Weak Antiferromagnetic Exchange Research Articles

A Unique Example of Structural and Magnetic Diversity in Four Interconvertible Copper(II)−Azide Complexes with the Same Schiff Base Ligand: A Monomer, a Dimer, a Chain, and a Layer

Four new Cu(II)-azido complexes of formula [CuL(N(3))] (1), [CuL(N(3))](2) (2), [Cu(7)L(2)(N(3))(12)](n) (3), and [Cu(2)L(dmen)(N(3))(3)](n) (4) (dmen = N,N-dimethylethylenediamine) have been synthesized using the same tridentate Schiff base ligand HL (2-[1-(2-dimethylaminoethylimino)ethyl]phenol, the condensation product of dmen and 2-hydroxyacetophenone). The four compounds have been characterized by X-ray structural analyses and variable-temperature magnetic susceptibility measurements. Complex 1 is mononuclear, whereas 2 is a single mu-1,1 azido-bridged dinuclear compound. The polymeric compound 3 possesses a 2D structure in which the Cu(II) ions are linked by phenoxo oxygen atoms and two different azide bridges (mu-1,1 and mu-1,1,3). The structure of complex 4 is a double helix in which two mu-1,3-azido-bridged alternating one-dimensional helical chains of CuL(N(3)) and Cu(dmen)(N(3))(2) are joined together by weak mu-1,1 azido bridges and H-bonds. The complexes interconvert in solution and can be obtained in pure form by carefully controlling the conditions. The magnetic properties of compounds 1 and 2 show the presence of very weak antiferromagnetic exchange interactions mediated by a ligand pi overlap (J = -1.77) and by an asymmetric 1,1-N(3) bridge (J = -1.97 cm(-1)), respectively. Compound 3 presents, from the magnetic point of view, a decorated chain structure with both ferro- and antiferromagnetic interactions. Compound 4 is an alternating helicoidal chain with two weak antiferromagnetic exchange interactions (J = -1.35 and -2.64 cm(-1)).

Spectroscopic, mechanical and magnetic characterization of some bismuth borate glasses containing gadolinium ions

The ultrasonic parameters, the optical parameters along with the IR spectroscopy and magnetic susceptibility studies have been employed to explore the role of Gd 2O 3 in the structure of the glasses xGd 2O 3–60B 2O 3–10MoO 3–(30- x)Bi 2O 3, with 0 ≤ x ≤ 7 mol %. IR analysis indicates that Gd 2O 3 is preferentially incorporated into the borate network-forming BO 4 units. It is assumed that Bi 2O 3 and MoO 3 enter the structure as modifiers in the form of BiO 6 and MoO 6 only. The compositional dependence of the mechanical and the optical parameters are interpreted in terms of the transformation of the structural units BO 3 into BO 4, the increase in the number of bridging oxygen atoms, and the substitution of high bond strength Gd–O, in the place of low bond strength Bi–O bond. The results of the magnetic susceptibility reveal the paramagnetic behavior as described by the Curie-Weiss law and indicating the presence of weak antiferromagnetic exchange interactions between Gd 3+ ions. The magnetic entropy change of the glasses was determined according to the temperature and magnetic field dependence of magnetization.

The use of trans-4-cotininecarboxylate to construct a polymeric copper(II) azido complex: Hydro(solvo)thermal synthesis, structure and magnetic properties

A new pyridyl-carboxylate ligand, the anion of trans-4-cotininecarboxylic acid, H L, 1, has been used to prepare a new polymeric copper(II) complex, [Cu LN 3] 2 n , 2, based on a [Cu LN 3] 2 dimeric building block. The single crystal structures of both 1 and 2 have been determined and 1 has been found to be in its zwitterionic configuration. The structure of 2 is a one-dimensional tape-like polymeric structure based on an end-on azido-bridged binuclear [Cu 2N 3] 2 backbone moiety. Magnetic studies reveal that 2 is close to paramagnetic from 2 to 300 K with a Curie constant of 1.094 emu K/mol, a Weiss temperature of 0.73 K and a corresponding μ eff of 2.09 μ B. A fit of χ MT for 2 with S 1 = S 2 = ½, yields g = 2.441(6), J = −0.49(3) cm −1, zJ = −0.38(2) cm −1 and N( α) = 0.00053(12) emu/mol, a fit that indicates the presence of both very weak intramolecular intrachain antiferromagnetic exchange coupling within the one-dimensional tape-like chains and very weak interchain antiferromagnetic exchange coupling between these chains.

