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International audience; The spin population distribution in the ferromagnetically coupled hetero-bimetallic chain compound [MnNi(NO(2))(4)(en)(2)] (en = 1,2-ethanediamine) has been investigated by means of polarized neutron diffraction experiments, and the results compared with those from theoretical estimates obtained via calculations based on density functional theory on dinuclear molecular models of the chain. The spin distributions obtained from experiment and from theory are consistent and reflect a larger spin delocalization from the Ni atom due to the more covalent character of the Ni-N bonds compared to the Mn-O ones. Also a nearly isotropic spin distribution is observed for the more ionic d(5) Mn(2+) ion and a clearly anisotropic distribution for the d(8) Ni(2+) ion. The use of dinuclear molecular models for the calculation of the exchange coupling constant between Ni and Mn provide upper and lower limits (+17.6 and -4.2 cm(-)(1)) for the experimentally determined value (+1.3 cm(-)(1)), depending on how the missing part of the chain is simulated, but yield essentially the same spin distribution. The Mn(II)-Ni(II) weak ferromagnetic coupling in the chain is interpreted in a spin delocalization mechanism as resulting from the weakness of the overlap between the magnetic orbitals centered on nickel and those centered on manganese which are only weakly delocalized on the ligands.

The compounds of formula {Ln2[Ni(opba)]3}·S (opba being o-phenelynebis(oxamato), Ln lanthanideIII ions, and S solvents molecules) have been structurally and magnetically characterized for Ln = La, ...

Palladium(II) and ruthenium(II) complexes containing aminoxyl radical-substituted triphenylphosphine ligands are reported. The novel spin-labeled phosphine ligands [(p(4,4,5,5,-tetramethylimidazolinyl-1-oxyl-3-oxide)phenyl)diphenylphosphine] (1) and [(p-(Noxyl-tert-butylamino-2-)phenyl)diphenylphosphine] (2) react with PdCl2 to yield transPd[1]2Cl2 and trans-Pd[2]2Cl2 (complexes 3 and 4, respectively), which show exchange-coupled EPR spectra. This through-space, intramolecular coupling provides a method of determining the number of radical phosphines coordinated to the Pd(II) center. Systems with only one coordinated phosphine show EPR spectra typical of the ligand. Phosphine 2 reacts with [( 3 C3H5)PdCl]2 and [( 6 -p-cymene)RuCl2]2 to form the mononuclear metal phosphine adducts ( 3 -C3H5)Pd[2]Cl (5) and ( 6 -p-cymene)Ru[2]Cl2 (6). All complexes show broad, shifted 1 H NMR spectra, and magnetic susceptibility measurements confirm the presence of one (complexes 5, 6) or two (complexes 3, 4) radicals per complex accordingly. The X-ray crystal structures of Pd[2]2Cl2 and ( 3 -C3H5)Pd[2]Cl are also reported. Complexes 5 and 6 are unusual examples of stable organometallic systems with peripheral free radicals, i.e., spin-labeled organometallics.

The goal of this paper is to obtain further information on the magnetic phase diagram of the cyano-bridged bimetallic ferromagnet of formula Mn2(H2O)5Mo(CN)7·4H2O (α phase). For that, the temperature dependence of the heat capacity has been measured. A λ peak has been observed at Tc = 50.5 K, corresponding to the transition between the ferromagnetic and paramagnetic states. The temperature dependencies of the alternating current (ac) in-phase and out-of-phase magnetic susceptibilities have also been measured on single crystals oriented along their magnetic axes, a, b, and c*. The effect of the frequency and of the value of the static field have been investigated. These data confirm the magnetic phase diagram determined previously from single-crystal direct current (dc) magnetic measurements. The effect of pressure on the magnetic properties has also been investigated. Tc was found to vary linearly as a function of pressure, with a positive dTc/dP slope. All these results have been discussed.

