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The systematic investigation of the general reaction scheme DyIII/LH2, where LH2is the organic ligand 2,6-diacetylpyridine bis(picolinoylhydrazone), has led to a family of mono-, di-, and tetranuclear DyIIIcomplexes.

In addition to previously studied {CuII3Gd6}, {CuII8Gd4}, {CuII15Ln7} and {CuII4Ln8} coordination clusters (Ln = trivalent lanthanide) containing pdm2− or Hpdm− ligands (H2pdm = pyridine-2,6-dimethanol) and ancillary carboxylate groups (RCO2−), the present work reports the synthesis and study of three new members of a fifth family of such complexes. Compounds [Cu5Ln4O2(OMe)4(NO3)4(O2CCH2But)2(pdm)4(MeOH)2] (Ln = Dy, 1; Ln = Tb, 2; Ln = Ho, 3) were prepared from the reaction of Ln(NO3)3·xH2O (x = 5, 6), CuX2·yH2O (X = ClO4, Cl, NO3; y = 6, 2 and 3, respectively), H2pdm, ButCH2CO2H and Et3N (2 : 2.5 : 2 : 1 : 9) in MeCN/MeOH. Rather surprisingly, the copper(II)/yttrium(III) analogue has a slightly different composition, i.e. [Cu5Y4O2(OMe)4(NO3)2(O2CCH2But)4(pdm)4(MeOH)2] (4). The structures of 1·4MeCN·1.5MeOH and 4·2MeOH were solved by single-crystal X-ray crystallography. The five CuII and four DyIII centres in 1 are held together by two μ5-O2−, four μ-MeO−, two syn,syn η1:η1:μ ButCH2CO2−, four η2:η1:η2:μ3 pdm2− (each of these groups chelates a CuII atom and simultaneously bridges two DyIII atoms through its two –CH2O− arms) and two μ-MeOH ligands. The four terminal nitrato groups each chelate (η1:η1) a DyIII centre. The five CuII atoms are co-planar (by symmetry) forming a bow-tie arrangement; the four outer CuII atoms form a rectangle with edges of 3.061(1) and 6.076(1) A. The four DyIII centres also form a rectangle that lies above and below the plane of the CuII centres, with edges of 3.739(1) and 5.328(1) A. The two strictly planar rectangles are almost perpendicular. Two trigonal bipyramidal μ5-O2− groups link the perpendicular Cu5 and Dy4 frameworks together. The molecule 4 has a very similar structure to that of 1, differences being the replacement of the two chelating nitrato groups of 1 by two chelating ButCH2CO2− ligands in 4 and the coordination polyhedra of the LnIII and YIII atoms (Snub diphenoids in 1 and biaugmented trigonal prisms in 4). Dc magnetic susceptibility data (χM) on analytically pure samples of 1–3, collected in the 300–2 K range, indicate that ferromagnetic exchange interactions dominate leading to large spin ground states. The χMT vs. T data for 4 suggest moderately strong antiferromagnetic CuII⋯CuII exchange interactions. Studies of the dynamic magnetic properties of the {Cu5Ln4} clusters show that 1 behaves as a SMM at zero field and 2 is a very weak field-induced SMM, while 3 exhibits only weak tails in the χ′′Mvs. T plots at various ac frequencies at zero dc field.

Two mixed-valence cobalt complexes, [CoIICoIII2(mpm)6](ClO4)2 (1) and [CoII2CoIII2(μ3-OMe)2(μ-mpm)4(NO3)4] (2), where mpm is the deprotonated form of R or S α-methyl-2-pyridinemethanol, have been structurally and magnetically characterized. Both complexes crystallize in chiral space groups, where 1 is a trinuclear compound with a linear Co(III)–Co(II)–Co(III) topology and 2 is a tetranuclear cluster with a defect dicubane-type structure that has two missing vertices. In both cases the mpm− ligand bridges adjacent Co ions in a η1:η2:μ manner. The molecular geometries of the complexes reveal the Co ions are octahedral, where the greatest deviation from Oh symmetry is apparent for the HS d7 Co(II) ions. The chirality of 1 and 2 were studied by circular dichroism spectroscopy where opposite Cotton effects are observed for the R- and S-enantiomers of both complexes. Magnetic susceptibility studies reveal the presence of largely quenched first order orbital angular momentum together with weak ion or intermolecular dipole exchange.

