Luis Lezama

Polynuclear NiII and MnII azido bridging complexes. Structural trends and magnetic behavior

Abstract The azide anion is a good bridging ligand for divalent metal ions, mainly Cu II , Ni II and Mn II . It may give end-to-end (1,3) or end-on (1,1) coordination modes. As a general trend, the 1,1 mode exhibits ferromagnetic coupling while the 1,3 mode creates antiferromagnetic coupling. This review focuses on polynuclear Ni II and Mn II azido bridging complexes. Polynuclear structures known to have these two cations are: discrete (normally dinuclear), one-, two- and three-dimensional nets. The main characteristics of these structures are reported together with their magnetic behavior. From a large number of known structures, magneto-structural correlations are made. Taking into account that M–N 3 distances are always similar, the angles within the M–(N 3 ) n –M unit are the main determinant of the type and magnitude of the exchange coupling. Moreover, some one-, two- and three-dimensional complexes exhibit cooperative effects (long-range magnetic order), behaving as molecular magnets. This behavior is also analyzed.

(C2H10N2)[Cr(HPO3)F3]: The First Organically Templated Fluorochromium(III) Phosphite†

� 3 gL � 1 ) with C32H66 ,C 44H90 ,C 50H102 (1.3 i 10 � 2 gL � 1 ) were spin-coated onto the basal plane of highly oriented pyrolytic graphite (HOPG, Advanced Ceramics Co., USA, quality ZYH at 40 rps). The coated graphite samples were dried for 10 min at 408C before SFM investigations were carried out with a Nanoscope IIIa (Digital Instruments, Santa Barbara, CA) in the tapping mode. An E-scanner over a range of scan lengths from 5 to 0.3 mm, and commercial Si cantilevers (length 125 mm and width 30 mm) with spring constants between 17 and 64 N m � 1

Synthesis and spectroscopic properties of copper(II) complexes derived from thiophene-2-carbaldehyde thiosemicarbazone. Structure and biological activity of [Cu(C6H6N3S2)2].

The synthesis, structure and spectroscopic properties on complexes with the formula [Cu(Lm)2] (1) and Cu(NO3)2(HLm)2 (2), where HLm = thiophene-2-carbaldehyde thiosemicarbazone, have been developed. The molecular structure of compound 1 consists of monomeric entities. The copper(II) ions exhibit distorted square-planar geometry with both bidentate thiosemicarbazone ligands placed in a centrosymmetric way. Metal to ligand pi-backdonation is proposed to explain several structural and spectroscopic features in these complexes. The EPR spectra of compound 1 show an orthorhombic g tensor indicating the presence of weak magnetic exchange interactions. The reaction of compound 1 with glutathione causes the reduction of the metal ion and the substitution of the thiosemicarbazone ligand by the thiol ligand. This mechanism seems to be related to the cytotoxicity of this complex against Friend Erithroleukemia cells (FLC) and melanome B16F10 cells.

High voltage cathode materials for Na-ion batteries of general formula Na3V2O2x(PO4)2F3−2x

Different samples of the sodium–vanadium fluorophosphate cathodic materials have been synthesized via the hydrothermal method, varying the type and content of carbon used in the synthesis. Structural characterization of the composites was performed by powder X-ray diffraction. Magnetic susceptibility measurements and EPR (Electron Paramagnetic Resonance) polycrystalline spectra indicate that some of the samples exhibit V3+/V4+ mixed valence, with the general formula Na3V2O2x(PO4)2F3−2x where 0 ≤ x < 1. The morphology of the materials was analyzed by Transmission Electron Microscopy (TEM). A correlation between the type and content of carbon with the electrochemical behavior of the different samples was established. Electrochemical measurements conducted using Swagelok-type cells showed two voltage plateaux at 3.6 and 4.1 V vs. Na/Na+. The best performing sample, which comprised a moderate percentage of electrochemical grade carbon as additive, exhibited specific capacity values of about 100 mA h g−1 at 1C (≈80% of theoretical specific capacity). Cyclability tests at 1C proved good reversibility of the material that maintained 98% of initial specific capacity for 30 cycles.

