Carlo Bellitto

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.

Feature article. Organic-intercalated halogenochromates(II): low-dimensional magnets

Ferromagnetism in non-metallic solids is quite a rare property. In solids containing molecular building blocks it is even rarer. One strategy for preparing ionic ferromagnets is to combine a low-dimensional continuous lattice containing transition-metal ions with organic molecular ions. In this article we review the synthesis, structures and magnetic and optical properties of halogenochromate(II) salts with substituted ammonium cations. The shape of the latter has a striking influence on the bulk magnetic behaviour of the solids. Monosubstituted cations yield tetrahalogenochromates(II) with layer structures which are ferromagnets with Curie temperatures up to 60 K. On the other hand, tetramethylammonium trihalogenochromates(II) are one-dimensional antiferromagnets. The striking difference in the intensities of the visible absorption spectra of the two classes of materials can be explained by an exchange-induced electric-dipole mechanism.

Tetrathiafulvalenium salts of planar PtII, PdII, and CuII 1,2-dithio-oxalato-S,S′ anions. Synthesis, chemistry and molecular structures of bis(tetrathiafulvalenium) bis(1,2-dithio-oxalato-S,S′)palladate(II), [ttf]2[Pd(S2C2O2)2], and of bis(tetrathiafulvalenium)tetrathiafulvalene bis(1,2-dithio-oxalato-S,S′)platinate(II), [ttf]3[Pt(S2C2O2)2]

Tetrathiafulvalenium (ttf) salts with inorganic dithio-oxalato anions, [ttf]2[Pd(S2C2O2)2](1), [ttf]2[Pt(S2C2O2)2](2) and [ttf]1.0[Cu(S2C2O2)2](3) were prepared by reaction of [ttf]3[BF4]2 and the corresponding [A]2[M(S2C2O2)2](where A = NEt4 or AsPh4; M = PdII PtII or CuII) in acetonitrile, or by electrocrystallization of neutral ttf in acetonitrile containing [NEt4]2[Pt(S2C2O2)2] in the case of [ttf]3[Pt(S2C2O2)2](4). The crystal and molecular structures of compounds (1) and (4) were determined by single-crystal X-ray diffraction. Compound (1) crystallizes in the monoclinic space group P21/c with unit-cell dimensions a= 9.447(2), b= 11.044(4), c= 12.299(2)A, β= 113.52(2)°, and Z= 2. The ttf molecules exist as dimeric (ttf˙+)2 and form mixed stacks with the anions along the b axis of the unit cell. Compound (4) crystallizes in the monoclinic space group P21/c with unit-cell dimensions a= 9.754(2), b= 13.905(3), c= 13.733(3)A, β= 119.21 (1)°, and Z= 2. Two crystallographically independent ttf units are present: the first comprises dimerized (ttf˙+)2, and the Second is neutral (ttf0) and perpendicular to the dimer. The compound is better formulated as [(ttf˙+)2(ttf0)][Pt(S2C2O2)2]. Electron spin resonance, infrared and X-ray photoelectron spectroscopic studies of the palladium and platinum derivatives indicate that, in each compound, the metal ion is in the oxidation state +2 and that ttf is present as (ttf˙+)2and ttf0 as found in the crystal structure. The copper compound contains the metal ion in the uncommon oxidation state +3. Infrared, photoelectron, and electronic spectra suggest that the molecular structure of this compound consists of (ttf˙+)2dimers and planar diamagnetic [Cu(S2C2O2)2]–.

Synthesis, Crystal Structure and Spectroscopic Studies of New Charge Transfer Compounds Obtained by Reaction of TTF and the Polyoxoanion [Mo 6 O 19 ] 2−

Two different tetrathiafulvalene radical cation salts of the [M0 6 O 19 ] 2− polyoxoanion have been isolated and characterized. Compound 1 corresponds to the chemical formula (TTF) 3 [Mo 6 0 19 ]. The crystal structure shows a ID stack of the donor TTF molecule, and each stack fits into channels formed by the anions. Within the stack a chain of trimers is identified, the inter-trimeric distance being 3.51 A. The I.R., electronic and XPS spectra suggest the compound to be a mixed-valence salt. The electrical conductivity at room temperature is σ = 10 −4 Ω −1 cm −1 Compound 2 corresponds to the chemical+formula (TTF) 2 [M0 6 0 19 ] . The compound consists of isolated (TTF +• ) 2 dimers, interspersed with the polyoxoanions. In agreement with this crystal structure the compound is a diamagnetic insulator.

Supramolecular architecture and magnetic properties of copper(II) and nickel(II) porphyrinogen-TCNQ electron-transfer salts.

