Syntheses, structures and magnetic properties of heterobimetallic complexes based on a new tetracyanometalate precursor

A new mononuclear tetracyanometallic complex, (n-Bu₄N)[(dbphen)Fe(CN)₄] (1, dbphen = 5,6-dibromo-1,10-phenanthroline), has been prepared by reacting [(dbphen)Fe^II(py)₂(SCN)₂] and KCN in water and further oxidized with chlorine. With the use of 1 as building block, two trinuclear Fe₂M complexes, [(dbphen)₂Fe₂(CN)₈Cu(Me₃tacn)]·3H₂O (2), [(dbphen)₂Fe₂(CN)₈Ni(dabhctd)]·2H₂O (3) and a chain complex of squares [(dbphen)₂Fe₂(CN)₈Co(MeOH)₂]_n (4), have been synthesized and structurally characterized. Magnetic studies show ferromagnetic coupling between Fe^III and M^II (M = Cu, 2; Ni, 3) ions bridged by cyanides in complexes 2 and 3, while complex 4 exhibits meta-magnetic behavior.     

Syntheses, crystal structures, and magnetic properties of two cyclic dimer M2L2 complexes constructed from a new nitronyl nitroxide ligand and M(hfac)2 (M = Cu, Mn)

Two new binuclear radical complexes derived from a new long nitronyl nitroxide ligand, 2-[4-(5-pyrimidyl)phenyl]-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (4-NITPhPyrim), and M(hfac)₂ (M²⁺ = Cu²⁺, Mn²⁺; hfac⁻ = hexafluoroacetylacetonato), [Cu(hfac)₂(4-NITPhPyrim)]₂ · 4H₂O (1) and [Mn(hfac)₂(4-NITPhPyrim)]₂ · 4H₂O (2), were synthesized as well as characterized structurally and magnetically. X-ray analysis indicates that 1 and 2 are rectangle-like centrosymmetric dimer M₂L₂ complexes. Magnetic measurements indicate that there are two types of magnetic exchanges in 1: the ferromagnetic (FM) exchange between the Cu(II) ion and the directly bonded nitroxide unit (J₁ = 24.20 cm⁻¹) and the weak FM exchange of Cu-NIT through the pyrimidine and phenyl rings (J₂ = 0.62 cm⁻¹). Besides the strong antiferromagnetic (AFM) coupling between the Mn(II) ion and the directly bonded nitroxide unit (J = −87.61 cm⁻¹), there is a weak FM interaction between the two Mn-NIT pairs (θ = 0.39 K) in 2.     

Synthesis, structures, and magnetic properties of one-dimensional Fe-M (M = Ni, Cu) coordination polymers bridged by nitroprusside

Self-assembling [Fe(CN)₅(NO)]²⁻ and [M(L)]²⁺ (M = Ni, Cu; L = macrocycles) led to one-dimensional coordination polymers, [Ni(L1)][Fe(CN)₅(NO)] · 2H₂O (1) with parallel chains and [Cu(L2)][Fe(CN)₅(NO)] · 3H₂O (2) exhibiting a slanted chain structure. Compound 1 contains a planar macrocycle L1 coordinated to a slightly distorted octahedral Ni(II) ion in which the planarity of L1 gives rise to piling up chains in parallel. In contrast, a more flexible macrocyclic ligand L2 in 2 that surrounds a Cu center with a tetragonal elongation has bulky cyclohexyl groups together with pendant methyl side groups. The presence of the methyl groups on L2 in a chain makes the cyclohexyl groups in an adjacent chain tilted against the CuN₄ basal plane with the methyl groups, eventually resulting in the slanted chain structure. Magnetic data demonstrate that antiferromagnetic interactions (J ≈ −0.13 cm⁻¹) are operating although the paramagnetic centers are linked by the long diamagnetic [Fe(CN)₅(NO)]²⁻ anion.     

