Magnetic characterization, synthesis and crystal structure of a heterodinuclear CuGd Schiff base complex bridged by the two phenolic oxygen atoms

A novel heterodinuclear complex formed by the reaction of gadolinium nitrate with Schiff base complex of copper(II) has been synthesized and characterized. Preparation, crystal structure and magnetic properties of the heterodinuclear complex, LCu(Me₂CO)Gd(NO₃)₃, (L=(N,N′-bis(2,3-dihydroxybenzylidene)-1,3-diaminopropane) are reported. The complex is consisting of a deca-coordinated Gd^III ion which is bridged to four coordinated Cu^II via both phenolate oxygen atoms of the L Schiff base ligand. The average CuGd separation is 3.475(2) Å. There is also one non-coordinating acetone molecule in the crystal structure. The magnetic susceptibility of the complex was measured over the range 4.5–350 K and the observed data were successfully simulated by the equation based on the spin-Hamiltonian operator H=−JS_Cu·S_Gd. The values of the intrachain interaction parameters have been deduced from the magnetic data: exchange integral J(Cu–Gd)=7.3 cm⁻¹, g_Cu=2.17, g_Gd=2.09. This indicates a weak ferromagnetic spin exchange interaction between Cu^II and Gd^III ions. The nature of the magnetic super-exchange interaction of the title compound is compared with similar Cu^IIGd^III heterodinuclear complexes.     

Coordination bond formation at charge-transfer phase transition in (BDTA)2[Co(mnt)2

The crystal structure of a charge-transfer salt, (BDTA)2[Co(mnt)2], where BDTA is 1,3,2-benzodithiazolyl and mnt is maleonitriledithiolate, consisted of an alternating stacking column of a head-to-head BDTA+ dimer and a planar [Co(mnt)2]2- dianion at 253 K. Magnetic measurements and structural analyses revealed a phase transition at 190 K, where a partial electron transfer occurred from [Co(mnt)2]2- to one of the BDTA+ cations, forming a coordination bond between the two.     

Synthesis, crystal structures and magnetic properties of Cu(II) compounds bridged by the terephthalate ligand and hydrogen bonds

A 3D network [Cu(tmen)(tp)(H₂O)₂]_n (1) (tmen = N,N,N′,N′-tetramethylethylenediamine; tp = terephthalate) and a 2D sheet [Cu(pyrazole)₂(tp)]_n (2), featuring 1D chains interwoven by hydrogen bonds, have been prepared and characterized by means of X-ray analyses and magnetic measurements. For 1, coordinative zigzag chains contain Cu(II) centers capped by the chelate ligand tmen, in which the tetragonal structure is elongated due to Jahn–Teller distortion. Coordinated water molecules are hydrogen-bonded to two free carboxylate oxygens of tp bridges, leading to the observed 3D structure. The use of the non-chelating capping ligand pyrazole produced the covalent-bonded 1D linear compound 2 with hydrogen bonds. A severe octahedral distortion of the Cu(II) center arises from a small bite angle (52.3(1)°) of two carboxylate oxygen atoms of tp, which are in turn hydrogen-bonded to the N–H groups of pyrazole ligands coordinated to Cu(II) atoms in neighboring chains. Magnetic data were fitted with the high-temperature series expansion for the Heisenberg chain spin Hamiltonian H = −J∑_iS_i · S_i + 1 together with consideration of the molecular field approximation (zJ′). Both compounds interestingly exhibit ferromagnetic interactions with g = 2.17, J = 4.08 cm⁻¹, zJ′ = −0.28 cm⁻¹ for 1 and g = 2.09, J = 1.47 cm⁻¹, zJ′ = −0.04 cm⁻¹ for 2. By taking into account structural parameters of distances between Cu atoms, it is reasonably assigned that the ferromagnetic couplings (J > 0) in these systems originate from the hydrogen bonds. The spin density of the d_x²-y² orbital on a Cu(II) atom in a chain is propagated and induced over the d_z² orbital of another Cu(II) atom in an adjacent chain. This orbital orthogonality gives rise to such interactions. The negative zJ′ term suggests that the tp bridges communicate only tiny antiferromagnetic interactions.     

