Search

The synthesis, crystal structure and magnetic properties of two trinuclear oxo-centered carboxylate complexes, [[Cr.sub.3]([[mu].sub.3]-O)[([[mu].sub.6]-PhCOO).sub.6][([H.sub.2]O).sub.3]]N[O.sub.3].4[H.sub.2]O.2C[H.sub.3]OH (complex 1) and [[Cr.sub.3]([[mu].sub.3]-O)[([[mu].sub.2]-PhCOO).sub.2][([[mu].sub.2]-OC[H.sub.2]C[H.sub.3]).sub.2][(bpy).sub.2][(NCS).sub.3]] (complex 2), are described. The antisymmetric exchange interaction has played a major role in the magnetic behavior of the complex 1 and unusual skeleton of the [[Cr.sub.3]O] core is most important feature of complex 2.

The reaction of Ln([N[O.sub.3]).sub.3) with [K.sub.3][Cr[CN.su.6)] and 2,2-bipyridine (bpy) in a water/ethanol solution is found to lead to two families of complexes. The magnetic results obtained in the full lanthanide series using {[Fe[CN.sub.6]}.sup.3-] and bpy as the blocking ligand are presented.

Research delineates the use of 1,10-phenanthroline in Fe(sup)III carboxylate reactions leading to the production of three new tetranuclear iron(III)/phenanthroline complexes. The core structure of two of the title complexes show the tetranuclear cluster arranged in a 'butterfly' fashion. All three exhibit magnetic properties.

Results show that a cobalt(II)--semiquinonato adduct is detected in the range 4-300 K in the antiferromagnetic coupling between the high spin cobalt(II) ion and the radical semiquinonato ligand complex.

Copper complexes with commercial oxin herbicides MCPA, 2,4-D and 2,4,5-T in the presence of nitrogen donor heterocyclic ligand, phenanthroline or 2,2'-bipyridylamine are synthesized and characterized. The available evidence supports a dimeric structure for the 2,4-D complex in the presence of bipyam while phen leads to monomeric forms and the EPR spectrum of the dimer at 4 K exhibits an axial signal corresponding to almost isolated S = 1/2 magnetic ions.

Three dimensional (3D) polymeric complex [Cu(btaO)(sub 2)(MeOH)](sub n), where btaO(super -) is the anion of 1-hydroxybenzotriazole, display interesting structural and magnetic characteristics. The magnetic study of [Cu(btaO)(sub 2)(MeOH)](sub n) reveals the presence of long-range ferromagnetic interactions with two critical transitions at 6.4 and 4.4 K.

The reactions of di-2-pyridyl ketone with Cu[([O.sub.2]CPh).sub.2] in the presence of Na[N.sub.3] and LiOH have led to an antiferromagnetically coupled (S = 0) [Cu.sub.6.sup.III] cluster with a novel core and to [([Cu.sub.8.sup.II]).sub.n] and [([Cu.sub.2.sup.II]).sub.n] coordination polymers with interesting structures. The cluster or polymer formation has depended on the reaction solvent.

The reaction between Mn[(Cl[O.sub.4]).sub.2] and di-(2-pyridyl)-ketone in the presence of the sodium salt of propanediol as a MeOH has led to the formation of a hexanuclear manganese cluster. The EPR spectra have shown that the spin ground state at a low temperature is not purely S = 1/2 but is populated with the S = 3/2 state, which is in accordance with the susceptibility and magnetization measurements.

Phenyl 2-pyridyl ketoxime (PhPyCNOH) has served as a scaffold for the formation of inverse-9-metallacrown-3 complexes accommodating one or two anions and the magnetic behavior has showed a large antiferromagnetic interaction. The vital role of [[mu].sub.3]-O ligand on the antiferromagnetic exchange coupling between the three Cu(II) magnetic centers is shown by the excellent linear correlation of the coupling constant J with the distance of the [[mu].sub.3]-O ligand from the centroid of the [Cu.sub.3] triangle.

A series of novel dodecanuclear [Mn.sub.6.sup.III][Fe.sub.6.sup.III] molecular wheels as well as one new archlike [Mn.sub.2.sup.III][Fe.sub.3.sup.III] cluster is prepared. The combination of the high-spin state and a negative magnetic anisotropy has resulted in the slow magnetization relaxation in [Mn.sub.2.sup.III][Fe.sub.3.sup.III] cluster.

Research has been conducted on compounds which contain Gd (super)3+, Sm (super)3+ and Yb (super)3+. The authors describe the synthesis, structure and magnetic properties of these compounds.

Research has been conducted on Ln (super)3+ -Fe (super)3+ and Ln (super)3+ -Co (super)3+ complexes, where Ln represents lanthanide(III) ions. The nature between the lanthanide(III) and iron(III) ion couplings has been investigated by studying Co (super)3+ ion diamagnetism, and the results are reported.

