Guido Righini

Versatile Synthesis of Carbon-Rich LiFePO4 Enhancing Its Electrochemical Properties

LiFePO 4 /C composites were prepared from thermal decomposition of Fe(II) organophosphonates Fe[(RPO 3 )(H 2 O)] (R = methyl or phenyl group) in the presence of Li 2 CO 3 at high temperature and under inert atmosphere. The compounds were characterized by chemical analysis, thermogravimetric analysis and differential scanning colorimetry, X-ray powder diffraction, and scanning electron microscopy. Electrodes were fabricated for the electrochemical characterization. The cathode material obtained from Fe[C 6 H 5 PO 3 (H 2 O)] showed a specific energy evaluated at C/10 rate of about 550 Wh kg - 1 . The specific power calculated at 30C rate in excess at 14,000 W kg - 1 , while the specific energy was about 28% of the theoretical one. No capacity fading was observed upon cycling.

Comparison of the structure and magnetic order in a series of layered Ni(II) organophosphonates, Ni[(RPO3)(H2O)] (R = C6H5, CH3, C18H37).

The reaction of nickel chloride with phenyl phosphonic acid under hydrothermal conditions resulted in the isolation of yellow-green single crystals of Ni[(C(6)H(5)PO(3))(H(2)O)]. The structure of the compound has been solved by X-ray single-crystal diffraction studies. Ni[(C(6)H(5)PO(3))(H(2)O)] crystallizes in the orthorhombic space group Pmn2(1) and is isostructural with the Mn(II), Fe(II), and Co(II) analogues. It presents the typical features of the hybrid 2D structures, consisting of alternating inorganic and organic layers. The former are formed by six-coordinated nickel(II) ions bridged by oxygen atoms into the layers. The inorganic layers are capped by the phenyl phosphonate groups, with phenyl groups of two adjacent ligands forming a hydrophobic bilayer region, and van der Waals contacts are established between them. The magnetic properties investigated by means of dc and ac susceptibility measurements point to an AF exchange coupling between nearest neighboring Ni(II) ions. Below 5 K, the compound orders magnetically showing the typical features of a canted antiferromagnet. The magnetic behavior and magnetic dimensionality of Ni[(C(6)H(5)PO(3))(H(2)O)] have been fully analyzed and compared to those of the Ni(II) parent compounds Ni[(RPO(3))(H(2)O)] (where R = CH(3), C(18)H(37)), which exhibit different symmetries of the inorganic layers and lengths of the R groups.

A Novel 1D-AF Hybrid Organic-Inorganic Chromium(II) Methyl Phosphonate Dihydrate: Synthesis, X-Ray Crystal and Molecular Structure, and Magnetic Properties

Light-blue crystals of chromium(II) methyl phosphonate dihydrate, [Cr(CH(3)PO(3))(H(2)O)].H(2)O, were obtained in water by mixing filtered solutions of methylphosphonic acid and chromium(II) chloride in the presence of urea in an inert atmosphere. The compound was characterized by elemental analysis, TGA-DSC, X-ray crystallography, magnetic measurements, and UV-visible and FT-IR spectroscopies. The crystal and molecular structures (orthorhombic Pnma (no. 62): a = 4.4714(5) A, b = 6.8762(7) A, c = 19.180(2) A, Z = 4) have been solved using single-crystal X-ray diffraction. The chromium(II) ion is six-coordinated by oxygens (4 + 2) to form an elongated octahedron, with the four equatorial oxygen atoms belonging to [-PO(3)](2-) phosphonate groups. This stereochemistry of the Cr(II) ion (high-spin d(4) electronic configuration) is ascribed to the Jahn-Teller effect. The [CrO(6)] chromophore, the [CH(3)PO(3)](2-) anions, and the water molecules build a novel one-dimensional (1D) metal(II) oxide chain, anchored to each other within the ab plane by two oxygens of the phosphonate ligand. Within the chain, each Cr(2+) ion is connected through double oxygen bridges to its two neighbors, forming edge-sharing octahedra running along the b axis. The chains are further connected with the adjacent chains by phosphonate [-PO(3)](2-) groups of the ligand, forming an inorganic layer that alternates along the c axis of the unit cell with bilayers, consisting of methyl groups and water of crystallization. The thermal variation of the magnetic susceptibility follows the Curie-Weiss law, with a large negative Weiss constant, theta = -60 K, indicating the presence of antiferromagnetic AF exchange interactions between neighboring Cr(II) ions. The magnetic behavior and the magnetic dimensionality have been analyzed in terms of Fishers classical limiting form of the Heisenberg chain theory, and a value of J = -9.3 cm(-1) was found. The negative value of the intra-chain exchange constant coupling J confirms the presence of an AF coupling. No sign of long-range magnetic ordering down to 2 K (the lowest measured temperature) is observed, in agreement with the predominant one-dimensional character of the exchange interactions.