Magnetic properties of stable N-[(dichlorophenyl)thio]-2,4,6-triphenylphenylaminyl and N-[(dichlorophenyl)thio]-2,4,6-tris(chlorophenyl)phenylaminyl radical crystals

The magnetic properties of N-[(dichlorophenyl)thio]-2,4,6-triarylphenylaminyl radical crystals are reported. The three stable thioaminyls show ferromagnetic behaviors described using the one-dimensional Heisenberg model with the large ferromagnetic interaction of 2J/k_B = 28.0, 11.4, and 3.6 K. The other two radicals show the antiferromagnetic alternating chain behaviors with 2J/k_B = −16.8 K, = 0.55 and 2J/k_B = −128.8 K, = 0.90. The low-temperature susceptibility and heat capacity measurements of the crystal showing 2J/k_B = 28.0 K reveal a magnetic phase transition at 0.4 K. The ordered phase shows spin-flop transition which reveals an antiferromagnetic long range order.     

Three new polynuclear tetracarboxylato-bridged copper(II) complexes: Syntheses, X-ray structure and magnetic properties

The synthesis, crystal structure and magnetic measurements of three new polynuclear tetracarboxylato-bridged copper(II) complexes, i.e. {[Cu₄(phen)₂(μ-O₂CC₂H₅)₈] · (H₂O)}_n (1), [Cu₂(μ-O₂CC₆H₄OH)₄(C₇H₇NO)₂] · 6H₂O (2) and [Cu₂(μ-O₂CCH₃)₄(C₇H₇NO)₂] (3) (phen = 1,10-phenanthroline, O₂CC₆H₄OH = 3-hydroxy benzoate, C₇H₇NO = 4-acetylpyridine) are reported. All compounds consist of dinuclear units, in which two Cu(II) ions are bridged by four syn,syn-η¹:η¹:μ carboxylates, showing a paddle-wheel cage type with a square-pyramidal geometry, arranged in different ways. The structure of compound 1 consists of an one-dimensional structure generated by an alternating classical dinuclear paddle-wheel unit and an unusual dinuclear Cu₂(μ-OCOC₂H₅)₂(μ-O₂CC₂H₅)₂(phen)₂unit, which are connected to each other via a syn,anti-triatomic propionato bridge in an axial-equatorial configuration. The adjacent chains are connected to generate a 2D structure through the face-to-face π–π interaction between phen rings. Structures of compounds 2 and 3 both consist of a symmetric dinuclear Cu(II) carboxylate paddle-wheel core and pyridyl nitrogen atoms of 4-acetylpyridine ligand at the apical position, and just differ in the substituents of the equatorial ligands.

The magnetic properties have been measured and correlated with the molecular structures. It is found that in the two classical paddle-wheel compounds the Cu(II) ions are strongly antiferromagnetically coupled with J = −278.5 and −287.0 cm⁻¹ for complexes 2 and 3, respectively. In compound 1 the magnetic susceptibility could be fitted with two different, independent Cu(II) units, one strongly coupled and one weakly coupled; the paddle-wheel dinuclear unit has the strongest antiferromagetic coupling with a value for J of −299.5 cm⁻¹, whereas the Cu(II) ions in the propionato-bridged dinuclear unit of 1 display a very weak antiferromagnetic coupling with a value for J = −0.75 cm⁻¹, due to the orthogonality of the magnetic orbitals. Also the exchange within the chain is therefore very weak. The magneto-structural correlations for complexes 1, 2, and 3 are discussed on the basis of the structural parameters and magnetic data for the complexes.     