The title compound, [Fe(btr)(3)](ClO(4))(2), has been synthesized. The investigation of its magnetic properties has revealed a low-spin--high-spin conversion occurring in two steps, each step involving 50% of the Fe(2+) ions. The low-temperature step is very abrupt and occurs with a thermal hysteresis whose width is about 3 K around T(1) = 184 K. The high-temperature step, centered around T(2) = 222 K, is rather gradual. Differential scanning calorimetric measurements have confirmed the occurrence of a two-step spin conversion. The enthalpy and entropy variations associated with the two steps have been found as DeltaH(1) = 5.7 kJ mol(-)(1) and DeltaS(1) = 30.1 J mol(-)(1) K(-)(1), and DeltaH(2) = 6.5 kJ mol(-)(1) and DeltaS(2) = 28.6 J mol(-)(1) K(-)(1), respectively. The crystal structure of [Fe(btr)(3)](ClO(4))(2) has been solved at three temperatures, namely, above the high-temperature step (260 K), between the two steps (190 K), and below the low-temperature step (150 K). The compound crystallizes in the trigonal system, space group Rthremacr;, at the three temperatures. The structure is three-dimensional. There are two Fe(2+) sites, denoted Fe1 and Fe2. Each of them is located on a 3-fold symmetry axis and an inversion center and is surrounded by six btr ligands through the nitrogen atoms occupying the 1- or 1'-positions. Each btr ligand bridges an Fe1 and an Fe2 site, with an Fe1-Fe2 separation of 8.67 Å at 260 K. The perchlorate anions are located in the voids of the three-dimensional architecture and are hydrogen bonded to the triazole rings of the btr ligands. These anions do not interact with the Fe1 and Fe2 sites exactly in the same way. At 260 K, both the Fe1 and Fe2 sites are high-spin (HS) with Fe-N bond lengths of 2.161(3) and 2.164(3) Å, respectively. At 190 K, the Fe1 site remains HS while the Fe2 site is low-spin (LS) with Fe-N bond lengths of 2.007(3) Å. Finally, at 150 K, both the Fe1 and Fe2 sites are LS with Fe-N bond lengths of 1.987(5) and 1.994(5) Å, respectively. It turns out that the two-step spin conversion is associated with the presence of two slightly different Fe(2+) sites. The spin conversion regime has also been followed by Mössbauer spectroscopy. These findings have been discussed and compared to the previously reported cases of two-step spin conversions.

Three new complexes involving nitronyl nitroxide and PhCOO- or N3- ligands have been synthesized and structurally and magnetically characterized. These compounds are formulated as Mn(L)4(X)2·nH2O, L = 2-(p-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PNN) or 2-(p-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl (PN) and X = PhCOO- or N3-. Compound A [Mn(PNN)2(PhCOO)2(H2O)2] presents the following structural parameters: triclinic, space group P1 (No. 2), a = 6.859(1) A, b = 11.271(2) A, c = 13.978(6) A, α = 88.88(2)°, β = 89.38(2)°, γ = 78.28(2)°, Z = 1. The complex has a centrosymmetric distorted octahedral geometry in which the manganese ion is bound to two radical ligands through the nitrogen atom of the pyridine rings, two benzoate groups, and two water molecules. The two compounds B [Mn(PNN)4(N3)2] and C [Mn(PN)4(N3)2] are isostructural with the following structural parameters: B; triclinic, space group P1 (No. 2), a = 7.177(4) A, b = 13.767(3) A, c = 13.928(4) A, α = 90.20(2)°, β = 102.94...

To date, most of the studies dealing with the magnetic properties of 4f-3d compounds have been limited to the case in which the 4f ion was Gd(III), with a pure spin ground state. For the lanthanide(III) ions with a first-order orbital momentum, the determination of the nature of the 4f-3d interaction is still a challenge. This paper addresses this problem. The magnetic properties of the compounds of formula {Ln(2)[M(opba)](3)}.S (abbreviated hereafter as Ln(2)M(3)) have been investigated; Ln stands for a lanthanide element, M for Cu or Zn, opba for ortho-phenylenebis(oxamato), and S for solvent molecules. All of these compounds have similar one-dimensional structures consisting of ladder-type motifs. Our approach consisted of comparing the magnetic properties of Ln(2)Cu(3) and Ln(2)Zn(3) for each Ln(III) ion. The former are governed by both the thermal population of the Stark components of Ln(III) and the Ln(III)-Cu(II) interaction; the latter are only governed by the thermal population of the Ln(III) Stark components. It has been confirmed that the Gd(III)-Cu(II) interaction was ferromagnetic, and it was found that the Tb(III)-Cu(II) and Dy(III)-Cu(II) interactions were ferromagnetic as well. The Tm(III)-Cu(II) interaction might also be ferromagnetic; the situation, however, is uncertain. On the other hand, in all other cases the Ln(III)-Cu(II) interaction is not ferromagnetic; it is either not detectable by the magnetic technique or antiferromagnetic. The difference between Dy(III)-Cu(II) (ferromagnetic) and Ho(III)-Cu(II) (not ferromagnetic) is particularly striking. These findings have been discussed.

The optical absorption spectroscopy for the trinuclear compounds Mn(CuL)2·xB with L standing for N-(4-methyl-6-oxo-3-azahept-4-enyl)oxamato and B = (CH3)2SO (x = 2) (1) or H2O (x = 5) (2) has been investigated in the 4−300 K temperature range. The crystal structure of 1 was known; it consists of isolated and neutral trinuclear units in which the central MnII ion is linked to two CuL complex ligands and two (CH3)2SO molecules in a cis configuration. The Cu−Mn−Cu linkage is bent with an angle of 127°. The spectra for 1 and 2 exhibit narrow and intense MnII spin-forbidden transitions in the 24000−28000 cm-1 range, activated by an exchange mechanism. The temperature dependences of the main feature corresponding to the 6A1 → 4A1, 4E(G) MnII transitions have been recorded. Using a model proposed first by Tanabe and co-workers and adapted to the CuMnCu topology, a theoretical expression for the temperature dependence of the intensity of the transition has been derived and compared to the experimental data. The p...