Synthesis, characterization, crystal structures and magnetic properties of dissymmetrical double schiff base heterotrinuclear complexes: [CuL(H2O)CoCuL] · H2O · CH3OH and [(CuL)2Ni] · 2H2O

A dissymmetrical double Schiff base Cu(II) mononuclear complex: CuHL (1) (where H₃L is N-3-carboxylsalicylidene-N^′-salicylaldehyde-1,2-diaminoethane) and two trinuclear complexes: [CuL(H₂O)CoCuL] · H₂O · CH₃OH (2) and [(CuL)₂Ni] · 2H₂O (3) have been synthesized and characterized by means of elemental analyses, IR and electronic spectra. The crystal structures of two heterotrinucler complexes were determined by X-ray analysis. Each dissymmetrical cell unit of the complex 2 contains two heterotrinucler neutral molecules. In each neutral molecule, the central Co²⁺ ion is located at the site of O₆ with a distorted octahedral geometry and one terminal Cu²⁺ ion at the four-coordination site of N₂O₂, but the other one at the square-pyramidal environment of N₂O₃. Each dissymmetrical unit of the complex 3 contains a heterotrinucler neutral molecule, whose structure is similar to that of 2 except two terminal Cu²⁺ ions both at the inner site of N₂O₂. The magnetic properties of two heterotrinucler complexes have been determined in the temperature range of 5-300 K, which indicate that the interaction between the central Co²⁺ ion or Ni²⁺ ion and the outer Cu²⁺ ions is antiferromagnetic. The exchange integrals are equal to −26.2 cm⁻¹ for 2 and −50.6 cm⁻¹ for 3.     

Transition metal halide salts of 8-methylquinolinium: Synthesis and structures of (8-methylquinolinium)2 MX4·nH2O (M = Cu, Co, Zn; X = Cl, Br; n = 0, 1)

The reactions of metal(II) chlorides and bromides with 8-methylquinoline (8-mequin) in neutral and acidic solutions were investigated. The reaction with ZnCl₂, ZnBr₂, CoCl₂, CoBr₂, CuCl₂ or CuBr₂ with the appropriate HX in water or aqueous ethanol gave complexes of the formula (8-mequin)₂MX₄ (1, M = Cu, X = Cl; 2, M = Cu, X = Br; 3, M = Co, X = Cl; 4, M = Co, X = Br) or (8-mequin)₂ZnX₄·nH₂O (5, X = Cl, n = 0; 6, X = Br, n = 0; 7, X = Cl, n = 1; 8, X = Br, n = 1). Crystals of 1, 2 and 4-8 suitable for single crystal X-ray diffraction were obtained and the structures reported. Compounds 1 and 2 crystallize in the monoclinic space group C2/c, while 4-8 crystallize in the triclinic space group, . Variable temperature magnetic susceptibility data indicate very weak interactions for the copper compounds 1 and 2, while the magnetic behavior of 3 and 4 is dominated by single ion anisotropy, with weaker antiferromagnetic interactions.     

The cyanocarbanion (C[C(CN)2]3) as monodentate ligand: Synthesis, structure and magnetic properties of [Mn2(bpym)3(tcpd)2(H2O)2] (tcpd = (C[C(CN)2]3) and bpym = 2,2′-bipyrimidine)

One-pot reaction between MnCl₂·4H₂O, K₂tcpd (tcpd²⁻ = [C₁₀N₆]²⁻ = (C[C(CN)₂]₃)²⁻ = 2-dicyanomethylene-1,1,3,3-tetracyanopropanediide anion) and 2,2′-bipyrimidine (bpym = C₈H₆N₄) in aqueous solution yields the new compound [Mn₂(bpym)₃(tcpd)₂(H₂O)₂] (1). The molecular structure of 1 consists of a centrosymmetrical binuclear complex which includes unprecedented unidentate tcpd ligands with two bidentate and a bis-chelate bpym units. Examination of the intermolecular distances reveals that the dinuclear units are held together by hydrogen bonds involving coordinated water molecules and two nitrile groups of the tcpd ligand, giving rise to a 2D structure overall. Variable-temperature magnetic susceptibility data show the occurrence of slight antiferromagnetic coupling (J = −0.58 cm⁻¹) between the Mn(II) ions through bridging bpym (the exchange Hamiltonian being defined as ).     