The synthesis, crystal structure, and magnetic properties of two trinuclear oxo-centered carboxylate complexes are reported and discussed: [Cr3(μ3-O)(μ2-PhCOO)6(H2O)3]NO3·H2O·2CH3OH (1) and [Cr3(μ3-O)(μ2-PhCOO)2(μ2-OCH2CH3)2(bpy)2(NCS)3] (2). For both complexes the crystal system is monoclinic, with space group C2/c for 1 and P1/n for 2. The structure of complex 1 consists of discrete trinuclear cations, associated NO3- anions, and lattice methanol and water molecules. The structure of complex 2 is built only by neutral discrete trinuclear entities. The most important feature of 2 is the unusual skeleton of the [Cr3O] core due to the lack of peripheral bridging ligands along one side of the triangular core, which is unique among the structurally characterized (μ3-oxo)-trichromium(III) complexes. Magnetic measurements were performed in the 2-300 K temperature range. For complex 1, in the high-temperature region (T > 8 K), experimental data could be satisfactorily reproduced by using an isotropic exchange model, H = -2J12S1S2 - 2J13S1S3 - 2J23S2S3 (J12 = J13 = J23) with Jij = -10.1 cm-1, g = 1.97, and TIP = 550 × 10-6 emu mol-1. The antisymmetric exchange interaction plays an important role in the magnetic behavior of the system, so in order to fit the experimental magnetic data at low temperature, a new magnetic model was used where this kind of interaction was also considered. The resulting fitting parameters are the following: Gzz = 0.25 cm-1, δ = 2.5 cm-1, and TIP = 550 × 10-6 emu mol-1. For complex 2, the experimental data could be satisfactorily reproduced by using an isotropic exchange model, H = -2J1(S1S2 + S1S3) - 2J2(S2S3) with J1 = -7.44 cm-1, J2 = -51.98 cm-1, and g = 1.99. The magnetization data allows us to deduce the ground term of S = ½, characteristic of equilateral triangular chromium(III) for complex 1 and S = 3/2 for complex 2, which is confirmed by EPR measurements. [ABSTRACT FROM AUTHOR]

Coordination polymers (CPs) with a dual emission spanning from the visible (vis) to near-infrared (NIR) regions of the electromagnetic spectrum are used for optical sensors, medical diagnostics, and telecommunication technologies. We herein report the synthesis, structural characterization, and optical response of heterometallic cyanido-bridged layered {[Eu x Nd y (4-OHpy) 2 (H 2 O) 3 ][Co(CN) 6 ]} CPs, where 4-OHpy = 4-hydroxypyridine, with a multicolor emission profile across the vis and NIR regions. The crystals show an efficient energy transfer (ET) from the 4-OHpy ligand and the [Co(CN) 6 ] ions to the Eu 3+ and Nd 3+ ions, resulting in an enhanced photoluminescence (PL) efficiency. We study the ET with steady-state and time-resolved PL, reporting an ET between the Ln 3+ centers. The excitation-dependent emission of the mixed Ln 3+ CPs and the control over the PL lifetime yield new insights into the optoelectronic properties of these materials.

The diamagnetic two-dimensional Hofmann-type metal-organic framework [Zn II (2-mpz) 2 Ni(CN) 4 ] has been successfully synthesized along with its isostructural hysteretic spin-crossover Fe II analogue in the form of both bulk microcrystalline powder and nanoparticles. Detailed atomic force microscopy topographic study revealed a nanogrowth relationship between the height and length of the nanoparticle.

While synthetic methods for the grafting of nanoparticles or photoactive molecules onto carbon nanotubes (CNTs) have been developed in the last years, a very limited number of reports have appeared on the grafting of single-molecule magnets (SMMs) onto CNTs. There are many potential causes, mainly focused on the fact that the attachment of molecules on surfaces remains not trivial and their magnetic properties are significantly affected upon attachment. Nevertheless, implementation of this particular type of hybrid material in demanding fields such as spintronic devices makes of utmost importance the investigation of new synthetic protocols for effective grafting. In this paper, we demonstrate a new experimental protocol for the noncovalent grafting of Dy III 2 SMM, [Dy 2 (NO 3 ) 2 (saph) 2 (DMF) 4 ], where H 2 saph = N-salicylidene- o-aminophenol and DMF = N, N-dimethylformamide, onto the surface of functionalized multiwalled CNTs (MWCNTs). We present a simple wet chemical method, followed by an extensive washing protocol, where the cross-referencing of data from high-resolution transmission electron microscopy combined with electron energy loss spectroscopy, conventional magnetic measurements (direct and alternating current), X-ray photoelectron spectroscopy, and Raman spectroscopy was used to investigate the physical properties, chemical nature, and overall magnetic behavior of the resulting hybrids. A key point to the whole synthesis involves the functionalization of MWCNTs with carboxylic groups, which proved to be a powerful strategy for enhancing the ability to process MWCNTs and facilitating the preparation of hybrid composites. While in the majority of analogous hybrid materials the raw carbon material (multiwalled or single-walled nanotubes) is heavily treated to minimize the contribution of contaminant traces of magnetic nanoparticles with important effects on their electronic properties, this method can lead easily to elimination of the largest part of the impurities and provide an effective way to investigate/discriminate the magnetic contribution of the SMM molecules.