The title compound, K2Mn3(H2O)6[Mo(CN)7]2·6H2O, has been synthesized by slow diffusion of aqueous solutions saturated in KNO3 and containing K4[Mo(CN)7]·2H2O and [Mn(H2O)6](NO3)2, respectively. The compound crystallizes in the monoclinic system, space group C2. The Mo site is surrounded by six −C−N−Mn linkages and one terminal cyano group in a strongly distorted pentagonal bipyramid fashion. There are two distorted octahedral Mn sites, both with four −N−C−Mo linkages and two water molecules in trans conformation. The structure is two-dimensional with anionic layers perpendicular to the a axis and K+ ions located between the layers. Each layer is constituted of two parallel gridlike sheets made of edge-sharing Mo2Mn2 lozenge motifs, connected by Mn(CN)4(H2O)2 units situated between the sheets. Thorough magnetic investigations have been carried out. First, it has been demonstrated that the magnetic axes are collinear with the a, b, and c* crystallographic directions. The temperature and field dependences of...

The title compound has been synthesized by slow diffusion of aqueous solutions containing K4[Mo(CN)7]·2H2O and [Mn(H2O)6](NO3)2, respectively. The compound crystallizes in the monoclinic system, space group P21/c. The Mo site is surrounded by seven −C−N−Mn linkages in a distorted pentagonal bipyramid fashion. There are two distorted octahedral Mn sites, one with four and the other with three Mn−N−C−Mo linkages. The structure is three-dimensional and of low symmetry. It consists of ladders made of edge-sharing lozenge motifs (MoCNMnNC)2 running along the a direction. These ladders are linked further along the b and c directions. Both temperature dependences of the magnetic susceptibility and field dependences of the magnetization have been investigated along the three crystallographic directions, a, b, and c*. The angular dependence of the magnetization in the ab plane as a function of the external field has also been measured. These single crystal magnetic measurements have revealed that the compound orde...

The new spin-crossover compound Fe(PM-BiA)(2)(NCS)(2) with PM-BiA = N-(2-pyridylmethylene)aminobiphenyl has been synthesized. The temperature dependence of chi(M)T (chi(M) = molar magnetic susceptibility and T = temperature) has revealed an exceptionally abrupt transition between low-spin (LS) (S = 0) and high-spin (HS) (S = 2) states with a well-reproducible hysteresis loop of 5 K (T(1/2) downward arrow = 168 K and T(1/2) upward arrow = 173 K). The crystal structure has been determined both at 298 K in the HS state and at 140 K in the LS state. The spin transition takes place without change of crystallographic space group (Pccn with Z = 4). The determination of the intermolecular contacts in the LS and HS forms has revealed a two-dimensional structural character. The enthalpy and entropy variations, DeltaH and DeltaS, associated with the spin transition have been deduced from heat capacity measurements. DeltaS (= 58 J K(-)(1) mol(-)(1)) is larger than for other spin transition bis(thiocyanato) iron(II) derivatives. At 10 K the well-known LIESST (light-induced excited spin state trapping) effect has been observed within the SQUID cavity, by irradiating a single crystal or a powder sample with a Kr(+) laser coupled to an optical fiber. The magnetic behavior recorded under light irradiation in the warming and cooling modes has revealed a light-induced thermal hysteresis (LITH) effect with 35T(1/2)77 K. The HS --LS relaxation after LIESST has been found to deviate from first-order kinetics. The kinetics has been investigated between 10 and 78 K. A thermally activated relaxation behavior at elevated temperatures and a nearly temperature independent tunneling mechanism at low temperatures have been observed. The slow rate of tunneling from the metastable HS state toward the ground LS state may be explained by the unusually large change in Fe-N bond lengths between these two states.

A precise structural study by wide-angle X-ray scattering (WAXS) has been carried out on two spin transition materials: [Fe(Htrz)2(trz)](BF4) (1) and [Fe(NH2trz)3](NO3)2 (2), with Htrz = 1,2,4-4H-triazole, trz = 1,2,4-triazolato, and NH2trz = 4-amino-1,2,4-triazole, both at room temperature in the low-spin state (LS) and at higher temperature in the high-spin state (HS). These compounds exhibit cooperative spin transitions between LS and HS state above room temperature with a large thermal hysteresis and a pronounced thermochromic effect. Both compounds have a polymeric chain structure where each Fe2+ metal ion is triply bridged to their neighbors through nitrogen atoms of the triazole or triazolato groups. In the LS state the polymeric chain is linear, whereas at higher temperature, in the HS state, the magnetic transition causes an elongation and a deformation of the chain. The chain loses its linear character. We explain this behavior by a rhombic-type distortion of the iron octahedral environment asso...