Structure and properties of the dinuclear complex [Co2(μ-OAc)2(OAc)2(μ-H2O)(phen)2]

The dinuclear complex [Co₂(μ-OAc)₂(OAc)₂(μ-H₂O)(phen)₂] has been prepared and its structure was determined. The compound crystallizes in the monoclinic space group P2(1)/c. The Co–Co distance is 3.574 Å and is similar to the Fe–Fe distance in the reduced methane monooxygenase hydroxylase. The electronic and IR spectra of the complex confirm octahedral coordination of the cobalt atoms and formation of strong O–HO hydrogen bonds in the solid state. The dependence of the magnetic susceptibility of the complex on temperature indicates an antiferromagnetic interaction, the value of the isotropic exchange parameter J was estimated to be −2.1 cm⁻¹. The ¹H NMR spectra show that in organic solvents the structure of compound is the same as in the solid state, however, in water solution the complex dissociates giving compounds with different Co:phen ratios.     

BDTA]2[Cu(mnt)2]: an almost perfect one-dimensional magnetic material

[BDTA]2[Cu(mnt)2] (BDTA = benzo-1,3,2-dithiazolyl, mnt = maleonitriledithiolate) was crystallized in the space group P with an inversion center on Cu giving a stacked structure with each metal complex anion sandwiched by two cations. Short intermolecular S...S contacts give rise to a one-dimensional chain lateral to the stacking axis. Variable-temperature magnetic susceptibility and EPR measurements indicate that the salt behaves as an ideal one-dimensional Heisenberg antiferromagnetic material from 2 K < or = T < or = 300 K, with a coupling constant of J/k(B) = 16-17 K; the very low temperature magnetic properties are in quantitative agreement with the predictions of quantum field theory. DFT calculations are consistent with the formation of a one-dimensional magnetic chain with interstack interactions mediated by the BDTA counterions.     

Infrared laser magnetic resonance spectroscopy of OD at 118.8, 96.5 and 215.4μ m

Zeeman spectral data are presented for the ²Π_3/2: J = _7/2 → J= _9/2,²Π_3/2: J= _7/2→²Π_1/2:J= _5/2 and²Π_3/2 J= _3/2→ J = _5/2 transitions in OD. Data for the ²Π_3/2. J=3/2→ J= 5/2 and ²Π_3/2 J= _5/2 → ²Π_l/2 : J= _3/2 transitions in OH, taken under similar conditions, are included.     

RPA MNDO analysis of the dihedral angle dependence of vicinal J(SnSn) and J(SnC) NMR coupling constants

Vicinal J(SnCCSn) and J(SnCCC) spin-spin coupling constants are calculated within the RPA MNDO method for different dihedral angles, θ, determined by the intervening bonds, in model compounds. For both types of couplings, calculated values closely follow Karplus-like dependences. Results are discussed in terms of experimental values, and the effects of substituents attached to the coupled atoms are briefly analyzed for the θ = 0 ° and θ = 180 ° conformations. These last values were also calculated using the RPA AM1 method. Results indicate that the RPA MNDO and RPA AM1 approaches show interesting potential for studying the structural dependences of ³J(SnSn) and ³J(SnC) couplings in tin-containing compounds.     

Syntheses, crystal structures and magnetic properties of a new nitronyl nitroxide NIT2-bithph and its manganese(II) compound [Mn(hfac)2(IMHBithph)]2·(NIT2-bithph)(C6H14)

A new nitronyl nitroxide NIT2-bithph (1) and its manganese(II) compound [Mn(hfac)₂(IMHBithph)]₂·(NIT2-bithph)(C₆H₁₄) (2) (hfac = hexafluoroacetylacetonate; NIT2-bithph = 4,4,5,5-tetramethyl-2-(bithiophenal-2-yl)imidazoline-1-oxyl-3-oxide; IMHBithph = 1-hydroxy-2-bithiophenal-4,4,5,5-tetramethyl-4,5-dihydro- 1H-imidazole) have been synthesized and structurally characterized by X-ray diffraction methods. The units of compound 1 were connected as one-dimensional chain by the intermolecular hydrogen bonds which afford an intermolecular antiferromagnetic interaction between nitronyl nitroxide radicals within the chain (J = −1.89 cm⁻¹). Compound 2 resulting from the reaction of Mn(hfac)₂·2H₂O and NIT2-bithph is dinuclear and includes the reduced amidino-oxide form of NIT2-bithph, it is made up of three parts: a [Mn(hfac)₂(IMHBithph)]₂ dimer unit, an uncoordinated NIT2-bithph radical and a noncoordinated solvent molecule of hexane, the molecule of radical is hydrogen bonded to its reduced form. Two reduced IMHBithph ligands bridge the two manganese(II) ions through their amidino-oxide oxygen atoms resulting in a small intramolecular antiferromagnetic interaction between the manganese ions (J = −1.55 cm⁻¹).     