In addition to previously studied {CuGd

The self-assembly reaction between NiI2, benzoic acid (PhCO2H) and the Schiff base chelate, N-naphthalidene-2-amino-5-chlorobenzoic acid (nacbH2), in the presence of the organic base triethylamine (NEt3), has resulted in the isolation and the structural, spectroscopic, and physicochemical characterization of the dodecanuclear [Ni12I2(OH)6(O2CPh)5(nacb)5(H2O)4(MeCN)4]I (1) cluster compound in ~30% yield. Complex 1 has a cage-like conformation, comprising twelve distorted, octahedral NiII ions that are bridged by five &mu, 3-OH&minus, one &mu, OH&minus, an I&minus, in 55% occupancy, five PhCO2&minus, groups (under the &eta, 1:&eta, 1:&mu, &eta, 2:&mu, 3 and &eta, 2:&eta, 4 modes), and the naphthoxido and carboxylato O-atoms of five doubly deprotonated nacb2&minus, groups. The overall {Ni12} cluster exhibits a nanosized structure with a diameter of ~2.5 nm and its metallic core can be conveniently described as a series of nine edge- or vertex-sharing {Ni3} triangular subunits. Complex 1 is the highest nuclearity coordination compound bearing the nacbH2 chelate, and a rare example of polynuclear NiII complex containing coordinating I&minus, ions. Direct current (DC) magnetic susceptibility studies revealed the presence of predominant antiferromagnetic exchange interactions between the NiII ions, while photophysical studies of 1 in the solid-state showed a cyan-to-green centered emission at 520 nm, upon maximum excitation at 380 nm. The reported results demonstrate the rich coordination chemistry of the deprotonated nacb2&minus, chelate in the presence of NiII metal ions, and the ability of this ligand to adopt a variety of different bridging modes, thus fostering the formation of high-nuclearity molecules with rare, nanosized dimensions and interesting physical (i.e., magnetic and optical) properties.

In this Feature Article, we highlight the feasibility of a new, recently developed approach towards the synthesis of high-spin molecules and single-molecule magnets (SMMs). The key to the preparation of such molecular compounds is the organic azide precursor Me3SiN3, which fosters the formation of 3d-metal azido clusters and coordination polymers without requiring the assistance of any organic chelating/bridging group. All the isolated compounds contain metallic cores which are surrounded by end-on bridging N3− groups. Consequently, the reported molecular materials exhibit ferromagnetic exchange interactions between the spin carriers, resulting in the stabilization of the maximum possible spin ground states. The additional presence of magnetic anisotropy, depending on the 3d-metal ion used, gives rise to SMM properties with interesting and rare features. This article intends to introduce the readers to an unexplored, but in coordination chemistry very useful azido-based reagent and emphasize the pronounced differences in the structures and magnetic properties of the compounds that result from the reactions between 3d-metals and NaN3 or Me3SiN3 in the presence of organic bridging groups, and 3d-metals with Me3SiN3 alone.

A rare disk-like single-molecule magnet (SMM) exclusively bridged by end-on azides with a spin ground state of S = 14 was prepared by the reaction of a divalent FeII precursor with Me3SiN3 under basic conditions. AC magnetic susceptibility studies revealed unusual, “Janus”-faced SMM behavior for the dried and pristine forms of the compound attributed to solvation/de-solvation effects of the coordinated MeCN ligands which leads to alterations in the crystal field and symmetry of the metal ions. DFT calculations confirmed the ferromagnetic nature of the interactions between the FeII spin carriers with the zero-field splitting parameters D = −0.2323 cm−1 and E/D = 0.027. The results have important implications for the future study of single-molecule magnets incorporating volatile solvent molecules in the first coordination sphere of the metal ions and their effect on the relaxation dynamics.

A relatively unexplored synthetic route in redox-active Mn(II/III) coordination chemistry has been employed toward the preparation of a new mixed-valence MnII/III 1-D linear chain from the reaction of [MnIII(sacb)2]− precursor with a MnII source, where sacbH2 is the Schiff base ligand N-salicylidene-2-amino-5-chlorobenzoic acid. The mononuclear (Pr2NH2)[MnIII(sacb)2] (1) compound was obtained in excellent yields (>85%) from the 1:2:3 reaction of Mn(O2CMe)2∙4H2O, sacbH2 and Pr2NH, respectively. In 1, the two doubly deprotonated sacb2− ligands act as Ocarboxylate,Nimine,Ophenoxide-tridentate chelates, while the second carboxylate O atom of sacb2− is dangling and H-bonded to the Pr2NH2+ countercation. Complex 1 was subsequently used as a ‘ligand’ to react stoichiometrically with the ‘metal’ Mn(NO3)2∙4H2O, thus leading to the 1-D coordination polymer {[MnIIMnIII(sacb)2(H2O)2(MeOH)2](NO3)}n (2) in good yields (~50%). The removal of Pr2NH2+ from the vicinity of the [MnIII(sacb)2]− metalloligand has rendered possible (vide infra) the coordination of the second Ocarboxylate of sacb2− to neighboring {MnII(H2O)2(MeOH)2}2+ units, and consequently the formation of the 1-D polymer 2. Direct-current (dc) magnetic susceptibility studies revealed the presence of very weak antiferromagnetic exchange interactions between alternating MnIII and MnII atoms with a coupling constant of J = −0.08 cm−1 for g = 2.00. The combined results demonstrate the potential of the ‘metal complexes as ligands’ approach to yield new mixed-valence Mn(II/III) coordination polymers with interesting structural motifs and physicochemical properties.

