Structural distortions upon oxidation in heteroleptic [Cp(2)W(dmit)] tungsten dithiolene complex: combined structural, spectroscopic, and magnetic studies

Four different cation radical salts are obtained upon electrocrystallization of [Cp(2)W(dmit)] (dmit = 1,3-dithiole-2-thione-4,5-dithiolato) in the presence of the BF(4)(-), PF(6)(-), Br(-), and [Au(CN)(2)](-) anions. In these formally d(1) cations, the WS(2)C(2) metallacycle is folded along the S···S hinge to different extents in the four salts, an illustration of the noninnocent character of the dithiolate ligand. Structural characteristics and the charge distribution on atoms, for neutral and ionized complexes with various folding angles, were calculated using DFT methods, together with the normal vibrational modes and theoretical Raman spectra. Raman spectra of neutral complex [Cp(2)W(dmit)] and its salts formed with BF(4)(-), AsF(6)(-), PF(6)(-), Br(-), and [Au(CN)(2)](-) anions were measured using the red excitation (λ = 632.8 nm). A correlation between the folding angle of the metallacycle and the Raman spectroscopic properties is analyzed. The bands attributed to the C═C and C-S stretching modes shift toward higher and lower frequencies by about 0.3-0.4 cm(-1) deg(-1), respectively. The solid state structural and magnetic properties of the three salts are analyzed and compared with those of the corresponding molybdenum complexes. Temperature dependence of the magnetic susceptibility shows the presence of one-dimensional antiferromagnetic interactions in the BF(4)(-), PF(6)(-), and [Au(CN)(2)](-) salts, while an antiferromagnetic ground state is identified in the Br(-) salt below T(Ne?el) = 7 K. Interactions are systematically weaker in the tungsten salts than in the isostructural molybdenum analogs, a consequence of the decreased spin density on the dithiolene ligand in the tungsten complexes.     

Anionic Halomolybdate(III) Chemistry. Tetrahydrofuran Loss from [MoX(3)Y(THF)(2)](-) (X, Y = Cl, Br, I), Preparation and Properties of [Mo(3)X(12)](3)(-) (X = Br, I), and Crystal Structure of the Edge-Sharing Trioctahedral [PPh(4)](3)[Mo(3)I(12)

By interaction of MoX(3)(THF)(3) with [Cat]X in THF, the salts [Cat][MoX(4)(THF)(2)] have been synthesized [X = I, Cat = PPh(4), NBu(4), NPr(4), (Ph(3)P)(2)N; X = Br, Cat = NBu(4), PPh(4) (Ph(3)P)(2)N]. Mixed-halide species [MoX(3)Y(THF)(2)](-) (X, Y = Cl, Br, I) have also been generated in solution and investigated by (1)H-NMR. When the tetraiodo, tetrabromo, and mixed bromoiodo salts are dissolved in CH(2)Cl(2), clean loss of all coordinated THF is observed by (1)H-NMR. On the other hand, [MoCl(4)(THF)(2)](-) loses only 1.5 THF/Mo. The salts [Cat](3)[Mo(3)X(12)] (X = Br, I) have been isolated from [Cat][MoX(4)(THF)(2)] or by running the reaction between MoX(3)(THF)(3) and [Cat]X directly in CH(2)Cl(2). The crystal structure of [PPh(4)](3)[Mo(3)I(12)] exhibits a linear face-sharing trioctahedron for the trianion: triclinic, space group P&onemacr;; a = 11.385(2), b = 12.697(3), c = 16.849(2) ?; alpha = 76.65(2), beta = 71.967(12), gamma = 84.56(2) degrees; Z = 1; 431 parameters and 3957 data with I > 2sigma(I). The metal-metal distance is 3.258(2) ?. Structural and magnetic data are consistent with the presence of a metal-metal sigma bond order of (1)/(2) and with the remaining 7 electrons being located in 7 substantially nonbonding orbitals. The ground state of the molecule is predicted to be subject to a Jahn-Teller distortion, which is experimentally apparent from the nature of the thermal ellipsoid of the central Mo atom. The [Mo(3)X(12)](3)(-) ions reacts with phosphines (PMe(3), dppe) to form products of lower nuclearity by rupture of the bridging Mo-X bonds.     