Syntheses, structures, and magnetic properties of two 1-D dicyanamide manganese(III) complexes with Schiff-base ligands

Two new 1-D manganese(III) Schiff-base complexes bridged by dicyanamide (dca), [Mn(III)(5-Brsalen)(dca)] ⋅ CH3OH (1) and [Mn(III)(3,5-Brsalen)(dca)] · CH3OH · CH3CN (2) (5-Brsalen = N,N′-ethylenebis(5-bromo salicylaldiminato) dianion; 3,5-Brsalen = N,N′-ethylenebis(3,5-dibromosalicylal diminato) dianion), have been synthesized and characterized. X-ray diffraction analyses reveal that the two complexes have 1-D chain structures constructed by μ 1,5-dca bridge. Magnetic susceptibility measurements exhibit weak antiferromagnetic exchange coupling in the complexes.

Syntheses and magnetic properties of trinuclear trithiocyanurato-bridged manganese(II) complexes involving bidentate aromatic N-donor heterocycles

Abstract Trinuclear manganese(II) complexes of the compositions [Mn 3 (phen) 6 (ttc)](ClO 4 ) 3 ( 1 ), [Mn 3 (dmbpy) 6 (ttc)](ClO 4 ) 3 ∙ 2H 2 O ( 2 ) and [Mn 3 (bpy) 6 (ttc)](ClO 4 ) 3 ∙ 3H 2 O ( 3 ), where phen = 1,10-phenanthroline, dmbpy = 4,4′-dimethyl-2,2′-bipyridine, bpy = 2,2′-bipyridine and H 3 ttc = trithiocyanuric acid (2,4,6-trimercapto-1,3,5-triazine), were prepared and characterized by elemental analysis, FTIR and Raman spectroscopies, MALDI-TOF mass spectrometry, magnetic and conductivity measurements. The magnetic analysis incorporating simultaneous fitting of the temperature dependence and the field dependence of the magnetization using the isosceles triangle spin Hamiltonian model revealed a weak antiferromagnetic exchange within the trinuclear units.

Diphenoxido‐Bridged CoII and ZnII Complexes of Tripodal N2O2 Ligands: Stabilisation of MII‐Coordinated Phenoxyl Radical Species

AbstractThree new tripodal ligands with an N2O2 donor set, namely2‐tert‐butyl‐6‐({(2‐hydroxybenzyl)[2‐(2‐pyridyl)ethyl]amino}methyl)‐4‐methylphenol (H2L1), 2‐tert‐butyl‐6‐({(2‐hydroxybenzyl)[2‐(2‐pyridyl)ethyl]amino}methyl)‐4‐methoxyphenol (H2L2) and 2‐tert‐butyl‐6‐({[2‐(dimethylamino)ethyl](2‐hydroxybenzyl)amino}methyl)‐4‐methoxyphenol (H2L3) have been synthesised. Treatment of the ligands with Co(CH3CO2)2·4H2O or [Zn(H2O)6][ClO4]2 in the presence of Et3N provides the corresponding CoII and ZnII complexes of composition [MII2(L1)2] [M = Co (1) (single‐crystals are a solvate with the composition [CoII2(L1)2]·2CHCl3, i.e. 1·2CHCl3); M = Zn (2)], [MII2(L2)2] [M = Co (3); Zn (4)] and [CoII2(L3)2] (5). Crystallographic analyses reveal that the complexes have closely similar diphenoxido‐bridged structures. Each metal centre assumes MIIN2O3 coordination. The geometry around each metal ion in 1·2CHCl3 (τ = 0.76), 2 (τ = 0.77), 3 (τ = 0.74), 4 (τ = 0.76) and 5 [one CoII (τ = 0.49) and the other CoII (τ = 0.63)] is intermediate between ideal square‐pyramidal (τ = 0) and trigonal‐bipyramidal (τ = 1). Temperature‐dependent magnetic studies reveal weak intramolecular antiferromagnetic exchange couplings for all the three CoII complexes(–J = 1.84, 1.32 and 5.70 cm–1 for 1, 3 and 5, respectively). Spectroscopic properties of the complexes have also been investigated. Cyclic voltammetric (CV) measurements of 1 and 2 show an irreversible oxidative response at Epa (anodic peak potential) in the range 0.60–0.75 V relative to the SCE (saturated calomel electrode), whereas two successive quasi‐reversible oxidative responses can be observed for 3–5 at E1/2 values in the range 0.40–0.53 V relative to the SCE. Oxidative responses are due to the formation of MII‐coordinated phenoxyl radical species. The metal‐coordinated phenoxyl radical species, generated by two‐electron coulometric oxidation of 3–5, were characterised by CV and by adsorption and EPR spectroscopy. The stability of such species was determined by measuring the decay constant (absorption spectroscopy), which reveals that the phenoxyl radical species of 5 is more stable than that of 3 and 4. EPR spectroscopic studies (120 K) of coulometrically generated two‐electron oxidised species of 4 in CH2Cl2 (containing 0.1 M TBAP) at 298 K reveal a combination of an isotropic S = ${1 \over 2}$ signal at g = 2 [(phenolato)(phenoxyl radical)‐coordinated dizinc(II) complex] and a spin‐triplet resonance (S = 1) that gives rise to the symmetric split‐line pattern [bis(phenoxyl radical)‐cordinated dizinc(II) complex]. To pinpoint the site of oxidation (metal‐ or ligand‐centred) in each case, DFT calculations were performed at the B3LYP level of theory.