Three compounds of general formula (NBu4)[MIIRuIII(ox)3] have been synthesized; NBu4+ stands for tetra-n-butylammonium, M for Mn, Fe, and Cu, and ox2- for the oxalate dianion. The X-ray powder patterns for the three derivatives have revealed that these compounds are isostructural with (NBu4)[MnIICrIII(ox)3], whose crystal structure was known, and the cell parameters have been refined in the R3c space group. The (NBu4)[MIIRuIII(ox)3] compounds are new examples of two-dimensional bimetallic assemblies with oxalate bridges. The temperature (T) dependences of the magnetic susceptibility (χM) in both the dc and ac modes and the field dependences of the magnetization have been investigated. The local spins are SRu = SCu = 1/2, SMn = 5/2, and SFe = 2. The RuIII−MII interaction has been found to be antiferromagnetic for M = Fe and Cu and ferromagnetic for M = Mn. The two compounds (NBu4)[FeIIRuIII(ox)3] and (NBu4)[CuIIRuIII(ox)3] exhibit a ferrimagnetic behavior, characterized by a minimum in the χMT versus T plo...

[Cu(hyetrz)3](ClO4)2·3H2O (hyetrz = 4-(2-hydroxyethyl)-1,2,4-triazole) represents the first structurally characterized metal(II) chain compound containing triple N1,N2-1,2,4-triazole bridges. The structure has been solved at 298 K by single-crystal X-ray analysis. catena-Poly[μ-tris(4-(2-hydroxyethyl)-1,2,4-triazole-N1,N2)copper(II)] diperchlorate trihydrate (C12H27N9Cl2O14Cu) crystallizes in the monoclinic space group P21/n, a = 13.877(3) A, b = 23.023(5) A, c = 15.351(2) A, β = 91.10(2)°, Z = 8 (Cu(II) units). The Cu(II) ions are linked by triple N1,N2-1,2,4-triazole bridges yielding a slightly alternating chain with Cu1−Cu2 = 3.853(2) A and Cu2−Cu3 = 3.829(2) A. The EXAFS results are consistent with the crystal structure. At 30 K, the EXAFS signature of the multiple scattering path Cu1−Cu2−Cu3 is clearly observed, confirming that such exceptional long distance EXAFS signals can be used to detect metal alignments in inorganic long chains when crystal structures are not available. The thermal behavior of...

The two compounds CoCu(obbz)(H2O)4·2H2O (I) and CoCu(obze)(H2O)4·2H2O (II) have been synthesized, and their crystal structures have been determined at room temperature. Both compounds crystallize in the monoclinic system, space group P21/n. The lattice parameters are a = 7.8190(6) A, b = 12.534(2) A, c = 20.2770(10) A, β = 97.306(6)°, and Z = 4 for CoCu(obbz)(H2O)4·2H2O and a = 17.966(5) A, b = 6.907(1) A, c = 13.678(3) A, β = 97.69(1)°, and Z = 4 for CoCu(obze)(H2O)4·2H2O. For both compounds, the structure consists of isolated Co2+Cu2+ pairs (in which the metal ions are bridged by an oxamide group) and noncoordinated water molecules. A thermogravimetric analysis has been carried out. Three water molecules are removed at a temperature T2 (96 °C for I and 120 °C for II), and five water molecules are removed at a temperature T3 (205 °C for I and 190 °C for II). When cooling down, the two compounds reabsorb water slowly and then return to the initial state. The dehydration−rehydration process is totally reve...

Three polymorphic modifications A-C of [Fe(II)(DPPA)(NCS)(2)], where DPPA = (3-aminopropyl)bis(2-pyridylmethyl)amine is a new tetradentate ligand, have been synthesized, and their structures, magnetic properties, and Mössbauer spectra have been investigated. For polymorph A, variable-temperature magnetic susceptibility measurements as well as Mössbauer spectroscopy have revealed the occurrence of a rather gradual HS if LS transition without hysteresis, centered at about 176 K. The same methods have shown that polymorph B is paramagnetic over the temperature range 4.5-295 K, whereas polymorph C exhibits a very abrupt S = 2 if S = 0 transition with a hysteresis. The hysteresis width is 8 K, the transitions being centered at T(c) downward arrow = 112 K for decreasing and T(c) upward arrow = 120 K for increasing temperatures. The crystal structures of the three polymorphs have been solved by X-ray diffraction at 298 K. Polymorph A is triclinic, space group Ponemacr; with Z = 2, a = 8.710(2) Å, b = 15.645(2) Å, c = 7.985(1) Å, alpha = 101.57(1) degrees, beta = 112.59(2) degrees, and gamma = 82.68(2) degrees. Polymorph B is monoclinic, space group P2(1)/c with Z = 4, a = 8.936(2) Å, b = 16.855(4) Å, c = 13.645(3) Å, and beta = 97.78(2) degrees. Polymorph C is orthorhombic, space group Pbca with Z = 8, a = 8.449(2) Å, b = 14.239(2) Å, and c = 33.463(5) Å. In the three polymorphs, the asymmetric units are almost identical and consist of one chiral complex molecule with the same configuration and conformation. The distorted [FeN(6)] octahedron is formed by four nitrogen atoms belonging to DPPA and two provided by the cis thiocyanate groups. The two pyridine rings of DPPA are in fac positions. The main differences between the structures of the three polymorphs are found in their crystal packing. The stabilization of the high-spin ground state of polymorph B is tentatively explained by the presence of two centers of steric strain in the crystal lattice resulting in the elongation of the Fe-N(aromatic) distance. The observed hysteresis in polymorph C seems to be due to the existence of an array of intermolecular contacts in the crystal lattice making the spin transition more cooperative than in polymorph A.

