Crystal structure and physical properties of conducting molecular antiferromagnets with a halogen-substituted donor: (EDO-TTFBr2)2FeX4 (X = Cl, Br)

The crystal structure and physical properties of radical ion salts (EDO-TTFBr2)2FeX4 (X = Cl, Br) based on halogen-substituted organic donor and magnetic anions are investigated, including the comparison with the isomorphous compounds (EDO-TTFBr2)2GaX4 with nonmagnetic anions. The crystal structure of these four salts consists of uniformly stacked donor molecules and tetrahedral counter anions, and the Br substituents of the donor molecules are connected to halide ligands of anions with remarkably short intermolecular atomic distances. These salts show metallic behavior around room temperature and undergo a spin-density-wave transition in the low-temperature range, as confirmed with the divergence of the electron spin resonance (ESR) line width. Although close anion-anion contacts are absent in these salts, the FeCl4 salt undergoes an antiferromagnetic transition at TN = 4.2 K, and the FeBr4 salt shows successive magnetic transitions at TN = 13.5 K and TC2 = 8.5 K with a helical spin structure as a candidate for the ground state of the d-electron spins. The magnetoresistance of the FeCl4 salt shows stepwise anomalies, which are explained qualitatively using a pi-d interaction-based frustrated spin system model composed of the donor pi-electron and the anion d-electron spins. Although on the ESR spectra of the FeX4 salts signals from the pi- and d-electron spins are separately observed, the line width of the pi-electron spins broadens under the temperature where the susceptibility deviates from the Curie-Weiss behavior, showing the presence of the pi-d interaction.     

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.     

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.     

Synthesis and structure of iron(iii) diamine-bis(phenolate) complexes

The structures and properties of six new iron(iii) diamine-bis(phenolate) complexes are reported. Reaction of anhydrous FeX(3) salts (where X = Cl or Br) with the diprotonated tripodal tetradentate ligands 2-pyridylamino-N,N-bis(2-methylene-4-methyl-6-tert-butylphenol), H(2)[L(1)], and N,N-dimethyl-N',N'-bis(2-methylene-4-methyl-6-tert-butylphenol)ethylenediamine, H(2)[L(2)], produces the trigonal bipyramidal iron(iii) complexes, [L(1)]FeCl , [L(1)]FeBr , [L(2)]FeCl and [L(2)]FeBr . Reaction of FeX(3) with the related linear tetradentate ligand N,N'-bis(4,6-tert-butyl-2-methylphenol)-N,N'-bismethyl-1,2-diaminoethane, H(2)[L(3)], generates square pyramidal iron(iii) complexes, [L(3)]FeCl and [L(3)]FeBr . Complexes have been characterized using electronic absorption spectroscopy and magnetometry. Single crystal X-ray molecular structures have been determined for complexes 1, 3, 5 and 6.     

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.     

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.     

Magnetic, electrochemical and spectroscopic properties of iron(III) amine-bis(phenolate) halide complexes

Eight new iron(III) amine-bis(phenolate) complexes are reported. The reaction of anhydrous FeX(3) salts (where X = Cl or Br) with the diprotonated tripodal tetradentate ligands 2-tetrahydrofurfurylamino-N,N-bis(2-methylene-4,6-di-tert-butylphenol), H(2)L1, 2-tetrahydrofurfurylamino-N,N-bis(2-methylene-4-methyl-6-tert-butylphenol), H(2)L2, and 2-methoxyethylamino-N,N-bis(2-methylene-4,6-di-tert-butylphenol), H(2)L3, 2-methoxyethylamino-N,N-bis(2-methylene-4-methyl-6-tert-butylphenol), H(2)L4 produces the trigonal bipyramidal iron(III) complexes, L1FeCl (1a), L1FeBr (1b), L2FeCl (2a), L2FeBr (2b), L3FeCl (3a), L3FeBr (3b), L4FeCl (4a), and L4FeBr (4b). All complexes have been characterized using electronic absorption spectroscopy, cyclic voltammetry and room temperature magnetic measurements. Variable temperature magnetic data were acquired for complexes 2b, 3a and 4b. Variable temperature M?ssbauer spectra were obtained for 2b, 3a and 4b. Single crystal X-ray molecular structures have been determined for proligand H(2)L4 and complexes 1b, 2b, and 4b.     