Bimetallic Materials Derived from Manganese(III) Schiff Base Complexes and Pentacyanidonitrosylferrate(II) Precursor: Structures and Magnetic Properties

Three complexes, [Mn(salphen)(H(2)O)](2)[Fe(CN)(5)(NO)] x 2 CH(3)OH (1) (salphen = N,N'-phenylenebis(salicylideneiminato) dianion), [Mn(naphtmen)(CH(3)OH)](2)[Fe(CN)(5)(NO)] (2) (naphtmen = N,N'-(1,1,2,2-tetramethylethylene)bis(naphthylideneiminato) dianion), and {[Mn(salen)](2)[Fe(CN)(5)(NO)] x H(2)O}(n) (3) (salen = N,N'-ethylene-bis(salicylideneiminato) dianion), were synthesized and structurally characterized by X-ray single-crystal diffraction. The structural analyses show that complexes 1 and 2 consist of the discrete linear trinuclear [Mn(SB)](2)[Fe(CN)(5)(NO)] units (SB = salphen for 1, naphtmen for 2); in complex 3, the nitroprusside anion coordinates to the axial sites of the four [Mn(salen)](+) entities through its four cyano nitrogen atoms, providing a two-dimensional network. The magnetic analysis indicates that the nitroprusside bridging ligand propagates a very weak antiferromagnetic exchange and single-ion anisotropy (D) plays an important role in the overall magnetic properties. Different from complexes 2 and 3, complex 1 shows a typical spin-flop transition with a critical field of 20 kOe.

A versatile V-shaped tetracarboxylate building block for constructing mixed-ligand Co(ii) and Mn(ii) complexes incorporating various N-donor co-ligands

Hydrothermal reactions of 3,3′,4,4′-diphenylsulfonetetracarboxylic dianhydride with Co(II) or Mn(II) acetate and systematically varied N-donor co-ligands leads to the formation of a series of supramolecular complexes, namely, [Co(H2dpstc)(trpy)·H2O] (1), [Co2(dpstc)(phen)2·4H2O]·2H2O (2), [Mn2(dpstc) (phen)2·5H2O] (3), [Mn2(dpstc)(bipy)2·3H2O]·H2O (4) and [Mn2(dpstc)(bpe)2·2H2O]·2H2O (5), where dpstc = 3,3′,4,4′-diphenylsulfonetetracarboxylate, trpy = 2,2′:6′,2′′-terpyridine, phen = 1,10-phenthro- line, bipy = 2,2′-bipyridine and bpe = 1,2-di(4-pyridyl)ethylene. Single-crystal X-ray analysis reveals that complex 1 shows a simple 1D linear array, 2 exhibits a unique 1D chain with pendant arms, and 3 displays a binuclear core. Interestingly, such 1D or dimeric coordination motifs in 1–3 hold the recognition sites of hydrogen bonding and/or π–π stacking, which result in the extended 3D architectures. In contrast, complexes 4 and 5 represent a 2D (4,4) layer and a 3D 4-connected (64·82) framework, respectively. By careful inspection of the structures for 1–5, it is clear that the tetracarboxylate with different coordination modes as well as the auxiliary N-donor ligands play a critical role in determining the coordination array and further packing modes of the final 3D lattice architectures. Magnetic susceptibilities of complexes 1–5 reveals the weak antiferromagnetic exchange interactions between the adjacent metal centers and their thermal stability has also been studied.