The goal of this work has been to propose a novel approach to fine tune the transition temperatures of spin transition materials, based on the concept of spin transition molecular alloys. It has concerned the alloys of composition [Fe(R1trz)3-3x(R2trz)3x]A2, where R1trz and R2trz stand for two different 4-substituted-1,2,4-triazole ligands, and A- stands for a counteranion. It has been shown that for any composition defined by x the alloy gives a unique spin transition regime, while the mixture (1 − x)[Fe(R1trz)3]A2 + x[Fe(R2trz)3]A2 of the same chemical composition shows two spin transition regimes with the relative intensities 1 − x and x, respectively. In the case of the alloys [Fe(Htrz)3-3x(NH2trz)3x](ClO4)2·H2O, the inversion temperatures T1/2↑ and T1/2↓ in the warming and cooling modes, respectively, have been found to vary almost linearly as a function of x. For x = 0.15, the alloy is bistable at room temperature. A theoretical treatment of this molecular alloy effect in the mean-field approximatio...

This paper is devoted to the determination of the spin density in the ferrimagnetic ground state of the bimetallic chain compound MnCu(pba)(H2O)(3) . 2H(2)O, with pba = 1,3-propylenebis(oxamato). The crystal structure, previously determined at room temperature through X-ray diffraction, was redetermined at 10 K through unpolarized neutron diffraction (orthorhombic system, space group Pnma, a = 12.727(11) Angstrom, b = 21.352(19) Angstrom, c = 5.153(3) Angstrom, Z = 4). The experimental spin density has been deduced from polarized neutron diffraction data recorded at 10 K under 50 kOe. Positive spin densities were observed on the manganese side and negative spin densities on the copper side. The delocalization of the spin density from the metal centers toward the oxamato bridging ligand was found to be more pronounced on the copper side than on the manganese side, so that the nodal surface (of zero spin density) is closer to manganese than to copper. The experimental spin distribution has been compared to the theoretical distributions deduced from density functional theory (DFT) calculations, using both DGauss and DMol programs. The experimental results for the title chain compound have also been compared to the spin distribution for the binuclear compound [Mn(Me-6-[14]ane-N-4)Cu(oxpn)](CF3SO3)(2) with Me-6-[14]ane-N-4 = (+/-)-5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane, and oxpn = N,N'-bis(3-aminopropyl)oxamido, recently reported. The most striking difference between pair and chain compounds concerns the positive P+ and negative P- spin populations carried by the manganese and copper sides, respectively. For the pair compound P+ was found as 4.67(8) mu(B), and P- as -0.67(8) mu(B) while for the chain compound these values are 5.05(7) mu(B) and -1.05(10) mu(B), respectively. The spin distribution for the ferrimagnetic chain compound is very close to a Neel state (P+ = 5 mu(B) and P- = -1 mu(B)).

The crystal structures of three compounds have been determined at room temperature, namely [Gd(hfa)3Cu(salen)] (1), [Y(hfa)3Cu(salen)] (2), and [Gd(hfa)3Cu(salen)(Meim)] (3), and the crystal structure of a fourth compound, [La(hfa)3(H2O)Cu(salen)] (4), has been determined at −100 °C; hfa = hexafluoroacetylacetonato, salen = N,N‘-ethylenebis(salicylideneaminato), and Meim = 1-methylimidazole. [La(hfa)3Ni(salen)] (5), isomorphous with 1, has also been synthesized. 1 crystallizes in the monoclinic system, space group P21/n, with a = 17.292(5) A, b = 22.370(5) A, c = 19.658(6) A, β = 90.07(2)°, and Z = 8. 2 crystallizes in the triclinic system, space group P1, with a = 12.207(3) A, b = 13.019() A, c = 13.011(6) A, α = 82.87(4)°, β = 83.55(3)°, γ = 70.91(3)°, Z = 2. 3 crystallizes in the monoclinic system, space group P21/n, with a = 16.521(9) A, b = 20.381(5) A, c = 12.758(6)°, β = 93.22(6)°, and Z = 4. 4 crystallizes in the monoclinic system, space group P21/n, with a = 12.826(2) A, b = 23.067(8) A, c = 13....

