José Ruiz

Structure and magnetic properties of a syn-anti carboxylate bridged linear trinuclear copper(II) complex with ferromagnetic exchange interaction

Abstract The synthesis, crystal structure and magnetic properties are reported for the trinuclear compound [Cu(H2O)4{Cu(HL)(H2O)(ClO4)}2][ClO4]2·2H2O, where HL is the monodeprotonated form of 6-methylamino-1,3-dimethyl-5-[(2′-carboxyphenyl)azo]uracil. The compound crystallizes in the triclinic system, space0 group P 1 , with cell constants a=7.824(3), b=12.278(3), c=13.705(9) A, α=104.34(3), β=91.80(3), γ=103.37(5)° and Z=1. The structure was solved and refined to R=0.071 (Rw=0.064). The structure consists of trinuclear [Cu(H2O)4{Cu(HL)(H2O)(ClO4)}2]2+ cations, non-coordinated perchlorate anions and crystal water molecules, held together by a network of hydrogen bonds. The central copper is in an elongated octahedral CuO6 chromophore and the terminal copper atoms in distorted square-pyramidal CuNO4 chromophores. Adjacent copper atoms are linked by carboxylate groups in a syn-anti conformation. From the magnetic susceptibility measurements, the complex is found to exhibit weak ferromagnetic interaction between nearest-neighbour copper(II) ions. The magnitude and nature of the exchange coupling are discussed on the basis of the structural data.

Structure, magnetism and DFT studies of dinuclear and chain complexes containing the tetrazolate-5-carboxylate multidentate bridging ligand.

The reaction of K(2)TzC (H(2)TzC = tetrazole-5-carboxylic acid) and either MnCl(2) x 4 H(2)O or CuCl(2) x 2 H(2)O under hydrothermal conditions leads to the formation of three new polynuclear complexes of formula [Mn(TzC)(H(2)O)(2)](n) 1 and [M(2)(TzC)(2)(H(2)O)(6)] x nH(2)O (M = Mn(II) 2, n = 4 and Cu(II) 3, n = 2). Complex 1 displays a 1D planar zig-zag chain structure where the ligand is disorderd into two positions and exhibits two mu(3)-chelating/bridging tetradentate coordination modes, one through the two carboxylate oxygen atoms and the neighbouring nitrogen atom of the tetrazolate ring and the other one through three neighboring nitrogen atoms belonging to the tetrazole ring and one of the carboxylate oxygen atoms. The structure of 2 and 3 consists of centrosymmetric dinuclear molecules, in which the ligands exhibit a mu(2)-chelating/bridging coordination mode through one of the carboxylate oxygen atoms and two neighbouring nitrogen atoms of the tetrazolate ring, generating a planar M(N-N)(2)M hexagon. Variable-temperature magnetic susceptibility studies reveal a weak antiferromagnetic interaction for 1 (J = -1.5 cm(-1)). In spite of the coplanarity of the tetrazolate and metal coordination planes in 2 and 3, they exhibit very weak antiferromagnetic interactions. DFT calculations have been performed in order to explain this unexpected magnetic behaviour.

A ferromagnetically coupled diphenoxo-bridged Gd3+-Mn2+ dinuclear complex with a large magneto-caloric effect

A novel diphenoxo-bridged Gd(3+)-Mn(2+) dimer is proposed as a good candidate for cryogenic magnetic refrigeration. The large MCE is enhanced by the ferromagnetic interaction between the two metal ions.

Preparation, crystal structures and magnetic properties of a syn-anti carboxylate-bridged dinuclear copper(II) complex and its precursor, a hydrogen-bonded polynuclear copper(II) complex

