Trinidad López

Synthesis, crystal structure and magnetic properties of two-dimensional malonato-bridged cobalt(II) and nickel(II) compounds

Two isostructural malonato-bridged complexes of formula {[M(H2O)2][M(mal)2(H2O)2]}n [M = Co(II) (1), Ni(II) (2); H2mal = malonic acid] have been synthesised and characterized by X-ray diffraction. Their structure consists of corrugated layers of trans-diaquabismalonatemetalate(II) and trans-diaquametal(II) units bridged by carboxylate–malonate groups in the anti–syn conformation. Two crystallographycally independent metal atoms occur in 1 and 2. The malonate anion acts simultaneously as a bidentate and bis-monodentate ligand. Variable-temperature (1.9–295 K) magnetic susceptibility measurements indicate the occurrence of weak antiferro- (1) and ferromagnetic (2) interactions between the cobalt(II) (1) and nickel(II) ions (2) through the anti–syn caboxylate–malonate bridge. A brief discussion on the structural diversity and crystal engineering possibilities of the malonate complexes with divalent first-row transition metal ions other than copper(II) is carried out.

Structural and dielectric characterization of cadmium tartrate

Polycrystalline samples of dimeric cadmium tartrate, [(Cd,C4H4O6)2H2O)]3H2O [labeled CdT(I)], were studied using impedance measurements and x-ray powder diffraction. The dependence of the real part of the dielectric constant on temperature showed a sharp peak at about 65 °C, revealing a structural phase transition, while the other broad peak in the temperature range (70<T<85 °C) was due to the loss of water molecules. The x-ray powder diffraction patterns at three temperatures (25, 60, and 70 °C) are consistent with three nonequivalent space groups. According to these results, it seems that this compound undergoes two successive phase transitions: P212121→P21→Pnmn, suggesting an intermediate ferroelectric behavior, labeled CdT(II) between a paraelectric CdT(I) and an anhydrous phase, labeled CdT(III).

Synthesis, crystal structure and magnetic properties of the three-dimensional compound [Na2Ni(mal)2(H2O)6]n (H2mal=malonic acid)

Abstract A new three-dimensional nickel–sodium compound of formula [Na 2 Ni(mal) 2 (H 2 O) 6 ] n (H 2 mal=malonic acid) was prepared and its structure was determined by X-ray diffraction methods. Four malonate–oxygen atoms and two trans -(Ni) or cis -(Na) coordinated water molecules build distorted octahedral surroundings around the metal atoms. The malonate group exhibits bidentate (Ni) and tetrakis-monodentate (Na) coordination modes. The structure can be described as corrugated sheets of malonato-containing Ni(II) and Na(I) cations which grow in the (101) plane, each sheet being linked to the adjacent one in the [101] direction through bis(μ-aqua)disodium(I) units. Within each corrugated sheet, the nickel atoms define a square lattice, the edge and the diagonal being 8.895(3) and 12.579(3) A, respectively. Variable-temperature magnetic susceptibility measurements (2.0–290 K) reveal the occurrence of a very weak antiferromagnetic interaction between the nickel(II) ions.

A phase transition in the novel three-dimensional compound [Eu2(mal)3(H2O)6](H2mal=malonic acid)

Slow diffusion of aqueous solutions of europium(III) chloride into gel of sodium metasilicate containing malonic acid (H2mal) yields single crystals of the three-dimensional compound of formula [Eu2(mal)3(H2O)6] whose structure was determined by X-ray diffraction methods at 293 and 173 K. It crystallizes in the monoclinic system but the spatial group changes from I2/a in the high temperature range (293 ≥ T ≥ 236 K) to Ia in the low temperature range (T < 236 K). In both cases, nine oxygen atoms forming a distorted monocapped square antiprism surround the Eu3+ ions. The structure at 293 K consists of a three-dimensional arrangement of triaquaeuropium(III) units bridged by malonate groups which result from cross-linking of the single chains running parallel to the c axis and the double zig-zag chains which grow in the ab plane. At low temperature the structure of the compound can be visualised as chains of europium(III) ions linked through two of the three crystallographically independent malonate ligands, whose chains run parallel to the b axis and a second family of chains (along the c axis) through the third independent malonate ligand forming a three-dimensional network. In both the crystal structure is stabilised through extensive hydrogen bonding involving carboxylate and water molecules. Studies of the magnetic behaviour, spectroscopic, thermogravimetric and calorimetric characteristics of [Eu2(mal)3(H2O)6] are reported. Laser-excited site selective spectroscopy shows a unique crystal-field site for EuIII ions in the crystal at room temperature and down to 236 K. However, below this temperature, two different sites are clearly identified, in agreement with a change in the crystal structure.

Characterization and thermal and electromagnetic behaviour of gadolinium-doped calcium tartrate crystals grown by the solution technique

Energy dispersive analysis by X-rays (EDAX), X-ray diffraction (XRD), infrared (IR), thermogravimetric (TG), differential thermogravimetric (DTG), differential scanning calorimetric (DSC) and electromagnetic studies carried out on crystalline materials obtained by diffusion of gadolinium and calcium ions through silica gel impregnated with tartaric acid and grown by means of slow cooling between 72°C and 40°C are reported. EDAX confirmed the presence of gadolinium. X-ray diffraction data did not show any appreciable differences between the structures of doped and undoped calcium tartrate. IR in the range of 500–4000 cm−1 and the description of peaks recorded for the material are given. Results of thermal analysis (TG, DTG and DSC) indicated that the material is thermally unstable. Dielectric and magnetic measurements were determined in the frequency range 45 MHz to 2 GHz.

