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Francesc Lloret

Publications and source records attributed to Francesc Lloret.

At least 37 records · Page 2Linked to original sources
PubMed2004

Nuclearity controlled cyanide-bridged bimetallic CrIII-MnII compounds: synthesis, crystal structures, magnetic properties and theoretical calculations.

The preparation, X-ray crystallography and magnetic investigation of the compounds PPh4[Cr(bipy)(CN)4].2 CH3CN.H2O (1) (mononuclear), [[Cr(bipy)(CN)4]2Mn-(H2O)4].4H2O (2) (trinuclear), [[Cr(bipy)(CN)4]2Mn(H2O)2] (3) (chain) and [[Cr(bipy)(CN)4]2Mn(H2O)].H2O.CH3CN (4) (double chain) [bipy=2,2'-bipyridine; PPh4 (+)=tetraphenylphosphonium] are described herein. The [Cr(bipy)(CN)4]- unit act either as a monodentate (2) or bis-monodentate (3) ligand toward the manganese atom through one (2) or two (3) of its four cyanide groups. The manganese atom is six-coordinate with two (2) or four (3) cyanide nitrogens and four (2) or two (3) water molecules building a distorted octahedral environment. In 4, two chains of 3 are pillared through interchain Mn-N-C-Cr links which replace one of the two trans-coordinated water molecules at the manganese atom to afford a double chain structure where bis- and tris-monodenate coordination modes of [Cr(bipy)(CN)4]- coexist. The magnetic properties of 1-4 were investigated in the temperature range 1.9-300 K. A Curie law behaviour for a magnetically isolated spin quartet is observed for 1. A significant antiferromagnetic interaction between CrIII and MnII through the single cyanide bridge [J=-6.2 cm(-1), the Hamiltonian being defined as H=-J(SCr1.SMn+SCr2.SMn] occurs in 2 leading to a low-lying spin doublet which is fully populated at T <5 K. A metamagnetic behaviour is observed for 3 and 4 [the values of the critical field Hc being ca. 3000 (3) and 1500 Oe (4)] which is associated to the occurrence of weak interchain antiferromagnetic interactions between ferrimagnetic Cr2III MnII chains. The analysis of the exchange pathways in 2-4 through DFT type calculations together with the magnetic bevaviour simulation using the quantum Monte Carlo methodology provided a good understanding of their magnetic properties.

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PubMed2004

Mono-, di- and trinuclear 2,3,5,6-tetrakis(2-pyridyl)pyrazine (tppz)-containing copper(II) complexes: syntheses, crystal structures and magnetic properties.

Three new copper(ii) complexes of formula [Cu(tppz)(NCO)(2)].0.4H(2)O (1), [Cu(2)(tppz)Br(4)](2) and [Cu(3)(tppz)(C(5)O(5))(3)(H(2)O)(3)].7H(2)O (3)[tppz = 2,3,5,6-tetrakis(2-pyridyl)pyrazine; C(5)O(5)(2-) = croconate, dianion of 4,5-dihydroxycyclopent-4-ene-1,2,3-trione] have been synthesised and structurally characterized by X-ray diffraction methods. The structure of complex is made up of neutral [Cu(tppz)(NCO)(2)] mononuclear units and uncoordinated water molecules. The mononuclear units are grouped by pairs to give a rather short copper-copper distance of 3.9244(4) angstroms. The structure of complex 1 consists of neutral tppz-bridged [Cu(2)(tppz)Br(4)] dinuclear units, the copper-copper separation across tppz being 6.6198(1) angstroms. The dinuclear units are further connected through weak, double out-of-plane Cu-Br...Cu bridges [Br(1)...Cu(1a) 4.0028(17) angstroms] creating tetranuclear entities, the copper-copper separation through this interaction being 4.3299(21) angstroms. The structure of complex 3 is built of neutral [Cu(3)(tppz)(C(5)O(5))(3)(H(2)O)(3)] trinuclear units and uncoordinated water molecules. Tppz and one of the croconate groups act as bridging ligands, the former exhibiting the bis-terdentate coordination mode and the latter adopting an unusual asymmetrical bis-bidentate bridging mode through three adjacent oxygen atoms. The other two croconate groups exhibit the bidentate coordination mode. The intramolecular copper-copper separations are 6.5417(9)(across tppz) and 4.3234(9) angstroms (through bis-bidentate croconato). The magnetic properties of 2 and 3 have been investigated in the temperature range 1.9-300 K. The magnetic behaviour of complex 2 is that of an antiferromagnetically coupled copper(II) dimer (J = -40.9 cm(-1), the Hamiltonian being H = -JS(A).S(B)). In the case of compound , the chi(M) T vs. T plot is typical of an overall antiferromagnetic coupling with a low-lying spin doublet being fully populated at T < 10 K. The values of the intramolecular antiferromagnetic interactions in 3 are -19.9 (across tppz) and -32.9 cm(-1)(through bridging croconato). Density functional type calculations were performed on model dinuclear fragments of 3 in order to analyze the efficiency of the exchange pathways involved and also to substantiate the coupling parameters.