PX4+, P2X5+, and P5X2+ (X=Br,I) salts of the superweak Al(OR)4- anion [R=C(CF3)3

PX(4) (+)[Al(OR)(4)](-) (X=I: 1 a, X=Br: 1 b) was prepared from X(2), PX(3), and Ag[Al(OR)(4)] [R=C(CF(3))(3)] in CH(2)Cl(2) at -30 degrees C in 69-86 % yield. P(2)X(5) (+) salts were prepared from 2 PX(3) and Ag[Al(OR)(4)] in CH(2)Cl(2) at -30 degrees C yielding almost quantitatively P(2)X(5) (+)[Al(OR)(4)](-) (X=I: 3 a, X=Br: 3 b). The phosphorus-rich P(5)X(2) (+) salts arose from the reaction of cold (-78 degrees C) mixtures of PX(3), P(4), and Ag[Al(OR)(4)] giving P(5)X(2) (+)[Al(OR)(4)](-) (X=I: 4 a, X=Br: 4 b) with a C(2v)-symmetric P(5) cage. Silver salt metathesis presumably generated unstable PX(2) (+) cations from PX(3) and Ag[Al(OR)(4)] (X=Br, I) that acted as electrophilic carbene analogues and inserted into the Xbond;X (Pbond;X/Pbond;P) bond of X(2) (PX(3)/P(4)) leading to the highly electrophilic and CH(2)Cl(2)-soluble PX(4) (+) (P(2)X(5) (+)/P(5)X(2) (+)) salts. Reactions that aimed to synthesize P(2)I(3) (+) from P(2)I(4) and Ag[Al(OR)(4)] instead led to anion decomposition and the formation of P(2)I(5)(CS(2))(+)[(RO)(3)Al-F-Al(OR)(3)](-) (5). All salts were characterized by variable-temperature solution NMR studies (3 b also by (31)P MAS NMR), Raman and/or IR spectroscopy as well as X-ray crystallography (with the exception of 4 a). The thermochemical volumes of the Pbond;X cations are 121 (PBr(4) (+)), 161 (PI(4) (+)), 194 (P(2)Br(5) (+)), 271 (P(2)I(5) (+)), and 180 A(3) (P(5)Br(2) (+)). The observed reactions were fully accounted for by thermochemical calculations based on (RI-)MP2/TZVPP ab initio results and COSMO solvation enthalpy calculations (CH(2)Cl(2) solution). The enthalpies of formation of the gaseous Pbond;X cations were derived as +764 (PI(4) (+)), +617 (PBr(4) (+)), +749 (P(2)I(5) (+)), +579 (P(2)Br(5) (+)), +762 (P(5)I(2) (+)), and +705 kJ mol(-1) (P(5)Br(2) (+)). The insertion of the intermediately prepared carbene analogue PX(2) (+) cations into the respective bonds were calculated, at the (RI-)MP2/TZVPP level, to be exergonic at 298 K in CH(2)Cl(2) by Delta(r)G(CH(2)Cl(2))=-133.5 (PI(4) (+)), -183.9 (PBr(4) (+)), -106.5 (P(2)I(5) (+)), -81.5 (P(2)Br(5) (+)), -113.2 (P(5)I(2) (+)), and -114.5 kJ mol(-1) (P(5)Br(2) (+)).     

Ultrafast photochemical dissociation of an equatorial CO ligand from trans(X,X)-[Ru(X)2(CO)2(bpy)] (X = Cl, Br, I): a picosecond time-resolved infrared spectroscopic and DFT computational study