The compounds [Cu(Tz)-(MeOH)2](TCNQ)2 (1), [Ni(Tz)-(MeOH)2](TCNQ)2 (2), [Cu(Tz)2]-(TCNQ)7 (3) and [Ni(Tz)2](TCNQ)7 (4) (Tz = 2,7,12,17-tetramethyl-1,6,11,16-tetraazaporphyrinogen) were obtained by metathesis reaction of [M(Tz)](ClO4)2 with LiTCNQ and Et3NH(TCNQ)2, respectively. They were characterized by a combination of spectroscopic and physical methods. Compound 1 crystallizes in the monoclinic space group P2(1)/n with a = 8.310(2), b = 25.180(4), c = 20.727(4) A, beta = 93.58(2) degrees; Z = 4. Compound 3 crystallizes in the triclinic space group P1 with a = 11.244(1), b = 16.700(1), c = 17.321(1) A, a = 113.47(1), beta = 108.52(1), gamma = 96.12(1) degrees; Z = 2. The asymmetric unit of the compound 1 is formed by cationic [Cu(Tz)(MeOH)2]2+ and by two crystallographically non equivalent TCNQ.- anions; these anions form dimeric units by overlap of the pi clouds. The dimers form hydrogen bonds with the metal-lomacrocyclic cation through the methanol ligands. According to this structure the compound is paramagnetic and behaves as an insulator in the temperature range studied. The paramagnetism arises only from the metal-complex moieties. Compound 3 shows an unprecedented structure due to the steric requirements of the macrocycle that favors the stacking of the TCNQ groups. The structure consists of infinite stacks of TCNQ units separated by the metal-macrocyclic units; there are seven TCNQ molecules per formula unit, one of which is formally mono-anionic, while the other six bear one half of an electron per molecule. The copper is six-coordinate in a very distorted octahedral environment. The Tz ligand is located in the equatorial plane and the apical nitrogens of the nitrile groups of two TCNQ molecules complete the coordination around the copper. The compound is a semiconductor and its magnetic behavior can be explained by the sum of the Curie contribution of the metal complex and the contribution arising from the magnetic-exchange interactions of the spins located on the TCNQ units. The latter is found to be typical of one-dimensional antiferromagnetic distorted chains of S = 1/2 spins and can be fitted according to a one-dimensional Heisenberg antiferromagnetic model.

Structures and properties of new charge transfer compounds derived from organic donor molecules and inorganic polyoxoanions PM12O403− and M6O192−, where M = Mo, W

Abstract A series of new charge-transfer salts based on TTF, BEDT-TTF and several polyoxometalate ions have been synthesized and characterized. In the case of TTF derivatives two types of compounds have been isolated. The first show a distorted one-dimensional structure, while the second contain completely ionized and dimerized (TTF +. ) 2 . A relationship between the crystal structure and the physical properties in these materials is discussed. Electrolysis of BEDT-TTF at constant current in the presence of (But 4 N) 2 Mo 6 O 19 gave a black microcrystalline product of formula (BEDT-TTF) 2 Mo 6 O 19 .

Magnetic and optical characterization of one-dimensional isostructural σ-bonded tetracyanoquinodimethanido complexes of nickel(II) and copper(II)

The complex [CuL(tcnq)2][L = 3,10-bis(2-hydroxyethyl-1,3,5,8,10,12-hexaazacyclotetradecane); tcnq = 7,7,8,8-tetracyanoquinodimethane] has been prepared and crystallographically characterized. Its structure consists of linear chains of alternating copper–macrocycle and tetracyanoquinodimethanide dimers σ bonded to the copper atoms through a nitrile group. The compound is an insulator. The magnetic properties of both the copper and corresponding nickel compounds are the sums of the contributions arising from the transition-metal ion in octahedral symmetry and of (tcnq)22– dimers. The magnetic data were fitted by a model which accounts for contributions from independent Curie spins for the cation and a thermally activated triplet state for the dimerized anions. No magnetic interactions between the metal ion and tcnqs have been observed, even at low temperatures.

Field dependence of the spin Peierls transition in α′-(BEDT-TTF)2Ag(CN)2

Abstract The spin Peierls transition in α′-(BEDT-TTF)2Ag(CN)2 has been studied as a function of magnetic field up to 5 Tesla. The data at temperatures above 20K are found to be best fitted to the Bonner-Fisher model for a linear chain antiferromagnet with J/kB59K. Below 6K the susceptibility is fitted with a Bulaevskii model for a temperature dependent dimerising chain with γ=0.75 at 500G increasing to 0.80 at 30000G. The electron-phonon coupling parameter λ is 0.27, the BCS gap Δ(0)=13.8K is higher than the theoretical value (10.2K) and the effective phonon frequency 7.5 cm−1.

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.