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PubMed2004

One-dimensional oxalato-bridged Cu(II), Co(II), and Zn(II) complexes with purine and adenine as terminal ligands.

The reaction of nucleobases (adenine or purine) with a metallic salt in the presence of potassium oxalate in an aqueous solution yields one-dimensional complexes of formulas [M(mu-ox)(H(2)O)(pur)](n) (pur = purine, ox = oxalato ligand (2-); M = Cu(II) [1], Co(II) [2], and Zn(II) [3]), [Co(mu-ox)(H(2)O)(pur)(0.76)(ade)(0.24)](n)(4) and ([M(mu-ox)(H(2)O)(ade)].2(ade).(H(2)O))(n) (ade = adenine; M = Co(II) [5] and Zn(II) [6]). Their X-ray single-crystal structures, variable-temperature magnetic measurements, thermal behavior, and FT-IR spectroscopy are reported. The complexes 1-4 crystallize in the monoclinic space group P2(1)/a (No. 14) with similar crystallographic parameters. The compounds 5 and 6 are also isomorphous but crystallize in the triclinic space group P (No. 2). All compounds contain one-dimensional chains in which cis-[M(H(2)O)(L)](2+) units are bridged by bis-bidentate oxalato ligands with M(.)M intrachain distances in the range 5.23-5.57 A. In all cases, the metal atoms are six-coordinated by four oxalato oxygen atoms, one water molecule, and one nitrogen atom from a terminal nucleobase, building distorted octahedral MO(4)O(w)N surroundings. The purine ligand is bound to the metal atom through the most basic imidazole N9 atom in 1-4, whereas in 5 and 6 the minor groove site N3 of the adenine nucleobase is the donor atom. The crystal packing of compounds 5 and 6 shows the presence of uncoordinated adenine and water crystallization molecules. The cohesiveness of the supramolecular 3D structure of the compounds is achieved by means of an extensive network of noncovalent interactions (hydrogen bonds and pi-pi stacking interactions). Variable-temperature magnetic susceptibility measurements of the Cu(II) and Co(II) complexes in the range 2-300 K show the occurrence of antiferromagnetic intrachain interactions.

Adenine↗
PubMed2004

The cation as a tool to get spin-canted three-dimensional ironIII networks.

Alkyl-substituted ammonium cations (X) allow the preparation of a series of spin-canted oxo- and oxalato-bridged three-dimensional iron(III) networks, exhibiting magnetic ordering at T(c) values ranging from 40 to 56 K. The value of T(c) varies with the cation despite the lack of significant structural modifications.

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PubMed2004

Ferromagnetic coupling through spin polarization in the hexanuclear [MnII(3)CuII(3)] complex.

A novel Cu(II)-Mn(II) hexanuclear complex of formula [[MnCuL](3)(tma)](ClO(4))(3).8H(2)O [H(2)L = macrocyclic Robson proligand; H(3)tma = trimesic acid] has been obtained by connecting three heterobinuclear [Cu(II)Mn(II)L](2+) cationic species through the trimesate anion. The complex exhibits a C(3) rotational symmetry, imposed by the geometry of the bridging ligand. The interaction within each Mn(II)-Cu(II) pair is antiferromagnetic (J = -16.7 cm(-1)). A weak ferromagnetic coupling among the three S = 2 resulting spins through the tricarboxylato bridge leads to a S = 6 ground spin state, for which the spin polarization mechanism is responsible.

Journal Article↗
PubMed2004

Synthesis, crystal structures and magnetic properties of single and double cyanide-bridged bimetallic Fe2(III)Cu(II) zigzag chains.

