New aspects of π-d interactions in magnetic molecular conductors.

The 2 : 1 cation radical salts of bent donor molecules of ethylenedithio-tetrathiafulvalenoquinone-1,3-dithiolemethide (EDT-TTFVO), ethylenedithio-diselenadithiafulvalenoquinone-1,3-dithiolemethide (EDT-DSDTFVO), ethylenedithio-diselenadithiafulvalenothioquinone-1,3-diselenolemethide (EDT-DSDTFVSDS), ethylenedioxy-tetrathiafulvalenoquinone-1,3-dithiolemethide (EDO-TTFVO) and ethylenedioxy-tetrathiafulvalenoquinone-1,3-diselenolemethide (EDO-TTFVODS) with FeX4- (X = Cl, Br) ions are prepared by electrocrystallization. The crystal structures of these salts are composed of alternately stacked donor molecule and magnetic anion layers. The band structures of the donor molecule layers are calculated using the overlap integrals between neighboring donor molecules and are compared with the observed electronic transport properties. The magnetic ordering of the Fe(III) d spins of FeX4- ions is determined from magnetization and heat capacity measurements. The magnetic ordering temperatures are estimated by considering a combination of a direct d-d interaction between the d spins and an indirect π-d interaction between the conduction π electron and the d spins, whose magnitudes are separately calculated from the crystal structures with an extended Hückel molecular orbital method. The occurrence of a π-d interaction is proved by the negative magnetoresistance, and the magnitude of magnetoresistance reflects the strength of the π-d interaction. The effect of pressure on the magnetoresistance is studied, and the result indicates that the magnitude of magnetoresistance increases, namely, the π-d interaction is enhanced with increasing pressure. From these experimental results it is shown that (EDT-TTFVO)2•FeBr4 is a ferromagnetic semiconductor, (EDT-DSDTFVO)2•FeX4 (X = Cl, Br) and (EDT-DSDTFVSDS)2•FeBr4 are metals exhibiting antiferromagnetic ordering of the d spins, and (EDO-TTFVO)2•FeCl4 and (EDO-TTFVODS)2•FeBr4•(DCE)0.5 (DCE =-dichloroethane) are genuine antiferromagnetic metals. Among them, the (EDT-TTFVO)2•FeBr4 salt is the first π-d molecular system where the d spins of FeBr4- ions are ferromagnetically ordered through antiferromagnetic interaction with the conduction π electrons. Corresponding to this ferromagnetic ordering, an anomalous dielectric slow-down phenomenon toward the ordering temperature is observed. The π-d interaction in (EDT-DSDTFVSDS)2•FeBr4 is very large and comparable to that in λ-(BETS)2•FeCl4, which has the highest reported value so far, while the d-d interaction is fairly small. Concerning the ratio between the magnitudes of π-d and d-d interactions (Jπd/Jdd), this salt is currently the best π-d molecular system.

A new crystal phase of N,N,N',N'-tetra-phenyl-1,1'-biphenyl-4,4'-diamine.

The complete molecule of the title compound, C(36)H(28)N(2), is generated by a crystallographic centre of inversion. The biphenyl unit is forced by symmetry to be essentially flat (r.m.s. deviation = 0.008 Å); the dihedral angles between it and the two terminal phenyl rings are 69.39 (5) and 59.53 (5)°.

Fe2OCl6(2-) salt formed by electrochemical oxidation of ethylenedioxytetrathiafulvalenoquinone-1,3-dithiolemethide in the presence of FeCl4- ion with a silicon wafer electrode.

Electrochemical oxidation of a bent donor molecule, ethylenedioxytetrathiafulvalenoquinone-1,3-dithiolmethide ( 2), in chlorobenzene (PhCl)/ethanol containing NBu 4FeCl 4 as a supporting electrolyte is performed using an undoped silicon wafer electrode. Black crystals of 2 6.Fe 2OCl 6.2PhCl are obtained that have a different molecular formula from that of 2 2.FeCl 4 crystals obtained previously using a platinum rod electrode. The new crystal has a structure composed of alternately stacked layers of 2 molecules and Fe 2OCl 6 (2-) ions, whose Fe-O-Fe bond is completely linear and for which the geometry around the Fe atom is almost tetrahedral. The electrical resistivity decreases with temperature until ca. 200 K, but below this temperature, it gently increases. The magnetic susceptibility (chi p) observed can be described by the sum of chi p obeying a Curie-Weiss law for the impurity spins and of chi p obeying a dimer model with a spin-exchange integral ( J approximately -180 K) in each Fe 2OCl 6 (2-) ion, which is also weakly coupled to neighboring Fe 2OCl 6 (2-) ions through an additional exchange interaction.

