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1.
Molecules ; 25(9)2020 May 07.
Artigo em Inglês | MEDLINE | ID: mdl-32392886

RESUMO

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(µ3-OH)3(µ3-OMe)}8+ cubanes that share a common metal vertex (Dy2). Peripheral ligation about the metal core is provided by the carboxylate groups of four η1:η1:η1:µ single-deprotonated nacbH- and two η1:η1:η2:η1:µ3 fully-deprotonated nacb2- 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.

2.
Nanoscale ; 11(32): 15131-15138, 2019 Aug 15.
Artigo em Inglês | MEDLINE | ID: mdl-31372609

RESUMO

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.

3.
Dalton Trans ; 48(31): 11632-11636, 2019 Aug 21.
Artigo em Inglês | MEDLINE | ID: mdl-31274137

RESUMO

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.

4.
Dalton Trans ; 48(28): 10427-10434, 2019 Jul 16.
Artigo em Inglês | MEDLINE | ID: mdl-31124546

RESUMO

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.

5.
Chem Sci ; 10(6): 1626-1633, 2019 Feb 14.
Artigo em Inglês | MEDLINE | ID: mdl-30842825

RESUMO

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.

6.
Chem Commun (Camb) ; 55(1): 11-26, 2018 Dec 18.
Artigo em Inglês | MEDLINE | ID: mdl-30499993

RESUMO

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.

7.
Inorg Chem ; 57(21): 13944-13952, 2018 Nov 05.
Artigo em Inglês | MEDLINE | ID: mdl-30351077

RESUMO

The organic chelating and bridging ligands 9,10-phenanthrenedione-9-oxime (phenoxH) and 9,10-phenanthrenedione-9,10-dioxime (phendoxH2) were synthesized and subsequently employed for the first time in heterometallic 3 d/4 f-metal cluster chemistry. The general reaction between CuCl2·2H2O, LnCl3·6H2O, phenoxH, and NEt3 in a 1:2:2:4 molar ratio, in a solvent mixture comprising MeCN and MeOH, afforded brown crystals of a new family of [Cu3LnCl3(phenox)6(MeOH)3] clusters (Ln = Gd (1), Tb (2), Dy (3)) that possess an unprecedented [Cu3Ln(µ-NO)6]3+ "propeller"-like core. Complexes 1-3 are the first {Cu3Ln} clusters in which the outer CuII and the central LnIII atoms are solely bridged by diatomic oximato bridges. The {Cu-N-O-Ln} bridging units are very distorted with torsion angles spanning the range 35.5-48.9° and 25.2-55.6° in 1 and 2, respectively. As a result, complexes 1-3 are antiferromagnetically coupled, in agreement with previously reported magnetostructural criteria for oximato-bridged Cu/Ln complexes. The magnetic susceptibility data for all complexes were nicely fit to an isotropic spin Hamiltonian (for 1) or a Hamiltonian that accounts for the spin of the CuII atoms, the spin component of the LnIII, the spin-orbit coupling (λ), an axial ligand-field component around the LnIII atoms (Δ), and the Zeeman effect (for the anisotropic 2 and 3). The resulting fit parameters were J = -1.34 cm-1 and g = 2.10 (1), J = -1.42 cm-1, gCu = 2.10, and Δ = -26.3 cm-1 (2), and J = -1.70 cm-1, gCu = 2.05, and Δ = -38.1 cm-1 (3). The reported fitting procedure, implemented in the PHI program, is here used for the first time. Even if this method is only valid in high-symmetry Ln environments, when it is properly used allows a very simple and efficient method to obtain the exchange parameters. In light of the negative anisotropy, compounds 2 and 3 were found to exhibit frequency-dependent tails of out-of-phase signals in the presence of a small external dc field, characteristic of the slow magnetization relaxation of a single-molecule magnet. By using the Kramers-Kronig equations, the effective energy barriers ( Ueff) were derived and reported as Ueff = 10.1 and 5.4 cm-1 for 2 and 3, respectively.

8.
Chem Commun (Camb) ; 54(88): 12499-12502, 2018 Nov 14.
Artigo em Inglês | MEDLINE | ID: mdl-30345439

RESUMO

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.