Synthesis, characterization, antitumoral and osteogenic activities of quercetin vanadyl(IV) complexes

The development of new vanadium derivatives with organic ligands, which improve the beneficial actions (insulin-mimetic, antitumoral) and decrease the toxic effects, is of great interest. A good candidate for the generation of a new vanadium compound is the flavonoid quercetin because of its own anticarcinogenic effect. The complex [VO(Quer)2EtOH]n (QuerVO) has been synthesized and characterized by means of different spectroscopic techniques (UV–vis, Fourier transform IR, electron paramagnetic resonance) and its magnetic and stability properties. The inhibitory effect on bovine alkaline phosphatase (ALP) activity has been tested for the free ligand, the complex as well as for the vanadyl(IV) (comparative purposes). The biological activity of the complex on the proliferation of two osteoblast-like cells in culture, a normal one (MC3T3E1) and a tumoral one (UMR106), has been compared with that of the vanadyl(IV) cation and quercetin. The differentiation osteoblast markers ALP specific activity and collagen synthesis have been also tested. In addition, the effect of QuerVO on the activation of the extracellular regulated kinase (ERK) pathway is reported. The bone antitumoral effect of quercetin alone was established with the cell proliferation assays (it inhibits the proliferation of the tumoral cells and does not exert any effect on the normal osteoblasts). Moreover, the complex exerts osteogenic effects since it stimulates the type I collagen production and is a weak inhibitory agent upon ALP activity. Finally, QuerVO stimulated the ERK phosphorylation in a dose–response manner and this activation seems to be involved as one of the possible mechanisms for the biological effects of the complex.

Hydrothermal synthesis of a new layered inorganic–organic hybrid cobalt(II) phosphite: (C2H10N2)[Co3(HPO3)4]: Crystal structure and spectroscopic and magnetic properties

The (C2H10N2)[Co3(HPO3)4] phosphite templated by ethylenediamine has been prepared by hydrothermal synthesis. It crystallizes in the triclinic space group P-1 with the parameters: a=5.351(2), b=5.347(4), c=14.010(6) A, α=80.98(5), β=85.66(4), γ=60.04(4)°, V=343.0(3) A3 and Z=1. The compound shows a layered structure stacked along the c-axis. The ethylenediammonium cations are placed between the sheets. Ionic interactions and hydrogen bonds are present between the ethylenediammonium cations and the inorganic layers. The layers are formed by Co3O12 trimeric entities which contain face-sharing CoO6 octahedra interconnected by (HPO3)2− tetrahedral phosphite anions. The spectroscopic study by diffuse reflectance allowed us to obtain the Dq=725 cm−1 and the Racah parameters, B=880 and C=3950 cm−1 for the high spin octahedral Co(II) ions. Magnetic measurements reveal the presence of antiferromagnetic exchange interactions in the trimeric units of (C2H10N2)[Co3(HPO3)4].

Synthetic strategy, magnetic and spectroscopic properties of the terpyridine complexes [Cu(terpy)X(H2O)n]Y (X = NCO, NCS or N3; n= 0 or 1; Y = NO3 or PF6). Crystal structures of the azidenitrate and azidehexafluoro-phosphate

Eight copper(II) complexes with 2,2′:6′,2″-terpyridine (terpy) and pseudohalide ligands. [Cu(terpy)X-(H2O)n]Y [X = NCO, NCS or N3; n= 0 or 1; Y = NO3 or PF6] have been prepared by following a described synthetic strategy. The crystal structures [Cu(terpy)(N3)(H2O)]x[NO3]x and [Cu(terpy)(N3)-(H2O)]2[PF6]2 have been determined: monoclinic, space group P21/n, a= 8.849(2), b= 10.343(1), c= 18.168(3)A, β= 97.71(2)°, Z= 4; triclinic, space group P, a= 9.0609(6), b= 10.2798(8), c= 11.309(1)A, α= 105.22(7), β= 86.58(7), γ= 112.90(6)°, Z = 2. In both complexes [Cu(terpy)(N3)-(H2O)]+ entities are present. For the first compound these form a chain structure, via hydrogen bonding between the co-ordinated water molecule and the nitrate ion. However, the structure of the second compound is built from dimeric [Cu2(terpy)2(N3)2(H2O)2]2+ cations in which the copper ions are connected by one-end bridging azide groups and PF6– counter ions. The co-ordination geometry of the copper(II) ion is square pyramidal and octahedral for the two compounds respectively. The complexes studied can be grouped into three structural types, within each of which the compounds are isostructural. The anhydrous and hydrated hexafluorophosphates have dimeric structures; however, the nitrate compounds are associated in chains. Magnetic susceptibility measurements revealed weak magnetic interactions for all of them. The EPR spectra show ‘half-field’ forbidden transitions for all the complexes and even singlet-to-triplet forbidden transitions for the nitrates. From the positions of these last signals the exchange parameters for the nitrate compounds have been determined. The magnetic interactions have been analysed taking into account several exchange pathways.