Nickel(II) 3,4;9,10-Perylenediimide bis-Phosphonate Pentahydrate: A Metal−Organic Ferromagnetic Dye

The new metal-organic compound nickel(II) 3,4;9,10-perylenediimide bis-phosphonate pentahydrate, i.e. Ni(2)[(PDI-BP)(H(2)O)(2)]·3H(2)O (1), has been synthesized and its structural and magnetic properties have been studied. Reaction of 3,4;9,10-perylenediimide bis-phosphonate (PDI-BP, hereafter) ligand and nickel chloride in water resulted in the precipitation of a red and poorly crystalline solid (1). As the solid shows a poor crystalline organization of aggregates, the energy dispersive X-ray diffraction analysis (EDXD) technique has been used to obtain short-range order structural information of the single nanoaggregates by radial distribution function analysis. The overall structure of the compound is characterized by layers containing perylene planes shifted in the direction perpendicular to the stacking axes in such a way that only the outer rings overlap. The edges of the perylene planes are connected to the phosphonate groups through an imido group. The oxygen atoms of the [-PO(3)](2-) group and those of the water molecules are bonded to the nickel ions resulting in a [NiO(6)] octahedral coordination sphere. The Ni-O bond lengths are 0.21 ± 0.08 nm and the Ni-O-Ni angles of aligned moieties are 95 ± 2°. The oxygen atoms of the water molecules and the nickel atoms are nearly planar and almost perpendicular to the perylene planes forming chains of edge-sharing octahedra. The magnetic properties of (1) show the presence of intrachain ferromagnetic Ni-Ni interactions and a long-range ferromagnetic order below 21 K with a canting angle and with a spin glasslike behavior due to disorder in the inorganic layer. Hysteresis cycles show a coercive field of ca. 272 mT at 2 K that decreases as the temperature is increased and vanishes at ca. 20 K.

Ni(II)octadecylphosphonate: an inorganic/organic layered weak-ferromagnet

Ni[CH3(CH2)17PO3]/H2O was prepared and characterized by several techniques and the magnetic properties were measured by using a SQUID magnetometer. Preliminary refinement of the X-ray diffraction powder data by structure-less Le Bail fitting could be obtained and the compound was found to crystallise in the orthorhombic space group Pmn21 with a � /5.478(7) A ˚ , b � /42.31(4) A ˚ , c � /4.725(3) A ˚ . Ni(II)octadecyl phosphonate is lamellar and the structure consists of alternating inorganic and organic layers. The inorganic layers are interspersed by by-layers of the octadecyl substituent and van der Waals contacts are established between them. IR spectroscopy revealed all-trans configuration of the hydrocarbonic chain. A tilt angle of 48.28 between the chain axis and the (ac ) plane could be estimated. The temperature dependence of the molar susceptibility plotted as 1/x vs. T is linear above 100 K and it follows the Curie � /Weiss law. The Curie, C , constant suggests the presence of Ni(II) ion in the S � /1 spin state and the negative Weiss, u , constant is indicative of antiferromagnetic nearest neighbour exchange interactions. Zero-field and field-cooled x vs. T plots were then recorded. The plots show no overlap below 20 K, thus indicating that the compound is in an ordered magnetic state. The critical temperature has been located at the onset of the x vs. T plot and was found to be TN � /21 K. The magnetization vs. field plots, measured at different temperatures, provide the indication that the compound is a weak-ferromagnet below TN. # 2003 Elsevier Science Ltd. All rights reserved.