Synthesis and spectroscopic, magnetic and EPR studies of di-μ-hydroxo-bis[(NN)(N-phenyl-2-pyridinamine)copper(II)]hexaflourophosphate, with NN=2,2′-bipyridine or 1,10-phenanthroline.: X-ray crystal structure of the 2,2′-bipyridine complex

Binuclear complexes [{Cu(NN)(PhNHpy)}₂(μ-OH)₂](PF₆)₂, where NN=2,2′-bipyridine (bipy) or 1,10-phenanthroline (phen), have been synthesized and characterized by chemical analysis, conductance measurements and IR and electronic spectroscopy. The X-ray crystal structure of [{Cu(bipy)(PhNHpy)}₂(μ-OH)₂](PF₆)₂ shows a distorted square-planar pyramidal coordination for Cu(II), defined by two nitrogen atoms of bipy, two bridging oxygen atoms and the pyridinic nitrogen atom of the ligand. Magnetic susceptibility measurements (in the 4.8–290 K range) reveal coupling which is antiferromagnetic for the bipy complex (2J=−24.2 cm⁻¹) and slightly ferromagnetic for the phen complex (2J=3.3 cm⁻¹). The EPR spectra show the expected triplet signals.     

Inelastic scattering matrix elements, cross sections and rate constants for transition B(P1/2) + H2(j = 0) ↔ B(P3/2) + H2(j = 0)

The non-adiabatic wave packet collisions of B(²P_1/2) + H₂(j = 0) ↔ B(²P_3/2) + H₂(j = 0) were calculated using the time dependent Channel Packet Method to compute transition probabilities, cross sections and rate constants. While the H₂ angular momentum j was fixed to 0, the total angular momentum of the system J, was varied from 1/2 to 153/2. The feature of the Stückelberg oscillation was shown in transition probabilities. The transition from B(²P_3/2) to B(²P_1/2) state was shown to be favored over the reverse process. The ratio of the computed rate constants was well compared with that of the analytic result obtained from the Boltzmann factor and the detailed balance.     

Synthesis and magnetism of the first tetranuclear copper(II)–iron(III) complexes of macrocyclic oxamides

Four novel tetranuclear macrocyclic complexes of the formula [(CuLⁱ)₃Fe](ClO₄)₃·3H₂O (i=1–4, Lⁱ are the dianions of the [14]N₄ and [15]N₄ macrocyclic oxamides, namely 2,3-dioxo-5,6:13,14-dibenzo-7,12-bis(ethoxycarbonyl)-1,4,8,11-tetraazacyclotetradeca-7,11-diene, 2,3-dioxo-5,6:13,14-dibenzo-9-methyl-7,12-bis(ethoxycarbonyl)-1,4,8,11-tetraazacyclotetradeca-7,11-diene and 2,3-dioxo-5,6:14,15-dibenzo-7,13-bis(ethoxycarbonyl)-1,4,8,12-tetraazacyclotetradeca-7,12-diene] have been prepared and characterized. These complexes are the first examples of oxamido-bridged Cu(II)–Fe(III) heterometallic species. Cryomagnetic studies on [(CuL¹)₃Fe](ClO₄)₃·3H₂O (1) and [(CuL³)₃Fe](ClO₄)₃·3H₂O (3) (77–300 K) revealed that the Cu(II) and Fe(III) ions interact antiferromagnetically through the oxamido bridge, with the exchange integral J=−30.8 cm⁻¹ for 1 and J=−28.7 cm⁻¹ for 3 based on . The interaction parameters have been compared with that of the related [Cu₃Mn] compound.     

