Magnetic Studies Of Complexes Research Articles

Significant magnetocaloric effect in a ferromagnetic {CrIII2GdIII3} cluster

A pentanuclear {Cr2Gd3} cluster (1) and its diamagnetic substituent-{Al2Gd3} (2) based on pivalic acid (Hpiv) were obtained with the formulas of {Et3NH[M2Gd3(OH)6(piv)10(H2O)2]} (M = CrIII, 1; AlIII, 2). The metallic core shows a triangle bipyramid-{Cr2Gd3} held together by six µ3-OH groups, and the piv- ligands located at the periphery. Magnetic studies for complex 1 exhibit dominant ferromagnetic interactions between CrIII and GdIII ions. Furthermore, ferromagnetic {Cr2Gd3} cluster (1) displays a considerable large magnetic entropy value (−ΔSm = 27.0 J kg−1 K−1) at high temperature among low-nuclearity 3d-4f clusters.

Synthesis, Crystal Structure and Magnetic Properties of a Nd(III) Coordination Polymer Constructed by 3-Carboxyphenoxyacetate and 1,10-Phenanthroline

Under hydrothermal conditions, NdCl3 center dot 6H(2)O reacts with 3-H(2)CPOA (3-H(2)CPOA=3-carboxyphenoxyacetatic acid) and phen (phen=1,10-phenanthroline), producing a novel coordination polymer [Nd(3-CPOA)(1.5)(phen)](n) (1). Complex 1 crystallizes in monoclinic space group P2(1)/c, with a=0.982 7(8), b=1.140 6(10), c=2.115 8(19) nm, beta=90.574(9)degrees, V=2.371(4) nm(3), and Z=4. X-ray diffraction studies show that complex 1 possesses a three-dimensional framework structure based on a binuclear unit. Magnetic studies for complex 1 indicate the presence of stronger antiferromagnetic coupling between the adjacent NO ions. CCDC: 888765.

Synthesis, structures and magnetic properties of a family of nitrate-bridged octanuclear [Na2Ln6] (Ln = Dy, Tb, Gd, Sm) complexes

A new family of octanuclear lanthanide compounds [Na2Ln6L8(C6H4NH2COO)2(C2H5OH)2(H2O)4(NO3)]·NO3·C2H5OH·nH2O [H2L = 2-{[(2-hydroxy-3-methoxyphenyl)methylidene]amino}benzoic acid; Ln = Dy (1) (n = 15); Tb (2), Gd (3) (n = 14); Sm (4) (n = 16)] have been prepared under hydrothermal conditions. The X-ray crystal structure analysis reveals that complexes 1-4 are isomorphous. The core of the structure is a [4 + 2] combination of an Ln4 cubane and an Ln2 unit. The two units are bridged by a nitrate ion, which is located in the center of the cluster and displays an unusual μ8-η(2):η(2):η(4) tridentate bridging mode. The magnetic studies for complex 1 show that the [Na2Dy6] unit exhibits slow magnetic relaxation behavior.

Structural diversity of transition-metal complexes derived from N-propionic acid functionalized 1,4,7-triazacyclononane: From enchanting cluster motifs to unprecedented homometallic polymeric networks

Self-assembly between perchlorate salts of Cu(II), Zn(II) and Cd(II) with tri-substituted N-propionic acid functionalized 1,4,7-triazacyclononane (H33L11) or the mono-substituted one (HL22) results in the formation of four novel complexes [Cu5(H2O)6(L11)2](ClO4)4 (1), [Zn9(L11)4(H2O)18](ClO4)6·9H2O (2), [Cd2(H22L11)2](ClO4)2 (3) and [Cd(L22)]ClO4·CH3OH (4) with different aggregation modes. All these complexes were structurally characterized by solid state X-ray diffraction measurement. Complex 1 belongs to a homometallic 2D polymer, where each [Cu(L11)]− complex entity acts as a three-connected node joined to three Cu(II) ions through μ2 bridged propionate arms to afford a puckered honeycomb framework. In complex 2, two face-to-face arranged [Zn(L11)]− moieties clip three Zn(II) ions by virtue of pendant propionate arms generating a macrotricyclic metallacryptate. Two such metallacryptates are fused via co-sharing one lateral Zn(II) ion into an unprecedented nonazinc cluster with a double-cage architecture. Complex 3 exhibits a discrete centrosymmetric dinuclear unit [Cd2(H22L11)2]2+ consisting of two pendant propionate groups linked to a [Cd2O2] core. Complex 4 reveals Cd(II) centers are associated through the unique propionate bridge of the L22− ligand leading to an infinite 1D zig–zag polymeric chain of [Cd(L22)]+ cations. Deduced from the structural investigations, the linkage patterns of the selected macrocyclic ligands towards metal centers may be exquisitely tuned according to the type of metals and the number of the coordinating pendant arms present in the macrocyclic ligands, and then the architectural variation of these metal–organic coordination species is achieved. In addition, magnetic studies for complex 1 show a weak Cu⋯Cu antiferromagnetic coupling in the 2D honeycomb layer with a Weiss temperature of −4.31 K.