The bimetallic complexes [[Fe(III)(phen)(CN)4]2Cu(II)(H2O)2].4H2O (1), [[Fe(III)(phen)(CN)4]2Cu(II)].H2O (2) and [[Fe(III)(bipy)(CN)4]2Cu(II)].2H2O (3) and [[Fe(III)(bipy)(CN)4]2Cu(II)(H2O)2].4H2O (4) (phen = 1,10-phenanthroline and bipy = 2,2'-bipyridine) have been prepared and the structures of 1-3 determined by X-ray diffraction. The structure of 1 is made up of neutral cyanide-bridged Fe(III)-Cu(II) zigzag chains of formula [[Fe(III)(phen)(CN)4]2Cu(II)(H2O)2] and uncoordinated water molecules with the [Fe(phen)(CN)4]- entity acting as a bis-monodentate bridging ligand toward two trans-diaquacopper(II) units through two of its four cyanide groups in cis positions. The structure of 2 can be viewed as the condensation of two chains of 1 connected through single cyanide-bridged Fe(III)-Cu(II) pairs after removal of the two axially coordinated water molecules of the copper atom. The structure of 3 is like that of 2, the main differences being the occurrence of bipy (phen in 2) and two (one in 2) crystallization water molecules. The crystals of 4 diffract poorly but the analysis of the limited set of diffraction data shows a chain structure like that of 1 the most important difference being the fact that elongation axis at the copper atom is defined by the two trans coordinated water molecules. 1 behaves as a ferromagnetic Fe(III)2Cu(II) trinuclear system. A metamagnetic-like behavior is observed for 2 and 3, the value of the critical field (Hc) being ca. 1100 (2) and 900 Oe (3). For H > Hc the ferromagnetic Fe(III)2Cu(II) chains exhibit frequency dependence of the out-of-phase ac susceptibility signal at T < 4.0 K. The magnetic behavior of 4 corresponds to that of a ferromagnetically coupled chain of low spin iron(III) and copper(II) ions with frequency dependence of the out-of-phase susceptibility at T < 3.0 K. Theoretical calculations using methods based on density functional theory (DFT) have been employed to analyze and substantiate the exchange pathways in this family of complexes.

Journal Article↗
PubMed2004

Magnetic studies on hexahalorhenate(IV) salts of ferrocenium cations [Fe(C5R5)2]2[ReX6] (R = H, CH3; X = Cl, Br, I).

The hexahalorhenate(IV) salts of formula [Fe(C5H5)2]2[ReX6], with X = Cl (1), Br (2), and I (3), and [Fe(C5Me5)2]2[ReX6], with X = Cl (4), Br (5), and I (6) ([Fe(C5Me5)2]+ = decamethylferrocenium cation), have been synthesized and the structures of 1, 2, and 4 determined by single-crystal X-ray diffraction. 1, 2, and 4 crystallize in the orthorhombic system, space groups Pbca (1 and 2) and Ibam (4), with a = 14.099(2) A, b = 16.125(2) A, and c = 22.133(15) A, for 1, a = 14.317(3) A, b = 16.848(3) A, and c = 22.099(2) A for 2, and a = 15.8583(5) A, b = 15.9368(5) A, and c = 16.9816(6) A for 4. The three structures are made up of discrete [ReX6]2- anions and ferrocenium cations held together by electrostatic forces. There are anion-anion contacts in 1 and 2 but only through one direction. The [ReX6]2- octahedra are arranged along the y axis forming chains of Re and X atoms, -Re-X...X-Re-X...X-Re-, where the intermolecular X...X distances are shorter than the van der Waals distances. A somewhat greater separation between the anions occurs in 4. The magnetic properties of 1-6 were investigated in the temperature range 2.0-300 K. 1, 2, 4, and 5 exhibit an antiferromagnetic coupling between the anions, whereas a ferromagnetic coupling between anions and cations is the dominant interaction in 3. 6 behaves as a magnetically isolated compound, its susceptibility being the simple addition of the independent contributions of the uncoupled paramagnetic cations and anions.

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PubMed2004

Spin control in ladderlike hexanuclear copper(II) complexes with metallacyclophane cores.

Two new hexanuclear oxamatocopper(II) complexes 3 and 4 have been synthesized from the binuclear copper(II) complexes of the meta- and para-phenylenebis(oxamate) ligands, respectively. Complexes 3 and 4 possess an overall ladderlike structure made up of two oxamate-bridged linear trinuclear units ("rails") connected through two phenylenediamidate bridges ("rungs") between the central copper atoms to give metallacyclic cores of the meta- and para-cyclophane type, respectively. They show different ground spin states, S = 1 (3) or S = 0 (4), depending on the substitution pattern in the aromatic spacers. The triplet state molecule 3 containing two spin doublet Cu(II)3 units connected by two m-phenylenediamidate bridges represents a successful extension of the concept of "ferromagnetic coupling units" to metal complexes, which is a well-known approach toward high spin organic radicals.