Ligand substitution in hexahalorhenate(IV) complexes: Synthesis, crystal structures and magnetic properties of NBu4[ReX5(DMF)] (X = Cl and Br)

The preparation, crystal structures, and magnetic properties of two rhenium(IV) mononuclear compounds of formula NBu₄[ReX₅(DMF)] with X = Cl (1) and Br (2) are reported. 1 and 2 are isostructural complexes which crystallize in the monoclinic system with the space group P2₁/n. The rhenium atom is six-coordinated with five X atoms and a DMF molecule forming a somewhat distorted octahedral surrounding [values of Re-X varying in the ranges 2.317(1)-2.358(1) (1) and 2.495(1)-2.518(1) Å (2)]. Magnetic susceptibility measurements on samples of 1 and 2 in the temperature range 1.9-300 K are interpreted in terms of magnetically isolated spin quartets with large values of the zero-field-splitting (|2D| is ca. 20.2 and 39.2 cm⁻¹ for 1 and 2, respectively).     

Solvothermal synthesis, crystal structure and magnetic property of a new dinuclear manganese(II)-azido complex: [Mn(2,2′-dpa)(N3)2]2 (2,2′-dpa = 2,2′-dipicolylamine)

A new dinuclear manganese(II)-azido complex: [Mn(2,2′-dpa)(N₃)₂]₂1 (2,2′-dpa = 2,2′-dipicolylamine) has been synthesized solvothermally. X-ray crystallography analysis reveals that it consists of two crystallographically independent dimeric manganese moieties; each manganese(II) atom is coordinated by one 2,2′-dipicolylamine, one terminal azido ligand, and double end-on bridging azido ligands, exhibiting a slightly distorted octahedral sphere. There are extensive short contacts among dimeric manganese moieties, which extend the structure into an interesting three-dimensional supramolecular array. Magnetic determination of 1 indicates that dominant ferromagnetic interaction and weak antiferromagnetic interaction, which are ascribed to the end-on azido bridges and the short contacts, respectively, co-exist in this complex.     

Spin crossover in a mononuclear compound [Fe(EPPA)(bpym)](ClO4)2 (EPPA = N-(2-aminoethyl)-N-(3-aminopropyl)-2-(aminomethyl)pyridine, bpym = 2,2′-bipyrimidine): Synthesis, structure, and magnetic properties

The synthesis, magnetic properties and single crystal study of a new spin crossover compound [Fe(EPPA)(bpym)](ClO₄)₂ with EPPA = N-(2-aminoethyl)-N-(3-aminopropyl)-2-(aminomethyl)pyridine, bpym = 2,2′-bipyrimidine are reported. Variable-temperature magnetic susceptibility data collected in the temperature range 10-294 K reveal the occurrence of a relatively cooperative spin transition with T_1/2 = 108 K. The crystal structure of [Fe(EPPA)(bpym)](ClO₄)₂ was determined by single-crystal X-ray diffraction method. The structure of the complex consists of mononuclear [Fe(EPPA)(bpym)](ClO₄)₂ units. The potentially bis-bidentate bpym ligand acting as a bidentate one, is coordinated to iron(II) in cis-position by two nitrogen atoms. The four remaining positions in the pseudooctahedral [FeN₆] core are occupied by one pyridinic and three aliphatic nitrogens of the EPPA ligand. The network of cooperative links in the crystal lattice is represented by H-bonding and π stacking interactions.     

Crystal structure and magnetic properties of lanthanide-trans-2-butenoate polymers (Ln = La, Pr, Dy, Ho)

Four lanthanide coordination polymers formulated as {[La₃L₉(H₂O)₃]EtOH · H₂O}_n1, {[Pr₂L₆(H₂O)₂]HL · H₂O}_n2, {[Dy₂L₆(H₂O)]0.5HL · H₂O}_n3 and {[Ho₂L₆(H₂O)]0.5HL · H₂O}_n4 and HL = trans-2-butenoic acid have been synthesized from the corresponding pure lanthanide oxide and HL acid in water at pH 3. The compounds were characterized by chemical analysis, IR spectroscopy, thermogravimetry, variable-temperature magnetic susceptibility and single crystal X-ray diffraction studies. A common feature in these materials is the presence of two differentiated lanthanide nodes linked by carboxylates into extended chains. These are further connected by inter- and intra-molecular hydrogen-bonds involving ligand and solvate molecules. Weak ferromagnetic interactions appear to be operative in the Dy material.     