9.
Dalton Trans ; 47(34): 11934-11941, 2018 Aug 29.
Artigo em Inglês | MEDLINE | ID: mdl-30024007

RESUMO

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.

10.
Chemistry ; 24(11): 2588-2592, 2018 Feb 21.
Artigo em Inglês | MEDLINE | ID: mdl-29315881

RESUMO

The self-assembly reaction of MnCl2 ⋅4H2 O, acenaphthenequinone dioxime (acndH2 ) and NEt3 has yielded an unprecedented, linear {MnIV2 MnIII } complex with an S=5 spin ground state and non-SMM behavior. The targeted replacement of the central MnIII ion with GdIII and DyIII ions has successfully increased the S and turned on the SMM dynamics without affecting the core structure and the nature of the magnetic exchange interactions.

11.
J Am Chem Soc ; 139(44): 15644-15647, 2017 11 08.
Artigo em Inglês | MEDLINE | ID: mdl-29052991

RESUMO

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.

12.
Inorg Chem ; 56(17): 10760-10774, 2017 Sep 05.
Artigo em Inglês | MEDLINE | ID: mdl-28817264

RESUMO

One-pot reactions between the [Mn3O(O2CPh)6(py)x]+/0 triangular 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 Mn4Ca2 octahedron bound to an additional Mn2 unit, 3 consists of a Mn8 "ring" surrounding a CaII atom, and 4 adopts a rectangular cuboidal motif of eight Mn atoms accommodating two CaII atoms. 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.

13.
Chem Commun (Camb) ; 53(30): 4266-4269, 2017 Apr 11.
Artigo em Inglês | MEDLINE | ID: mdl-28361136

RESUMO

A family of nanosized {Cu6Ln12} clusters with a 'windmill'-like topology was prepared from the employment of 2,6-diacetylpyridine dioxime, in conjunction with bridging N3-, in 3d/4f-metal chemistry; the octadecanuclear compounds exhibit single-molecule magnetism behavior and large magnetic entropy changes, depending on the 4f-metal ion present.

14.
Inorg Chem ; 56(6): 3568-3578, 2017 Mar 20.
Artigo em Inglês | MEDLINE | ID: mdl-28267321

RESUMO

The introduction of the Schiff base ligand N-salicylidene-2-amino-5-chlorobenzoic acid (sacbH2) in 4f-metal chemistry has afforded a new dinuclear complex, [Dy2(NO3)4(sacbH)2(H2O)2(MeCN)2] (1), with the metal ions adopting a rare spherical tricapped trigonal prismatic coordination geometry. The deprotonated phenoxido O atoms of the organic chelate occupy the axial triangular faces of the prism and were found to be very close to the main anisotropy axes of the two DyIII ions. As a result, the {DyIII2} compound exhibits frequency- and temperature-dependent out-of-phase ac signals below ∼25 K in the absence of a static dc field, yielding an energy barrier of 109.3(1) K for the reversal of magnetization. Fast and efficient quantum tunneling of magnetization, attributed to the strong tails of signals below ∼15 K, was suppressed through the application of a small dc field, yielding entirely visible χM″ signals below 27 K. Single-crystal magnetic hysteresis studies confirmed the single-molecule magnet (SMM) behavior of 1; the hysteresis loops appear at temperatures below ∼5 K, which is one of the highest blocking temperatures in the field of 4f-SMMs to date. This joint magneto-structural and ab initio study demonstrates the ability of more common coordination numbers (i.e., 9), but with rare coordination geometries (i.e., spherical tricapped trigonal prismatic), to promote axiality that enhances the molecular anisotropy and subsequently the magnetization dynamics of the system.

15.
Inorg Chem ; 55(23): 12118-12121, 2016 Dec 05.
Artigo em Inglês | MEDLINE | ID: mdl-27934429

RESUMO

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.

16.
Dalton Trans ; 45(25): 10256-70, 2016 Jun 21.
Artigo em Inglês | MEDLINE | ID: mdl-27240998

RESUMO

The employment of the fluorescent bridging and chelating ligand N-naphthalidene-2-amino-5-chlorobenzoic acid (nacbH2) in Ni(II) cluster chemistry has led to a series of pentanuclear and hexanuclear compounds with different structural motifs, magnetic and optical properties, as well as an interesting 1-D coordination polymer. Synthetic parameters such as the inorganic anion present in the NiX2 starting materials (X = ClO4(-) or Cl(-)), the reaction solvent and the nature of the organic base employed for the deprotonation of nacbH2 were proved to be structure-directing components. Undoubtedly, the reported results demonstrate the rich coordination chemistry of nacbH2 in the presence of Ni(II) metal ions and the ability of this chelate to adopt a variety of different modes, thus fostering the formation of high-nuclearity molecules with many physical properties.