Ultrafast photochemistry of the complexes trans(X,X)-[Ru(X)(2)(CO)(2)(bpy)] (X = Cl, Br, I) was studied in order to understand excited-state reactivity of equatorial CO ligands, coordinated trans to the 2,2'-bipyridine ligand (bpy). TD-DFT calculations have identified the lowest electronic transitions and singlet excited states as mixed X -->bpy/Ru --> bpy ligand to ligand/metal to ligand charge transfer (LLCT/MLCT). Picosecond time-resolved IR spectroscopy in the region of nu(CO) vibrations has revealed that, for X = Cl and Br, subpicosecond CO dissociation is accompanied by bending of the X-Ru-X moiety, producing a pentacoordinated intermediate trans(X,X)-[Ru(X)(2)(CO)(bpy)]. Final movement of an axial halide ligand to the vacant equatorial position and solvent (CH(3)CN) coordination follows with a time constant of 13-15 ps, forming the photoproduct cis(X,X)-[Ru(X)(2)(CO)(CH(3)CN)(bpy)]. For X = I, the optically populated (1)LLCT/MLCT excited state undergoes a simultaneous subpicosecond CO dissociation and relaxation to a triplet IRuI-localized excited state which involves population of an orbital that is sigma-antibonding with respect to the axial I-Ru-I bonds. Vibrationally relaxed photoproduct cis(I,I)-[Ru(I)(2)(CO)(CH(3)CN)(bpy)] is formed with a time constant of ca. 55 ps. The triplet excited state is unreactive, decaying to the ground state with a 155 ps lifetime. The experimentally observed photochemical intermediates and excited states were assigned by comparing calculated (DFT) and experimental IR spectra. The different behavior of the chloro and bromo complexes from that of the iodo complex is caused by different characters of the lowest triplet excited states.     

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.     

A theoretical study on the formation of EX4+ and E2X5+(E = P, As; X = Br, I) from Ag+ and EX3/X2

The mechanism and the thermodynamics of the formation of EX2+, EX4+ and E2X5+ (E = As, P; X = Br, I) was carefully analyzed with MP2/TZVPP calculations and inclusion of entropy and solvation effects (COSMO model approximating CH2Cl2). Thus, as likely intermediates the complexes of Ag+ and one or two EX3 as well as EX3/X2 were optimized. The global minimum isomers of the Ag(EX3)2+ intermediates were found to be P-coordinated Ag(PI3)2+ and (BrPBr2)Ag(PBr3)+ but exclusively halogen coordinated Ag(X2AsX)2+ complexes. Similarly complicated is the situation for the Ag(EX3)(X2)+ intermediates: (I3E)Ag(I2)+, (BrAsBr2)Ag(Br2)+ and (Br3P)(Br-Br)Ag+ complexes were found to be the global minima. Based on all available results likely mechanisms for the formation of the known PX4+, AsBr4+, P2X5+ salts (X = Br, I) from these intermediates were proposed. An explanation for the failure to prepare an AsI4+ salt is also given.     

Solid-state coordination chemistry of the Cu/triazolate/X system (X = F-, Cl-, Br-, I-, OH-, and SO4(2-))

Hydrothermal reactions of 1,2,4-triazole with the appropriate copper salt have provided eight structurally unique members of the Cu/triazolate/X system, with X = F-, Cl-, Br-, I-, OH-, and SO4(2-). The anionic components X of [Cu3(trz)4(H2O)3]F2 (1) and [Cu6(trz)4Br]Cu4Br4(OH) (4) do not participate in the framework connectivity, acting as isolated charge-compensating counterions. In contrast, the anionic subunits X of [Cu(II)Cu(I)(trz)Cl2] (2), [Cu6(trz)4Br2] (3), [Cu(II)Cu(I)(trz)Br2] (5), [Cu3(trz)I2] (6), [Cu6(II)Cu2(I)(trz)6(SO4)3(OH)2(H2O)] (8), and [Cu4(trz)3]OH.7.5H2O (9.7.5H2O) are intimately involved in the three-dimensional connectivities. The structure of [Cu(II)Cu(I)(trz)2][Cu3(I)I4] (7) is constructed from two independent substructures: a three-dimensional cationic {Cu2(trz)2}n(n+) component and {Cu3I4}n(n-) chains. Curiously, four of the structures are mixed-valence Cu(I)/Cu(II) materials: 2, 5, 7, and 8. The only Cu(II) species is 1, while 3, 4, 6, and 9.7.5H2O exhibit exclusively Cu(I) sites. The magnetic properties of the Cu(II) species 1 and of the mixed-valence materials 5, 7, 8, and the previously reported [Cu3(trz)3OH][Cu2Br4] have been studied. The temperature-dependent magnetic susceptibility of 1 conforms to a simple isotropic model above 13 K, while below this temperature, there is weak ferromagnetic ordering due to spin canting of the antiferromagnetically coupled trimer units. Compounds 5 and 7 exhibit magnetic properties consistent with a one-dimensional chain model. The magnetic data for 8 were fit over the temperature range 2-300 K using the molecular field approximation with J = 204 cm(-1), g = 2.25, and zJ' = -38 cm(-1). The magnetic properties of [Cu3(trz)3OH][Cu2Br4] are similar to those of 8, as anticipated from the presence of similar triangular {Cu3(trz)3(mu3-OH)}(2+) building blocks. The Cu(I) species 3, 4, 6, and 9 as well as the previously reported [Cu(5)(trz)3Cl2] exhibit luminescence thermochromism. The spectra are characterized by broad emissions, long lifetimes, and significant Stokes' shifts, characteristic of phosphorescence.     

