Scott S. Turner

Fermi-surface topology and the effects of intrinsic disorder in a class of charge-transfer salts containing magnetic ions, \beta''-(BEDT-TTF)_4[(H_3O)M(C_2O_4)_3]Y

We report high-field magnetotransport measurements on β″ -(BEDT-TTF)[(HO)M(CO) ]Y, where M =Ga, Cr, and Fe and Y=CHN. We observe similar Shubnikov-de Haas oscillations in all compounds, attributable to four quasi-two-dimensional Fermi-surface pockets, the largest of which corresponds to a cross-sectional area ≈8.5% of the Brillouin zone. The cross-sectional areas of the pockets are in agreement with the expectations for a compensated semimetal, and the corresponding effective masses are ∼m , rather small compared to those of other BEDT-TTF salts. Apart from the case of the smallest Fermi-surface pocket, varying the M ion seems to have little effect on the overall Fermi-surface topology or on the effective masses. Despite the fact that all samples show quantum oscillations at low temperatures, indicative of Fermi liquid behavior, the sample and temperature dependence of the interlayer resistivity suggest that these systems are intrinsically inhomogeneous. It is thought that intrinsic tendency to disorder in the anions and/or the ethylene groups of the BEDT-TTF molecules leads to the coexistence of insulating and metallic states at low temperatures. A notional phase diagram is given for the general family of β″-(BEDT-TTF) [(HO)M(CO)]Y salts.

The first one-dimensional copper(II)-radical system with alternating double end-on and end-to-end azido bridges

A novel one-dimensional copper(II)-radical complex [Cu(NITmPy)(N3)2(CH3OH)] [NITmPy = 2-(3′-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide] has been synthesized and structurally characterized. The structure consists of neutral chains of copper(II) ions alternatively bridged by double symmetric end-on and asymmetric end-to-end azide groups. The NITmPy radical ligand coordinates to the copper(II) ions through the nitrogen atom of the pyridyl ring. The magnetic properties were investigated in the temperature range 5–300 K. The complex exhibits ferromagnetic interactions between the copper(II) ions through the end-on and end-to-end azido bridging ligands, and between the copper(II) ion and NITmPy radical. The magnetic behavior is discussed with reference to the crystal structure.

Preparation, X-ray crystal structures and properties of α-(BEDT-TTF)2[FeIII(phen)(NCS)4]·2CH2Cl2 and (BEDT-TTF)[CrIII(isoq)2(NCS)4] (phen = 1,10-phenanthroline; isoq = isoquinoline)

This paper reports the preparation, X-ray crystal structure, conducting and magnetic properties of α-(BEDT-TTF)2[FeIII(phen)(NCS)4] (1) [BEDT-TTF = bis(ethylenedithio)tetrathiafulvalene, phen = 1,10-phenanthroline] together with the crystal structure of (BEDT-TTF)[CrIII(isoq)2(NCS)4] (2) (isoq = isoquinoline) for which the physical properties have been reported previously. Compound 1 crystallizes in the triclinic space group P (no. 2), a = 12.1528(1), b = 16.8269(3), c = 27.0703(4) A, α = 95.726(1), β = 95.834(1), γ = 108.080(1)°, Z = 4, R = 0.0610 for 9764 reflections with I > 2σ(I); 2 crystallizes in the monoclinic space group P21/c (no. 14), a =10.623(5), b = 14.656(8), c = 12.701(7) A, β = 100.19(2)°, Z = 2, R = 0.0737 for 2747 reflections with I > 2σ(I). The magnetic and transport properties have shown that compound 1 is a paramagnetic semiconductor with σ300 K = 2.2 × 10−2 Ω−1 cm−1.

Suppression of superconductivity in a molecular charge transfer salt by changing guest molecule: β″-(BEDT-TTF)4[(H3O)Fe(C2O4)3](C6H5CN)x(C5H5N)1−x

SQUID magnetometry and transport measurements combined with crystal structure refinement have been used to examine the variation in superconducting properties (Tc and Meissner fraction) in the molecular superconductor β″-(BEDT-TTF)4[(H3O)Fe(C2O4)3]·C6H5CN on replacing the C6H5CN guest molecule with pyridine (C5H5N). Up to approximately 65% pyridine substitution there is only a small decrease in Tc and Meissner fraction but above that the superconductivity is suppressed.