d-Electron-induced negative magnetoresistance of a pi-d interaction system based on a brominated-TTF donor

A new pi-d interaction system (EDT-TTFBr2)2FeBr4 (EDT-TTFBr2 = 4,5-dibromo-4',5'-ethylenedithiotetrathiafulvalene) and its nonmagnetic anion analogue (EDT-TTFBr2)2GaBr4 based on a brominated TTF-type organic donor are investigated. The salts featured by quasi-1D pi-electronic systems are metallic with metal-insulator transitions taking place at about 20 and 70 K for the FeBr4- and GaBr4- salts, respectively, where the low-temperature insulating state is associated with charge ordering or a Mott insulator followed by an antiferromagnetic transition at lower temperatures. The FeBr4- salt is featured with an antiferromagnetic transition of the anion d spins at a Neel temperature (TN) = 11 K, which is significantly high despite its long anion-anion Br-Br contact, suggesting the importance of the pi-d interaction in the magnetism. The surprisingly strong pi-d interaction, ca. -22.3 K estimated from the magnetization curve, evidences the usefulness of the chemical modification of the donor molecule with bromine substitution to achieve strong intermolecular interaction. The antiferromagnetic state of the anion d spins affects the transport of the conducting pi electrons through the strong pi-d interaction, as evidenced by the presence of a resistivity anomaly of the FeBr4- salt at TN. Below TN, the FeBr4- salt shows negative magnetoresistance that reaches -23% at the highest magnetic field investigated (B=15 T), whereas only a small positive magnetoresistance is observed in the pi-electron-only GaBr4- salt. The mechanism of the negative magnetoresistance is explained by the stabilization of the insulating state of the pi electrons by the periodic magnetic potential of the anion d spins in the FeBr4- salt, which is modified by applying the external magnetic field.     

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.     

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.     

Synthesis of a new donor, BEDT-HBDST and crystal structures, electrical and magnetic properties of (BEDT-HBDST)2MX4 (M=Fe, Ga, X=Cl, Br), where BEDT-HBDST=2,5-bis(4,5-ethylenedithio-1,3-diselenol-2-ylidene)-2,3,4,5-tetrahydrothiophene

A novel conjugation-elongated bis(ethylenedithio)tetraselenafulvalene (BETS) type donor, 2,5-bis(4,5-ethylenedithio-1,3-diselenol-2-ylidene)-2,3,4,5-tetrahydrothiophene (BEDT-HBDST) and its magnetic and non-magnetic anion salts, (BEDT-HBDST)₂MX₄ (MX₄⁻=FeCl₄⁻, GaCl₄⁻, FeBr₄⁻ and GaBr₄⁻), were prepared. These four salts are isostructural and belong to the space group of P2/c. They showed semiconducting behavior with small activation energies (59-64 meV). The band structures of these salts are quasi one-dimensional and there is a midgap between the upper band and the lower band, since the degree of dimerization is significant in the stacking direction. The MX₄⁻ ions are located between the donor columns and near to the ethylenedithio moieties of the donor molecules. The magnetic susceptibilities of the FeCl₄⁻ and FeBr₄⁻ salts follow the Curie-Weiss law with Curie constants of 4.6 and 4.8 emu K mol⁻¹ (sum of the spins of S=5/2 and S=1/2) and negative Weiss temperatures of θ=−1.2 and −4.9 K, respectively, revealing a weak antiferromagnetic interaction of 3d spins of the FeCl₄⁻ and FeBr₄⁻ anions. The Fe?Fe (6.66-7.60 Å), Cl?Cl (4.81-4.82 Å) and Br?Br (4.74-4.77 Å) distances in the crystal structures of these salts are significantly long. Therefore, the direct magnetic interaction between the 3d spins of the nearest neighboring Fe³⁺ ions appears to be not readily accessible.     