Experimental study of a dynamic filtration system with overlapping ceramic membranes and non-permeating disks rotating at independent speeds

In a previous paper [Ding et al., J. Membr. Sci. 276 (2006) 232], we have investigated the performance in microfiltration of mineral suspensions of a novel filtration pilot consisting in overlapping ceramic membranes disks rotating at same speed on two parallel shafts. In this paper, we investigate a modification of this concept in which the ceramic disks of one shaft were replaced by non-permeating metal disks of same size rotating at a speed different from that of membranes. We also operated the pilot without disks on the 2nd shaft in order to eliminate membrane overlapping. When using metal disks with radial vanes, permeate fluxes were found to be 50–60% higher than those obtained in the same conditions with the previous design using only ceramic disks. By comparing permeate fluxes in different configurations, membranes on both shafts, membranes on the 1st shaft with and without metal disks on the 2nd shaft, we showed that, at a feed concentration of 200 g L⁻¹, the effect on permeate flux J, of shear rate increment due to membrane overlapping, could be completely offset by the high concentration increase between two adjacent and overlapping membranes. Raising the ceramic disks rotation speed N_c had a larger effect on J than increasing the metal disks speed N_m. For N_c = 32.16 Hz (1930 rpm) and N_m = 2.4 Hz (144 rpm), J reached 1790 L h⁻¹ m⁻² at 310 kPa, versus 1100 L h⁻¹ m⁻² for N_c = 12.3 Hz (738 rpm) and N_m = 22.26 Hz (1336 rpm) (for the same total sum N_c + N_m). Measurements of electrical power consumed by friction on rotating disks showed that the energy spent per m³ of permeate was lowest when using metal disk with vanes rotating at low speed and ceramic disks rotating at high speed.     

Photoexcitation spectroscopy of BO2 with a single frequency dye laser

The (0,0,0) ²Π_3/2−(1,0,0) ²Π_3/2 bandhead of ¹¹BO₂ has been studied with a tunable dye laser. Rotational transitions between J = 1.5 and J = 33.5 were assigned. For the measurements a combination of photoexcitation and laser induced fluorescence spectroscopy has been used; the method is extremely useful for the assignment and deconvolution of unresolved complex bands.     

Hydrogen-bonded materials based on organic tautomeric molecules: Theoretical treatment

The crystalline Br, I and CH₃ derivatives of 9-hydroxyphenalenone (5X–9HPO) and their deuteroxy analogues (5X–9DPO) are treated by application of the Ising model approaches. The molecular field parameter (J₀) as well as the tunneling parameter (Ω) are evaluated for each material with the help of different quantum chemistry procedures. As our evaluations show both relations Ω(D)/J₀ and Ω(H)/J₀ are less than unity in the case of 5CH₃–9(H/D)PO derivatives that leads to an appearance of the low-temperature ordered (anti-ferroelectric) phase. A relatively small Ω(D)/J₀ (0.2–0.4) values derived in the case of 5Br– and 5I–9DPO imply the tendency to transition into the similar phase in these species. At the same time a rather large values of Ω(H)/J₀ (0.9–1.7) derived in the case of their hydroxy analogues speak in favor of their quantum paraelectric behavior. The obtained theoretical estimations and conclusions are compared with the available experimental data.     