Synthesis, Crystal Structures and Magnetic Properties of Two Three-Dimensional Cerium(III) and Erbium(III) Coordination Polymers

Two lanthanide(III) coordination polymers, namely [Ce(pzdc)1.5(H2O)] n (1), [Er(pzdc)(μ2-OH)(H2O)] n ·nH2O (2) (H2pzdc = pyrazine-2,5-dicarboxylic acid), have been hydrothermally synthesized and characterized by single crystal X-ray diffraction and magnetic measurements. Polymer 1 crystallizes in triclinic space group P-1, with a = 6.2875(6), b = 6.7396(6), c = 13.3858(14) A, α = 82.858(4), β = 83.118(4), γ = 63.452(4)°, V = 502.16(8) A3, and Z = 2. Polymer 2 crystallizes in monoclinic space group P2(1)/c, with a = 11.706(4), b = 6.151(2), c = 14.063(5) A, β = 92.255(3), V = 502.16(8) A3, and Z = 4. Single-crystal X-ray diffraction studies show that compound 1 possess a 3D framework structure consisted of double chains. Compound 2 features a 3D open framework structure with a dinuclear Er(III) secondary building unit. Magnetic studies for complex 1 show stronger antiferromagnetic coupling between the Ce(III) ions. Two lanthanide(III) coordination polymers, namely [Ce(pzdc)1.5(H2O)]n (1), [Er(pzdc)(μ2-OH)(H2O)]n·nH2O (2), have been hydrothermally synthesized and characterized. Compound 1 possess a 3D framework structure consisted of double chains. Compound 2 features a 3D open framework structure with a dinuclear Er(III) secondary building unit. Magnetic studies for complex 1 show stronger antiferromagnetic coupling between the Ce(III) ions.

Synthesis, Crystal Structure, Magnetic Properties of a Manganese(II) Coordination Polymer with Double-Helix Chains

A new heterocyclic carboxylate ligand, 5-(4'-pyridyl)-3-methyl-benzoic acid (Hpmba), was synthesized to construct a Mn(II) coordination polymer, namely [Mn(pmba)(2)](n) (1). Complex 1 crystallizes in monoclinic space group C2/c, with a = 17.44(2), b = 17.040(12), c = 8.680(15) angstrom, beta = 111.258(13), V = 2404(5) angstrom(3), and Z = 4. Single-crystal X-ray diffraction studies show that complex 1 has a 3D metal-organic supramolecular framework consisting of double helical chains. Magnetic studies for complex 1 show antiferromagnetic coupling between the nearest Mn( II) ions, with g = 2.11 and J = -10.1 cm(-1).

Study of the coordination behaviour of (3,5-diphenyl-1 H-pyrazol-1-yl)ethanol against Pd(II), Zn(II) and Cu(II)

A new easily synthetic route with a 96% yield of ligand 2-(3,5-diphenyl-1 H-pyrazol-1-yl)ethanol ( L) is obtained. The reactivity of L against Pd(II), Zn(II) and Cu(II) leads to [PdCl 2( L) 2] ( 1), [ZnCl 2( L)] ( 2) and [CuCl( L′)] 2 ( 3) ( L′ is the ligand L without alcoholic proton), respectively. According to the different geometries imposed by the metallic centre and the capability of L to present various coordination links, it has been obtained complexes with square planar ( 1 and 3) or tetrahedral ( 2) geometry and different nuclearity: monomeric ( 1 and 2) or dimeric ( 3). Complete characterisation by analytical and spectroscopic methods, resolution of L and 1– 3 by single-crystal X-ray diffraction and magnetic studies for complex 3 are presented.