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PubMed2004

mer-[Fe III(bpca)(CN)3]-: a new low-spin iron(III) complex to build heterometallic ladder-like chains.

The novel mononuclear complex PPh(4)-mer-[Fe(III)(bpca)(3)(CN)(3)].H(2)O (1) [PPh(4)(+) = tetraphenylphosphonium cation and bpca = bis(2-pyridylcarbonyl)amidate anion] and ladder-like chain compound [[Fe(III)(bpca)(micro-CN)(3)Mn(II)(H(2)O)(3)] [Fe(III)(bpca)(CN)(3)]].3H(2)O (2) have been prepared and characterized by X-ray diffraction analysis. Compound 1 is a low-spin iron(III) compound with three cyanide ligands in mer arrangement and a tridentate N-donor ligand building a distorted octahedral environment around the iron atom. Compound 2 is an ionic salt made up of cationic ladder-like chains [[Fe(III)(bpca)(micro-CN)(3)Mn(II)(H(2)O)(3)]](+) and uncoordinated anions [Fe(III)(bpca)(3)(CN)(3)](-). The magnetic properties of 2 correspond to those of a ferrimagnetic chain with significant intrachain antiferromagnetic coupling between the low-spin iron(III) centers and the high-spin manganese(II) cations. This compound exhibits ferrimagnetic ordering below 2.0 K.

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PubMed2004

Oxamidate-bridged dinuclear five-coordinate nickel(II) complexes: a magneto-structural study.

The preparation, spectroscopic characterization, and magnetic study of three new oxamidate-bridged nickel(II) dinuclear complexes of formulas ([Ni(Me3[12]aneN3)]2(mu-oa))(PF6)2 (1), ([Ni(Me3[12]aneN3)]2(mu-dmoa))(PF6)2 (2), and ([Ni(Me3[12]aneN3)]2(mu-dpoa))(PF6)2 (3) (Me3[12]aneN3 = 2,4,4-trimethyl-1,5,9-triazacyclododec-1-ene, oa = oxamidate, dmoa = N,N'-dimethyloxamidate, and dpoa = N,N'-diphenyloxamidate) are reported. The crystal structures of two of them (1 and 3) have been determined. 1 and 3 crystallize in the monoclinic system, space group P2(1)/c, with Z = 2 and a = 7.901(4) A, b = 13.597(6) A, c = 17.565(10) A, and beta = 96.46(4) degrees for 1 and a = 13.854(3) A, b = 17.469(4) A, c = 12.543(3) A, and beta = 116.22(3) degrees for 3. The structures of 1 and 3 consist of dinuclear ([Ni(Me3[12]aneN3)]2(mu-oa))2+ and ([Ni(Me3[12]aneN3)]2(mu-dpoa))2+ cations and hexafluorophosphate anions. Each nickel in 1-3 is five-coordinate, and the substitution of the hydrogen atom of the amidate nitrogen of 1 by a methyl (2) or a phenyl (3) group causes a significant modification of the stereochemistry of the nickel(II) ions from square pyramidal toward trigonal bipyramidal (tau values of 0.12 and 0.48 for 1 and 3, respectively). The NOESY spectrum of 3 has allowed us to achieve the assignment of the phenyl protons of the N,N'-diphenyloxamidate. The value of magnetic coupling between the two nickel(II) ions across the oxamidate bridge [J = -57.0 (oa, 1), -38.0 (dmoa, 2) and -30.5 cm(-1) (dpoa, 3)] is very sensitive to this stereochemical change, and its variation is explained on the basis of orbital considerations. DFT type calculations have been performed to analyze and substantiate the trend of the magnetic coupling in 1-3.

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PubMed2004

Inter-string arrays of bimetallic assemblies with alternative Cu2+-Cl-Cu2+ and Cu-NC-M (M = Co3+, Fe+3, Cr+3) bridges: syntheses, crystal structure, and magnetic properties.