Abstract Reaction of the polynuclear zig-zag chain complex [{Cu(L)(H2O)}n] (H2L=5-[(2-carboxyphenyl)azo]-1,3-dimethylbarbituric acid) and pyrazole (Hpz) produces the complex of formula [{Cu(L)(Hpz)(H2O)}·H2O] (1). By heating 1 at 110 °C and further recrystallization in dry acetone the complex [{Cu(L)(Hpz)}2] (2) is isolated. Complex 1 crystallizes in the triclinic space group P 1 , with a=8.011(1), b=10.399(2), c=12.815(3) A, α=104.15(2), β=107.43(2), γ=105.80(2)° and Z=2, and complex 2 crystallizes in the monoclinic space group P21/c, with a=9.539(5), b=20.791(10), c=8.723(4) A, β=103.88(1)° and Z=2. The structure of 1 consists of neutral [{Cu(L)(Hpz)(H2O)}·H2O] molecules which are interconnected by hydrogen bonds giving rise to a zig-zag chain of copper(II) ions with two different Cu···Cu distances of 7.862(2) and 7.221(1) A. The structure of 2 consists of centrosymmetrical dinuclear molecules [{Cu(L)(Hpz)}2], in which copper(II) atoms of the mononuclear fragments are connected by carboxylate groups displaying syn-anti conformation, with a Cu···Cu distance of 5.054(2) A. In both complexes, copper atoms exhibit distorted square-pyramidal environments. In the basal plane, four bonds are formed with the doubly deprotonated L2− ligand and the molecule of pyrazole, while the apical position is occupied either by a molecule of water in 1 or an oxygen atom belonging to the carboxylate group of an adjacent and symmetry-related fragment in 2. From magnetic susceptibitity measurements, complex 1 is found to exhibit a weak intermolecular antiferromagnetic exchange interaction with J=−0.30 cm−1 whereas a Curie-Weiss law with C=0.40 cm3 mol−1 K and θ=0.45 K is observed for 2. Magnetic experimental data are discussed on the basis of the structural results and compared to those of other related complexes.

Spectroscopic and magnetic properties, and crystal structure of a dimer copper(II) complex via hydrogen bonding with a weak ferromagnetic interaction

The preparation, spectroscopic and magnetic properties, and crystal structure of [Cu(Cl)(HL)(H2O)]2·6H2O (HL stands for the monodeprotonated form of 4-methyl-amino-1,3-dimethyl-5((2′-carboxyphenyl)azo)uracil) are reported. Crystals are monoclinic, of space group P21/n, with cell constants a = 7.358(1), b = 20.542(4) and c = 13.130(3) A, β = 93.23(3)° and Z = 4. The structure was solved and refined to R = 0.059 (Rw = 0.047). The structure consists of Cl···HO hydrogen- bonded dinuclear units, which are also coupled via hydrogen bonds to form the tridimensional network. The geometry of each CuNO3Cl chromophore is almost that corresponding to an ideal square-pyramid. The magnetic results indicate a ferromagnetic ground state. The nature of the magnetic interaction is discussed on the basis of structural data.

The preparation, spectroscopic study and crystal structures of two copper(II) complexes of closely related carboxyphenylazopyrimidine ligands, involving distorted square-pyramidal CuN4O and CuN3O2 chromophores

Abstract The preparation, spectroscopic properties and crystal structures of two isostructural complexes [Cu(L1)(dpa)] (1) [H2L1-6-amino-1,3-dimethyl-5(2′-carboxyphenyl)azouracil, dpa-2,2′-dipyridylamine] and [Cu(L2)(dpa)] (2) [H2L2 is 1,3-dimethyl-5(2′-carboxyphenyl)azobarbituric acid] are reported. The H2L ligands act in a double-deprotonated tridentate mode giving rise to CuN4O and CuN3O2 chromophores with distorted square-pyramidal geometry. The EPR spectra of 1 and 2 show that the replacement of the 6-amino group in the former by a hydroxyl group in the latter increases g‖ and decreases A‖ values, clearly indicating that the in-plane ligand field strength of L1 is greater than that of L2 in 2.

Aurophilicity as a cofactor in crystal engineering. Dicyanoaurate(I) anion as a building block in a novel Co(II)-Au(I) bimetallic assembly

A 2D grid-shaped cyanide-bridged Co(II)-Au(I) bimetallic coordination polymer, [Co(DMF)2(Au(CN)2)2], has been prepared from the [Au(CN)2]- building block; sheets associate pair-wise by aurophilic interactions and the compound exhibits zeolite-like properties.