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.     

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.     

Unusual iron(III) ate complexes stabilized by Li-pi interactions

Several iron(III) complexes incorporating diamidoether ligands are described. The reaction between [Li(2)[RN(SiMe(2))](2)O] and FeX(3) (X=Cl or Br; R=2,4,6-Me(3)Ph or 2,6-iPr(2)Ph) form unusual ate complexes, [FeX(2)Li[RN(SiMe(2))](2)O](2) (2, X=Cl, R=2,4,6-Me(3)Ph; 3, X=Br, R=2,4,6-Me(3)Ph; 4, X=Cl, R=2,6-iPr(2)Ph) which are stabilized by Li-pi interactions. These dimeric iron(III)-diamido complexes exhibit magnetic behaviour characteristic of uncoupled high spin (S= 5/2 ) iron(III) centres. They also undergo halide metathesis resulting in reduced iron(II) species. Thus, reaction of 2 with alkyllithium reagents leads to the formation of iron(II) dimer [Fe[Me(3)PhN(SiMe(2))](2)O](2) (6). Similarly, the previously reported iron(III)-diamido complex [FeCl[tBuN(SiMe(2))](2)O](2) (1) reacts with LiPPh(2) to yield the iron(II) dimer [Fe[tBuN(SiMe(2))](2)O](2) but reaction with LiNPh(2) gives the iron(II) product [Fe(2)(NPh(2))(2)[tBuN(SiMe(2))](2)O] (5). Some redox chemistry is also observed as side reactions in the syntheses of 2-4, yielding THF adducts of FeX(2): the one-dimensional chain [FeBr(2)(THF)(2)](n) (7) and the cluster [Fe(4)Cl(8)(THF)(6)]. The X-ray crystal structures of 3, 5 and 7 are described.     

A novel antiferromagnetic organic superconductor kappa-(BETS)(2)FeBr(4) [where BETS = bis(ethylenedithio)tetraselenafulvalene].

The electrical and magnetic properties of kappa-(BETS)(2)FeBr(4) salt [where BETS = bis(ethylenedithio)tetraselenafulvalene] showed that this system is the first antiferromagnetic organic metal at ambient pressure (T(N) = 2.5 K). The characteristic field dependence of the magnetization at 2.0 K indicates a clear metamagnetic behavior. The small resistivity drop observed at T(N) clearly shows the existence of the interaction between pi metal electrons and localized magnetic moments of Fe(3+) ions. In addition, this system underwent a superconducting transition at 1.1 K. That is, kappa-(BETS)(2)FeBr(4) is the first antiferromagnetic organic metal exhibiting a superconducting transition below Néel temperature. The magnetic field dependence of the superconducting critical temperature indicated that the superconductivity in this system is strongly anisotropic also in the conduction plane because of the existence of the metamagnetically induced internal field based on the antiferromagnetic ordering of the Fe(3+) 3d spins in contrast to the cases of the other conventional organic superconductors. Furthermore, the specific heat measurement exhibited a lambda-type large peak of zero-field specific heat corresponding to the three-dimensional antiferromagnetic ordering of high-spin Fe(3+) ions. The lack of distinct anomaly in the C(p) vs T curve at T(c) suggests the coexistence of the superconductivity and the antiferromagnetic order below T(c).     

Bulk weak ferromagnet in ferrimagnetic chains of organic-inorganic hybrid materials based on BDH-TTP and paramagnetic thiocyanato complex anions: (BDH-TTP)[M(isoq)(2)(NCS)(4)], M = Cr(III), Fe(III)