Magnetic behavior control in niccolite structural metal formate frameworks [NH2(CH3)2][Fe(III)M(II)(HCOO)6] (M = Fe, Mn, and Co) by varying the divalent metal ions

By changing template cation but introducing trivalent iron ions in the known niccolite structural metal formate frameworks, three complexes formulated [NH(2)(CH(3))(2)][Fe(III)M(II)(HCOO)(6)] (M = Fe for 1, Mn for 2, and Co for 3) were synthesized and magnetically characterized. The variation in the compositions of the complexes leads to three different complexes: mixed-valent complex 1, heterometallic but with the same spin state complex 2, and heterometallic heterospin complex 3. The magnetic behaviors are closely related to the divalent metal ions used. Complex 1 exhibits negative magnetization assigned as Ne?el N-Type ferrimagnet, with an asymmetric magnetization reversal in the hysteresis loop, and complex 2 is an antiferromagnet with small spin canting (α(canting) ≈ 0.06° and T(canting) = 35 K), while complex 3 is a ferrimagnet with T(N) = 32 K.     

Multi-configurational quantum chemical studies of the Tc2X8(n-) (X = Cl, Br; n = 2, 3) anions. Crystallographic structure of octabromoditechnetate(3-)

The [Cs((2 + x))][H(3)O((1 - x))]Tc(2)Br(8)·4.6H(2)O (x = 0.221) salt has been synthesized and characterized by single crystal XRD. Multi-configurational quantum chemical calculations on Tc(2)X(8)(n-) (X = Cl, Br; n = 2, 3) have been performed and indicate the π component in the Tc-Tc bond to be stronger for n = 3.     

Five-coordinate complexes [FeX(depe)(2)]BPh(4), X = Cl,Br: electronic structure and spin-forbidden reaction with N(2)

The bonding of N(2) to the five-coordinate complexes [FeX(depe)(2)](+), X = Cl (1a) and Br (1b), has been investigated with the help of X-ray crystallography, spectroscopy, and quantum-chemical calculations. Complexes 1a and 1b are found to have an XP(4) coordination that is intermediate between square-pyramidal and trigonal-bipyramidal. M?ssbauer and optical absorption spectroscopy coupled with angular overlap model (AOM) calculations reveal that 1a and 1b have (3)B(1) ground states deriving from a (xz)(1)(z(2))(1) configuration. The zero-field splitting for this state is found to be 30-35 cm(-1). In contrast, the analogous dinitrogen complexes [FeX(N(2))(depe)(2)](+), X = Cl (2a) and Br (2b), characterized earlier are low-spin (S = 0; Wiesler, B. E.; Lehnert, N.; Tuczek, F.; Neuhausen, J.; Tremel, W. Angew. Chem, Int. Ed. 1998, 37, 815-817). N(2) bonding and release in these systems are thus spin-forbidden. It is shown by density functional theory (DFT) calculations of the chloro complex that the crossing from the singlet state (ground state of 2a) to the triplet state (ground state of 1a) along the Fe-N coordinate occurs at r(C) = 2.4 A. Importantly, this intersystem crossing lowers the enthalpy calculated for N(2) release by 10-18 kcal/mol. The free reaction enthalpy Delta G degrees for this process is calculated to be 4.7 kcal/mol, which explains the thermal instability of N(2) complex 2a with respect to the loss of N(2). The differences in reactivity of analogous trans hydrido systems are discussed.     