ORTHOMETALATION OF 6-AMINO-1,3-DIMETHYL-5-PHENYLAZOURACIL : CRYSTAL STRUCTURE AND SPECTROSCOPIC PROPERTIES OF TRANS-RHIIICL2(L)(H2O).3H2O

Abstract The preparation and spectroscopic characterization of two iso-structural complexes trans-[RhIIIX2(L)(H2O)]·3H2O (HL is 6-amino-1,3-dimethyl-5-phenylazouracil and X stands for Cl and Br) are reported. In addition, the crystal structure of the complex trans-[RhIIIX2(L)(H2O)]·3H2O has been solved and refined to R = 0.039 (Rw = 0.045). The compound crystallizes in the triclinic space group P 1 (No. 2) with cell constants a = 57.395(4), b = 11.412(3), c = 11.776(4) A , α = 77.42(2) , β = 75.14(3), γ =78.67(2)°, V = 927(2) A 3 , Z = 2, D c = 1.74 g cm −3 , D exp = 1.75(2) g cm −3 , F(000) = 5 , μ(Mo Kα) = 1.305 mm−1. In this complex the ligand undergoes orthometalation, coordinating in a monodeprotonated fashion tridentate through an exocyclic oxo group, the azo group and the carbon atom of the phenyl ring ortho to the azo group. The three remaining positions are occupied by two chlorine atoms in trans position and a water molecule.

Reactions of the polynuclear chain complex [Cu(L)(H2O)]n (H2L is 5-[(2′-carboxyphenyl)azo]-1,3-dimethylbarbituric acid) with imidazole. Crystal structures of the dinuclear and mononuclear derivatives and EPR study of the dimer-monomer equilibrium in solution

On treating the polynuclear chain complex [Cu(L)(H2O)]n (H2L is 5-[(2′-carboxyphenyl)azo]-1, 3-dimethylbarbituric acid) with imidazole the complexes [Cu(L)(Him)]2 (1) and [Cu(L)(Him)2] (2) are obtained. The structures of 1 and 2 have been determined by X-ray crystallographic methods. The structure of 1 consists of dinuclear units in which the copper ions are bridged by the barbituric ring. It crystallizes in the monoclinic space group P21/c with cell constants a = 8.654(2), b = 22.64(2), c = 8.8048(8) A, β = 103.76(1)°, Z = 2, R = 0.051 and Rw = 0.041. The structure of 2 consists of discrete [Cu(L)(Him)2] molecules held together by intermolecular hydrogen bonds to form infinite chains. It crystallizes in the triclinic space group P1 with cell constants a 8.268(2), b = 9.412(3), c = 13.798(5) A, α = 99.07(3), β = 91.20(3), γ = 108.64(2)°, Z = 2, R = 0.041 and Rw = 0.035. Comparison of the crystal structure of 1 with analogous complexes containing nitrogen heterocyclic ligands reveals that the replacement of imidazole by pyrazole or pyridine leads to very different crystal structures, which has been attributed to the different nature of the nitrogen heterocyclic ligand used in their syntheses. In dmso solution, EPR spectra of both complexes clearly indicate the existence of a monomer-dimer equilibrium.

Component-based derivation of a parallel stiff ODE solver implemented in a cluster of computers

A component-based methodological approach to derive distributed implementations of parallel ODE solvers is proposed. The proposal is based on the incorporation of explicit constructs for performance polymorphism into a methodology to derive group parallel programs of numerical methods from SPMD modules. These constructs enable the structuring of the derivation process into clearly defined steps, each one associated with a different type of optimization. The approach makes possible to obtain a flexible tuning of a parallel ODE solver for several execution contexts and applications. Following this methodological approach, a relevant parallel numerical scheme for solving stiff ODES has been optimized and implemented on a PC cluster. This numerical scheme is obtained from a Radau IIA Implicit Runge–Kutta method and exhibits a high degree of potential parallelism. Several numerical experiments have been performed by using several test problems with different structural characteristics. These experiments show satisfactory speedup results.