CoCu(pbaOH)(H2O)3·2H2O (1) is a Co(II)Cu(II) chain compound in which the ferrimagnetic chains interact antiferromagnetically within the lattice. Removing the two noncoordinated water molecules through a thermal treatment results in the new chain compound CoCu(pbaOH)(H2O)3 (2) which exhibits a ferromagnetic ordering of the ferrimagnetic chains at Tc = 9.5 K. Removing a third water molecule, occupying the apical position in the copper coordination sphere, results in CoCu(pbaOH)(H2O)2 (3) which again exhibits a three-dimensional ferromagnetic ordering, but at Tc = 38 K. The field dependence of the magnetization for 3 reveals a coercive field of 5.66 × 103 Oe at 2 K, probably a record in the field of molecular-based magnets. This dehydration process giving rise to a crossover between long-range antiferro- and ferromagnetic states is reversible, and can be repeated.

This paper is devoted to the determination of the spin density in the S = 2 ground state of [Mn(Me6-[14]ane-N4)Cu(oxpn)](CF3SO3)2 with Me6-[14]ane-N4 = (±)-5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraa...

The goal of our work was to design in a controlled manner open-shell supramolecular assemblies with dominant intermolecular ferromagnetic interactions. Along this line, the compounds of formula rad...

Several decamethylferroceniudtransition-metal maleonitriledithiolate compounds have been synthesized and structurally characterized. The compounds [Fe(cp*)2Ix[M(mnt)2],(CH3CN); (M = Cu(II), Co(m), Fe(II1)) crystallize in the triclinic space group Pi (No. 2). For M = Co(II1) two solid-state phases have been isolated. a-[Fe(cp*),l2[Co(mnt)2]~(CHFN)2 (FezCo2A): a = 9.894(4) A, b = 12.942(6) A, c = 15.056(6) A, a = 110.13(3)", p = 98.41(4)", y = 107.78(3)", V = 1657 A3, M, = 1413.3, d, = 1.419 g/cm:, Z = 1, and R = 0.061 for 2351 reflections with I 1 30(I). /?-[Fe(cp*)2]2[Co(mnt)2]2 (FezCozB): a = 9.576(8) A, b = 12.849(4) A, c = 13.641(7) A, a = 108.13(4)", p = 90.91(6)", y = 103.54(4)", V = 1544 A3, M, = 1331.2, d, = 1.431 g/cm3, Z = 1, and R = 0.043 for 2407 reflections with I 2 3a(I). The isostructural a modification is observed for M = Fe(II1). a-[Fe(cp*)2]2[Fe(mnt)2]2(CH3CN)2 (FezFezA): a = 9.905(7) A, b = 12.966(5) A, c = 15.142(3) A, a = 109.77(2)", p = 98.64(4)", y = 108.06(6)", V = 1668 A3, Mr = 1407.2, d, = 1.401 g/cm3, Z = 1, and R = 0.063 for 3125 reflections with I I 30(I). The dimeric anionic species show a syuare pyramidal coordination for the metal (the apical M-S bonds are Co-S = 2.39, 2.35 8, and Fe-S = 2.49 A). Orthogonal arrangement of adjacent cations is observed in the decamethylferrocenium chains of the two a compounds, while a parallel packing exists in the p modification. [Fe(cp*)212Cu(mnt)2 (FeFu): a = 9.713(5) A, b = 11.407(4) A, c = 11.958(5) A, a = 100.90(2)", p = 113.20(5)", y = 92.66(3)", V = 1185 A3, Mr = 996.5, d, = 1.396 g/cm3, 2 = 1, and R = 0.041 for 2724 reflections with I I 3a(I). The dianion [Cu(mnt)2I2exhibits a planar monomeric structure and the mixed anioncation stacks adopt a ... A2-D+D+A2-D+D+A2-... arrangement with short anion-cation distances: d(Fe-S) = 5.54 8, and d(Fe-Cu) = 6.37 8,. The magnetic properties of all the compounds have been investigated. In both FezCozA and FezCozB the decamethylferrocenium cations have been found to be magnetically isolated. In FezFezA, a strong antiferromagnetic interaction within the { [Fe(mr1t)]2}~dimeric unit has been characterized. In FezCu, finally, each [Cu(mnt)2I2is found to interact antiferromagnetically with two adjacent [Fe(C,*)2]+ cations.