Synthesis, crystal structures, magnetic and luminescent properties of nickel(II) and cadmium(II) coordination polymers bearing 5-(2′-carboxylphenyl) nicotate ligands

Two coordination polymers, namely [M(cpna)(phen)(H2O)] n (M = Ni, 1; Cd, 2, H2cpna = 5-(2′-carboxylphenyl) nicotic acid, phen = 1,10-phenanthroline), have been hydrothermally synthesized and characterized by single-crystal X-ray diffraction, magnetic and luminescence measurements. Single-crystal X-ray diffraction studies show that the two complexes are isostructural polymers. They have 1D step-like chain structures, which are further extended into 3D metal–organic supramolecular frameworks by π–π stacking interactions. Magnetic studies for complex 1 show antiferromagnetic coupling between the adjacent Ni(II) centers, with g = 2.10 and J = −4.30 cm−1. Complex 2 displays strong green fluorescent emission at room temperature.

Structure, adsorption and magnetic properties of chiral metal–organic frameworks bearing linear trinuclear secondary building blocks

The reactions of new chiral organic ligands trimesoyltri(L-alanine) (L-TMTAH(3)) or trimesoyltri(D-alanine) (D-TMTAH(3)) with transition metal salts in the presence of an ancillary ligand of 4,4'-bipyridine gave two pairs of three dimensional frameworks [Co(3)(L-TMTA)(2)(4,4'-bpy)(4)]·28H(2)O (1), [Co(3)(D-TMTA)(2)(4,4'-bpy)(4)]·28H(2)O (2) [Ni(3)(L-TMTA)(2)(4,4'-bpy)(4)]·2C(2)H(5)OH·14H(2)O (3) and [Ni(3)(D-TMTA)(2)(4,4'-bpy)(4)]·2C(2)H(5)OH·14H(2)O (4). These compounds were characterized by elemental analysis, IR, and X-ray powder diffraction analysis and the structures of 1-3 were determined from X-ray single crystal diffraction analysis. Complexes 1-4 feature linear trinuclear secondary building blocks [M(3)(COO)(4)](2+) formed via the connection of three metal ions by four carboxylato groups from four TMTA(3-) ligands. Every adjacent two linear trinuclear secondary building blocks are linked by one and three 4,4'-bipyridine molecules along the a and c axis, respectively, to form two-dimensional sheets, which are further connected by TMTA(3-) ligands to construct a porous three dimensional framework with one-dimensional channels. Compound 3 was taken as an example to investigate the adsorption properties of compounds 1-4. It revealed a saturated hydrogen uptake of 216.6 cm(3) g(-1) (2.0 wt%) at 11.1 atm measured at 77 K, a maximum CO(2) uptake of 119.4 cm(3) g(-1) (23.5 wt%) at 19.5 atm measured at 298 K and a saturated CH(4) uptake of 77.8 cm(3) g(-1) (5.6 wt%) at 27.1 atm measured at 298 K. The magnetic studies of complexes 1 and 3 indicate the presence of antiferromagnetic interactions between the metal ions in the two compounds.

Two Lanthanide Coordination Polymers Constructed from Diphenic Acid: Syntheses, Crystal Structures, and Magnetic Properties

Two lanthanide(III) coordination polymers, [Ln2(dpa)3 (H2O)2]n (Ln = Pr, 1; Ce, 2), were self-assembled from diphenic acid (H2dpa) and corresponding lanthanide(III) salts under hydrothermal conditions. The compounds were found to be isostructural. Single-crystal X-ray diffraction studies show that both compounds are one-dimensional chain structures, which are further extended into three-dimensional supramolecular frameworks through π − π interactions. Magnetic studies for complex 1 show weaker antiferromagnetic coupling between the Pr(III) ions.

Magnetic Investigation of a Double-Helix Chain Framework Based on Dinuclear Cobalt(II) SBUs

A coordination polymer [Co(dpa)pyz0.5] n (1) with double-helix chains has been constructed hydrothermally using H2dpa (H2dpa = diphenic acid), pyz (pyz = pyrazine) and Co(NO3)2· 6H2O. Its structure and magnetic properties were investigated. The compound crystallizes in the triclinic space group P -1. Each Co atom is five-coordinated and takes a distorted tetragonal pyramid geometry. Two carboxylates of the H2dpa ligands bridge four Co(II) ions to form infinite right-handed or left-handed helical ─C─O─Co─ chains. The two types of helical chains are interconnected to each other through the Co(II) centers to produce double-helix chains. The chains form a 2D sheet through the coordination interaction of pyz molecules between adjacent chains. Magnetic studies for complex 1 show stronger antiferromagnetic coupling between the Co(II) ions.

