Slow Relaxation of Magnetization in an Isostructural Series of Zinc–Lanthanide Complexes: An Integrated EPR and AC Susceptibility Study

We report the synthesis, structure, and spectroscopic and dynamic magnetic properties of a series of heterodinuclear complexes, [ZnLn(LH4 )2 ](NO3 )3 ⋅6 H2 O (Ln=Nd, Tb, Dy, Ho, Er, and Yb), with the singly deprotonated form of a new compartmentalized Schiff-base ligand, LH5 . The Ln(III) ions in these systems show a distorted square-antiprism geometry with an LnO8 coordination sphere. EPR spectroscopy and DC magnetic studies have shown that the anisotropic nature of the complexes is far more complicated than predicted on the basis of a simple electrostatic model. Among the investigated systems, only the Dy(III) derivative showed single-ion magnet behavior, in zero and an applied magnetic field, both in pure polycrystalline samples and in a series of polycrystalline samples with different degrees of dilution at the single-crystal level in the isostructural Y(III) derivative. The rich dynamics observed as functions of frequency, field, and temperature reveals that multiple relaxation mechanisms are at play, resulting in a barrier of 189 cm(-1) , which is among the highest reported for a dinuclear Zn-Dy system. Analysis of the dynamic behavior as a function of dilution degree further evidenced the persistence of non-negligible intermolecular interactions, even at the lowest concentration of 1 %

Dimers and chains of {3d-4f} single molecule magnets constructed from heterobimetallic tectons.

International audienceA tetranuclear complex and a 1-D coordination polymer with a ladder-like topology have been obtained by connecting [Ni(II)Dy(III)] nodes with dicarboxylato ligands: [Ni₂(valpn)₂Dy₂(III)(pdca)₂(NO₃)(H₂O)₆](NO₃)*4H₂O 1, and (∞)¹[Ni₂(H₂O)₂(valpn)₂Dy₂(tfa)₃]*4CH₃CN 2 (valpn²⁻ = the dianion of the Schiff base resulting from reacting o-vanillin with 1,3-propanediamine; pdca²⁻ = the dianion of 2,6-pyridinedicarboxylic acid; tfa²⁻ = the dianion of the terephthalic acid). The magnetic measurements show a ferromagnetic interaction between Ni(II) and Dy(III), and that both compounds behave like SMM with strong tunnelling. The barrier of 2 (17.4 K) is higher than that of 1 (13.6 K)

A missing high-spin molecule in the family of cyano-bridged heptanuclear heterometal complexes, [(LCuII)6FeIII(CN)6]3+, and its CoIII and CrIII analogues, accompanied in the crystal by a novel octameric water cluster

Three isostructural cyano-bridged heptanuclear complexes, [{CuII(saldmen)(H2O)}6{MIII(CN)6}](ClO4)3$\cdotp$8H2O (M = FeIII 2; CoIII, 3; CrIII 4), have been obtained by reacting the binuclear copper(II) complex, [Cu2(saldmen)2(mu-H2O)(H2O)2](ClO4)2$\cdotp$2H2O 1, with K3[Co(CN)6], K4[Fe(CN)6], and, respectively, K3[Cr(CN)6] (Hsaldmen is the Schiff base resulted from the condensation of salicylaldehyde with N,N-dimethylethylenediamine). A unique octameric water cluster, with bicyclo[2,2,2]octane-like structure, is sandwiched between the heptanuclear cations in 2, 3 and 4. The cryomagnetic investigations of compounds 2 and 4 reveal ferromagnetic couplings of the central FeIII or CrIII ions with the CuII ions (JCuFe = +0.87 cm-1, JCuCr = +30.4 cm-1). The intramolecular Cu-Cu exchange interaction in 3, across the diamagnetic cobalt(III) ion, is -0.3 cm-1. The solid-state1H-NMR spectra of compounds 2 and 3 have been investigated

Supramolecular Bimetallic Systems Constructed through Π-Π Stacking and hydrogen Bond Interactions

Five new bimetallic compounds have been synthesized and crystallographically characterized: [{Cu(acac)(phen)}2{Ni(CN)4}] * H2O (1), [{Cu(acac)(bipy)}2{Ni(CN)4}] (2); [Cu(acac)(bipy)(H2O)]2[Ni(CN)4] (3), [(Cu(acac)(Me2bipy)]2[Ni(mnt)2] (4), [Cu(acac)(bipy)][Ni(mnt)2] (5) (Me2bipy=4,4′‐dimethyl‐2,2′‐bipyridine; mnt=maleonitriledithiolate). The molecular structures of complexes 1 and 2 are similar: they consist of neutral [{Cu(acac)(BB)}2{Ni(CN)4}] entities, which result by connecting two [Cu(acac)(BB)]+ ions through two trans‐cyano groups from the bridging ligand, [Ni(CN)4]2− (BB=1,10‐phenanthroline and, respectively, 2,2′‐bipyridine). The intermolecular π‐π stacking interactions established between the organic ligands attached to the copper ions lead to supramolecular chains. In the ionic compound 3, the [Ni(CN)4]2− anions and the [Cu(acac)(bipy)(H2O)]+ cations generate a 3D supramolecular architecture by convolution of hydrogen bonding with π‐π stacking interactions. The crystal structure of compound 4, [(Cu(acac)(Me2bipy)]2[Ni(mnt)2], consists of cationic, [(Cu(acac)(Me2bipy)]+, and anionic species, [Ni(mnt)2]2−, which are connected through Cu *** S interactions, resulting in supramolecular {CuNiCu} trimers. Crystal 5 is an ionic compound containing [Cu(acac)(bipy)]+ and [Ni(mnt)2]− ions