Syntheses and structure of heterobimetallic helical polymeric Mo-M(II) (M = Mn, Co, Zn, Cd or Ni) complexes using a flexidentate metalloligand

A series of heterobimetallic polymeric complexes of manganese, cobalt, zinc, cadmium and nickel, [M(Mo₂O₅L₂)(MeOH)₂(H₂O)₂]_n·nH₂O {M = Mn (2), n = 1, Co (3), n = 0, Zn (4), n = 1 and Cd (5), n = 1} and [Ni(Mo₂O₅L₂)(MeOH)(H₂O)₃]_n·2H₂O·MeOH (6) have been synthesized form the reaction of [{Na₄(H₂O)₄(μ-H₂O)₂} ⊂ (Mo₂O₅L₂)₂] (1) {LH₂ = 2-(3,5-di-tert-butyl-2-hydroxybenzylamino)acetic acid} with the corresponding metal salts. The complexes have been structurally characterized. The Complexes, 3 and 6 undergo thermal decomposition to afford mixed oxides of the type, MMoO₄·MoO₃ {M = Co or Ni}.     

Synthesis, structures and magnetic properties of oxamido-bridged trinuclear Cu-M-Cu macrocyclic complexes (M = Mn(II) and Co(II))

Two oxamido-bridged trinuclear complexes of formula {[(LCu)(EtOH)]₂Mn(EtOH)₂}(ClO₄)₂ (1) and {[(LCu)(EtOH)]₂Co(EtOH)₂}(ClO₄)₂ · 2H₂O (2) (H₂L = 2,3-dioxo-5,6:13,14-dichlorobenzo-7,12-diphenyl-1,4,8,11-tetraazacyclo-pentadeca-7,11-diene) have been synthesized and structurally characterized. The central ions of complexes 1-2 (Mn(II), Co(II)) are all bridged by macrocyclic oxamido groups. Their magnetic properties were studied by susceptibility versus temperature measurement, the best fitting of the experimental data led to J = −16.91 cm⁻¹ for 1 and J = −27.73 cm⁻¹ for 2.     

Synthesis and characterization of Fe(III)(3-CH3O-qsal)2PF6 · nH2O (n = 0, 2)

Compounds Fe^III(3-CH₃O-qsal)₂PF₆ · nH₂O (n = 0, 2) (1, 1 · 2H₂O) were synthesized and characterized: the structure of 1 and the magnetic properties of both compounds were determined. Compound 1 · 2H₂O presents properties characteristic of high-spin Fe(III), while 1 presents properties of low-spin Fe(III) with an onset of a gradual spin crossover at ca. 300 K.     

Hybrid materials composed of tetravanadate motifs: Synthesis, structure and magnetic properties of the open framework structure solids [{M(C5H5N)4}2]V4O12 (M = Cu, Co)

Two new inorganic-organic hybrid materials - [{M(C₅H₅N)₄}₂]V₄O₁₂ (M = Cu, 1; M = Co, 2) have been synthesized and characterized by spectroscopic methods, X-ray powder diffraction, thermogravimetry, magnetometry and complete single crystal structure analysis. The structures of 1-2 are comprised of layers containing centrosymmetric {V₄O₁₂} rings connected to {M(C₅H₅N)₄} units by V-O-M bridges (M = Cu, 1; M = Co, 2). The layers are parallel to the (1 0 1) crystal planes and there are pyridine stacking interactions between layers. The effective magnetic moment, μ_eff, values for 1 and 2 are 1.9 μ_B and 3.9 μ_B, respectively, indicating some orbital contributions in each case. Both compounds exhibit Curie-Weiss magnetic behavior over the entire range above the critical temperature.     

Synthesis, crystal structure and magnetic properties of the first structurally characterized 1,2-dithiocroconato-containing Cu(II) complex, [Cu(bpca)(H2O)]2[Cu(1,2-dtcr)2]·2H2O

