Search

Cyano‐bridged 4d–4f molecular nanomagnets have re‐called increasing research interests in molecular magnetism since they offer more possibilities in achieving novel nanomagnets with versatile structures and magnetic interactions. In this work, four β‐diketone ligands bearing different substitution N‐sites were designed and synthesized, namely 1‐(2‐pyridyl)‐3‐(3‐pyridyl)‐1,3‐propanedione (HL1), 1,3‐Bis (3‐pyridyl)‐1,3‐propanedione (HL2), 1‐(4‐pyridyl)‐3‐(3‐pyridyl)‐1,3‐propanedione (HL3), and 1,3‐Bis (4‐pyridyl)‐1,3‐propanedione (HL4), to tune the magnetic relaxation behaviors of cyano‐bridged {DyIIIMoV} systems. By reacting with DyCl3 ⋅ 6H2O and K4Mo(CN)8 ⋅ 2H2O, four cyano‐bridged complexes, namely {[Dy[MoV(CN)8](HL1)2(H2O)3]} ⋅ 6H2O (1), {[Dy[MoV(CN)8](HL2)(H2O)3(CH3OH)]}2 ⋅ 2CH3OH ⋅ 3H2O (2), {[Dy[MoV(CN)8](HL3)(H2O)2(CH3OH)] ⋅ H2O}n (3), and {[Dy[MoV(CN)8](HL4)2(H2O)3]} ⋅ 2H2O⋅CH3OH (4) were obtained. Structural analyses revealed that 1 and 4 are binuclear complexes, 2 has a tetragonal structure, and 3 exhibits a stair‐like polymer chain structure. The DyIII ions in all complexes have eight‐coordinated configurations with the coordination spheres DyO7N1 for 1 and 4, DyO6N2 for 2, and DyO5N3 for 3. Magnetic measurements indicate that 1 is a zero‐field single‐molecule magnet (SMM) and complexes 2–4 are field‐induced SMMs, with complex 4 featuring a two‐step relaxation process. The magnetic characterizations and ab initio calculations revealed that changing the N‐sites in the β‐diketone ligands can effectively alter the structures and magnetic properties of cyano‐bridged 4d–4f nanomagnets by adjusting the coordination environments of the DyIII centers. [ABSTRACT FROM AUTHOR]

Using a novel tricompartmental hydrazone ligand, a set of trinuclear Dy3 complexes has been isolated and structurally characterized. Complexes Dy3 ⋅ Cl, Dy3 ⋅ Br, and Dy3 ⋅ ClO4 feature a similar overall topology but different anions (Cl−, Br−, or ClO4−) in combination with exogenous OH− and solvent co‐ligands, which is found to translate into very different magnetic properties. Complex Dy3 ⋅ Cl shows a double relaxation process with fast quantum tunneling of the magnetization, probably related to the structural disorder of μ2‐OH− and μ2‐Cl− co‐ligands. Relaxation of the magnetization is slowed down for Dy3 ⋅ Br and Dy3 ⋅ ClO4, which do not show any structural disorder. In particular, fast quantum tunneling is suppressed in case of Dy3 ⋅ ClO4, resulting in an energy barrier of 341 K and magnetic hysteresis up to 3.5 K; this makes Dy3 ⋅ ClO4 one of the most robust air‐stable trinuclear SMMs. Magneto‐structural relationships of the three complexes are analyzed and rationalized with the help of CASSCF/RASSI‐SO calculations. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: Precise modulation of the magnetic anisotropy of metal ions remains highly important for the development of high–performance single‐molecule magnets (SMMs). We herein reported the synthetic, structural, spectral, magnetic, and computational studies on four mononuclear CoII complexes in a distorted octahedral environment. The change of the organosulfonate anions triggers significant modification of the distorted octahedral CoN6 coordination sphere, which enables us to tackle the influence of the structural distortion on the magnetic anisotropy in these complexes. Magnetic measurements revealed that the four complexes possess easy–plane magnetic anisotropy with large and positive zero‐field splitting parameters, which decrease with the increasing distortion of the pseudo–octahedral CoII coordination geometry. This correlation was further confirmed by high–frequency/–field EPR (HF–EPR) spectra and theoretical calculations. Dynamic magnetic susceptibility measurements indicate that these complexes both exhibit slow magnetic relaxation under an external dc field, indicating the field‐induced single‐ion magnets (SIMs) of the four complexes. These results indicate that structural distortion plays an important role in the magnetic anisotropy of CoII complexes and should be carefully considered in the design of molecular complexes with high magnetic anisotropy. [ABSTRACT FROM AUTHOR]

