Search

Two families of lanthanide metal–organic frameworks (Ln-MOFs), namely {[Ln2L2(DMF)4]·xDMF·yH2O}n (Ln = Ce(1), Pr(2), Sm(3), Eu(4), Gd(5); x = 0, 1; y = 0, 1) and {[Ln2L2(H2O)2.5]}n (Ln = Dy(6), Ho(7)), have been solvothermally synthesized based on the semi-rigid tripodal ligand 5-(4-carboxybenzyloxy)isophthalic acid (H3L). Utilizing the excellent luminescence property and water stability, Eu(4) exhibited efficient luminescence responses toward Fe3+, Cr2O72−, and NFT/NZF antibiotics in aqueous medium with high sensitivity and selectivity. The detection limits (LODs) are 3.69 μM for Fe3+ ion, 4.01 μM for Cr2O72− anion and 9.92 μM/11.4 μM for NFT/NZF antibiotics, suggesting that Eu(4) is a good and simple multifunctional luminescent sensor. Additionally, the Gd(III) ions exhibit a weak antiferromagnetic interaction in the dinuclear SBUs of Gd(5), and Dy(6) shows slow magnetic relaxation behaviors under zero dc field. [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]

Using dicyanamides, three two-dimensional coordination polymers (CPs) [CuII(valdmpn)LnIII(μ-1,5-dca)3]n (LnIII = Gd (1), Tb (2) and Dy (3)) were synthesized and characterized. Compounds 1–3 are two-dimensional coordination polymers bridged with μ-1,5-dca connecting the [CuII(valdmpn)LnIII]3+ units. In compounds 1–3, the Cu atom was pentacoordinated with an elongated square pyramidal (C4v) geometry, while the Ln (Gd, Tb and Dy) atom was nine-coordinated with a muffin (Cs) geometry. Detailed direct current (dc) magnetic measurements and simulated data demonstrated the existence of a ferromagnetic CuII–GdIII interaction for compound 1. Alternating current (ac) magnetic measurements revealed that compound 2 exhibited a slow magnetic relaxation behavior under a zero dc field. A hysteresis loop at 1.8 K was observed in compound 2, characteristic of typical single-molecule magnets (SMMs). However, compound 3 showed a slow magnetic relaxation behavior under a dc field. This system provides a good opportunity to determine the character of the Ln(III) ions incorporated and/or the origin of the slow magnetic relaxation behavior. [ABSTRACT FROM AUTHOR]

Using an asymmetric tetradentate ligand N-((6-(1H-pyrazol-1-yl)pyridin-2-yl)methylene)benzohydrazide (pypzbeyz), two high-coordinate 3d transition metal compounds [CoII(pypzbeyz)(NO3)2] (1) and [FeII(pypzbeyz)2](BF4)2(CH3CN) (2) have been synthesized and characterized by structural and magnetic measurements. X-ray crystallographic analyses revealed that compound 1 is seven-coordinate with a distorted pentagonal bipyramidal geometry (pseudo-D5h) and compound 2 is eight-coordinate with a triangular dodecahedral geometry (pseudo-D2d). Direct current (dc) magnetic susceptibilities revealed that compound 1 shows easy-plane magnetic anisotropy (D = +29.9 cm−1, E = 0.31 cm−1) and 2 shows easy-axis magnetic anisotropy (D = −6.6 cm−1, E = 0.02 cm−1). Alternating current (ac) magnetic measurements indicate that both compounds exhibit field-induced slow magnetic relaxation behavior. Furthermore, ab initio calculations also demonstrate that compound 1 presents a strong easy-plane magnetic anisotropy and 2 presents an easy-axis magnetic anisotropy, which are further identified by the calculated orientations of the local magnetic axes. These results demonstrate an effective way to achieve the targeted synthesis of high-coordinate 3d SIMs. [ABSTRACT FROM AUTHOR]