The initial use of quinoline-2-aldoxime (qaoH) and 2,6-diacetylpyridine dioxime (dapdoH2) in heterometallic Mn–Ca chemistry has afforded a mixed-valence {MnII/III22Ca2} cluster containing several {Mn4CaOx} subunits and a ‘butterfly’-like {MnIV2Ca2} complex, respectively. The one-pot reaction of Mn(O2CPh)2·2H2O and Ca(O2CPh)2·H2O with qaoH and NEt3 in a 1:1:1:1 molar ratio in a solvent mixture comprising MeCN/MeOH gave complex [Mn22Ca2O14(OH)4(OMe)6(O2CPh)22(qao)2(MeCN)2(H2O)4](OH)2 (1; 6MnII/16MnIII) in 20% yield. A similar reaction with that of 1, albeit with Mn(O2CPh)2·2H2O and Ca(NO3)2·4H2O in the presence of dapdoH2 and NEt3, in a molar ratio of 1:1:2:2 in MeCN/MeOH, led to the smaller nuclearity complex [Mn2Ca2(OMe)2(NO3)2(dapdo)4] (2; 2MnIV) in 40% yield. The reported compounds demonstrate structural and magnetic relevance to both low- and high-valent states of the OEC.

The employment of a relatively unexplored reagent, namely the Me3SiN3, in the coordination chemistry of Zn(II) and Cd(II), in the absence of any external organic chelating/bridging ligand, has led to two new, azido-bridged coordination polymers with formulae [Zn2(N3)4(MeCN)3]n (1) and [Cd3(N3)6(MeCN)2]n (2), respectively. The reaction between Zn(ClO4)2·6H2O, Me3SiN3 and NEt3 in an 1:8:2 molar ratio afforded colorless needle-like crystals of the 1-D chain 1, whereas the exact same reaction but with Cd(ClO4)2·6H2O in place of the ZnII starting material resulted in the formation of colorless needles of the 2-D polymer 2. The repeating unit of 1 consists of a [Zn4(N3)8(MeCN)6] cluster with a defective dicubane core; the vertices of the latter are occupied by the four metal ions and the bridging ligation is provided by two μ3-1,1,1 (or 3.30) and six μ-1,1 (or 2.20) end-on N3− groups. In contrast, compound 2 comprises a central [Cd4(μ3-N3)4(MeCN)4]4+ cubane-like unit, unprecedented in the coordination chemistry of CdII, which is linked to [Cd(N3)4]2− tetrahedra through μ-1,1 end-on N3− groups, eventually forming the overall layered structure of 2. Topological analysis of 2 shows a trinodal (3,4,5) network with stoichiometry (3-c)2(4-c)(5-c)2 and a very rare topological type of 3,4,5L6. Terminal ligation in both 1 and 2 is solely provided by MeCN solvate molecules. Despite the optical inactivity of complex 1, the 2-D polymer 2 exhibits an intense violet-to-blue emission upon excitation at 225 or 277 nm in the solid-state, which is tentatively ascribed to an intra-ligand fluorescence from the coordinated azido groups within the robust 2-D network. Although it is strongly evidenced that the chemistry of ZnII and CdII follows the same general trends, and thus the majority of these coordination compounds are isomorphous, the present study demonstrates the formation of two chemically, structurally and optically different compounds of divalent Group 12 metal ions, under the exact same experimental conditions. This work may pave the way to further study the chemical, structural and physicochemical properties of organic chelate-free coordination polymers and clusters using different Me3SiX (X = OCN−, SCN−, CN− and RCO2−) reagents.

The synthesis of a new family of ferromagnetically-coupled {Ni10} clusters counterbalanced by various [Ln(NO3)5]2− ions is herein described. The resulting compounds are organic chelate-free and the metal ions are exclusively bridged by end-on azido ligands to stabilize a beautiful disk-like topology reminiscent of the structure of the brucite mineral.

A new family of {Cu4Ln2} (Ln = Gd, Tb and Dy) complexes bearing the gem-diol form of di-2-pyridyl ketone [(py)2CO] ligand is reported. Magnetic studies reveal the presence of predominant ferromagnetic exchange interactions between the metal ions. As a result, the hexanuclear compounds exhibit single-molecule magnetism behavior and large magnetic entropy changes, depending on the 4f-metal ion present.