Functionalised organosulfur donor molecules: Synthesis of racemic hydroxymethyl-, alkoxymethyl- and dialkoxymethyl-bis(ethylenedithio)tetrathiafulvalenes

Abstract Short synthetic routes to racemic derivatives of bis(ethylenedithio)tetrathiafulvalene carrying one hydroxymethyl (HMET), alkoxymethyl or dialkoxymethyl side chain are reported along with cyclic voltammetry measurements and conversion of HMET to (2:1) radical cation salts.

Anion-cation interdependency in bedt-ttf charge transfer salts of [MIII(C2O4)]3−

Abstract Metal(III)tris(oxalate) charge transfer salts of bis(ethylenedithio)tetrathiafulvalene, bedt-ttf, display a rich variety of magnetic and conducting properties. The series contains both semiconductors and the first molecular superconductor containing paramagnetic d electrons. Most of the compounds in the series follow the general formula (bedt-ttf) 4 M(C 2 O 4 ) 3 . A.solvent (M = metal(III); A = K + , NH 4 + or H 2 O). The conducting properties arise from different arrangements of the bedt-ttf molecules; packing motifs, conformational changes and charge distribution. We examine how changes in the oxalate co-ordination mode can promote specific donor packing motifs.

Polymorphism and variable structural dimensionality in the iron(III) phosphate oxalate system: a new polymorph of 3D [Fe2(HPO4)2(C2O4)(H2O)2]·2H2O and the layered material [Fe2(HPO4)2(C2O4)(H2O)2]

Two new iron (III) phosphate oxalates have been isolated under hydrothermal conditions as phase-pure samples and their crystal structures determined from single crystal X-ray diffraction. [Fe(2)(HPO(4))(2)(C(2)O(4))(H(2)O)(2)] x 2 H(2)O, I, is a polymorph of a known phase and differs in the local arrangement of hydrophosphate, oxalate and coordinated water about iron, presenting a mer orientation of three coordinated phosphates, rather than fac as previously seen. The structure of I is three-dimensionally connected with similar network connectivity to the known phase but different overall topology. [Fe(2)(HPO(4))(2)(C(2)O(4))(H(2)O)(2)], II, has a layered structure constructed from octahedral Fe(III) centres coordinated by hydrophosphate, oxalate and water in a fac arrangement. The amount of water used in synthesis is one of the key experimental parameters in stabilising one phase over the other. Thermogravimetric analysis shows that both I and II ultimately collapse into dense tridymite type FePO(4) above 600 degrees C and variable temperature powder XRD shows that this occurs via crystalline intermediate phases. Variable temperature magnetisation measurements show that both materials order antiferromagnetically at low temperatures, with similar Néel temperatures (approximately 29 K) despite their long-range structural differences.

New molecular superconductor containing paramagnetic chromium(iii) ions

The molecular charge-transfer salt β″-(bedt-ttf) 4 [(H 2 O)Cr(C 2 O 4 ) 3 ]·PhCN [bedt-ttf = bis(ethylenedithio)tetrathiafulvalene], containing paramagnetic Cr III ions (S = 3/2), is a superconductor with T c = 6.0(5) K.

Isomeric Fe(II) MOFs: from a diamond-framework spin-crossover material to a 2D hard magnet

Two Fe(II) coordination polymers formed from isomeric ligands give a diamond-like 3D network exhibiting a gradual SCO and a 2D hard magnet with a large coercive field.

Organic-soluble optically pure anionic metal complexes PPh4[MIII(S,S-EDDS)]·2H2O (M = Fe, Co, Cr)

The first organic-soluble, optically and diastereomerically pure EDDS metal complexes have been synthesised. A number of synthetic approaches were attempted, but finally the tetraphenylphosphonium series emerged as providing readily accessible compounds of trivalent Cr, Fe and Co in reasonable yields via the silver salts without the need to perform ion-exchange chromatography. The species PPh(4)[M(III)(S,S-EDDS)] are very soluble in methanol, acetonitrile and even THF but isolation was facilitated by addition of stoichiometric water giving the highly crystalline but still conveniently soluble title compounds. The structures of the three isomorphous crystals comprise H(2)O-bridged extended hydrogen bonded structures with large channels occupied by the counterion molecules. The magnetic properties and circular dichroism spectra are reported along with comparative data for water-soluble NH(4)[Fe(III)(S,S-EDDS)]. Phase purity (and hence diastereomeric purity) in the paramagnetic systems is assessed through powder XRD. The practical utility of this type of compound was confirmed by optical resolution of (+/-)-[Ru(II)(bpy)(3)]Cl(2).