorial donor atoms fail to negate, opening up the possibility to other higher‐order symmetry SMMs.

Density functional calculations have been performed on a [Gd(III)Cu(II)] complex [L¹CuGd(O₂CCF₃)₃(C₂H₅OH)₂] (1) (where L¹ is N,N′-bis(3-ethoxy-salicylidene)-1,2-diamino-2-methylpropanato) with an aim of assessing a suitable functional within the DFT formalism to understand the mechanism of magnetic coupling and also to develop magneto-structural correlations. Encouraging results have been obtained in our studies where the application of B3LYP on the crystal structure of 1 yields a ferromagnetic J value of −5.8 cm⁻¹ which is in excellent agreement with the experimental value of −4.42 cm⁻¹ (Ĥ = JŜ_Gd·Ŝ_Cu). After testing varieties of functional for the method assessment we recommend the use of B3LYP with a combination of an effective core potential basis set. For all electron basis sets the relativistic effects should be incorporated either via the Douglas–Kroll–Hess (DKH) or zeroth-order regular approximation (ZORA) methods. A breakdown approach has been adopted where the calculations on several model complexes of 1 have been performed. Their wave functions have been analysed thereafter (MO and NBO analysis) in order to gain some insight into the coupling mechanism. The results suggest, unambiguously, that the empty Gd(III) 5d orbitals have a prominent role on the magnetic coupling. These 5d orbitals gain partial occupancy viaCu(II) charge transfer as well as from the Gd(III) 4f orbitals. A competing 4f–3d interaction associated with the symmetry of the complex has also been observed. The general mechanism hence incorporates both contributions and sets forth rather a prevailing mechanism for the 3d–4f coupling. The magneto-structural correlations reveal that there is no unique parameter which the J values are strongly correlated with, but an exponential relation to the J value found for the O–Cu–O–Gd dihedral angle parameter is the most credible correlation.

In this communication, we have proposed a novel synthetic strategy to increase the effective energy barrier ( U _eff ) of dysprosium( iii ) single ion magnets using a diamagnetic metal ion such as Zinc( ii ).

Theoretical calculations using density functional methods have been performed on two dinuclear {Ni^II–Gd^III} and two trinuclear {Ni^II–Gd^III–Ni^II} complexes having two and three μ-OR (R = alkyl or aromatic groups) bridging groups. The different magnetic behaviour, having moderately strong ferromagnetic coupling for complexes having two μ-OR groups and weak ferromagnetic coupling for complexes having three μ-OR groups, observed experimentally is very well reproduced by the calculations. Additionally, computation of overlap integrals MO and NBO analysis reveals a clear increase in antiferromagnetic contribution to the net exchange for three μ-OR bridged {Ni–Gd} dimers and also provides several important clues regarding the mechanism of magnetic coupling. Besides, MO and NBO analysis discloses the role of the empty 5d orbitals of the Gd^III ion on the mechanism of magnetic coupling. Magneto-structural correlations for Ni–O–Gd bond angles, Ni–O and Gd–O bond distances, and the Ni–O–Gd–O dihedral angle have been developed and compared with the published experimental {Ni–Gd} structures and their J values indicate that the Ni–O–Gd bond angles play a prominent role in these types of complexes. The computation has then been extended to two trinuclear {Ni^II–Gd^III–Ni^II} complexes and here both the {Ni–Gd} and the {Ni–Ni} interactions have been computed. Our calculations reveal that, for both structures studied, the two {NiGd} interactions are ferromagnetic and are similar in strength. The {Ni–Ni} interaction is antiferromagnetic in nature and our study reveals that its inclusion in fitting the magnetic data is necessary to obtain a reliable set of spin Hamiltonian parameters. Extensive magneto-structural correlations have been developed for the trinuclear complexes and the observed J trend for the trinuclear complex is similar to that of the dinuclear {Ni–Gd} complex. In addition to the structural parameters discussed above, for trinuclear complexes the twist angle between the two Ni–O–Gd planes is also an important parameter which influences the J values.

Four novel mononuclear tetrahedral cobalt(II) complexes containing exocyclic mesoionic ligands of molecular formulae [Co^II(L₁)(X)₂(MeCN)] X = Cl (1) or Br (2) and [Co^II(L₂)(X)₂(MeCN)], X = Cl (3) or Br (4) have been reported. It is found that simple substitution of L₁ (O donor in 1 and 2) by L₂ (S donor in 3 and 4) results in switching of the single ion magnetic anisotropy parameter (D) from positive to negative, with a significant change in magnitude.