The one-pot reaction between Mn(O2CMe)2·4H2O, salicylhydroxamic acid (shaH2) and Me4NOH·5H2O in a molar ratio of 2:1:2, and a solvent mixture comprising MeCN and MeOH, affords the new mixed-valence cluster compound (Me4N)4[MnII2MnIII9O4(O2CMe)9(shi)6] (1) in moderate yields. The anion of the tetradentate (N,O,O,O) chelating/bridging ligand shi3− resulted from the in-situ metal ion-assisted amide-iminol tautomerism of shaH2. The [MnII2MnIII9(μ3-O)4(μ-OR)3(μ3-NO)6]14+ core of 1 comprises four vertex-sharing {MnIII3(μ3-O2−)}7+ triangular subunits of different types, which are linked to each other and the MnII atoms through the oximato arms and the carboxylate O-atoms of six η1:η1:η1:η2:μ3 shi3− and three η1:η2:μ3 MeCO2− groups, respectively. Peripheral ligation about the core is provided by six η1:η1:μ MeCO2− groups and the chelating parts of the shi3− ligands. Solid-state direct-current (dc) magnetic susceptibility studies revealed the presence of predominant antiferromagnetic exchange interactions between the Mn centers, mainly promoted by the coplanarity of the μ3-O2− within the {Mn3} triangular planes and the insignificant distortion of the Mn N O Mn bridging units. Low-lying excited states precluded obtaining a good fit from the magnetization data, and the ground state was instead determined from the alternating-current (ac) data, which indicated an S = 3 ground state for 1. The combined results emphasize the continuing supply from the use of the salicylhydroxime chelating/bridging ligand of new 3d-metal clusters of very rare nuclearities and beautiful molecular structures.

The use of Me3SiN3 in CuII chemistry, under basic conditions, in the absence of any ancillary organic chelate, has led to an unusual 1-D coordination polymer (1) composed of {Cu6(N3)12} repeating units. The metal ions in 1 are exclusively bridged by μ3-1,1,1 and μ-1,1 end-on N3– groups. Peripheral ligation about the {Cu6(N3)12} core is provided by eight MeCN solvate molecules. IR and UV/Vis spectroscopic data fully support the presence of end-on azides and d-d transitions of the metal ions, respectively. Magnetic susceptibility measurements revealed a continuous drop of the χΜΤ product and an overall antiferromagnetic response, which results in a local S = 0 spin for the {Cu6(N3)12} repeating units of 1. The combined results demonstrate the flexibility of this synthetic approach to purely inorganic-bridged coordination complexes (clusters and polymers) and its ability to yield new molecule-based materials with several potential applications, i.e., in molecular magnetism, catalysis, high energy materials and photochemistry.

© 2017 American Chemical Society. One-pot reactions between the [Mn3O(O2CPh)6(py)x]+/0triangular precursors and either CaBr2·xH2O or CaCl2·6H2O, in the presence of salicylhydroxamic acid (shaH2), have afforded the heterometallic complexes [MnIII4Ca2(O2CPh)4(shi)4(H2O)3(Me2CO)] (1) and (pyH)[MnII2MnIII4Ca2Cl2(O2CPh)7(shi)4(py)4] (2), respectively, in good yields. Further reactions but using a more flexible synthetic scheme comprising the Mn(NO3)2·4H2O/Ca(NO3)2·4H2O and Mn(O2CPh)2·2H2O/Ca(ClO4)2·4H2O "metal blends" and shaH2, in the presence of external base NEt3, led to the new complexes (NHEt3)2[MnIII4MnIV4Ca(OEt)2(shi)10(EtOH)2] (3) and (NHEt3)4[MnIII8Ca2(CO3)4(shi)8] (4), respectively. In all reported compounds, the anion of the tetradentate (N,O,O,O)-chelating/bridging ligand salicylhydroxime (shi3-), resulting from the in situ metal-ion-assisted amide-iminol tautomerism of shaH2, was found to bridge both Mn and Ca atoms. Complexes 1-4 exhibit a variety of different structures, metal stoichiometries, and Mn oxidation-state descriptions; 1 possesses an overall octahedral metal arrangement, 2 can be described as a Mn4Ca2octahedron bound to an additional Mn2unit, 3 consists of a Mn8"ring" surrounding a CaIIatom, and 4 adopts a rectangular cuboidal motif of eight Mn atoms accommodating two CaIIatoms. Solid-state direct-current magnetic susceptibility studies revealed the presence of predominant antiferromagnetic exchange interactions between the Mn centers, leading to S = 0 spin ground-state values for all complexes. From a bioinorganic chemistry perspective, the reported compounds may demonstrate some relevance to both high-valent scheme (3) and lower-oxidation-level species (1, 2, and 4) of the catalytic cycle of the oxygen-evolving complex.

The synthesis, characterization, and stability study of the first uranium complex bearing 2,6-diacetylpyridine dioxime (dapdoH2) is reported. The dimeric complex [UO2(dapdoH)Cl]2 is stable in solution as shown by ESI-MS and NMR spectrometry, and its solid-state structure was further analyzed by X-ray crystallography, IR, Raman and luminescence studies.