A three-dimensional ferromagnet based on linked copper–azido clusters

Two novel three-dimensional coordination polymers [Cu(6)(N(3))(12)(N-Eten)(2)](n) (1) (N-Eten=N-ethylethylenediamine) and {[Cu(9)(N(3))(18)(1,2-pn)(4)].H(2)O}(n) (2) (1,2-pn=1,2-diaminopropane) have been synthesized by the self-assembly reactions of Cu(NO(3))(2).3H(2)O, NaN(3) and small diamine ligands. Their molecular structures were determined by single-crystal X-ray diffraction. Complex 1 is composed of a neutral 3D coordination framework based on unprecedented hexanuclear copper(ii) clusters which features three types of bridging modes for azide (mu-1,1, mu-1,3 and mu-1,1,3). Complex 2 is a novel 3D coordination polymer featuring octanuclear copper-azido clusters and [Cu(diamine)(2)](2+) units which are linked by azido bridges. Magnetic studies for complex show ferromagnetic ordering at 3.5 K, where the azido bridges mediate ferromagnetic coupling between adjacent Cu(II) ions. The magnetic data for 1 were fitted to a uniform hexanuclear copper model which yielded g=2.21, J=6.26 cm(-1), zJ'=0.39 cm(-1). Complex 2 shows ferromagnetic coupling in the octanuclear unit and antiferromagnetic interaction between neighboring units.

Cyano-Bridged Pentanuclear FeIII3MII2(M = Ni, Co, Fe) Clusters: Synthesis, Structures, and Magnetic Properties

The reactions of [M(II)(Tpm(Me))(H2O)3]2+ (M = Ni, Co, Fe; Tpm(Me) = tris(3,5-dimethyl-1-pyrazoyl)methane) with [Bu4N][(Tp)Fe(III)(CN)3] (Bu4N+ = tetrabutylammonium cation; Tp = tris(pyrazolyl)hydroborate) in MeCN-Et2O afford three pentanuclear cyano-bridged clusters, [(Tp)3(Tpm(Me))2Fe(III)3M(II)2(CN)9]ClO4.15H2O (M = Ni, 1; M = Co, 2) and [(Tp)3(Tpm(Me))2Fe(III)3Fe(II)2(CN)9]BF4.15H2O (3). Single-crystal X-ray analyses reveal that they show the same trigonal bipyramidal structure featuring a D3h-symmetry core, in which two opposing Tpm(Me)-ligated M(II) ions situated in the two apical positions are linked through cyanide bridges to an equatorial triangle of three Tp-ligated Fe(III) (S = 1/2) centers. Magnetic studies for complex 1 show ferromagnetic coupling giving an S = 7/2 ground state and an appreciable magnetic anisotropy with a negative D(7/2) value equal to -0.79 cm(-1). Complex 2 shows zero-field splitting parameters deducted from the magnetization data with D = -1.33 cm(-1) and g = 2.81. Antiferromagnetic interaction was observed in complex 3.

Different topologies in heterometallic frameworks of copper(II) with [formula omitted] bridging ligand: Syntheses, crystal structures, thermal and magnetic properties

Four cyano bridged Cu(II)–Ni(II) heterometallic complexes of general formula, [{Cu 2(L) 2Ni(CN) 4}(ClO 4) 2 · xH 2O] n (for 1, L = bis(3-aminopropyl) methylamine = medpt and x = 2.5; for 2, L = N-(2-aminoethyl)-1,3-propanediamine = aepn and x = 2; for 3, L = diethylenetriamine = dien and x = 1), [Cu(medien)Ni(CN) 4] n ( 4) (medien = bis(2-aminoethyl)methylamine) have been synthesized and characterized by single-crystal X-ray diffraction analysis and low temperature magnetic study. In complexes 1– 3, all the cyanide ligands of tetracyanonickelate(II) take part in bonding, connecting four adjacent copper(II) ions whereas in 4 trans-dicoordinated cyanide of Ni ( CN ) 4 2 - links two Cu(II) ions only. We have already reported, as communication, the structural features of complex 1 and of its dehydrated species 1a. A different chain stereochemistry is detected in the related polymeric frameworks 1– 3, mainly dictated by the orientation assumed by the ancillary tridentate L ligand. Thermogravimetric analyses and X-ray powder diffraction of complexes 1– 3 reveal that the complexes retain their crystallinity upon removal of lattice water molecules. The magnetic studies of complexes 1–4 were performed in the 2–300 K temperature range. For all the complexes, the χ M T values from 300 to 60 K are very close and correspond to isolated Cu(II) ions with different average g values (>2.00). From 60 to 2 K, χ M T values decrease indicating weak antiferromagnetic coupling.