Three rare isostructural heterometallic complexes [Na2{Ln4(μ3‐OH)2(ppt)4(Hppt)2(OAc)2}(DMF)4] ⋅ xH2O (H2ppt=3‐(2‐hydroxyphenyl)‐5‐(pyrazin‐2‐yl)‐1,2,4‐triazole, x=2.5, Ln=Dy (1); x=2, Ln=Er (2); x=0, Ln=Yb (3)) have been obtained. The structural analysis displayed that two NaI and four LnIII ions were linked together through N−N groups and O atoms to form a metallmacrocycle with the connectivity pattern [Dy−O−Na−N−N−Dy−O]2. Such cases possess rare hexametallic ring, which further displays one tetrametallic and two trimetallic cyclic units. Magnetic measurements reveal single‐molecule magnet (SMM) behavior for 1 with the effective energy barrier of 51.6 K and pre‐exponential factor of 6.16×10−6 s deduced from frequency‐dependent magnetic susceptibilities. Ab initio calculations prove that the weak ferromagnetic coupling mainly originats from the dipolar interaction. The transversal magnetic moments in the ground Kramers could suppressed the quantum tunneling of magnetization. [ABSTRACT FROM AUTHOR]

Tuning the magnetic anisotropy of metal ions remains highly interesting in the design of improved single‐molecule magnets (SMMs). We herein report synthetic, structural, magnetic, and computational studies of four mononuclear CoII complexes, namely [Co(hfac)2(MeCN)2] (1), [Co(hfac)2(Spy)2] (2), [Co(hfac)2(MBIm)2] (3), and [Co(hfac)2(DMF)2] (4) (MeCN=acetonitrile, hfac=hexafluoroacetylacetone, Spy=4‐styrylpyridine, MbIm=5,6‐dimethylbenzimidazole, DMF=N,N‐dimethylformamide), with distorted octahedral geometry constructed from hexafluoroacetylacetone (hfac) and various axial ligands. By a building block approach, complexes 2–4 were synthesized by recrystallization of the starting material of 1 from various ligands containing solution. Magnetic and theoretical studies reveal that 1–4 possess large positive D values and relative small E parameters, indicating easy‐plane magnetic anisotropy with significant rhombic anisotropy in 1–4. Dynamic alternative current (ac) magnetic susceptibility measurements indicate that these complexes exhibit slow magnetic relaxation under external fields, suggesting field‐induced single‐ion magnets (SIMs) of 1–4. These results provide a promising platform to achieve fine tuning of magnetic anisotropy through varying the axial ligands based on Co(II) bis(hexafluoroacetylacetonate) complexes. [ABSTRACT FROM AUTHOR]

For a long time, the cobalt(II) complex ([Co(napy)4](ClO4)2) (napy=1, 8‐naphthyridine) has been considered as an eight‐coordinate complex without any structural proof. After careful considerations, two complexes [Co(napy)2Cl2] (1) and [Co(napy)4](ClO4)2 (2) based on the bidentate ligand napy were synthesized and structurally characterized. X‐ray single‐crystal structural determination showed that the cobalt(II) center in [Co(napy)2Cl2] (1) is four‐coordinate with a tetrahedral geometry (Td), while [Co(napy)4](ClO4)2 (2) is seven‐coordinate rather than eight‐coordinate with a capped trigonal prism geometry (C2v). Direct‐current (dc) magnetic data revealed that complexes 1 and 2 possess positive zero‐field splitting (ZFS) parameters of 11.08 and 25.30 cm−1, respectively, with easy‐plane magnetic anisotropy. Alternating current(ac) susceptibility measurements revealed that both complexes showed slow magnetic relaxation behaviour. Theoretical calculations demonstrated that the presence of easy‐plane magnetic anisotropy (D>0) for complexes 1 and 2 is in agreement with the experimental data. Furthermore, these results pave the way to obtain four‐coordinate and seven‐coordinate cobalt(II) single‐ion magnets (SIMs) by using a bidentate ligand. [ABSTRACT FROM AUTHOR]

The structural characterization and magnetic studies of three mononuclear MnIII complexes based on the dibenzoylmethanido (dbm-) ligand, Mn(dbm)3 ( 1) and [Mn(dbm)2(L)2](ClO4) (L = dimethyl sulfoxide, 2; L = pyridine, 3), are reported. The MnIII ions are in an axially elongated octahedral coordination geometry. The axial zero-field-splitting parameters D, ranging from -3.42 to -4.52 cm-1 for the three complexes, were obtained by fitting magnetic-susceptibility and magnetization data. Ab initio calculations also show the axial magnetic anisotropy in the molecules of 1- 3. With an applied dc field, the ac susceptibility measurements reveal slow magnetic relaxation in 1- 3. The possible relationship between the structures and the magnetic properties in these complexes are discussed. [ABSTRACT FROM AUTHOR]