EPR of layered magnetic metal-amino acid salts. II. Cu(L-Met)2

Single crystals of bis(L-methioninato)copper(II), Cu(L-Met)₂, were studied by EPR at 9.7 and 33.6 GHz, at 300 K. The position and the peak-to-peak linewidth of the single observed EPR line were measured in three perpendicular planes of the samples. This single resonance is due to the collapse of the resonances of the two magnetically inequivalent copper ions in the lattice caused by the exchange interaction. The components of the molecular g tensor for isolated copper ions were obtained using a model which assumes axial symmetry. The results indicate that the unpaired electron occupies the d(x² − y²) orbital, and the orientation of the molecule obtained from the EPR data agrees with the crystallographic result. The linewidth data support a model which assumes exchange narrowing of the magnetic dipolar interaction in a two-dimensional magnetic lattice, an incomplete collapse of the hyperfine structure, and a frequency-dependent contribution in the planes where the g factors for the two sites of copper are different. An analysis of this latter contribution, allows to evaluate an exchange coupling constant |J′| = 0.10 K between inequivalent copper neighbors. Besides, the analysis of the hyperfine contribution to the linewidth gives |J| = 0.18 K for the average value of the exchange interaction of one copper ion with its six nearest neighbors within the layer. Concerning the possible superexchange paths between inequivalent copper ions, we suggest they can be of two types: the Cu---N---H…O---Cu one, involving hydrogen bonds between equatorial nitrogens and equatorial oxygens, and the other consisting of Cu---O---C---O---Cu carboxylate bridges involving apical and equatorial oxygens. They are discussed in view of the experimental results.     

Ferromagnetic anomaly associated with the antiferromagnetic transitions in (donor)[Ni(mnt)2]-type charge-transfer salts

Three newly prepared [Ni(mnt)2] complexes, (HMTTF)[Ni(mnt)2], (ChSTF)[Ni(mnt)2], and (DBTTF)2[Ni(mnt)2], are reported (DBTTF = dibenzotetrathiafulvalene, ChSTF = 2,3-cyclohexylenedithio-1,4-dithia-5,8-diselanafulvalene, HMTTF = bis(trimethylene)-tetrathiafulvalene, and mnt = maleonitrile dithiolate). The former two compounds have usual DA-type (D = donor, A = acceptor) mixed stacks, whereas the DBTTF complex has DDDDAA-type 6-fold columns. These compounds are electrical insulators, but the HMTTF and ChSTF complexes exhibit chiT minima at 16 and 55 K, respectively, followed by chiT peaks at 8 and 16 K. Below these temperatures the ESR signal disappears, indicating antiferromagnetic transitions. The origin of the ferromagnetic interaction is explained either from the difference of the g values between the donor and the anion or from the intrinsic ferromagnetic interaction of the [Ni(mnt)2] anions.     

Synthesis and crystal structures of two new lead(II) hexafluoroarsenates(V)

In the system PbF₂/AsF₅/anhydrous hydrogen fluoride (aHF) two new lead(II) hexafluoroarsenates(V) Pb(HF)(AsF₆)₂ and PbFAsF₆ were isolated. Pb(HF)(AsF₆)₂ is formed when the molar ratio AsF₅:PbF₂ is 2 or higher. It crystallizes in the space group Pbcn with a=1058.3(3) pm, b=1520.9(6) pm, c=1079.4(3) pm, V=1.7374(10) nm³ and Z=8. The HF molecule is directly connected to the Pb center, eight fluorine atoms from three different AsF₆⁻ ions (Pb–F distances ranging from 248(4) to 276(2) pm) and one further fluorine at 306(3) pm complete the coordination sphere. PbFAsF₆ is obtained when equimolar amounts of PbF₂ and AsF₅ react in aHF. PbFAsF₆ crystallizes in the space group P with: a=466.10(10) pm, b=723.70(10) pm, c=747.40(10) pm, =105.930(10)°, β=101.49(2)°, γ=90.660(10)°, V=0.23698(7) nm³ and Z=2. The basic unit in the structure of PbF(AsF₆) consists of a four-membered ring of two Pb and two F atoms. The Pb atoms in the ring are further connected by two AsF₆⁻ units via cis-fluorine bridges, thus forming a [PbF(AsF₆)]₂ cluster, which interacts by additional Pb–F bonds thus forming a ribbon-like polymer.