A relatively unexplored synthetic route in redox-active Mn(II/III) coordination chemistry has been employed toward the preparation of a new mixed-valence MnII/III 1-D linear chain from the reaction of [MnIII(sacb)2]&minus, precursor with a MnII source, where sacbH2 is the Schiff base ligand N-salicylidene-2-amino-5-chlorobenzoic acid. The mononuclear (Pr2NH2)[MnIII(sacb)2] (1) compound was obtained in excellent yields (&gt, 85%) from the 1:2:3 reaction of Mn(O2CMe)2∙4H2O, sacbH2 and Pr2NH, respectively. In 1, the two doubly deprotonated sacb2&minus, ligands act as Ocarboxylate,Nimine,Ophenoxide-tridentate chelates, while the second carboxylate O atom of sacb2&minus, is dangling and H-bonded to the Pr2NH2+ countercation. Complex 1 was subsequently used as a &lsquo, ligand&rsquo, to react stoichiometrically with the &lsquo, metal&rsquo, Mn(NO3)2∙4H2O, thus leading to the 1-D coordination polymer {[MnIIMnIII(sacb)2(H2O)2(MeOH)2](NO3)}n (2) in good yields (~50%). The removal of Pr2NH2+ from the vicinity of the [MnIII(sacb)2]&minus, metalloligand has rendered possible (vide infra) the coordination of the second Ocarboxylate of sacb2&minus, to neighboring {MnII(H2O)2(MeOH)2}2+ units, and consequently the formation of the 1-D polymer 2. Direct-current (dc) magnetic susceptibility studies revealed the presence of very weak antiferromagnetic exchange interactions between alternating MnIII and MnII atoms with a coupling constant of J = &minus, 0.08 cm&minus, 1 for g = 2.00. The combined results demonstrate the potential of the &lsquo, metal complexes as ligands&rsquo, approach to yield new mixed-valence Mn(II/III) coordination polymers with interesting structural motifs and physicochemical properties.

The synthesis of a new {Ni8} cluster bearing tetrazolate- and azido-bridging ligands, and supported by chelating α-methyl-2-pyridine-methanol (mpmH) groups, is described herein. The reported compound has a unique trapezoidal prismatic topology, resulting from an unexpected in situ click reaction between the MeCN reaction solvent and the N3- ions under mild, room-temperature conditions. Such a click chemistry approach to the preparation of 0-D compounds is relatively unexplored and represents a fruitful strategy for the synthesis of new coordination clusters and molecule-based magnetic materials.

The enhancement of toroic motifs through coupling toroidal moments within molecular nanomagnets is a new, interesting and relevant approach for both fundamental research and potential quantum computation applications. We investigate a Dy8 molecular cluster and discover it has a antiferrotoroic ground state with slow magnetic relaxation. The experimental characterization of the magnetic anisotropy axes of each magnetic center and their exchange interactions represents a considerable challenge due to the non-magnetic nature of the toroidal motif. To overcome this and obtain access to the low energy states of Dy8 we establish a multi-orientation single-crystal micro Hall sensor magnetometry approach. Using an effective Hamiltonian model we then unpick the microscopic spin structure of Dy8, leading to a canted antiferrotoroidic tetramer molecular ground state. These findings are supported with electrostatic calculations that independently confirm the experimentally determined magnetic anisotropy axes for each DyIII ion within the molecule.

The synthesis of a new {Ni

Homometallic {NiII4} cubane-like clusters with a rare chiral core have been prepared via the employment of enantiomerically pure 2-(1-hydroxyethyl)pyridine (Hmpm). Comparison with the achiral cubanes derived from the related 2-pyridinemethanol (Hpym) ligand reveals drastic structural changes as a consequence of the transfer of chirality from the ligands to the whole structure. Their magnetic properties have been related to the structural features of their cubane-type cores.

Homometallic {NiII4} cubane-like clusters with a rare chiral core have been prepared via the employment of enantiomerically pure 2-(1-hydroxyethyl)pyridine (Hmpm). Comparison with the achiral cubanes derived from the related 2-pyridinemethanol (Hpym) ligand reveals drastic structural changes as a consequence of the transfer of chirality from the ligands to the whole structure. Their magnetic properties have been related to the structural features of their cubane-type cores.

The comproportionation reaction between MnII and MnVII sources in the presence of 3,3-dimethylacrylic acid and azides has led to a new {Mn29} molecular cluster with a spherical structure and dimensions of ∼2.2 nm, comparable in size to the smallest classical and magnetic nanoparticles.