Three bimetallic assemblies with alternate homometallic bridges through chloride ligands and heterometallic bridges through cyanide ligands of formula [(323)(2)Cu(2)(Cl)M(CN)(6)](n).2n(H(2)O), where 323 = N,N'-bis(3-aminopropyl)ethylenediamine and M = Co(3+) for 1, Fe(3+) for 2, and Cr(3+) for 3, were synthesized. They have been characterized structurally, analytically, spectroscopically, and magnetically. All three assemblies crystallize in the monoclinic system in the same space group P2(1)/n, with a = 11.642(2) A, b = 10.285(3) A, c = 13.622(2) A, beta = 95.69(3) degrees, V = 1623.1(6) A(3), and Z = 4 for 1; a = 11.681(4) A, b = 10.315(3) A, c = 13.567(5) A, beta = 95.62(3) degrees, V = 1626.8(9) A(3), Z = 4 for 2, and a = 11.782(4) A, b = 10.386(2) A, c = 13.755(4) A, beta = 95.51(3) degrees, V = 1657.4(8) A(3), Z = 4 for 3. Crystal structure analyses reveal that one-dimensional zigzag chains propagate in two different crystallographic directions (a and b) which are held together during the course of their propagation. All three assemblies have a homometallic Cu-Cl-Cu core in common. Assembly 1 exhibits metamagnetic behavior and shows weak antiferromagnetic interactions between Cu(2+) paramagnetic centers, through the chloride bridges. The Neel temperature, T(N), is 3.5 K, and the critical field is 4 T. In the presence of a magnetic field larger than 4 T, the local spin doublets of Cu(2+) in the assembly 1 remain in parallel arrangements. Assemblies 2 and 3 may be described as an alternative repetition of the antiferromagnetically coupled Cu-Cl-Cu fragment and ferromagnetically coupled Cu-CN-Fe(3+)/Cr(3+)fragment. The overall magnetic character of the strings in assemblies 2 and 3 are antiferromagnetic. Ferromagnetic interaction evidenced by the (Cu-CN-Fe(3+)/Cr(3+)) fragment was masked by the antiferromagnetic interaction between the Cu(2+) centers through the chloride bridge. The magnetic properties agree well with those expected for two [323 Cu(2+)] and a [Fe(CN)](3+) unit with spin-orbit coupling effect of the low-spin iron(III) ions for 2 and for two [323 Cu(2+)] and a [Cr(CN)](3+) unit for 3. In aqueous solution, trinuclear [(323)(2)Cu(2)M(CN)(6)](+) and dinuclear [(323)CuM(CN)(6)](-) species were observed.

Journal Article↗
PubMed2003

Crystal structures and magnetic properties of 2,3,5,6-tetrakis(2-pyridyl)pyrazine (tppz)-containing copper(II) complexes.