The goal of this paper is to study to what extent information on the interaction between magnetic centers in a Mn II Cu II Mn II molecular compound can be deduced from the optical spectra. The compound of interest is {[Mn(Me 6 -[14]ane-N 4 )] 2 Cu(pba)}(CF 3 SO 3 ) 2 -2H 2 O with Me 6 -[14]ane-N 4 =(±)-5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane and pba=1,3-propylenebis(oxamato). A central Cu(II) ion is bridged by oxamato groups to two peripheral Mn(II) ions. The absorption spectra have been recorded both in pyridinesolution at room temperature and in KBr pellets in the 10-290 K temperature range

The title compound has been sunthesized, and its crystal structure has been solved. It crystallizes in the triclinic system, space group P1; the lattice parameters are a=7.300(3) A, b=10.734(3) A, c=12.585(6) A, α=68.43(3) o , β=84.92(4) o , γ=73.97(3) o , and Z=2. The structure consists of oxamato-bridged Mn II Cu II chains running along the b axis with a Mn---Cu intrachain separation of 5.387(1) A

Four compounds have been synthesized, the formulas of which are MnCu(opba)(DMSO) 3 (1), MnCu(opba)-0.7DMSO (2), (NBu 4 ) 2 Mn 2 [Cu(opba)] 3 .6DMSO.H 2 O (3), and (NBu 4 ) 2 [Mn 2 Cu(opba)] 3 (4), with opba standing for o-phenylenebis(oxamato). The crystal structure of 1 has been determined. I crystallizes in the monoclinic system, space group P2 1 /n. The lattice parameters are a=16.966(7) A, b=8.367(1) A, c=18.258(7) A, and Z=4. Thestructure consists of well-separated Mn II Cu II zigzag chains

The compounds [ML[sub 2](H[sub 2]O)[sub 4]](ClO[sub 4])[sub 3][center dot]4H[sub 2]O ((1)M), where M is a trivalent rare earth metal and L the bidentate liquid 2-formyl-4-methyl-6-(N-(2-pyridylethyl)formimidoyl)phenol, have been synthesized. Single crystals of [GdL[sub 2](H[sub 2]O)[sub 4]](ClO[sub 4])[sub 2]Cl[center dot]2.75H[sub 2]O have been obtained, and its crystal structure has been solved. This compound crystallizes in the monoclinic system, space group P2[sub 1]/c. The structure consists of [GdL[sub 2](H[sub 2]O)[sub 4]][sup 3+] cations, perchlorate and chloride anions and noncoordinated water molecules. The Gd atom is surrounded by eight oxygen atoms, four belonging to water molecules and the other four to the carbonyl and phenolic functions of two L ligands. The coordination sphere of Gd is very close to a perfect square antiprism. (1)Eu exhibits a strong luminescence in the solid state. The transition energies of the luminescence spectrum have been determined. The temperature dependences of the molar magnetic susceptibility [chi][sub M] for (1)M (M = Gd, Nd, Eu, Sm) have been measured. A perfect Curie law is observed for (1)Gd. The EPR spectrum reveals a zero-field splitting within the [sup 8]S[sub 7/2] ground state characterized by an axial parameter [vert bar]D[vert bar] = 4.0 [times] 10[sup [minus]2] cm[sup [minus]1]. [chi][sub M]T for (1)Ndmore » decreases from 1.64 cm[sup 3] K mol[sup [minus]1] at 300 K down to 0.8 cm[sup 3] K mol[sup [minus]1] at 4.2 K as the temperature T is lowered, due to the crystal-field splitting of the [sup 4]I[sub 9/2] free-ion state. For both (1)Eu and (1)Sm compound, the first free-ion excited states are thermally populated at 300 K; hence, their magnetic behaviors significantly deviate from the Curie law. The magnetic data have been satisfactorily interpreted in the free-ion approximation. For (1)Eu, an excellent agreement between optical and magnetic properties has been obtained. 29 refs., 7 figs., 3 tabs.« less

The strong oxophilic character of the Gd(III) ion has been utilized to protect one of the carbonyl functions of 2,6-diformyl-4-methylphenol, which has allowed the quantitative synthesis of mono(Schiff bases), then dissymmetric di(Schiff bases). The synthetic process is as follows: the reaction of 2,6-diformyl-4-methylphenol with a primary amine RNH[sub 2] in the presence of Gd(III) affords a complex in which Gd(III) is coordinated to two mono(Schiff bases) through their carbonyl and phenolic oxygen atoms. The mono(Schiff base) may be isolated by precipitation of Gd(III) in the form of gadolinium(III) oxalate. The reaction of another primary amine, R[prime]NH[sub 2], on this mono(Schiff base) affords a dissymmetric di(Schiff base), from which dissymmetric dinuclear compounds can be synthesized. For example, this reaction has been carried out with RNH[sub 2] = 2-(2-aminoethyl)pyridine and R[prime]NH[sub 2] = N,N-dimethylpropylenediamine. The mono(Schiff base) 2-formyl-6-(N-(2-pyridylethyl)formimidoyl)-4-methylphenol (HL) and the di(Schiff base) 2-[N-(2-pyridylethyl)formimidoyl]-6-[N-((dimethylamino)propyl)formimidoyl]-4-methylphenol (HL[prime]) have been unambiguously characterized from their [sup 1]H NMR spectra. The copper(II) dinuclear compound [CuL[prime](OH)](ClO[sub 4])[sub 2][center dot]H[sub 2]O obtained from this di(Schiff base) has been synthesized, and its crystal structure has been solved. 36 refs., 2 figs., 5 tabs.