The reaction of Cu(valdmpn) (H2valdmpn = N,N′-bis-(3-methoxysalicylidene)-1,3-diamino-2,2-dimethylpropane), LnCl3·nH2O (Ln = La(1), Ce (2), Pr(3), Nd(4), Sm(5), Eu(6), Gd(7), Tb(8), Dy(9), Ho(10), Er(11), Tm(12), Yb(13), Lu(14)) and NaN3 in methanol led to a whole series of heterometallic CuII–LnIII complexes. The basic structural components of these complexes are the [CuII(valdmpn)LnIII] units with a compartmental Schiff-base ligand. These [CuIILnIII] units were then further connected by the end-on (EO) azides between the Ln3+ centers to form tetranuclear {[CuLn](μ-N3)n[LnCu]} motifs, where n is 3 for the complexes of larger radii lanthanides (1CuLa to 5CuSm) and 2 for the complexes of smaller radii lanthanides (6CuEu to 14CuLu). While compounds 6CuEu to 14CuLu remain isolated tetranuclear clusters, compounds 1CuLa to 5CuSm are one-dimensional chains where tetranuclear motifs are further connected by end-to-end (EE) azides between CuII and LnIII centers. Direct current (dc) magnetic susceptibilities have been measured in the range of 1.8–300 K for all complexes, revealing the different nature of magnetic interactions between the spin centers. Among them, dominant ferromagnetic interactions were found in compounds 7CuGd, 8CuTb and 9CuDy. Alternating current (ac) magnetic measurements performed on 8CuTb, 9CuDy, and 10CuHo demonstrated the presence of slow magnetic relaxation under zero applied dc field. The spin relaxation barrier Ueff was determined to be 19.54 cm−1 (28.12 K) and 10.34 cm−1 (14.87 K) for compounds 8CuTb and 9CuDy. The SMM behavior of 8CuTb was further confirmed by the presence of magnetic hysteresis loops; while no hysteresis loop was observed for 9CuDy and 10CuHo. These results demonstrated that azido-bridged copper(ii)–lanthanide(iii) complexes could be synthesized successfully despite the generally weak azido–lanthanide interaction. [ABSTRACT FROM AUTHOR]

Two one-dimensional (1-D) chain complexes with pentagonal bipyramidal DyIII centers have been synthesized and magnetically characterized. Field-induced single molecule magnet behavior has been revealed in both compounds, which is still rarely reported in a lanthanide compound with a pentagonal bipyramidal coordination geometry. Their crystal field parameters and orientations of the magnetic easy axes were obtained from the simulation of the magnetic data and the electrostatic model calculation. [ABSTRACT FROM AUTHOR]

Reactions of a perfluorinated ligand, tetrafluorophthalic acid (o-H2BDC-F4), with KNO3and M(OAc)2(M = Co, Mn) led to the formation of perfluorinated metal-organic frameworks [CoK2(o-BDC-F4)2(MeOH)]n(1) and [MnK2(o-BDC-F4)2(DMF)]n(2). The structures were characterized by elemental analyses, infrared spectra, and single-crystal X-ray diffraction. Both complexes show similar 2-D heterometallic-organic frameworks containing unusual layered inorganic K–O–M connectivities. For1and2,orthofluorines ofo-BDC-F4are bound to the K(I) ion, while the other fluorines participate in the linkage of adjacent coordination layers forming 3-D supramolecular architectures via intermolecular FF interactions. Spectroscopic, thermal, and fluorescence properties have been investigated. Variable-temperature magnetic susceptibility studies indicate that1displays a weak antiferromagnetic effect between adjacent Co(II) ions. [ABSTRACT FROM AUTHOR]

Magneto-structural relationships were studied experimentally and theoretically for two enantiomorphic tetranuclear [CuTb]2 SMMs. For the first time, the determination of the magnetic anisotropy axis of an individual magnetic ion, Tb3+, was achieved in a polynuclear Tb3+-based SMM. [ABSTRACT FROM AUTHOR]

A ligand 1,3-bis(1-benzylbenzimidazol-2-yl)-2-oxopropane (Bobb) and the zinc(II) complex, [Zn(Bobb)2](picrate)2 · 2DMF, were synthesized and characterized by elemental analyses, electrical conductivities, IR, and UV. The crystal structures of the ligand and the zinc complex have been determined by single crystal X-ray diffraction. The ligand displays a V-shaped configuration and the Zn(II) cation is six-coordinate by four nitrogens and two oxygens from Bobb. The N4O2 donor set is a distorted octahedron. [ABSTRACT FROM AUTHOR]

For a long time, the cobalt(II) complex ([Co(napy) 4 ](ClO 4 ) 2 ) (napy=1, 8-naphthyridine) has been considered as an eight-coordinate complex without any structural proof. After careful considerations, two complexes [Co(napy) 2 Cl 2 ] (1) and [Co(napy) 4 ](ClO 4 ) 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) 2 Cl 2 ] (1) is four-coordinate with a tetrahedral geometry (T d ), while [Co(napy) 4 ](ClO 4 ) 2 (2) is seven-coordinate rather than eight-coordinate with a capped trigonal prism geometry (C 2v ). 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., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)