Cyanido-bridged heterometallic oligonuclear complexes and coordination polymers constructed using tridentate schiff-base ligands: Synthesis, crystal structures, and magnetic and luminescence properties. A new trimeric water cluster

Five new Cu-II-Ag-I, Cu-II-Cu-I, and Zn-II-Au-I complexes have been obtained starting from copper(II) and, respectively, zinc(II) complexes with (NNO) Schiff-base ligands: [{(H2O)(saldmen)Cu}-{(NC)Ag(CN)}] 1, (1)(infinity)[{Cu-2(salaepipH)(2)(mu-CN)}{mu-[Ag(CN)(2)]}]-(ClO4)(2)center dot 4H(2)O 2, (1)(infinity)[{(salaepy)-Cu}{mu-[Ag(CN)(2)]}] 3, (1)(infinity)[{(salaepy)-Cu}{mu-[Cu(CN)(2)]}] 4, [(salaepy)Zn-NCAuCN](2)center dot H2O 5. The Schiffbase ligands (Hsaldmen, Hsalaepip, Hsalaepy) have been obtained by reacting the salicylaldehyde with N,N-dimethyletylenediamine, N-(2-aminoethyl)piperazine, and, respectively, 2-(2-aminoethyl)-pyridine. The structures of compounds 1 and 5 consist of discrete bi- and, respectively, tetranuclear species. The analysis of the packing diagram for crystal 1 reveals the formation of supramolecular double chains sustained by hydrogen-bond interactions involving the aqua ligand. Compounds 2, 3, and 4 are one-dimensional coordination polymers. The structure of 2 consists of chains constructed from {Cu(salaepip)} nodes bridged alternatively by [Ag(CN)(2)](-) and CN- ions, resulted from the partial decomposition of the silver complex. The 3-D architecture of the crystal is constructed from 1-D coordination polymers, [{Cu-2(salaepipH)(2)(mu-CN)}{mu-[Ag(CN)(2)]}](n)(2n+), which are connected by three water molecules that form a triangular water cluster, resulting in a scaffold-like structure with large channels. Compounds 3 and 4 are similar. Their structures can be described as resulting from zigzag anionic chains, [M(CN)(2)](n)(n-) (M = Ag-I or Cu-I), with three-coordinated silver(I) or copper(I) ions, to which monocationic complexes, {(salaepy)Cu}, are attached. The cryomagnetic properties of compounds 1 and 2 have been investigated. Weak antiferromagnetic interactions (J = -2.8 cm(-1), H = -jS(1)S(2)) mediated by hydrogen bonds are observed for compound 1. The cyanido bridge connecting the basal coordination sites of two copper(II) ions in 2 mediates a moderate antiferromagnetic coupling (J = 55.2 cm(-1)). Compound 5 exhibits blue luminescence (lambda = 464 nm, lambda(ex) = 400 nm)

Octanuclear [Ni(II)₄Ln(III)₄] complexes. Synthesis, crystal structures and magnetocaloric properties

Two original heterooctanuclear [Ni(II)4Ln(III)4] complexes (Ln(III) = Sm(III), Gd(III)) have been obtained starting from the [Ni(II)(valpn)(H2O)2] mononuclear precursor [H2valpn = 1,3-propanediylbis(2-iminomethylene-6-methoxy-phenol)] and the corresponding lanthanide nitrates, in the presence of azide anions, through slow capture of atmospheric CO2. Three weak and competitive exchange interactions, J(GdGd), J(GdNi), J(NiNi), make the ground state of this magnetic system degenerate at cryogenic temperature and zero field. This, along with the high spin of Gd(III), lead to a significant magnetocaloric effect spread in the temperature range 1 to 20 K (ΔSm[0-7 T, 3.5 K] = 19 J kg(-1) K(-1))

A heterotrimetallic 3d-3d '-4f single chain magnet constructed from anisotropic high-spin 3d-4f nodes and paramagnetic spacers

International audienceBy connecting [LCuTb](3+) nodes with [Fe(CN)(6)](3-) spacers a 1-D coordination polymer with slow relaxation of magnetization is obtained (L(2-) is the N, N'-propylene-bis(3-methoxy-salicylideneiminato) anion)