Synthesis, crystal structure and properties of the cyano-bridged heteropolynuclear [Cu(meso)]3[Co(CN)6]2•9.5H2O compound

The novel compound [Cu(meso)]3[Co(CN)6]2•9.5H2O was prepared and characterized structurally, magnetically and spectroscopically (UV-vis, FTIR and EPR). The crystal structure is result of the self-assembly of three [Cu(meso)]2+ and two [Co(CN)6]3- units leading to a polymeric zigzag chain. Isolated [Cu(meso)(H2O)2]2+ units counterbalance the charge of the whole structure. The crystal packing shows a large hollow space in the structure and a significant number of water molecules are found in these cavities. Magnetic properties exhibited a very weak antiferromagnetic exchange interaction between the copper ions, with J = -0.3 cm-1. FTIR spectrum showed typical frequencies of n(O-H) at 3604 cm-1 and bridging and non-bridging n(CN) at 2184 and 2128 cm-1, respectively. The electronic spectrum of the title complex presented a broad and symmetric band at 547 nm, assigned to the overlaid z2 → x2-y2, xy → x2-y2 and (xz, yz) → x2-y2 transitions. EPR data at 77 K presented a typical axial spectrum with g// = 2.33 and g⊥ = 2.01, in accordance with the tetragonal distortion of the copper(II) ion as supported by the single-crystal X ray diffraction data.

Magnetism of Zn 0.98Co 0.02O nanopowders

We prepared Zn 0.98Co 0.02O nanopowders by conventional sol–gel method. The powders were sintered at different temperatures. The X-ray diffraction patters showed only wurtzite structure without any impurity phase, better crystalline structure and larger grain size with higher sintering temperature. The magnetic measurements showed that all the powders exhibited paramagnetism with weak antiferromagnetic exchange interaction. The quenched magnetic moment of Co ions was attributed to the weak antiferromagnetic exchange interaction between single Co ions and the antiparallel spin alignment of neighboring aggregated Co ions.

Monofluoride Bridged, Binuclear Metallacycles of First Row Transition Metals Supported by Third Generation Bis(1-pyrazolyl)methane Ligands: Unusual Magnetic Properties

The reaction of M(BF(4))(2).xH(2)O, where M is Fe, Co, Cu, and Zn, and the ditopic, bis(pyrazolyl)methane ligand m-[CH(pz)(2)](2)C(6)H(4), L(m), where pz is a pyrazolyl ring, yields the monofluoride bridged, binuclear [M(2)(mu-F)(mu-L(m))(2)](BF(4))(3) complexes. In contrast, a similar reaction of L(m) with Ni(BF(4))(2).6H(2)O yields dibridged [Ni(2)(mu-F)(2)(mu-L(m))(2)](BF(4))(2). The solid state structures of seven [M(2)(mu-F)(mu-L(m))(2)](BF(4))(3) complexes show that the divalent metal ion is in a five-coordinate, trigonal bipyramidal, coordination environment with either a linear or nearly linear M-F-M bridging arrangement. NMR results indicate that [Zn(2)(mu-F)(mu-L(m))(2)](BF(4))(3) retains its dimeric structure in solution. The [Ni(2)(mu-F)(2)(mu-L(m))(2)](BF(4))(2) complex has a dibridging fluoride structure that has a six-coordination environment about each nickel(II) ion. In the solid state, the [Fe(2)(mu-F)(mu-L(m))(2)](BF(4))(3) and [Co(2)(mu-F)(mu-L(m))(2)](BF(4))(3) complexes show weak intramolecular antiferromagnetic exchange coupling between the two metal(II) ions with J values of -10.4 and -0.67 cm(-1), respectively; there is no observed long-range magnetic order. Three different solvates of [Cu(2)(mu-F)(mu-L(m))(2)](BF(4))(3) are diamagnetic between 5 and 400 K, thus showing strong antiferromagnetic exchange interactions of -600 cm(-1) or more negative. Mossbauer spectra indicate that [Fe(2)(mu-F)(mu-L(m))(2)](BF(4))(3) exhibits no long-range magnetic order between 4.2 and 295 K and isomer shifts that are consistent with the presence of five-coordinate, high-spin iron(II).