Electrical conductivity of doped and undoped calcium tartrate

The electrical conductivity of polycrystalline samples of calcium tartrate tetrahydrate ([CaC4H4O6 2H2O] 2H2O) in pure form and doped with barium and with strontium were studied in the temperature range (65<T<95°C). According to these results, it seems that two types of conduction exist in these compounds, one at low temperature and the other at high temperature, by the way of extrinsic and intrinsic conduction, respectively. This behavior may be attributed to the rotation of the tartrate ions by thermal energy.

Building-block process for the synthesis of new chromium(III) malonate complexes

We describe the crystal structures of two bimetallic compounds with the malonate and an exo-polydentate N-donor ligand {[Cu(tren)]4[Cr2(mal)4(OH)2]}(ClO4)4·8H2O (3) and [Ni(Htren)2][Cr2(mal)4(OH)2]·8H2O (4) which are prepared from the dinuclear K4[Cr2(mal)4(OH)2]·6H2O precursor (2) [tren = tris(2-aminoethyl)amine and H2mal = malonic acid]. Their crystal packing and supramolecular structures are analyzed in the context of the influence of the dichromium(III) [Cr2(mal)4(OH)2]4− unit, which acts as a building-block. Different supramolecular motifs built up from hydrogen bonds are discussed, and their self-assembly to yield a 3D arrangement is described. The magnetic properties of the compounds 2–4 have been investigated as a function of the temperature. Weak ferro- (J = +2.41 cm−1) and antiferromagnetic (J = −0.21 cm−1) interactions within the di-μ-hydroxodichromium(III) unit occur in 2 and 4, respectively, their different nature being mainly dictated by small structural changes in the centrosymmetric di-μ-hydroxodichromium(II) core [Cr(1)–O–Cr(1a) = 99.48(7) (2) and 100.55(13)° (4) and Cr(1)⋯Cr(1a) = 3.0137(6) (2) and 3.0061(6) A (4)]. An overall antiferromagnetic behaviour is observed for 3 with a maximum of the magnetic susceptibility at ca. 10.0 K, the intramolecular Cr(III)⋯Cr(III) (though the double hydroxo bridge) and Cu(II)⋯Cr(III) (across the carboxylate-malonate in the anti–syn conformation) magnetic couplings being J = −5.53 and −2.78 cm−1, respectively. These magnetic parameters are discussed in terms of the structure of the compounds and compared with previous magneto-structural data on di-μ-hydroxodichromium(III) complexes

Characterization and thermal and electromagnetic behaviour of manganese tartrate crystals grown by the silica gel technique

We report here on the dielectric properties (dielectric constant, ɛ′ and dielectric losses ɛ″), magnetic properties (μ′ and μ″), infrared spectroscopic, thermal studies (thermogravimetric analysis (TGA)), differential thermogravimetry (DTG) and differential scanning calorimetry (DSC) and X-ray diffraction (XRD) for the polycrystalline powdered samples of manganese tartrate MnC4H4O6·2H2O obtained by diffusion of manganese ions through silica gel impregnated with tartaric acid. The aforementioned properties are used as a probe for the detection and study of the different transitions that have been found in this salt. Energy dispersive analysis of X-rays (EDAX) confirmed the presence of manganese. X-ray diffraction data giving 2gq, intensity andd-values are reported for the first time. Infrared wavelengths in the range 500–4000 cm−1 and the description of peaks recorded for the material are given. Results of thermal analysis indicated that the material is thermally unstable. Dielectric and magnetic measurements were determined in the frequency range of 45 MHz to 2 GHz.

Polymeric (aqua-1κo)bis[(R,R)-tartrato-1κ2O1,O2 :2κ2O3,O4]dimanganese(II) trihydrate

The structure of the title compound, {[Mn 2 (C 4 H 2 O 6 ) 2 -(H 2 O)].3H 2 O} n , is comprised of corrugated polymeric sheets of dimeric [Mn 2 {(R,R)-C 4 H 2 O 6 } 2 (H 2 O)] units and water molecules (O2W, O3W and O4W). The manganese ions are coordinated by two (R,R)-tartrate ligands in a cis arrangement. The Mn1...Mn2 intradimeric distance is 5.527 (2) A.

Polymeric aqua-1κo-bis[μ-(R, R)-tartrato-1κ2o1, o2 :2κ2o3, o4]dicadmium(II) trihydrate

The structure of the title compound, {[Cd 2 (C 4 H 4 O 6 ) 2 -(H 2 O)].3H 2 O} n , consists of corrugated polymeric sheets of dimeric [Cd 2 (C 4 H 4 O 6 ) 2 (H 2 O)] units and three water molecules of crystallization. Both cadmium ions are coordinated by two (R,R)-tartrate ligands in a cis arrangement, and the octahedral geometry for each cation is completed by two carboxyl O atoms of different neighbouring dimers or by one carboxyl O atom and a water molecule. Additional water molecules are held in the crystal lattice, forming a hydrogen-bonding network to keep the dimers together in the non-planar sheets.