Weak ferromagnetism in a semiconducting (ethylenedithiodiselena- dithiafulvalenoquinone-1,3-diselenolemethide)2.FeBr4 salt.

The 2:1 salts of a new bent donor molecule, ethylenedithiodiselenadithiafulvalenoquinone-1,3-diselenolemethide (EDT-DSDTFVODS) and either an FeBr(4)- or a GaBr(4)- ion exhibit semiconducting properties and had small activation energies. The Fe(III) d spins of the FeBr(4)- salt are initially subject to a strong antiferromagnetic interaction and afterward exhibited a weak ferromagnetism at 3.8 K with a very small remanent magnetization of ca. 4 x 10(-2) mu(B) and a spin-flop near 25 kOe along the intercolumnar direction.

Antiferromagnetic or canted antiferromagnetic orderings of Fe(III) d spins of FeX4- ions in BEDT-TTFVO(S).FeX4 (X = Cl, Br) [BEDT-TTFVO(S) = bis(ethylenedithio)tetrathiafulvalenoquinone(-thioquinone)-1,3-dithiolemethide].

By the reaction of new donor molecules, bis(ethylenedithio)tetrathiafulvalenoquinone(-thioquinone)-1,3-dithiolemethides [BEDT-TTFVO (1) and BEDT-TTFVS (2)] with FeX3 (X = Cl, Br) in CS2/CH3CN, 1:1 salts of 1 or 2 with an FeX4- ion (1.FeX4 and 2.FeX4) were obtained as black needle crystals. Their crystal structures are very similar to each other, in which the donor molecules are strongly dimerized and the dimers construct a one-dimensional uniform chain along the a axis, while the FeX4- ions are located at an open space surrounded by the neighboring donor molecules and also construct a one-dimensional uniform chain along the a axis. There are close contacts between the donor molecules and the FeX4- ions and significant differences in the contact distances among the four salts. All of the salts are semiconductors with room-temperature electrical conductivities of 10-4-10-2 S cm-1. The Fe(III) d spins of the FeX4- ions are subject to dominant ferromagnetic interaction through the participation of one of the singlet pi spins to form a short-range ferromagnetic d-spin chain. Such neighboring chains interact antiferromagnetically with each other through the singlet pi spins and are ordered at 1.0, 2.4, and 0.8 K for 1.FeCl4, 1.FeBr4, and 2.FeCl4, respectively. On the other hand, the antiferromagnetic ordering occurred with some canted angle at 1.9 K to leave a small magnetization for 2.FeBr4.

A metallic (EDT-DSDTFVSDS)2.FeBr4 salt: antiferromagnetic ordering of d spins of FeBr4- ions and anomalous magnetoresistance due to preferential pi-d interaction.

The 2:1 salt of a new donor molecule, EDT-DSDTFVSDS with FeBr4- ion, (EDT-DSDTFVSDS)2.FeBr4 showed an essentially metallic behavior despite a small upturn in the electrical resistance below ca. 30 K (electrical conductivities at 290 and 4.2 K are 200 and 170 S cm-1, respectively). The Fe(III) d spins of the FeBr4- ions in this salt were subject to antiferromagnetic ordering at 3.3 K by virtue of a strong pi-d interaction (Jpid) which is comparable to that in a molecular metallic conductor, lambda-(BETS)2.FeCl4, and of a very weak d-d interaction (Jdd). This strong pi-d interaction was evidenced by a large and negative magnetoresistance effect (ca. 20% at 5 T) as well as by the appearance of a large dip in the resistance at the magnetic field (ca. 2.0 T) parallel to the easy axis for the spin-flop transition of the Fe(III) d spins.

Magnetoresistance effects evidencing the pi-d interaction in metallic organic conductors, (EDT-DSDTFVO)2*MX4 (M = Fe, Ga; X = Cl, Br).