Syntheses, crystal structures, and magnetic properties of five new coordination compounds bearing ferrocenedicarboxylate ligands

Five new coordination compounds, {[Mn(L)(CH3OH)2] · CH3OH · H2O} n (1), {[Cd(L)(DMF)2(H2O)] · H2O} n (2), {[Co(L)(CH3OH)4] · CH3OH}2 (3), {[Cd(L)(phen)(CH3OH)] · CH3OH} n (4), and {[Mn(L)(phen)(H2O)] · CH3OH} n (5) (L = 5-ferrocene-1,3-benzenedicarboxylic acid, phen = 1,10-phenanthroline) were obtained from different metal salts and L with or without 1,10-phen under mild conditions. Complex 1 is a 1-D ladder-like chain composed of 8-membered rings A and 16-membered rings B, which arrange alternately. Complex 2 is an infinite linear chain, further bridged to form a parallel double chain through different hydrogen-bond interactions. Complex 3 is a discrete dinuclear structure, while 4 is a neutral 1-D infinite zigzag coordination chain. Complex 5 is a 1-D linear chain with phen and ferrocene groups of L as pendants hanging on the different sides of the main chain. Variable temperature magnetic susceptibilities of 1 were measured and weak antiferromagnetic exchange interactions between the neighboring Mn(II) ions were found with J = −0.95 cm−1.

The investigation of complexation properties and synthesis of the (salen and salophen)-bridged Fe/Cr(III) capped complexes of novel Schiff bases

This article describes synthesis of novel Schiff base and its complexation properties with Fe(III) and Cr(III). Firstly 1,3,5-tris (formylphenoxymethyl)benzene (1, TRIPOD) with tris aldehyde groups were synthesized using the 1,3,5-trisbromomethylbenzene and 4-hydroxybezaldehyde. The compound 1 was converted to the Schiff base derivative (2, TCPIM-TRIPOD) with p-aminobenzoic acid. The prepared TCPIM-TRIPOD were reacted with four new trinuclear Fe(III) and Cr(III) complexes involving tetradenta Schiff bases N,N-bis(salicylidene)ethylenediamine-(salenH2) or bis(salicylidene)-o-phenylenediamine-(salophenH2) and characterized by means of elemental analysis carrying out infrared spectroscopy (IR), thermogravimetric analysis (TG), nuclear magnetic resonance (1H-NMR), elemental analysis and magnetic susceptibility measurement. The complexes can also be characterized as low-spin distorted octahedral Fe(III) and Cr(III) bridged by carboxylic acids. The tricarboxylic acids play a role as bridges for weak antiferromagnetic intramolecular exchange.

Assembly Chemistry between Lanthanide Cations and Monovacant Keggin Polyoxotungstates: Two Types of Lanthanide Substituted Phosphotungstates [{(α-PW11O39H)Ln(H2O)3}2]6− and [{(α-PW11O39)Ln(H2O)(η2,μ-1,1)-CH3COO}2]10−