Electronic structure and nature of the ground state of the mixed-valence binuclear tetra(mu-1,8-naphthyridine-N,N')-bis(halogenonickel) tetraphenylborate complexes: experimental and DFT characterization

The ground state electronic structure of the mixed-valence systems [Ni(2)(napy)(4)X(2)](BPh(4)) (napy=1,8-naphthyridine; X=Cl, Br, I) was studied with combined experimental (X-ray diffraction, temperature dependence of the magnetic susceptibility, and high-field EPR spectroscopy) and theoretical (DFT) methods. The zero-field splitting (zfs) ground S=3/2 spin state is axial with /D/ approximately 3 cm(-1). The iodide derivative was found to be isostructural with the previously reported bromide complex, but not isomorphous. The compound crystallizes in the monoclinic system, space group P2(1)/n, with a=17.240(5), b=26.200(5), c=11.340(5) A, beta=101.320(5) degrees. DFT calculations were performed on the S=3/2 state to characterize the ground state potential energy surface as a function of the nuclear displacements. The molecules can thus be classified as Class III mixed-valence compounds with a computed delocalization parameter, B=3716, 3583, and 3261 cm(-1) for the Cl, Br, and I derivatives, respectively.     

Metal-insulator transition of charge-transfer salts based on unsymmetrical donor DMET and metal halide anions (DMET)4(MCl4)(TCE)2 (M = Mn, Co, Cu, Zn; TCE = 1,1,2-trichloroethane)

New charge-transfer salts based on an unsymmetrical donor DMET [dimethyl(ethylenedithio)diselenadithiafulvalene] and metal halide anions (DMET)4MIICl4(TCE)2 (M = Mn, Co, Cu, Zn; TCE = 1,1,2-trichloroethane) have been synthesized and characterized by transport and magnetic measurements. The crystal structures of the DMET salts are isostructural, consisting of a quasi-one-dimensional stack of DMET and insulating layers containing metal halide anions and TCE. Semimetallic band structures are calculated by the tight-binding approximation. Metal-insulator transitions are observed at TMI = 25, 15, 5-20, and 13 K for M = Mn, Co, Cu, and Zn, respectively. The M = Cu salt exhibits anisotropic conduction at ambient pressure, being semiconducting in the intralayer current direction but metallic for the interplane current direction, down to T(MI). The metal-insulator transitions are suppressed under pressure. In the M = Co and Zn salts, large magnetoresistances with hysteresis are observed at low temperatures, on which Shubnikov-de Haas oscillations are superposed above 30 T. In the M = Cu salt, no hysteresis is observed but clear Shubnikov-de Haas oscillations are observed. The magnetoresistance is small and monotonic in the M = Mn salt. Paramagnetic susceptibilities of the spins of the magnetic ions are observed for the M = Mn, Co, and Cu salts with small negative Weiss temperatures of approximately 1 K. In the nonmagnetic M = Zn salt, Pauli-like pi-electron susceptibility that vanishes at TMI is observed. The ground state of the pi-electron system is understood as being a spin density wave state caused by imperfect nesting of the Fermi surfaces. In this pi-electron system, the magnetic ions of the M = Mn, Co, and Cu salts interact differently, exhibiting a variety of transport behaviors.     