The synthesis, crystal structure, and magnetic properties of two trinuclear oxo-centered carboxylate complexes are reported and discussed: [Cr3(mu3-O)(mu2-PhCOO)6(H2O)3]NO3.4H2O.2CH3OH (1) and [Cr3(mu3-O)(mu2-PhCOO)2(mu2-OCH2CH3)2(bpy)2(NCS)3] (2). For both complexes the crystal system is monoclinic, with space group C2/c for 1 and P1/n for 2. The structure of complex 1 consists of discrete trinuclear cations, associated NO3- anions, and lattice methanol and water molecules. The structure of complex 2 is built only by neutral discrete trinuclear entities. The most important feature of 2 is the unusual skeleton of the [Cr3O] core due to the lack of peripheral bridging ligands along one side of the triangular core, which is unique among the structurally characterized (mu3-oxo)trichromium(III) complexes. Magnetic measurements were performed in the 2-300 K temperature range. For complex 1, in the high-temperature region (T > 8 K), experimental data could be satisfactorily reproduced by using an isotropic exchange model, H = -2J12S1S2 - 2J13S1S3 - 2J23S2S3 (J12 = J13 = J23) with Jij = -10.1 cm(-1), g = 1.97, and TIP = 550 x 10(-6) emu mol(-1). The antisymmetric exchange interaction plays an important role in the magnetic behavior of the system, so in order to fit the experimental magnetic data at low temperature, a new magnetic model was used where this kind of interaction was also considered. The resulting fitting parameters are the following: Gzz = 0.25 cm(-1), delta = 2.5 cm(-1), and TIP = 550 x 10(-6) emu mol(-1). For complex 2, the experimental data could be satisfactorily reproduced by using an isotropic exchange model, H = -2J1(S1S2 + S1S3) - 2J2(S2S3) with J1 = -7.44 cm(-1), J2 = -51.98 cm(-1), and g = 1.99. The magnetization data allows us to deduce the ground term of S = 1/2, characteristic of equilateral triangular chromium(III) for complex 1 and S = 3/2 for complex 2, which is confirmed by EPR measurements.

The reaction of Ln(NO(3))(3).aq with K(3)[Fe(CN)(6)] or K(3)[Co(CN)(6)] and 2,2'-bipyridine in water led to five one-dimensional complexes: trans-[M(CN)(4)(mu-CN)(2)Ln(H(2)O)(4) (bpy)](n)().XnH(2)O.1.5nbpy (M = Fe(3+) or Co(3+); Ln = Sm(3+), Gd(3+), or Yb(3+); X = 4 or 5). The structures for [Fe(3)(+)-Sm(3+)] (1), [Fe(3)(+)-Gd(3+)] (2), [Fe(3)(+)-Yb(3+)] (3), [Co(3)(+)-Gd(3+)] (4), and [Co(3)(+)-Yb(3+)] (5) have been solved; they crystallize in the triclinic space P1 and are isomorphous. The [Fe(3+)-Sm(3+)] complex is a ferrimagnet, its magnetic studies suggesting the onset of weak ferromagnetic 3-D ordering at 3.5 K. The [Fe(3+)-Gd(3+)] interaction is weakly antiferromagnetic. The isotropic nature of Gd(3+) allowed us to evaluate the exchange interaction (J = 0.77 cm(-)(1)).

The reaction of Ln(NO3)3.aq with K3[Fe(CN)6] or K3[Co(CN)6] in N,N'-dimethylformamide (DMF) led to 25 heterodinuclear [Ln(DMF)4(H2O)3(mu-CN)Fe(CN)5].nH2O and [Ln(DMF)4(H2O)3(mu-CN)Co(CN)5].nH2O complexes (with Ln = all the lanthanide(III) ions, except promethium and lutetium). Five complexes (Pr(3+)-Fe3+), (Tm(3+)-Fe3+), (Ce(3+)-Co3+), (Sm(3+)-Co3+), and (Yb(3+)-Co3+) have been structurally characterized; they crystallize in the equivalent monoclinic space groups P21/c or P21/n. Structural studies of these two families show that they are isomorphous. This relationship in conjunction with the diamagnetism of the Co3+ allows an approximation to the nature of coupling between the iron(III) and the lanthanide(III) ions in the [Ln(DMF)4(H2O)3(mu-CN)Fe(CN)5].nH2O complexes. The Ln(3+)-Fe3+ interaction is antiferromagnetic for Ln = Ce, Nd, Gd, and Dy and ferromagnetic for Ln = Tb, Ho, and Tm. For Ln = Pr, Eu, Er, Sm, and Yb, there is no sign of any significant interaction. The isotropic nature of Gd3+ helps to evaluate the value of the exchange interaction.