The preparation, X-ray crystal structures, and magnetic properties of two new isostructural charge transfer salts, (BDH-TTP)M(isoq)(2)(NCS)(4) (M = Cr(III) (1), Fe(III) (2), BDH-TTP = 2,5-bis(1,3-dithiolan-2-ylidene)-1,3,4,6-tetrathiapentalene, isoq = isoquinoline), are reported. Crystal data for 1: monoclinic, space group C2/c (#15), a = 16.1363(9) A, b = 19.0874(12) A, c = 12.5075(6) A, beta = 95.70(4) degrees, V = 3833.2(4) A(3), Z = 4, R = 0.0516 for 2844 reflections with I > 2 sigma(I); for 2: monoclinic, C2/c (#15), a = 16.1938(8) A, b = 19.1117(11) A, c = 12.5100(10) A, beta = 94.265(3) degrees, V = 3861.0(4) A(3), Z = 4, R = 0.0479 for 2969 reflections with I > 2 sigma(I). The crystal structure consists of zigzag mixed organic and inorganic layers, and each layer is formed by mixed columns of BDH-TTP radical cations and paramagnetic metal complex anions. Short intermolecular atomic contacts between donor and anion are observed within the column in the c-direction. The two compounds have weak room-temperature electrical conductivities. ESR measurements show a single signal without separating the donor and anion spins, suggesting a pi interaction between the d and pi electrons. For both compounds ferrimagnetic interactions are observed between the nonequivalent donor and anion spins. These materials exhibit bulk canted weak ferromagnetism below 7.6 K for both 1 and 2.     

Structural and magnetic properties of three one-dimensional azido-bridged copper(II) and manganese(II) coordination polymers

Three one-dimensional (1D) azido-bridged coordination polymers of formula [Cu(L)(N3)2]n (1), [Cu2(Me-L)(N3)4]n (2), and [Mn(L)(N3)2]n (3) have been synthesized and structurally characterized, and their magnetic properties studied, where L and Me-L are 2-(pyrazol-1-ylmethyl)pyridine and 2-(3-methylpyrazol-1-ylmethyl)pyridine, respectively. Compound 1 consists of 1D chains in which the Cu(II) ions with a square pyramidal geometry are alternately bridged by an end-to-end (EE) and an end-on (EO) azido ligands, both adopting a basal-apical disposition. Compound 2 exhibits an unprecedented chain topology built via three different kinds of EO azido bridges. Four Cu(II) ions in the square pyramidal environment are alternately bridged by single and double EO bridges to form a tetranuclear cyclic ring, and neighboring rings are interlinked by double EO bridges to generate a "chain of rings". The intraannular double azido ions are disposed between metal ions in a basal-basal fashion, and the other two kinds of azido ions adopt the basal-apical disposition. Compound 3 consists of 1D concave-convex chains in which cis-octahedrally coordinated Mn(II) ions are alternately bridged by double EE and double EO bridges. There exist pi-pi interactions between the ligands bound to the neighboring Mn(II) ions bridged by the EO bridges. Temperature- and field-dependent magnetic analyses reveal alternate ferromagnetic interactions for 1, dominating ferromagnetic interactions for 2, and alternating ferro- and antiferromagnetic interactions through the EO and EE azido bridges for 3, respectively.     

Novel example of a chain structure formed by 1,4-dioxane and cobalt(II) links. Chain [Co3(mu-OOCCF3)4(mu-H2O)2(OOCCF3)2(H2O)2(C4H8O2)].2C4H8O2

The trimer [Co3(mu-OOCCF3)4(mu-H2O)2(OOCCF3)2(H2O)2(C4H8O2)].2C4H8O2. (1) is composed of three tetragonally distorted Co(II) centers bridged by four trifluoroacetates and two bridging water molecules. 1,4-Dioxane is coordinated at a distance of 2.120(3) A from the terminal cobalt Co2; the remaining oxygen of this 1,4-dioxane links the terminal cobalt to a neighbor trimer, forming a one-dimensional chain. The crystal structure displays a network of hydrogen bonds between four noncoordinated 1,4-dioxane molecules and the coordinated terminal water molecules. The magnetic properties of 1 were analyzed with the use of the Hamiltonian including isotropic exchange interactions between real spins of a high-spin Co(II), spin-orbit coupling and a low-symmetry crystal field acting within the (4)T(1g) ground manifold of each cobalt ion. A weak antiferromagnetic exchange interaction between cobalt ions in 1 was found. The results of the magnetic model are in good agreement with the experimental observations.