Superconductivity in LaT(M)BN and La3T(M2)B2N3 (T(M) = transition metal) synthesized under high pressure

Various layered boronitrides (LaN)(n)(T(M2)B(2)) (T(M) = transition metal; n = 2, 3) have been prepared using a high-pressure synthesis technique in which an inverse α-PbO-type T(M2)B(2) layer is separated by two or three rock salt-type LaN layers and these layers are connected through linear (BN) units. The electronic states of the distinguishing (BN) unit and intermediate rock salt-type LaN layer are discussed on the basis of density functional theory calculations. Bulk superconductivity has been found in LaNiBN (T(c) ≈ 4.1 K), CaNiBN (T(c) ≈ 2.2 K), and LaPtBN (T(c) ≈ 6.7 K), where the Fermi level E(F) is located in the bands composed of the T(M)(d)-B(2p) antibonding state and the main T(M)(d) band resides well below E(F). The non-superconductive T(M)-based compounds exhibit Pauli paramagnetic behavior, in which the highly itinerant nature of the electrons caused by strong T(M)(d)-B(2p) covalent bonding suppresses the long-range magnetic ordering.     

Investigation of anion-dependence in the spin-state switching properties of [(H2bip)2Fe(6-Mebpy)]X2

We report the syntheses, characterisations and magnetic properties of salts of the heteroleptic Fe(II) complex [(H(2)bip)(2)Fe(6-Mebpy)]X(2) (X = Br (1), BPh(4) (2), H(2)bip = 2,2'-bi-1,4,5,6-tetrahydropyrimidine, 6-Mebpy = 6-methyl-2,2'-bipyridine). The ditopic H(2)bip ligand serves as an anion binding group while 6-Mebpy is intended to adjust the complex ligand field. Thermally induced spin-crossover properties are observed in the solid state and solution, and are heavily influenced by the nature of the anion. Anion-triggered spin-state switching is observed for the heteroleptic complex in dichloromethane solution at 193 K, above background processes of ligand dissociation and rearrangement. Although substitution of 6-Mebpy appears to increase the ligand field encountered by the Fe(II) ion, salt 2 responds to bromide at a significantly lower temperature than the parent homoleptic complex salt [Fe(H(2)bip)(3)](BPh(4))(2).     

Soluble mu-Fi bridged niobium clusters: synthesis and crystal structures of (Et4N)6[Nb6Fi6Bri6(NCS)a6]Br2 and Cs1.6K2.4[Nb6Fi6Ii6(NCS)a6

Two new anions [Nb(6)F(i)(6)X(i)(6)(NCS)(a)(6)](4-)(X = Br, I) based on octahedral niobium clusters with edge-bridging F ligands have been prepared by reaction of Cs(3)Nb(6)F(6)Br(12) and Cs(4)Nb(6)F(8.5)I(9.5) with aqueous solution of KSCN. The anions were isolated as (Et(4)N)(6)[Nb(6)F(6)Br(6)(NCS)(6)]Br(2) (1)and Cs(1.6)K(2.4)[Nb(6)F(6)I(6)(NCS)(6)] (2) salts.     

Strong rail spin 1/2 antiferromagnetic ladder systems: (dimethylammonium)(3,5-dimethylpyridinium)CuX4, X = Cl, Br

The mixed cation salts, (dimethylammonium)(3,5-dimethylpyridinium)CuX4 (X = Cl, Br), henceforth (DMA)(35DMP)CuX4, are new examples of spin-ladders based on nonbonded halide...halide interactions between CuX4(2-) anions. In these structures, double rows of the CuX4(2-) anions are sheathed by the 35DMP(+) cations, while the edges are capped by the DMA(+) cations. For the Br salt, the Br...Br contacts that define the rungs of the ladder are 4.017 A in length, while those that define the rails are 3.983 A. For the Cl salt, the corresponding lengths are 3.967 and 4.045 A. The susceptibility data for the Br salt exhibits a maximum at approximately 5.5 K, and fitting the data to the spin 1/2 antiferromagnetic ladder model yields 2J(rail)/k = -7.95 K and 2J(rung)/k = -4.07 K. The exchange coupling is much weaker in the Cl salt, no maximum in chi is observed down to 1.8 K, and the corresponding exchange constants are -1.59 and -1.25 K, respectively. An analysis is made of the structural factors involved in the J(rung) pathway.     

