Search

Abstract: A novel magnetic coupling is observed in a unpublished crystal that consists of a mono-nuclear manganese(II) complex, namely, [Mn(DPP)(NCS)2] (DPP=2-(3,5-dimethyl-1H-pyrazol-1-yl)-1,10-phenanthroline), in which neutral DPP molecule functions as tridentate chelated ligand. In the complex Mn(II) ion assumes a distorted trigonal bipyramidal geometry and in the crystal there is a π–π stacking interaction between the adjacent complexes, which involves pyridyl ring and the symmetry-related pyrazolyl ring and pyridyl ring. The fitting for the data of the variable-temperature magnetic susceptibilities with infinite uniform Mn(II) chain formula gave the magnetic coupling constant J =−0.11cm−1, and theoretical calculations reveal that there exists a very weak anti-ferromagnetic coupling between the adjacent Mn(II) ions with J =−0.02cm−1. The magnetic coupling sign is explained based on McConnell I spin-polarization mechanism with the analysis of the spin density population and the factors that dominate the magnetic coupling magnitude. [Copyright &y& Elsevier]

Abstract A series of dinuclear lanthanide complexes bridged by three pyridine- N -oxide (PyNO) ligands with formula [Dy 2 (hfac) 6 (4-cpyNO) 3 ]·4H 2 O (Dy1), [Gd 2 (hfac) 6 (4-cpyNO) 3 ]·4H 2 O (Gd1), [Dy 2 (hfac) 6 (4-mepyNO) 3 ] (Dy2), [Gd 2 (hfac) 6 (4-mepyNO) 3 ] (Gd2) (hfac− = hexafluoroacetylacetonate, 4-cpyNO = 4-cyanopyridine N -oxide, 4-mepyNO = 4-Methylpyridine N -oxide), and series of dinuclear lanthanide complexes bridged by two PyNO ligands with formula [Dy 2 (hfac) 6 (4-cpyNO) 2 ] (Dy3), [Y 2 (hfac) 6 (4-cpyNO) 2 ] (Y1), [Gd 2 (hfac) 6 (4-cpyNO) 2 ] (Gd3), [Dy 2 (hfac) 6 (4-mepyNO) 2 ] (Dy4), [Y 2 (hfac) 6 (4-mepyNO) 2 ] (Y2), [Gd 2 (hfac) 6 (4-mepyNO) 2 ] (Gd4), were structurally and magnetically characterized. The crystal structures revealed that pyridine- N -oxide serves as an effective bridge to link two Ln(III) centers, and periphery β-diketonate ligands complete the coordination sphere. The number of PyNO bridge can be rationally controlled by the stoichiometric ratio of reagents, which leads to different local coordination models and intramolecular Ln-Ln distances. Furthermore, elaborate modulation on the strength of magnetic coupling transmitted by PyNO bridge was successfully carried out by introducing electron-donating or -withdrawing substituents on the bridge ligand backbone. Magnetic measurements revealed that complex Dy3 displayed significant double zero-field slow magnetic relaxation process, while Dy1 and Dy2 showed field-induced SMM behavior. Significantly enhanced SMMs performance was observed in Dy4 with a hysteresis temperature of 2.5 K. The distinct slow magnetic relaxation behaviors were strongly related to their different individual Dy(III) ion magnetic anisotropy and Dy(III)-Dy(III) coupling, which were further confirmed by ab initio calculation. Graphical abstract The favourable Dy(III)-Dy(III) coupling in combination with the individual coordination symmetry after altering the number of pyridine- N -oxide bridges result in the improvement from field-induced SMMs to the zero-field SMMs. Image 1 Highlights • The field-induced SMMs to the zero-field SMMs transformation can be realized by modulating the number of bridges. • The pyridine-N-oxide serves as an effective bridge to transmit weak magnetic exchange interactions between the Ln(III) ions. • Introduction of electron-donating or withdrawing substituent on the bridges can influence the magnetic relaxation properties. [ABSTRACT FROM AUTHOR]

• Two trinuclear compounds 1 and 2 were synthesized and characterized. • Antiferromagnetic interactions were determined in compound 2. • Complex 1 displays field-induced single-molecule magnet (SMM) behavior. Two trinuclear complexes of formulae [Dy 3 (µ 3- H 2 O)(hmp) 3 (CH 3 COO) 3 ] (1) and [Gd 3 (µ 3 -H 2 O)(hmp) 3 (CH 3 COO) 3 ] (2) were synthesized by employing Dy(CH 3 COO) 3 ·6H 2 O and Gd(CH 3 COO) 3 ·6H 2 O as lanthanide sources and a Schiff-base H 2 hmp (H 2 hmp = 2-(((2-hydroxy-3-methoxybenzyl)imino)methyl)-5-methoxyphenol) as a ligand. Single crystal X-ray diffraction analyses reveal that compounds 1 and 2 are isostructural. The three LnIII ions are bridged by three doubly-deprotonated Schiff-base ligands hmp2−, three acetate ions and one µ 3 -H 2 O molecule, forming a regular triangle structure (Ln...Ln...Ln angles of 60°, and Ln...Ln distances of 3.812 Å for 1 , and 3.838 Å for 2). Magnetic property studies for 1 and 2 indicate that complex 1 displays field-induced single-molecule magnet (SMM) behavior, and there are weak antiferromagnetic interactions among three GdIII ions in complex 2. The main magnetic axes on DyⅢ ions of 1 are calculated by complete-active-space self-consistent field (CASSCF) calculations. Two complexes [Dy 3 (µ 3- H 2 O)(hmp) 3 (CH 3 COO) 3 ] (1) and [Gd 3 (µ 3 -H 2 O)(hmp) 3 (CH 3 COO) 3 ] (2) were synthesized and characterized. Compound 1 displays field-induced single-molecule magnet (SMM) behavior. [Display omitted] [ABSTRACT FROM AUTHOR]