Two 2:2 types of monolanthanide substituted polyoxometalates [{(α-PW11O39H)Ln(H2O)3}2]6− (Ln = NdIII for 1 and GdIII for 2) and [{(α-PW11O39)Ln(H2O)(η2,μ-1,1)-CH3COO}2]10− (Ln = SmIII for 3, EuIII for 4, GdIII for 5, TbIII for 6, HoIII for 7 and ErIII for 8) have been synthesized in aqueous solution and characterized by elemental analyses, IR spectra, UV−vis−NIR spectra, thermogravimatric analyses and single-crystal X-ray diffraction. The common structural features are that they are constructed from monovacant Keggin-type polyoxoanions [α-PW11O39]7− and trivalent lanthanide cations. Both 1 and 2 are essentially isomorphous, and the molecular structure is built by two symmetrically related monolanthanide substituted Keggin units [α-PW11O39Ln(H2O)3]4− linked via two Ln−O−W bridges, representing the first monovacant Keggin polyoxotungstate dimers constituted by two [α-PW11O39]7− polyoxoanions and two lanthanide cations in polyoxometalate chemistry. 3−8 are also isostructural and display another dimeric structure constructed from two monolanthanide substituted units [(α-PW11O39)Ln(H2O)(η2,μ-1,1)-CH3COO]5− bridged by two (η2,μ-1,1)-acetato ligands. The photoluminescence properties of 4 and 6 were investigated at room temperature. Magnetic susceptibility measurements of 1, 3, 4, 7 and 8 between 2 and 300 K exhibit that their magnetic behaviors mainly result from the spin−orbital coupling interactions as well as weak antiferromagnetic exchange interactions within magnetic centers. The electrochemical properties of 1, 3, 4, 5, 7 and 8 were studied by means of cyclic voltammetry in aqueous solution with 0.5 M Na2SO4 as supporting electrolyte.

Spectroscopic analysis and magnetic susceptibility of CuO–TeO 2–V 2O 5 glasses

This article reports on the structure of the glassy system xCuO–65TeO 2–(35− x)V 2O 5, 5≤ x≤10 mol% which was studied using infrared (IR) and Raman spectroscopy methods as well as magnetic susceptibility measurements. IR and Raman spectroscopy analysis reveals the presence of four main absorption bands attributed to [TeO 3], [TeO 4], [VO 4], and [VO 5] structure units. It suggests that Cu 2+ ions occupy the available open spaces of the Te–O network without straining the bonds too much. Increasing the concentration of Cu 2+ ions beyond 5 mol% results in the modification of the glass by straining and locally distorting the surrounding of the Te–O network. The magnetic susceptibility of these materials was investigated in the temperature range of 5–200 K revealing the paramagnetic behavior described by the Curie–Weiss law and indicating the presence of weak antiferromagnetic exchange interactions between Cu ions. The magnetic entropy change of the glasses was determined based on the temperature and magnetic field dependence of magnetization.

(4, 5)-Connected 3D Supramolecular Framework Based on 1D Tube-Shaped Coordination Armed-Chains [Mn(4,4′-bipy)(OAc)2

A novel manganese(II) compound, namely, [Mn(4,4′-bipy)(OAc)2] n (1) (4,4′-bipy = 4,4′-bipyridine), has been hydrothermally synthesized and characterized. Single crystal X-ray diffraction reveals that it crystallizes in triclinic, P_ space group with a = 8.043 (4) Å, b = 9.319 (5) Å, c = 10.769 (6) Å, α = 109.342 (5)°, β = 99.823 (7)°, γ = 101.808 (7), V = 720.2(7) Å3, C24H14MnN2O4, Mr = 329.21, Dc = 1.518 g·cm−3, Z = 1, F(000) = 338, the final R = 0.0485 and wR = 0.1028 for 3754 observed reflections [I > 2σ]. In 1, the cyclic dimeric metal acetate secondary building units are linked through 4,4′-bipyridine to yield 1D tube-shaped infinite armed-chains, which are further extended to a 3D supramolecular network with (4,5)-connected (44·62)(4465·8) topology through R2 1(5) and R2 1(7) C─H─O hydrogen bonds. Variable-temperature magnetic susceptibility measurements indicate weak antiferromagnetic exchange interactions between adjacent Mn2 + centers.

A novel 18-metallacrown-6 complex: Synthesis, structural characterization and magnetic properties

The novel 18-metallacrown-6 complex, with the formula of [Mn 6(C 11H 11N 2O 3) 6(CH 3CH 2OH) 6]·3C 3H 7NO·2CH 3CH 2OH ( 1) (pmshz = N-propanoyl-3-methyl-salicylhydrazide), has been prepared and characterized. The self-assembled, manganese complex assumes a nearly planar cyclic structure with an [Mn–N–N] 6 backbone. Due to the coordination, the ligand enforces the stereochemistry of the Mn 3+ ions as a propeller shape with alternating …ΔΛΔΛ… configurations. The magnetic properties of the metallacrown molecule are characterized by a weak antiferromagnetic exchange interaction between the Mn 3+ ion spins with S = 2 in the cyclic system.