The hexanuclear clusters [Ln 2 C 4 (fsaaep) 4 (NO 3 ) 6 ].0.5(CH 3 OH.H 2 O) (abbreviated as [Ln 2 Cu 4 ]) have been synthesized; Ln is a trivalent lanthanide and (fsaaep) 2- is the ligand deriving from 3-(N-2-(pyridylethyl)formimidoyl)salicylic acid. The crystal structure of the compound with Ln=Pr has been solved. This compound crystallizes in the orthorhombic system, space group P2 1 2 1 2 1 . The lattice parameters are a=18.746(4) A, b=24.196(4) A, c=17.053(4) A, and Z=4

After 3 years of efforts, we succeeded in obtaining single crystals of MnCu(obbz)(H 2 O) 3 .DMF (1) (obbz=N,N'-oxamidobis(benzoato) and DMF=dimethylformamide). 1 is a precursor of the molecular-based magnet MnCu(obbz)-H 2 O (2) exhibiting a spontaneous magnetization below T c =14 K. 1 crystallizes in the orthorhombic system, space group Pbca. The lattice parameters are a=10.3006 (6) A, b=22.375 (2) A, c=19.639 (1) A, and Z=8 (MnCu units)

This paper is concerned with the first two-step spin crossover presented by a polynuclear molecular compound, viz., the dinuclear iron(II) complex [Fe(bt)(NCS) 2 ] 2 bpym, where bt stands for 2,2'-bi-2-thiazoline and bpym for the bridging ligand 2,2'-bipyrimidine. The synthesis of the compound is described. Variable-temperature magnetic susceptibility and 57 Fe Mossbauer spectrometry data provide evidence for an overall S=2 (HS)↔S=0 (LS) spin-crossover behavior. They show that the transition takes place in two steps

The two compounds Cu(ta)(3-pic) 2 .0.5(3-pic)-0.5CH 3 OH (1) and Cu(ta)(3-pic).H 2 O (2) have been synthesized, ta standing for terephthalato and 3-pic for 3-picoline. The crystal structure of 1 has been determined. 1 crystallizes in the monoclinic system, space group P2 1 /c, with a=9.703 (4) A, b=13.184 (8) A, c=19.825 (4) A, β=115.12 (2) o , and Z=4

The compound Gd 2 (ox) [Cu(pba)] 3 [Cu(H 2 O) 5 ]-20H 2 O (1), where ox stands for oxalato and pba for 1,3-propylenebis(oxamato), has been synthesized. 1 crystallizes in the monoclinic system, space group C2/m. The lattice parameters are a=21.18(7) A, b=21.098 (2) A, c=15.079 (1) A, and β=92.06 (2) o , with Z=4. The crystal structure consists of layers of double-sheet polymers separated by water molecules

The new trinuclear cluster Mn II 3 (CH 3 CO 2 ) 6 (bpy) 2 has been synthesized, and its crystal structure was determined. It crystallizes in the triclinic system, space group P1, with a=12.849 (4) A, b=9.790 (3) A, c=8.187 (2) A, α=108.50 (2) o , β=96.69 (2) o , γ=106.41 (3) o , Z=1, and V=912.5 (5) A 3 . The structure was solved and refined by using 2071 reflections

The two compounds MnCu(Cl 4 obbz)(H 2 O) 5 and MnCu(Br 4 obbz)(H 2 O) 3 •2.5H 2 O have been synthesized. Cl 4 obbz stands for oxamido-N,N'-bis(3,5-dichlorobenzoato) and Br 4 obbz for oxamido-N,N'-bis(3,5-dibromobenzoato). Their crystal structures have been determined. The tetrachloro derivative crystallizes in the monoclinic system, space group P2 1 /n

Structural, magnetic, and EPR studies of diaquatetrakis({mu}-acetato)dicopper(II) have provided important insight into the magnetic interaction phenomenon in polynuclear species involving 3d ions. This compound may be considered at the archetype of the exchange-coupled copper(II) dimers. Until now, no compound of the same nature involving lanthanide(III) ions had been reported, and the factors determining the sign and the magnitude of the magnetic interaction between lanthanide(III) ions are far from being well understood. Herein the authors report on the synthesis, the structure and the magnetic properties of two lanthanide(III) dimers, namely [Ln{sub 2}(CH{sub 3}CO{sub 2}){sub 6-} (phen){sub 2}] with phen = o-phenanthroline and Ln = Ce (1) and Gd (2).