The reaction between Dy(NO3)3∙6H2O and the bulky Schiff base ligand, N-naphthalidene-2-amino-5-chlorobenzoic acid (nacbH2), in the presence of the organic base NEt3 has led to crystallization and structural, spectroscopic and magnetic characterization of a new heptanuclear [Dy7(OH)6(OMe)2(NO3)1.5(nacb)2(nacbH)6(MeOH)(H2O)2](NO3)1.5 (1) compound in ~40% yield. Complex 1 has a unique hourglass-like metal topology, among all previously reported {Dy7} clusters, comprising two distorted {Dy4(&mu, 3-&Omicron, &Eta, )3(&mu, 3-OMe)}8+ cubanes that share a common metal vertex (Dy2). Peripheral ligation about the metal core is provided by the carboxylate groups of four &eta, 1:&eta, 1:&mu, single-deprotonated nacbH&minus, and two &eta, 2:&eta, 3 fully-deprotonated nacb2&minus, ligands. Complex 1 is the first structurally characterized 4f-metal complex bearing the chelating/bridging ligand nacbH2 at any protonation level. Magnetic susceptibility studies revealed that 1 exhibits slow relaxation of magnetization at a zero external dc field, albeit with a small energy barrier of ~5 K for the magnetization reversal, most likely due to the very fast quantum-tunneling process. The combined results are a promising start to further explore the reactivity of nacbH2 upon all lanthanide ions and the systematic use of this chelate ligand as a route to new 4f-metal cluster compounds with beautiful structures and interesting magnetic dynamics.

The enhancement of toroic motifs through coupling toroidal moments within molecular nanomagnets is a new, interesting and relevant approach for both fundamental research and potential quantum computation applications. We investigate a Dy8 molecular cluster and discover it has a antiferrotoroic ground state with slow magnetic relaxation. The experimental characterization of the magnetic anisotropy axes of each magnetic center and their exchange interactions represents a considerable challenge due to the non-magnetic nature of the toroidal motif. To overcome this and obtain access to the low energy states of Dy8 we establish a multi-orientation single-crystal micro Hall sensor magnetometry approach. Using an effective Hamiltonian model we then unpick the microscopic spin structure of Dy8, leading to a canted antiferrotoroidic tetramer molecular ground state. These findings are supported with electrostatic calculations that independently confirm the experimentally determined magnetic anisotropy axes for each DyIII ion within the molecule. ARO W911NF-13-1-1025 NSF-DMR-1309008 NSF-DMR-1309202 MAT2017-89528 CTQ2017-89993 MDM-2015-0538 ERC-CoG-647301 DECRESIM COST-MOLSPIN CA15128 Prometeo Program of excellence The enhancement of toroic motifs through coupling toroidal moments within molecular nanomagnets is a new, interesting and relevant approach for both fundamental research and potential quantum computation applications. We investigate a Dy8 molecular cluster and discover it has a antiferrotoroic ground state with slow magnetic relaxation. The experimental characterization of the magnetic anisotropy axes of each magnetic center and their exchange interactions represents a considerable challenge due to the non-magnetic nature of the toroidal motif. To overcome this and obtain access to the low energy states of Dy8 we establish a multi-orientation single-crystal micro Hall sensor magnetometry approach. Using an effective Hamiltonian model we then unpick the microscopic spin structure of Dy8, leading to a canted antiferrotoroidic tetramer molecular ground state. These findings are supported with electrostatic calculations that independently confirm the experimentally determined magnetic anisotropy axes for each DyIII ion within the molecule.

In this Feature Article, we highlight the feasibility of a new, recently developed approach towards the synthesis of high-spin molecules and single-molecule magnets (SMMs). The key to the preparation of such molecular compounds is the organic azide precursor Me3SiN3, which fosters the formation of 3d-metal azido clusters and coordination polymers without requiring the assistance of any organic chelating/bridging group. All the isolated compounds contain metallic cores which are surrounded by end-on bridging N3- groups. Consequently, the reported molecular materials exhibit ferromagnetic exchange interactions between the spin carriers, resulting in the stabilization of the maximum possible spin ground states. The additional presence of magnetic anisotropy, depending on the 3d-metal ion used, gives rise to SMM properties with interesting and rare features. This article intends to introduce the readers to an unexplored, but in coordination chemistry very useful azido-based reagent and emphasize the pronounced differences in the structures and magnetic properties of the compounds that result from the reactions between 3d-metals and NaN3 or Me3SiN3 in the presence of organic bridging groups, and 3d-metals with Me3SiN3 alone.