Magnetic structure of Ni(DCOO)2(D2O)2

Ni(HCOO)(2)(H(2)O)(2) is a structurally simple coordination polymer showing interesting magnetic phase transitions at low temperature (<16K). Previously published studies of these phase transitions have yielded inconsistent results, questioning the correctness of the published magnetic structure. Here heat capacity and magnetic susceptibility of a fully, a partly and a non-deuterated sample were measured, and they all exhibit magnetic phase transitions around 3 and 15 K. Neutron powder diffraction data was collected on the fully deuterated sample at various temperatures between 1.5 and 25 K. A magnetic model was refined against the neutron diffraction data using a spin system composed of two canted antiferromagnetic sublattices. The magnetic moments of the two sublattices show different magnitude, 1.7 μ(B) and 1.3 μ(B), and the temperature dependence of the magnetic sublattices is quite different. One of the sublattices shows the expected temperature behavior of an antiferromagnetic compound whereas the other sublattice follows a Brillouin like function with a slowly increasing magnetization below the Ne?el temperature.     

The syntheses of carbocations by use of the noble-gas oxidant, [XeOTeF5][Sb(OTeF5)6]: the syntheses and characterization of the CX3+ (X = Cl, Br, OTeF5) and CBr(OTeF5)2+ cations and theoretical studies of CX3+ and BX3 (X = F, Cl, Br, I, OTeF5)

The CCl(3)(+) and CBr(3)(+) cations have been synthesized by oxidation of a halide ligand of CCl(4) and CBr(4) at -78 degrees C in SO(2)ClF solvent by use of [XeOTeF(5)][Sb(OTeF(5))(6)]. The CBr(3)(+) cation reacts further with BrOTeF(5) to give CBr(OTeF(5))(2)(+), C(OTeF(5))(3)(+), and Br(2). The [XeOTeF(5)][Sb(OTeF(5))(6)] salt was also found to react with BrOTeF(5) in SO(2)ClF solvent at -78 degrees C to give the Br(OTeF(5))(2)(+) cation. The CCl(3)(+), CBr(3)(+), CBr(OTeF(5))(2)(+), C(OTeF(5))(3)(+), and Br(OTeF(5))(2)(+) cations and C(OTeF(5))(4) have been characterized in SO(2)ClF solution by (13)C and/or (19)F NMR spectroscopy at -78 degrees C. The X-ray crystal structures of the CCl(3)(+), CBr(3)(+), and C(OTeF(5))(3)(+) cations have been determined in [CCl(3)][Sb(OTeF(5))(6)], [CBr(3)][Sb(OTeF(5))(6)].SO(2)ClF, and [C(OTeF(5))(3)][Sb(OTeF(5))(6)].3SO(2)ClF at -173 degrees C. The CCl(3)(+) and CBr(3)(+) salts were stable at room temperature, whereas the CBr(n)(OTeF(5))(3-n)(+) salts were stable at 0 degrees C for several hours. The cations were found to be trigonal planar about carbon, with the CCl(3)(+) and CBr(3)(+) cations showing no significant interactions between their carbon atoms and the fluorine atoms of the Sb(OTeF(5))(6)(-) anions. In contrast, the C(OTeF(5))(3)(+) cation interacts with an oxygen of each of two SO(2)ClF molecules by coordination along the three-fold axis of the cation. The solid-state Raman spectra of the Sb(OTeF(5))(6)(-) salts of CCl(3)(+) and CBr(3)(+) have been obtained and assigned with the aid of electronic structure calculations. The CCl(3)(+) cation displays a well-resolved (35)Cl/(37)Cl isotopic pattern for the symmetric CCl(3) stretch. The energy-minimized geometries, natural charges, and natural bond orders of the CCl(3)(+), CBr(3)(+), CI(3)(+), and C(OTeF(5))(3)(+) cations and of the presently unknown CF(3)(+) cation have been calculated using HF and MP2 methods have been compared with those of the isoelectronic BX(3) molecules (X = F, Cl, Br, I, and OTeF(5)). The (13)C and (11)B chemical shifts for CX(3)(+) (X = Cl, Br, I) and BX(3) (X = F, Cl, Br, I) were calculated by the GIAO method, and their trends were assessed in terms of paramagnetic contributions and spin-orbit coupling.     