The 2:1 salts of a new donor molecule, EDT-DSDTFVO with MX4- (M = Fe, Ga; X = Cl, Br) ions, were prepared. The crystal structures of the donor molecules had a beta-type packing motif. All the salts essentially exhibited metallic behaviors despite the small upturns in the resistances below 30-70 K. A large negative magnetoresistance (MR) effect [-14.7% (rho(perpendicular)) at 4.0 K and 5 T] was observed in the FeCl4- salt, while a positive MR effect [+4.0% (rho(perpendicular)) at 4.0 K and 5 T] was observed in the GaCl4- salt, suggesting that there is a pi-d interaction in the FeCl4- salt. The pressure application suppressed the resistivity upturns, increased the negative MR effect (-17.7% at 9.5 kbar) in the FeCl4- salt, and decreased the positive MR effect (+3.3% at 15 kbar) in the GaCl4- salt.

Stable metallic behavior and antiferromagnetic ordering of Fe(III) d spins in (EDO-TTFVO)2.FeCl4.

We report the crystal structure and physical properties of the 2:1 FeCl4- salt of a new donor molecule, EDO-TTFVO. Crystal structure analysis of this salt revealed that the donor molecules formed a beta' '-type two-dimensional conducting layer, and there is a short S...Cl contact between the donor molecules and the FeCl4- ions, which is expected to mediate a strong pi-d interaction. This salt showed a stable metallic conducting behavior down to 0.3 K and an antiferromagnetic ordering at TN approximately 3.0 K, indicating that this salt becomes a new antiferromagnetic molecular metal at ambient pressure. The appearance of the magnetic ordering is considered to originate from the strong pi-d interactions between the donor molecules and the FeCl4- ions because the field dependence of magnetoresistances was remarkably affected below the antiferromagnetic transition temperature.

Ferromagnetic ordering of Fe(III) d spins of FeBr4- ions in (ethylenedithiotetrathiafulvalenothioquinone-ethylenedithio-1,3-dithiolemethide) x FeBr4.

The 1:1 salt of a new donor molecule, ethylenedithiotetrathiafulvalenothioquinone-ethylenedithio-1,3-dithiolemethide (1), with FeBr4- ion, 1 x FeBr4, was prepared and found to exhibit a room-temperature electrical conductivity of 4 x 10(-2) S cm(-1) and semiconducting behavior with an activation energy of 170 meV. The paramagnetic susceptibility obeyed the Curie-Weiss law with a Curie constant of 4.42 emu K mol(-1) and a Weiss temperature of +3.4 K, and below 15 K, this short-range ferromagnetic interaction increasingly extended to two- and/or three-dimensional interactions, eventually giving rise to a ferromagnetic ordering, whose temperature (TC) was determined to be 1.8 +/- 0.2 K using a resonant circuit method. The magnetic field dependence of magnetization showed that the saturation of magnetization was accomplished at ca. 60 kOe and the saturated value was ca. 5 microB, which is very close to the value obtained only due to Fe(III) (S = 5/2) d spins of one FeBr4- ion.

Ferrimagnetic ordering due to Fe(III) d and donor pi spins in (ethylenedithiotetrathiafulvalenoquinone-1,3-dithiolemethide)2.FeBr4.

Magnetization and heat capacity were measured down to 0.4 K in a 2:1 charge-transfer (CT) salt of a new donor molecule, ethylenedithiotetrathiafulvalenoquinone-1,3-dithiolemethide (1) with a magnetic FeBr(4)(-) ion (1(2).FeBr(4)). The Fe(III) d spins of FeBr(4)(-) ions were subject to apparently ferromagnetic interaction with each other through the interaction with the pi spins developed by localization of the conducting pi electrons on the donor columns, eventually giving rise to ferrimagnetic ordering (FI) near 1 K, which provides the first example in a molecular pi-d system.

One-dimensional CuBr4(2-) ion array and CuBr3- ion chain included in the pi conducting framework composed of bis(methylthio)tetrathiafulvalenothioquinone-1,3-dithiocarbonatodithiolemethide molecules.