A new {Dy5} cluster compound has been synthesized and structurally characterized from the initial use of the Schiff base ligand N-naphthalidene-2-amino-5-chlorophenol (nacpH2) in coordination chemistry. The 1:1 reaction between Dy(hpd)3∙2H2O and nacpH2, in a solvent mixture comprising CH2Cl2 and MeOH, afforded orange crystals of [Dy5(OH)2(hpd)3(nacp)5(MeOH)5] (1) in 70% yield, where hpd&minus, is the anion of 3,5-heptadione. The {Dy5} complex can be described as two vertical {Dy3(&mu, 3-OH)}8+ triangles sharing a common vertex, such a metal topology is unprecedented in 4f-metal cluster chemistry. Direct current (dc) magnetic susceptibility studies revealed the presence of some weak ferromagnetic exchange interactions between the five DyIII ions at low temperatures. Alternating current (ac) magnetic susceptibility measurements at zero applied dc field showed that complex 1∙3MeOH∙CH2Cl2 exhibits temperature- and frequency-dependent out-of-phase signals below ~20 K, characteristics of a single-molecule magnet (SMM). The resulting relaxation times were used to construct an Arrhenius-type plot and determine an effective energy barrier, Ueff, of 100 K for the magnetization reversal. The application of a small dc field of 200 Oe resulted in the surpassing of the quantum tunneling process and subsequently the increase of the Ueff to a value of 170 K. The reported results are part of a long-term program aiming at the preparation of structurally and magnetically interesting lanthanide complexes bearing various Schiff base chelating/bridging ligands.

The organic chelating and bridging ligands 9,10-phenanthrenedione-9-oxime (phenoxH) and 9,10-phenanthrenedione-9,10-dioxime (phendoxH

The synthesis of a new family of ferromagnetically-coupled {Ni

A new family of {Cu4Ln2} (Ln = Gd, Tb and Dy) complexes bearing the gem-diol form of di-2-pyridyl ketone [(py)2CO] ligand is reported. Magnetic studies reveal the presence of predominant ferromagnetic exchange interactions between the metal ions. As a result, the hexanuclear compounds exhibit single-molecule magnetism behavior and large magnetic entropy changes, depending on the 4f-metal ion present.

The employment of the tripyridyl/diketone ligand 2,6-di-(2-pyridylcarbonyl)pyridine [(py)CO(py)CO(py)], in conjunction with azides (N3−), in Mn cluster chemistry has afforded the mixed-valence (II/III) complexes [MnII4MnIII2(N3)6Cl4(L1)2(DMF)4] (1) and [MnII4MnIII6O2(N3)12(L1)2(L2H)2(DMF)6] (2) in good yields. The resulting ligands L12− and L2H3− are the dianion and trianion of the ketone/gem-diol (L1H2) and bis(gem-diol) (L2H4) forms of (py)CO(py)CO(py), respectively, as derived from the metal-assisted hydrolysis of the parent dicarbonyl organic compound. Under the same synthetic conditions (i.e., reaction solvents, temperature and stirring time), the chemical identity of the two complexes was found to depend on the MnII starting material; in the presence of MnCl2, complex 1 is the only isolated product, while complex 2 can be only obtained if Mn(ClO4)2 is used. Complexes 1 and 2 are the second and third highest nuclearity products reported to date from any different form of coordinated ligands derived from (py)CO(py)CO(py). Magnetic susceptibility studies on both 1 and 2 revealed the presence of predominant antiferromagnetic exchange interactions between the metal centers. The combined results demonstrate the rich chemical reactivity of carbonyl groups and the ability of poly-ketone ligands to stabilize cluster compounds with unprecedented structural motifs and interesting molecular architectures.

The syntheses, structures, and magnetic properties are reported of two new high nuclearity Ce–Mn oxo carboxylate clusters at high CeIV/MnIII oxidation states and with nuclearities of Ce5Mn11 and Ce3Mn7. The compounds are (NnBu4)2[Ce5Mn11O13(OH)2(O2CPh)24(NO3)2](NO3) (1) and [Ce3Mn7O8(O2CPh)17(H2O)4] (2). 1 was prepared from the oxidation of Mn(O2CPh)2 by (NnBu4)2Ce(NO3)6, whereas 2 was obtained from the comproportionation reaction of Mn(O2CPh)2 and NnBu4MnO4 in the presence of Ce(NO3)3. Both compounds possess unprecedented structures, comprising an irregular metal topology of several edge-fused triangular units with overall virtual C2 symmetry. Variable-temperature, solid-state dc and ac magnetization studies on 1 and 2 in the 1.8–300 K range revealed predominantly weak antiferromagnetic exchange interactions within the complexes. For 1, the combined dc and ac data indicate an S = 5 ground state but with low-lying excited states consistent with the high nuclearity. For 2, even lower-lying excited states were observed, precluding clear determination of the ground state but with an estimate of S = 2 or 3, or less. Complexes 1 and 2 are new additions to the Ce–Mn family of clusters and the broader class of 3d/4f molecular systems, and 1 is the highest nuclearity Ce–Mn cluster to date.