Spectroscopic and magnetic properties of copper(II) complexes derived from pyridine-2-carbaldehyde thiosemicarbazone. Structures of [Cu(NO3)(C7H8N4S)(H2O)](NO3) and [{Cu(NCS)(C7H7N4S)}2]

Abstract Complexes with the formula CuX(L) (X=N3 1, NCO 2 and NCS 3) and [Cu(NO3)(HL)(H2O)](NO3) 4, where HL=C7H8N4S, (pyridine-2-carbaldehyde thiosemicarbazone), have been characterised. Single-crystal X-ray diffraction studies on compounds 3 and 4 have been carried out. The structure of compound 4 consists of monomeric distorted square pyramidal copper(II) species. The copper(II) ions are coordinated to the NNS atoms from the tridentate thiosemicarbazone ligand and one oxygen atom of a nitrate group in the equatorial position. The oxygen atom of the water molecule occupies the apical position. The structure of compound 3 consists of non-centrosymmetric {Cu2(μ-SR)2} entities in which the copper(II) ions exhibit five-coordinate square–pyramidal geometry. The thiosemicarbazone ligand and one nitrogen atom from the thiocyanate ion are in a basal position. The sulfur atom of the tridentate ligand acts as a bridge occupying the apical position. Structural and spectroscopic results suggest the presence of relevant σ ligand-to-metal charge transfer and metal-to-ligand π-backdonation character in these compounds. The ESR spectra of compounds 3 and 4 show rhombic symmetry. For complexes 1 and 2 the ESR spectra exhibit axial signals. Magnetic measurements on compounds 1, 2 and 3 show antiferromagnetic couplings. The susceptibility data were fitted by the Bleaney–Bowers’ equation for copper(II) dimers. The obtained J/k values are −4.22, −6.10 and −7.33 K for compounds 1, 2 and 3, respectively.

Synthesis, characterisation and magnetic properties of cobalt(II) complexes with picolinic acid derivatives: the crystal and molecular structures of [Co(MeC5H3NCOO)2(H2O)2] and [CoCl2(C5H4NCOOPri)2]

The reaction of Co(AcO) 2 with 6-methyl-2-pyridinecarboxylic acid, and that of CoCl 2 with the isopropyl ester of 2-pyridinecarboxylic acid, both with a 1:2 metal to ligand molar ratio, afford optimum yields for the synthesis of cis -[Co(MeC 5 H 3 NCOO) 2 (H 2 O) 2 ] and cis -[CoCl 2 (C 5 H 4 NCOOPr i ) 2 ], respectively. According to X-ray crystallography they both consist of mononuclear discrete molecules with octahedral coordination around Co(II). The ESR powder spectra of the related Zn phases doped with 0.25% Co(II) show the strong anisotropy of the g and A tensors. The magnetic behaviour of the solid complexes is characteristic of Co(II) systems with important spin–orbit coupling and weak antiferromagnetic interactions. Electronic UV–Vis and magnetic data indicate that these complexes, as well as the already known trans -[Co(C 5 H 4 NCOO) 2 (H 2 O) 2 ], have a high-spin octahedral geometry in solution.

New Type of Heterometallic 3d-4f Rhomblike Core in Weakley-Like Polyoxometalates

The first heterometallic copper-cerium polyoxometalate, [{Ce(IV)(OAc)}Cu(II)(3)(H(2)O)(B-α-GeW(9)O(34))(2)](11-) (1), is composed of an unprecedented copper(II)-trisubstituted Weakley-type tungstogermanate subunit stabilized by coordination of a {Ce(OAc)}(3+) group at the vacant position. The title species contains a central {Ce(IV)Cu(II)(3)O(18)} rhomblike cluster that belongs to a new {(4f(ext))(3d(ext))(3d(int))(2)} type and magnetically behaves as a triangular Cu(3) system with overall antiferromagnetic exchange affected by the structural distortions the vicinity of diamagnetic Ce(IV) induces.