Butterfly magnet: The replacement of diamagnetic CoIII for CrIII in a 3d‐4f butterfly complex results in vastly improved single‐molecule magnet properties. Longer relaxation times are found, with magnetic hysteresis observed. This is due to exchange interactions between the DyIII and CrIII ions, resulting in a multilevel exchange barrier with significantly reduced quantum tunneling of the magnetization.

Field induced single-molecule-magnet behaviour is observed for both a heterodinuclear [ZnDy(L(-))2](3+) complex (1) and a mononuclear [Dy(HL)2](3+) complex (2), with effective energy barriers of 83 cm(-1) and 16 cm(-1), respectively. Insights into the relaxation mechanism(s) and barrier heights are provided via ab initio and DFT calculations. Our findings reveal an interesting observation that the U(eff) of SMMs can be enhanced by incorporating diamagnetic metal ions.

A family of mononuclear tetrahedral cobalt(II) thiourea complexes, [Co(L)](NO) (1) and [Co(L)](ClO) where x = 2 (2), 3 (3), 4 (4) (where L = thiourea, L = 1,3-dibutylthiourea, L = 1,3-phenylethylthiourea, and L = 1,1,3,3-tetramethylthiourea), has been synthesized using a rationally designed synthetic approach, with the aim of stabilizing an Ising-type magnetic anisotropy (-D). On the basis of direct-current, alternating-current, and hysteresis magnetic measurements and theoretical calculations, we have identified the factors that govern the sign and magnitude of D and ultimately the ability to design a single-ion magnet for a tetrahedral cobalt(II) ion. To better understand the magnetization relaxation dynamics, particularly for complexes 1 and 2, dilution experiments were performed using their diamagnetic analogues, which are characterized by single-crystal X-ray diffraction with the general molecular formulas of [Zn(L)](NO) (5) and [Zn(L)](ClO) (6). Interestingly, intermolecular interactions are shown to play a role in quenching the quantum tunneling of magnetization in zero field, as evidenced in the hysteresis loop of 1. Complex 2 exhibits the largest U value of 62 cm and reveals open hysteresis loops below 4 K. Furthermore, the influence of the hyperfine interaction on the magnetization relaxation dynamics is witnessed in the hysteresis loops, allowing us to determine the electron/nuclear spin S(Co) = //I(Co) = / hyperfine coupling constant of 550 MHz, a method ideally suited to determine the hyperfine coupling constant of highly anisotropic metal ions stabilized with large D value, which are otherwise hard to determine by conventional methods such as electron paramagnetic resonance.

The use of an amino-pyridyl substituted b-diketone, N-(2-pyridyl)-ketoacetamide (paaH), has allowed for the isolation of two new families of isostructural mononuclear lanthanide complexes with general formulae: [Ln(paaH*) 2 (H 2 O) 4 ][Cl] 3 $2H 2 O (Ln ¼ Gd (1), Tb (2), Dy (3), Ho (4), Er (5) and Y (6)) and [Ln(paaH*) 2 (NO 3 ) 2 (MeOH)][NO 3 ] (Ln ¼ Tb (7), Dy (8), Ho (9) and Er (10)). The dysprosium members of each family (3 and 8) show interesting slow magnetic relaxation features. Compound 3 displays Single Molecule Magnet (SMM) behaviour in zero DC field with an energy barrier to thermal relaxation of E a ¼ 177(4) K ( 123(2) cm À1 ) with s 0 ¼ 2.5(8) Â 10 À7 s, while compound 8 shows slow relaxation of the magnetization under an optimum DC field of 0.2 T with an energy barrier to thermal relaxation of E a ¼ 64 K (44 cm À1 ) with s 0 ¼ 6.2 Â 10 À7 s. Ab initio multiconfigurational calculations of the Complete Active Space type have been employed to elucidate the electronic and magnetic structure of the lowlying energy levels of compounds 2-5 and 8. The orientation of the anisotropic magnetic moments for compounds 2-5 are rationalized using a clear and succinct, chemically intuitive method based on the electrostatic repulsion of the aspherical electron density distributions of the lanthanides.

Using a heterometallic approach the synthesis, structures, and magnetic properties are reported for the complexes [Ln(III)(2)Co(III)(2)(OMe)(2)(teaH)(2)(O(2)CPh)(4)(MeOH)(4)](NO(3))(2)·MeOH·H(2)O {Ln = Gd (1a), Tb (2a), and Dy (3a)} and [Ln(III)(2)Co(III)(2)(OMe)(2)(teaH)(2)(O(2)CPh)(4)(MeOH)(2)(NO(3))(2)]·MeOH·H(2)O {Ln = Gd (1b), Tb (2b), and Dy (3b)}. Both compounds for the respective lanthanide ions are found to be isolated within the same crystal. Each Ln(III) dinuclear unit is incorporated within a diamagnetic Co(III)/organic ligand backbone utilizing triethanolamine and benzoic acid as bridging ligands. Magnetic studies reveal an absence of any observable coupling interaction for the Gd case. The Dy analogue displays single molecule magnet (SMM) behavior with a large energy barrier to magnetization reversal of 88.8 K, and the quantum tunneling of the magnetization (QTM) is effectively suppressed because of the nonmagnetic exchange ground state of the molecule. Dilution of the Dy complex into an isostructural diamagnetic yttrium matrix allowed us to determine aspects of the relaxation mechanism within the system.