A family of interwoven molecular inorganic knots, shaped like the 'Star of David', was prepared by the employment of naphthalene-2,3-diol in 3d/4f-metal cluster chemistry; the isoskeletal dodecanuclear compounds exhibit slow relaxation of the magnetization and magnetocaloric properties, depending on the metal ion., This work was supported by Brock University, NSERC-DG and ERA (to Th.C.S), the Ontario Trillium Foundation (graduate scholarship to D.I.A), the Fundaçao para a Ciencia e a Tecnologia (FCT, Portugal) financial support to REQUIMTE/LAQV (UID/ QUI/50006/2013), the European Synchrotron Radiation Facility (Grenoble, France) (for granting access time to the Swiss Norwegian BM01a beamline under the CH-3613 and CH-3849 research proposals), MINECO (FEDER-MAT2012-38318-C03 to M. E and postdoctoral contract to G. L), and the National Natural Science Foundation of China (grants 21371166, 21331003 and 21221061 to J. T).

Stimulation of the energy sensor AMP-activated kinase (AMPK) has been viewed as a targeted approach to increase glucose uptake by skeletal muscle and control blood glucose homeostasis. Rosemary extract (RE) has been reported to activate AMPK in hepatocytes and reduce blood glucose levels in vivo but its effects on skeletal muscle are not known. In the present study, we examined the effects of RE and the mechanism of regulation of glucose uptake in muscle cells. RE stimulated glucose uptake in L6 myotubes in a dose- and time-dependent manner. Maximum stimulation was seen with 5 μg/mL of RE for 4 h (184% ± 5.07% of control, p < 0.001), a response comparable to maximum insulin (207% ± 5.26%, p < 0.001) and metformin (216% ± 8.77%, p < 0.001) stimulation. RE did not affect insulin receptor substrate 1 and Akt phosphorylation but significantly increased AMPK and acetyl-CoA carboxylase phosphorylation. Furthermore, the RE-stimulated glucose uptake was significantly reduced by the AMPK inhibitor compound C, but remained unchanged by the PI3K inhibitor, wortmannin. RE did not affect GLUT4 or GLUT1 glucose transporter translocation in contrast with a significant translocation of both transporters seen with insulin or metformin treatment. Our study is the first to show a direct effect of RE on muscle cell glucose uptake by a mechanism that involves AMPK activation.

The successful organic synthesis of a new dipyrazole/pyridine-dicarbonyl organic molecule, namely pyridine-2,6-diylbis(pyrazine-2-ylmethanone) [(pz)CO(py)CO(pz)], followed by its employment in Mn coordination chemistry has yielded the neutral cluster compound [Mn3Na2O(N3)3(L)3] (1), where L(2-) is the (pz)C(CH2COCH3)(O(-))(py)C(CH2COCH3)(O(-))(pz) dianion. The latter group was formed in situ, presumably by the nucleophilic attack of the carbanion (-)CH2COCH3 to the carbonyl carbon atoms of (pz)CO(py)CO(pz), in the presence of Mn(n+) ions under basic conditions and in solvent Me2CO. Complex 1 possesses an almost ideal trigonal bipyramidal topology, with the two Na(I) ions occupying the apical positions and the three Mn(III) ions residing in the equatorial trigonal plane. The bridging ligation about the metal ions is provided by a μ3-O(2-) ion and six μ-OR(-) groups from the L(2-) ligand, while peripheral ligation is completed by three terminal azido groups and the pyridine N and carbonyl O atoms of L(2-). Magnetic susceptibility studies revealed the presence of predominant antiferromagnetic exchange interactions between the paramagnetic Mn(III) centres; the use of an anisotropic, equilateral Mn(III)3 triangle model allowed us to fit the magnetic data and obtain the best-fit parameters: J = -10.8 cm(-1), D = -5.3 cm(-1), and g = 1.99. The combined results demonstrate the rich chemical reactivity of carbonyl groups and the ability of poly-ketone ligands to stabilize cluster compounds with unprecedented structural motifs and interesting architectures.

The employment of N-salicylidene-o-aminophenol in 4f-metal cluster chemistry has led to a family of {Ln7} clusters with a new core topology that comprises two {Ln4} butterflies sharing a common metal vertex; the {Dy7} derivative exhibits slow magnetization relaxation whereas all heptanuclear compounds show ligand-centred blue-green emissions.

The self-assembly reaction of MnCl

The first {Mn31} cluster (1) has been prepared from carboxylate ions and the chelating/bridging ligand α-methyl-2-pyridine-methanol. Compound 1 possesses a unique nanosized structural topology with one of the largest energy barriers reported to-date for high-nuclearity 3d-metal clusters. Single-crystal magnetic hysteresis studies reveal the presence of hysteresis loops below 5 K, one of the highest temperatures below which molecular hysteresis has been observed for 3d-based SMMs.

The first {Mn

One-pot reactions between the [Mn

A family of nanosized {Cu

The introduction of the Schiff base ligand N-salicylidene-2-amino-5-chlorobenzoic acid (sacbH