17.
Inorg Chem ; 55(3): 1270-7, 2016 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-26788587

RESUMO

The initial employment of the fluorescent bridging ligand N-naphthalidene-2-amino-5-chlorobenzoic acid (nacbH2) in metal cluster chemistry has led to new Ni12 (1) and Ni5 (2) clusters with wheel-like and molecular-chain topologies, respectively. The doubly-deprotonated nacb(2-) ligands were found to adopt four different coordination modes within 1 and 2. The nature of the ligand has also allowed unexpected organic transformations to occur and ferromagnetic and emission behaviors to emerge. The combined work demonstrates the ability of some "ligands-with-benefits" to yield beautiful structures with exciting topologies and interesting physicochemical properties.

18.
Chem Commun (Camb) ; 52(8): 1693-6, 2016 Jan 28.
Artigo em Inglês | MEDLINE | ID: mdl-26666673

RESUMO

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.

19.
Inorg Chem ; 54(15): 7555-61, 2015 Aug 03.
Artigo em Inglês | MEDLINE | ID: mdl-26200217

RESUMO

The first use of tert-butylacetate as bridging ligand in 3d/4f-metal cluster chemistry, in conjunction with the versatile chelate ligand pyridine-2,6-dimethanol, has afforded a new family of [Cu4Ln8(OH)6(NO3)2(O2CCH2Bu(t))16(pdm)4] clusters with unprecedented structures and slow magnetization relaxation for the {Cu(II)4Dy(III)8} member. The molecular structure of representative complex 1 consists of a {Cu(II)4Gd(III)8} cage-like cluster built from two {CuGd3} cubanes which are linked to each other and to two {CuGd} subunits on opposite sides through two η(2):η(2):η(2):µ5 NO3(-) ions. The metal ions are additionally bridged by µ3-OH(-), µ3-OR(-), and µ-OR(-) groups to give an overall [Cu4Gd8(µ5-NO3)2(µ3-OH)6(µ3-OR)2(µ-OR)8](14+) core. Peripheral ligation about the core is provided by the N,O,O-chelating part of the pdm(2-) groups and, more impressively, by the oxygen atoms of 16 bridging Bu(t)CH2CO2(-) ligands; the latter are arranged into five classes, adopting a total of six different binding modes with the metal centers. The combined work demonstrates the ligating flexibility of tert-butylacetate ion and its usefulness in the synthesis of new 3d/4f-metal cluster compounds.

20.
Appl Physiol Nutr Metab ; 40(4): 407-13, 2015 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-25794239

RESUMO

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.


Assuntos
Proteínas Quinases Ativadas por AMP/metabolismo , Metabolismo dos Carboidratos/efeitos dos fármacos , Glucose/metabolismo , Músculo Esquelético/efeitos dos fármacos , Extratos Vegetais/farmacologia , Rosmarinus/química , Proteínas Quinases Ativadas por AMP/genética , Acetil-CoA Carboxilase/genética , Acetil-CoA Carboxilase/metabolismo , Animais , Células Cultivadas , Transportador de Glucose Tipo 1/genética , Transportador de Glucose Tipo 1/metabolismo , Transportador de Glucose Tipo 4/genética , Transportador de Glucose Tipo 4/metabolismo , Hepatócitos/efeitos dos fármacos , Hepatócitos/metabolismo , Hipoglicemiantes/farmacologia , Insulina/metabolismo , Proteínas Substratos do Receptor de Insulina/genética , Proteínas Substratos do Receptor de Insulina/metabolismo , Fibras Musculares Esqueléticas/efeitos dos fármacos , Fibras Musculares Esqueléticas/metabolismo , Músculo Esquelético/metabolismo , Fosforilação , Proteínas Proto-Oncogênicas c-akt/genética , Proteínas Proto-Oncogênicas c-akt/metabolismo , Ratos
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