Four new copper(II) complexes of formula [Cu(2)(tppz)(dca)(3)(H(2)O)].dca.3H(2)O (1), [Cu(5)(tppz)(N(3))(10)](n)() (2), [[Cu(2)(tppz)(N(3))(2)][Cu(2)(N(3))(6)]](n)() (3), and [Cu(tppz)(N(3))(2)].0.33H(2)O (4) [tppz = 2,3,5,6-tetrakis(2-pyridyl)pyrazine and dca = dicyanamide anion] have been synthesized and structurally characterized by X-ray diffraction methods. The structure of complex 1 is made up of dinuclear tppz-bridged [Cu(2)(tppz)(dca)(3)(H(2)O)](+) cations, uncoordinated dca anions, and crystallization water molecules. The copper-copper separation across bis-terdentate tppz is 6.5318(11) A. Complex 2 is a sheetlike polymer whose asymmetric unit contains five crystallographically independent copper(II) ions. These units are building blocks in double chains in which the central part consists of a zigzag string of copper atoms bridged by double end-on azido bridges, and the outer parts are formed by dinuclear tppz-bridged entities which are bound to the central part through single end-on azido bridges. The chains are furthermore connected through weak, double out-of-plane end-on azido bridges, yielding a sheet structure. The intrachain copper-copper separations in 2 are 6.5610(6) A across bis-terdentate tppz, 3.7174(5) and 3.8477(5) A across single end-on azido bridges, and from 3.0955(5) to 3.2047(7) A across double end-on azido bridges. The double dca bridge linking the chains into sheets yields a copper-copper separation of 3.5984(7) A. The structure of 3 consists of centrosymmetric [Cu(2)(tppz)(N(3))(2)](2+) and [Cu(2)(N(3))(6)](2)(-) units which are linked through axial Cu.N(azido) (single end-on and double end-to-end coordination modes) type interactions to afford a neutral two-dimensional network. The copper-copper separations within the cation and anion are is 6.5579(5) A (across the bis-terdentate tppz ligand) and 3.1034(6) A (across the double end-on azido bridges), whereas those between the units are 3.6652(4) A (through the single end-on azido group) and 5.3508(4) A (through the double end-to-end azido bridges). The structure of complex 4 is built of neutral [Cu(tppz)(N(3))(2)] mononuclear units and uncoordinated water molecules. The mononuclear units are grouped by pairs to give a rather short copper-copper separation of 3.9031(15) A. The magnetic properties of 1-4 have been investigated in the temperature range 1.9-300 K. The magnetic behavior of complexes 1 and 4 is that of antiferromagnetically coupled copper(II) dimers with J = -43.7 (1) and -2.1 cm(-)(1) (4) (the Hamiltonian being H = -JS(A).S(B)). An overall ferromagnetic behavior is observed for complexes 2 and 3. Despite the structural complexity of 2, its magnetic properties correspond to those of magnetically isolated tppz-bridged dinuclear copper(II) units with an intermediate antiferromagnetic coupling (J = -37.5 cm(-)(1)) plus a ferromagnetic chain of hexanuclear double azido-bridged copper(II) units (the values of the magnetic coupling within and between the hexameric units being +61.1 and +0.0062 cm(-)(1), respectively). Finally, the magnetic properties of 3 were successfully analyzed through a model of a copper(II) chain with regular alternating of three ferromagnetic interactions, J(1) = +69.4 (across the double end-on azido bridges in the equatorial plane), J(2) = +11.2 (through the tppz bridge), and J(3) = +3.4 cm(-)(1) (across the single end-on azido bridge).

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PubMed2003

Crystal structures and magnetic properties of two octacyanotungstate(IV) and (V)-cobalt(II) three-dimensional bimetallic frameworks.

The synthesis, X-ray structures, and magnetic behavior of two new, three-dimensional compounds [W(IV)[(mu-CN)(4)Co(II)(H(2)O)(2)](2).4H(2)O](n) (1) and [[W(V)(CN)(2)](2)[(mu-CN)(4)Co(II)(H(2)O)(2)](3).4H(2)O](n) (2) are presented. Compound 1 crystallizes in the tetragonal system, space group I4/m with cell constants a = b = 11.710(3) A, c = 13.003(2) A, and Z = 4, whereas 2 crystallizes in the orthorhombic system, space group Cmca with cell constants a = 13.543(5) A, b = 16.054(6) A, c = 15.6301(9) A, and Z = 4. The structure of 1 shows alternating eight-coordinated W(IV) and six-coordinated Co(II) ions bridged by single cyanides in a three-dimensional network. The geometry of each [W(IV)(CN)(8)](4-) entity in 1 is close to a square antiprism. Its eight cyanide groups are coordinated to Co(II) ions which have two coordinated water molecules in trans position. The structure of 2 consists of alternating eight-coordinated W(V) and six-coordinated Co(II) ions linked by single cyanide bridges in a three-dimensional network. Each [W(V)(CN)(8)](3-) unit shows a geometry close to a square antiprism. Only six of its eight cyanide groups are coordinated to Co(II) ions while the other two are terminal. The Co(II) ion in 2 has the same CoN(4)O(2) environment as in 1. The magnetic behavior of 1 is that of magnetically isolated high spin Co(II) ions (S(Co) = 3/2), bridged by the diamagnetic [W(IV)(CN)(8)](3-) units (S(W(IV)) = 0). The magnetic behavior of 2, where the high spin Co(II) ions are bridged by the paramagnetic [W(V)(CN)(8)](3-) units [S(W(V)) = 1/2], is that of ferromagnetically coupled Co(II) and W(V) giving rise to an ordered ferromagnetic phase below 18 K. The magnetic properties of 1 are used as a blank to extract the parameters that are useful to analyze the magnetic data of compound 2.

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PubMed2003

A novel one-dimensional cyano-bridged Ni3Fe2 ferromagnet constructed from bimetallic molecular squares.

