Bi-Compartmental Schiff-Base with Peripheral Ester Functionalization: Synthesis and Magnetic Behavior of Bi-metallic Zn-Ln Complexes (Ln = Dy, Tb, Gd)

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A ferromagnetic Ni( ii )–Cr( iii ) single-chain magnet based on pentagonal bipyramidal building units

International audienceA Ni(II) complex harnessed in a pentagonal bipyramidal environment by a rigid N5-macrocyclic ligand (i.e. 1,3,10,12-tetramethyl-1,2,11,12-tetraaza[3](2,6)-pyridino[3](2,9)-1,10-phenanthrolinophane-2,10-diene) is shown to exhibit axial anisotropy with a ZFS D parameter in the order of −10 to −15 cm−1, and this anisotropy is not significantly changed by apical ligand substitution. Using the latter complex as a building unit, a ferromagnetic 1-D CN-bridged Ni–Cr coordination polymer with SCM behavior characterized by a barrier of magnetization reversal Ueff/kB = 54 K (37 cm−1) with τ0 = 2.28 × 10−11 s was obtained. The Cr(III) complex involved in the design was chosen to favor parallel organization of the anisotropy axes of the Ni units along the 1-D array, and thus maximize the magnetic anisotropy of the supramolecular system. A related chain compound prepared with diamagnetic [Ni(CN)4]2− units, and a trinuclear CN-bridged [NiCr2] complex enabled assessing respectively the magnetic anisotropy of Ni(II) in this coordination sphere and its exchange interaction with Cr(III) found to be ferromagnetic and of the order of 10 cm−1. The crystal structures and magnetic behaviors of all compounds are reported

Substantial exchange coupling for {Mo-NCS-M} combination: illustration for 1-D [{Mo(NCS)6}{NiL}2(NCS)]n.

An antiferromagnetic interaction of J = -51 cm(-1) has been obtained in a NCS-bridged {Mo(III)-Ni} compound (i.e. [{Mo(NCS)(6)}{NiL}(2)(NCS)](n)), a value twice as large as for the homologous {Cr(III)-Ni} derivative. The DFT calculated spin distribution on {Mo(NCS)(6)}(3-) reveals noticeable spin on the S atoms

Substantial exchange coupling for {Mo-NCS-M} combination: illustration for 1-D [{Mo(NCS)6}{NiL}2(NCS)]n.

An antiferromagnetic interaction of J = -51 cm(-1) has been obtained in a NCS-bridged {Mo(III)-Ni} compound (i.e. [{Mo(NCS)(6)}{NiL}(2)(NCS)](n)), a value twice as large as for the homologous {Cr(III)-Ni} derivative. The DFT calculated spin distribution on {Mo(NCS)(6)}(3-) reveals noticeable spin on the S atoms

Molybdenum(III) Thiocyanate- and Selenocyanate-Based One-Dimensional Heteronuclear Polymers: Coordination Affinity-Controlled Assemblage of Mixed Spin and Mixed Valence Derivatives with Ni(II) and Co(II/III)

International audienceOne-dimensional coordination polymers constructed with the 4d metallo-ligand [Mo(NCS)6]3– associated with NiII and CoII complexes are reported. The first series consists of anionic NCS-bridged [Mo-MII]− coordination polymers associated with a discrete paramagnetic complex or a diamagnetic CoIII complex acting as cations. The latter takes advantage of the coordination preference of the S-ligand for the soft 3d ions and has led to hetero-trimetallic [MoIIINiIICoIII] and mixed valence [MoIIICoIICoIII] compounds. A second series concerns neutral chains in which trinuclear [Mo M2II] units are bridged by an additional NCS anion. The soft character of the S atom was also the key to a rare example of a compound involving both high-spin and low-spin CoII centers associated with [Mo(NCS)6]. A [Mo–Ni] derivative obtained with [Mo(NCSe)6]3– has been considered in order to evaluate the effect of Se versus S on the exchange interaction. The spin distribution for selenocyanate metallo-ligand has been assessed by density functional theory calculations. The crystal structures for all compounds have been characterized, and their magnetic behaviors have been investigated. These ferrimagnetic systems are characterized by antiferromagnetic Mo-MII interactions in the range of −40 to −90 cm–1 (based on H = −JSaSb formalism) operative both with CoII and with NiII, thus demonstrating the potential of the MoIII–NCS combination for molecular systems in which exchange interactions play an important role

First magnets based on thiocyanato-bridges

2-D NCS-bridged {3d-4d} molecule-based magnets, formed by reaction of [Mo(III)(NCS)(6)](3-) with either Ni(II) or Co(II) complexes, have been found to exhibit magnetic ordering with T(C) = 39 K for {Co(3)Mo(2)} while {Ni(3)Mo(2)} has a non-magnetic ground state as a result of exact compensation by the individual sub-lattices

Magnetic anisotropy of transition metal and lanthanide ions in pentagonal bipyramidal geometry

International audienceThe magnetic anisotropy associated with a pentagonal bipyramidal (PBP) coordination sphere is examined on the basis of experimental and theoretical investigations. The origin and the characteristics of this anisotropy are discussed in relation to the electronic configuration of the metal ions. The effects of crystal field, structural distortion, and a second-coordination sphere on the observed anisotropies for transition meal and lanthanide ions are outlined. For the Ln derivatives, we focus on compounds showing SMM-like behavior (i.e. slow relaxation of their magnetization) in order to highlight the essential chemical and structural parameters for achieving strong axial anisotropy. The use of PBP complexes to impart controlled magnetic anisotropy in polynuclear species such as SMMs or SCMs is also addressed. This review of the magnetic anisotropies associated with a pentagonal bipyramidal coordination sphere for transition metal and lanthanide ions is intended to highlight some general trends that can guide chemists towards designing a compound with specific properties

Concomitant emergence of circularly polarized luminescence and single-molecule magnet behavior in chiral-at-metal Dy complex

International audienceCircularly polarized luminescence (CPL) was evidenced for the first time in single crystals of a chiral-at-metal Dy(III) single-molecule magnet. This CPL is opposite for the enantiomers and was found to appear and become stronger at lower temperatures when the relaxation of the magnetization for the Dy centers is slower. The luminescence dissymmetry factor (glum up to ±0.18) was found to have little dependence on the emission angle which permitted observing a similar CPL for an ensemble of micro-crystals of random orientations. The investigated Dy(III) compounds consist of bimetallic ZnLn units assembled by a Schiff base ligand, control of the stereochemistry of the Ln center was achieved using chiral [3-(trifluoromethylhydroxymethylene)-camphorate]− as anionic ligands. CPL was not found for the Eu(III) homologues