The reaction of a new donor molecule having a planar but largely bent skeleton, bis(methylthio)tetrathiafulvalenothioquinone-1,3-dithiocarbonatodithiolemethide (1), with CuBr(2) in CH(3)CN/CS(2) afforded a black-colored crystal with a formula of 1(4).CuBr(4).2CuBr(3). In the crystal 1 molecules are one-dimensionally stacked to form half-cut pipelike columns, which are arranged to construct two different shapes of channels included by a one-dimensional array of CuBr(4)(2)(-) ions and a bibromide-bridged linear chain of CuBr(3)(-) ions with a square-pyramidal geometry at the Cu atom, [CuBr(3)(-)](n)(), respectively. The room-temperature electrical conductivity on the single crystal of 1(4).CuBr(4).2CuBr(3) was 2.0 x 10(-)(2) S cm(-)(1), and the temperature dependence of electrical conductivity was semiconducting with a large activation energy of 160 meV. The interactions between the neighboring Cu(II) d spins in the one-dimensional S = 1/2 spin systems due to CuBr(4)(2)(-) ions and CuBr(3)(-) ions in [CuBr(3)(-)](n)() were both antiferromagnetic, and the magnitudes were moderate (Weiss temperature, THETAV; = -18 K) in the former spin system and fairly large (coupling constant, J/k(B) = -120 K) in the latter spin system, which was in marked contrast to a moderate and ferromagnetic [CuBr(3)(-)](n)() chain in the cyclohexylammonium salt already known.

Electrical conducting and magnetic properties of (ethylenedithiotetrathiafulvalenothioquinone-1,3-diselenolemethide)2.FeBr4 (GaBr4) crystals with two different interlayer arrangements of donor molecules.

Two donor molecules newly synthesized, dimethylthio- and ethylenedithio-tetrathiafulvalenothioquinone-1,3-diselenolemethides (1 and 2), were used to prepare their charge-transfer (CT) salts with a magnetic FeBr(4)(-) counteranion. For 1, a low electrical conducting 1:1 salt (1.FeBr(4)) was obtained, in which molecules of 1 are tightly dimerized in a one-dimensional (1D) stacking column. On the other hand, 2 gave a 2:1 salt (2(2).FeBr(4)) as two different kinds of plate crystals (I and II). Both I and II possess similar stacking structures of molecules of 2 in each 1D column with a half-cut pipelike structure along the c axis. However, for I, the stacking columns are aligned in the same direction along the a and b axes, while for II they are in the same direction along the a axis, but in the reverse direction along the b axis, resulting in the difference in the relative arrangement of molecules of 2 and FeBr(4)(-) ions between the two crystals. The room-temperature electrical conductivities of the single crystals of I and II were 13.6 and 12.7 S cm(-)(1), respectively. The electrical conducting behavior in I was metallic above 170 K but changed to be semiconducting with a very small activation energy of 7.0 meV in the temperature range 4-170 K. In contrast, II showed the semiconducting behavior in the whole temperature range 77-285 K. The corresponding nonmagnetic GaBr(4)(-) salts with almost the same crystal structure as I and II showed definitively different electrical conducting properties in the metal to semiconductor transition temperature in I as well as in the magnitude of activation energy in the semiconducting region of I and II. The interaction between the d spins of FeBr(4)(-) ions was weak and antiferromagnetic in both I and II, but the magnitude of the spin interaction was unexpectedly larger compared with that in the FeBr(4)(-) salt of the corresponding sulfur derivative of 2 with closer contact between the neighboring FeBr(4)(-) ions. These electrical conducting and magnetic results suggest a significant interaction between the conducting pi electrons and the d spins of FeBr(4)(-) ions located near the columns or layers.

Metallic conductivity and ferromagnetic interaction of iron(III) d spins in the needle crystals of (ethylenedithiotetrathiafulvalenoquinone-1,3-dithiolemethide)(2).FeBr(4) salt.

The 2:1 charge-transfer (CT) salts (1(2).FeBr(4) and 1(2).GaBr(4)) of ethylenedithiotetrathiafulvalenoquinone-1,3-dithiolemethide (1) with FeBr(4)(-) and GaBr(4)(-) counteranions were obtained as needle crystals, whose structures are almost the same as each other. The 1 molecules form a one dimensionally stacked column with alternation of their molecular axis direction, while the counteranions are aligned in parallel with the 1-stacked columns with the direction of their distorted-tetrahedral geometry maintained. The room-temperature electrical conductivities measured on the single crystals of 1(2).FeBr(4) and 1(2).GaBr(4) were 4.6 and 2.1 S cm(-1), respectively. From the temperature dependences of their electrical conductivities in both cases the electrical conducting properties were metallic between ca. 170 and 300 K, but below ca. 170 K converted to be semiconducting and continued till 5 K, although the activation energies are very small (4-10 meV). For 1(2).FeBr(4) very weak and antiferromagnetic interaction occurred between the d spins of FeBr(4)(-) ions in the temperature range of ca. 1-300 K. However, below ca. 15 K the ferromagnetic interaction was reversely preferential possibly by participation of the pi spin of 1.