Mercury complexes with 1,2,6,7-tetracyano-3,5-dihydro-3,5-diimino-pyrrolizinide

The anion 2-(5-amino-3,4-dicyano-2H-pyrrol-2-ylidene)-1,1,2-tricyanoethanide (L′, C11H2N7−), after isomerization to 1,2,6,7-tetracyano-3,5-dihydro-3,5-diimino-pyrrolizinide (L), forms different metal-complexes with mercury depending on the experimental conditions. Pure compounds were isolated from the reactions HL+CH3HgAc in CH3CN and NaL′+HgAc2 in AcH/H2O. They are CH3HgL and HgL2. From their optical spectra, compared to those of phthalocyaninato- or other well-known pyrrolizinato-complexes, the coordination geometry of Hg(II) in these species is supposed to be trigonal planar and trigonal monopyramidal, respectively. CH3HgL was characterized also by 1H NMR: (CD3CN, δ, ppm) 0.886 (CH3), 8.733 (NH). From the reactions in water between NaL′ and HgCl2 or HgClO4 complex mixtures of polynuclear complexes were isolated of composition: 0.826 [Hg2ClL2(OH)]·0.174 [Hg4L3(OH)5]·2.06 H2O (A) or 0.588 [Hg2L2]·0.412 [Hg2L(OH)3]·3.53 H2O (B), respectively. The formulae A and B were based on thermogravimetric and elemental analysis data. Indirect evidences, based on XPS data, for the existence of the pyrrolizinato–Hg(I) complex are also given.

Azetidinium lead iodide: synthesis, structural and physico-chemical characterization

The synthesis of an azetidinium lead iodide perovskite (CH2)3NH2PbI3 (AzPbI3), and its extensive characterization are reported. The compound was synthesized through a simple approach based on the reaction between an azetidine aqueous solution and lead acetate dissolved in an excess of hot concentrated aqueous HI. The compound was recrystallized by the vapor diffusion method. Since the synthesized AzPbI3 crystals consistently turned out to be twinned and disordered, the structure determination was performed by using powder X-ray diffraction data analysis procedures. The material was found to possess a quite complex and large rhombohedral crystal structure with a zig-zag array of groups composed of three PbI6 octahedra sharing faces along the c-axis. Unfortunately, because of the extended cationic sublattice disorder and of the large X-ray scattering factor difference between the atoms composing the (CH2)3NH2PbI3 (AzPbI3) unit cell, the position of azetidinium cations could not be determined with confidence. The material was also characterized by CHN, ESI-MS analyses and FT-IR spectroscopy in order to verify its chemical composition. Furthermore, TG-DTA coupled to quadrupole mass spectrometry, temperature-controlled powder XRD and Knudsen effusion mass spectrometry were employed to evaluate the thermal stability of the material. Besides, diffuse reflectance UV-vis spectroscopy and PL measurements were carried out to investigate the optical properties of the material. Optical properties turned out to be very sensitive to preparative conditions. In addition, a test of mutual solid solubility with methylammonium lead iodide, CH3NH3PbI3, was performed by co-precipitation of both perovskites. Powder XRD clearly showed mutual solubility. Hence, the higher basicity of azetidine compared to that of methylamine may enhance the stability of solid solutions made out of the two perovskites with respect to the hydrolysis of pure CH3NH3PbI3 thus increasing the lifetime of perovskite solar devices.