Reaction of the complex [Ni(rac-CTH)](2+) (rac-CTH = rac-5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane) with [Fe(CN)(6)](3-) leads to a novel cyano-bridged Ni(3)Fe(2) complex, [[Ni(rac-CTH)](3)[Fe(CN)(6)](2)](4). The structure consists of an alternating arrangement of [Fe(CN)(6)Ni(rac-CTH)](2) squares and trans-planar [Ni(rac-CTH)](2+) units bridged by cyanide groups to give a neutral 1D chain running along the a axis. Magnetic measurements reveal the occurrence of ferromagnetic coupling between Fe(III) and Ni(II) ions and 3D magnetic ordering at 3 K due to interchain interactions. Canting of the moments is inferred from the low value of the magnetization of the saturation below T(c).

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PubMed2003

Design of high-dimensional copper(II) malonate complexes with exo-polydentate N-donor ligands.

Two polymeric malonato-bridged copper(II) complexes of formulas [(H(2)bpe)[Cu(mal)2]]n.4nH2O (1) and [Cu(4")(mal)(4)(bpe)(3)]n.6nH(2)O (2) [mal = malonate dianion; bpe = 1,2-bis(4-pyridyl)ethylene] have been synthesized and characterized by X-ray diffraction. Complex 1 crystallizes in triclinic space group P(-)1, Z = 1, with unit cell parameters a = 4.8831(10) A, b = 9.585(2) A, c = 11.813(2) A, alpha = 77.29(3) degrees, beta = 82.18(3) degrees, and gamma = 84.92(3) degrees, whereas complex 2 crystallizes in the monoclinic space group P2(1)/n, Z = 4, with unit cell parameters a = 13.462(3) A, b = 10.275(5) A, c = 19.579(4) A, and beta = 105.21(3) degrees. The structure of 1 consists of anionic malonato-bridged uniform copper(II) chains which are connected through hydrogen bonds involving malonate-oxygen atoms, noncoordinated water molecules, and H(2)bpe(2+) cations. The intrachain copper-copper separation through carboxylate-malonate bridge in the anti-syn conformation is 4.8831(10) A. Complex 2 possesses a three-dimensional structure made up of neutral corrugated malonated-bridged copper(II) layers linked through bis-monodentate bpe molecules. The copper(II) atoms within each layer are bridged by a double mu-oxo and four carboxylato-malonate bridges with copper-copper separations of 3.4095(7) A (through oxo) and 4.9488(11)-6.5268(13) A (through carboxylato). The shortest interlayer copper-copper separation across bridging bpe is 13.434(3) A. Variable-temperature magnetic measurements (2-290 K) show an overall ferromagnetic behavior for both compounds. The magnetic pathway of complex 1 is through a single carboxylate-malonate bridge connecting apical and equatorial positions of adjacent copper(II) atoms, and the value of the magnetic coupling (J) for 1 through a numerical expression for a ferromagnetic uniform chain of interacting local doublets is J = +0.049(1) cm(-1). The values for the magnetic couplings through the main intralayer exchange pathways in 2 which correspond to carboxylate-malonate bridges connecting equatorial-equatorial (J(1)) and equatorial-apical (J(2)) coordination sites and to the double mu-oxo bridge linking equatorial-apical (J(5)) positions have been determined through a simplified model. The three magnetic couplings are weak, two of them being ferromagnetic (J(1) = +23(1) cm(-1) and J(2) = +6.5(1) cm(-1)) and the other one antiferromagnetic [zJ' = -1.0(1) cm(-1)]. The values of the magnetic couplings in 1 and 2 compare well with those previously reported for similar malonato-bridged copper(II) complexes of different dimensionalities.

Journal Article↗
PubMed2003

Long-range magnetic coupling through extended pi-conjugated aromatic bridges in dinuclear copper(II) metallacyclophanes.

Self-assembly of 1,4-phenylenebis(oxamate) and 4,4'-biphenylenebis(oxamate) ligands and Cu2+ ions gives two new dinuclear copper(II) metallacyclophanes where the two metal centers are connected by double para-substituted aromatic diamide bridges. Despite the relatively large intramolecular Cu-Cu distance of ca. 8 and 12 A for each complex, magnetic susceptibility measurements evidence strong to moderately strong intramolecular antiferromagnetic couplings (-J values of the order of 100 and 10 cm-1, respectively). Density functional theory calculations on these compounds and their homologues with linear oligo-p-phenylenediamide bridges predict a rather slow exponential decay of magnetic coupling with increasing intermetal distance (r values up to 25 A) along this novel series of dicopper metalla-amidocyclophanes.

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