A novel 2D copper(II) coordination polymer with bidentate coligands and alternating double EO- and single EE-azido bridges

A novel azido-bridged Cu(II) coordination polymer, [CuL(N 3 ) 2 ] n ( 1 ), ( L = 2-aminomethylpyridine), has been synthesized and structurally characterized. Complex 1 displays a 2D (6, 3) layered structure formed by alternating double EO- and single EE-azido bridges between Cu(II) ions. The complex also reveals an overall weak antiferromagnetic coupling between Cu(II) ions. A novel two-dimensional (2D) copper(II) coordination polymer, [CuL(N 3 ) 2 ] n ( 1 ) (L = 2-aminomethylpyridine), has been synthesized and characterized by elemental analysis, IR, X-ray crystallography and magnetic susceptibility. The complex crystallizes in space group P 2 1 / c with a = 9.940(3), b = 8.057(2), c = 12.310(4) Å, β = 104.119(4)°, V = 956.1(5) Å 3 , Z = 4, with final R = 0.0543. The copper(II) ion in 1 is coordinated through two N atoms of the ligand L and four N atoms from the azido ligands in an elongated octahedron. The polymer consists of (6, 3) layers in which alternate double end-on (EO) and single end-to-end (EE) N 3 - bridging modes are found. The pyridine rings coming from adjacent layers are stacked by π – π interactions. Magnetic measurements reveal a weak antiferromagnetic exchange between copper(II) ions in 1 .

Four novel Co(II) and Mn(II) coordination polymers with triazolyl derivate: Syntheses, crystal structures and magnetic properties

Four novel coordination polymers, one-dimensional chains [M(PTE) 2(N 3) 2] n (M = Mn for 1 and Co for 2), and two-dimensional layers [M(PTE) 2(dca) 2] n (M = Mn for 3 and Co for 4) (PTE = 1-(2,4-difluorophenyl-2-(1H-1,2,4-triazol-1-yl)ethanone, dca = dicyanamide anion, N(CN) 2 −), have been synthesized under mild ambient conditions and structurally characterized by single crystal X-ray diffraction. In all four crystal structures, the metal atoms adopt octahedral coordination geometry with six nitrogen atoms from two monodentate PTE ligands and four azido (or dca) bridging ligands. The crystal structures of 1 and 2 are isostructural 1-D polymeric chains, alternatively linked by double end-on and double end-to-end azido bridges. However, the bent dca ligands as bidentate μ 2-1,5 bridging ligands interlink the octahedral metal units to lead to 2-D (4,4) grid networks in 3 and 4. Temperature-dependent magnetic measurements in 2–300 K have been performed for these four polymers, and suggest alternative ferro- and antiferromagnetic couplings for end-on and end-to-end azido bridges in 1, and the dominant ferromagnetic coupling in 2, respectively. Both polymers 3 and 4 show weak antiferromagnetic exchanges through the μ 2-1,5-dca bridges. The effects of auxiliary coligands on the structure and the nature of these magnetic exchanges are discussed in the light of the crystal structures in detail.

Novel 18-membered hexanuclear manganese metalladiazamacrocycle

The novel macrocyclic hexanuclear manganese(III) 18-Metallacrowns-6, [Mn 6[(amshz) 6(DMA) 5(H 2O)]·3DMA·H 2O ( 1), has been synthesized by a self-assembly and characterized, where amshz 3− is N-acetyl-4-methyl-salicylhydrazide. The ring is formed by the succession of six structural moieties of the type [Mn(III) N N] through hydrazide N N groups bridging the ring Mn ions. The ligand enforces the metal ions to form the stereochemistry of a propeller configuration with alternate …ΔΛΔΛ…-type chiral forms. The disc molecule offers a oval cavity with an entrance diameter ∼6.7 Å, inner largest diameter ∼9.6 Å and height ∼4.6 Å. The magnetic properties of the metallacrown are characterized by a weak antiferromagnetic exchange interaction, with the value of μ eff = 12.10 μ B at 300 K between the Mn 3+ ion spins with S = 2 in the cyclic system.