Effect of counteranion X on the spin crossover properties of a family of diiron(II) triazole complexes [Fe(II)2(PMAT)2](X)4

Seven diiron(II) complexes, [Fe(II)(2)(PMAT)(2)](X)(4), varying only in the anion X, have been prepared, where PMAT is 4-amino-3,5-bis{[(2-pyridylmethyl)-amino]methyl}-4H-1,2,4-triazole and X = BF(4)(-) (1), Cl(-) (2), PF(6)(-) (3), SbF(6)(-) (4), CF(3)SO(3)(-) (5), B(PhF)(4)(-) (6), and C(16)H(33)SO(3)(-) (7). Most were isolated as solvates, and the microcrystalline ([3], [4]·2H(2)O, [5]·H(2)O, and [6]·?MeCN) or powder ([2]·4H(2)O, and [7]·2H(2)O) samples obtained were studied by variable-temperature magnetic susceptibility and Mo?ssbauer methods. A structure determination on a crystal of [2]·2MeOH·H(2)O, revealed it to be a [LS-HS] mixed low spin (LS)-high spin (HS) state dinuclear complex at 90 K, but fully high spin, [HS-HS], at 293 K. In contrast, structures of both [5]·?IPA·H(2)O and [7]·1.6MeOH·0.4H(2)O showed them to be [HS-HS] at 90 K, whereas magnetic and M?ssbauer studies on [5]·H(2)O and [7]·2H(2)O revealed a different spin state, [LS-HS], at 90 K, presumably because of the difference in solvation. None of these complexes undergo thermal spin crossover (SCO) to the fully LS form, [LS-LS]. The PF(6)(-) and SbF(6)(-) complexes, 3 and [4]·2H(2)O, appear to be a mixture of [HS-LS] and [HS-HS] at low temperature, and undergo gradual SCO to [HS-HS] on warming. The CF(3)SO(3)(-) complex [5]·H(2)O undergoes gradual, partial SCO from [HS-LS] to a mixture of [HS-LS] and [HS-HS] at T(1/2) ≈ 180 K. The B(PhF)(4)(-) and C(16)H(33)SO(3)(-) complexes, [6]·(1)/(2)MeCN and [7]·2H(2)O, are approximately [LS-HS] at all temperatures, with an onset of gradual SCO with T(1/2) > 300 K.     

Nonoxovanadium(IV) and oxovanadium(V) complexes with mixed O, X, O-donor ligands (X = S, Se, P, or PO)

Ligating properties of four potentially tridentate bisphenol ligands containing [O, X, O] donor atoms (X = S 1, Se 2, P 3, or P=O 4) toward the vanadium ions in +IV or +V oxidation states have been studied. Each ligand with different heterodonor atoms yields as expected nonoxovanadium(IV) complexes, V(IV)L(2), whose structures have been determined by X-ray diffraction methods as having six-coordinate V(IV), VO(4)X(2), core. Compounds 1-4 have also been studied with electrochemical methods, variable-temperature (2-295 K) magnetic susceptibility measurements, X-band electron paramagnetic resonance (EPR) (2-60 K) spectroscopy, and magnetic circular dichroism (MCD) (5 K) measurements. Electrochemical results suggest metal-centered oxidations to V(V) (i.e., no formation of phenoxyl radicals from the coordinated phenolates). A combination of density functional theory calculations and experimental EPR investigations indicates a dramatic effect of the heteroatoms on the electronic structure of 1-4 with consequent reordering of the energy levels; 1 and 3 possess a trigonal ground state (d(z)()(2))(1), but 4 with the phosphoryl oxygen as the heterodonor atom in contrast exhibits a tetragonal ground state, (d(xy)())(1). On the basis of the intense electronic transitions in absorption spectra, all electronic transitions observed for 4 have been assigned to ligand-to-metal charge-transfer transitions, which have been confirmed by preliminary resonance Raman measurements and C/D ratios obtained from low-temperature MCD spectroscopy. Moreover, diamagnetic complexes 5 and 6 containing mononuclear and dinuclear oxovanadium(V) units have also been synthesized and structurally and spectroscopically ((51)V NMR) characterized.