The first crystal and molecular structure of a transition metal complex containing 1,2-dithiocroconate (1,2-dtcr, dianion of 1,2-dimercaptocylopent-1-ene-3,4,5-trione), [Cu(bpca)(H₂O)]₂[Cu(1,2-dtcr)₂]·2H₂O (where bpca is the bis(2-pyrdidylcarbonyl)amide anion), has been determined by single crystal X-ray diffraction methods. The compound crystallizesin the monoclinic syste, space group P2₁/c, with a = 11.661(3), b = 20.255(6), c = 8.265(3) Å, ß = 107.26(2)° and Z = 2. The structure is formally built of [Cu(1,2-dtcr)₂]²⁻ and [Cu(bpca)(H₂O)]⁺ ions and water of hydration. The copper atom of the anion is situated at a crystallographic inversion centre, bonded to four sulfur atoms in a planar, approximately square arrangement. In the cation the copper equatorial plane is formed by the three nitrogen atoms of the bpca ligand and a water oxygen atom. In addition there is a very weak axial bond to one of the sulfur atoms of a 1,2-dtcr ligand in the anion. Through these latter weak bonds each anion is connected to, and sandwiched between, two cations, resulting in neutral, trinuclear, centrosymmetric formula units. The triple-decker molecules are arranged in stacks along the crystallographic a-axis creating close contacts between the terminal copper atoms and bpca groups of the neighbouring molecules. This intermolecular interaction is, however, too weak to define the structure as a chain compound. The distance between adjacent copper atoms within the trinuclear unit is 4.189(1) Å, while the shortest intra-stack metal-metal separation between terminal copper atoms is 5.281(1) Å. Variable-temperature magnetic susceptibility measurements in the temperature r.2–140 K reveal that a Curie law is followed; with three non-interacting copper(II) ions in the formula unit.     

Syntheses, structures and magnetic properties of mono- and di-manganese inclusion compounds

Mono- and di-manganese inclusion compounds 1 and 2 are reported. Two mono-manganese molecules Mn(bpy)₂(NO₃)₂ (bpy=2,2′-bipyridine) and [Mn(bpy)₂(NO₃)(H₂O)]·NO₃ coexist in the mole ratio of 1:1 in the structure of 1, while two di-manganese molecules [Mn₂O(bpy)₂(phtha)₂(H₂O)₂]·(NO₃)₂ (phtha=phthalate) and [Mn₂O(bpy)₂(phtha)₂(NO₃)(H₂O)]·NO₃ in the structure of 2. Refluxing Mn(NO₃)₂/bpy/phthalic acid reaction mixtures in CH₃CN leads to the isolation of 1, further concentration of the reaction solution in raising temperature results in 2. The Mn₁ and Mn₂ units in the inclusion compounds 1 and 2 are similar to other reported Mn₁ and Mn₂ analogs, respectively. The Jahn–Teller distortion was observed to give rise to the elongation along the O_terminal---Mn---O_carboxyl axes for all the four Mn(III) sites in 2, leading to unexpected longer Mn(III)---O_aqua than Mn(II)---O_aqua in 1. Extensive hydrogen bonding interactions among H₂O, NO₃ ⁻ and COOH were observed in the two inclusion compounds. Cyclic voltammetry of 2 in DMF displays two quasi-reversible redox couples at +0.10/+0.22 and −0.43/−0.36 V assigned to the Mn(III)Mn(IV)/2Mn(III) and 2Mn(III)/Mn(III)Mn(II), respectively. Variable temperature magnetic susceptibilities of 1 and 2 were measured. The data were fit to a model including axial zero-field splitting term and a good fit was found with D=1.77 cm⁻¹, g=1.98 and F=1.48×10⁻⁵ for 1. For 2, the least-squares fitting of the experimental data led to J=2.37 cm⁻¹, g=2.02 and D=0.75 cm⁻¹ with R=1.45×10⁻³.     

Transition metal complexes (M = Cu, Ni and Mn) of Schiff-base ligands: Syntheses, crystal structures, and inhibitory bioactivities against urease and xanthine oxidase

Six new transition metal complexes (M = Cu(II), Ni(II) and Mn(III)) of tridentate (H₂L¹, HL²) and/or bidentate (HL³, HL⁴) Schiff-base ligands, obtained from the condensation of salicylaldehyde with glycine, N-(2-aminoethyl)morpholine, 4-(2-aminoethyl)phenylic acid and 4-(2-aminoethyl)benzsulfamide, respectively, were synthesized and structurally determined by single-crystal X-ray analysis. Complexes 1-6 were evaluated for their effect on the jack bean urease and xanthine oxidase (XO). Copper(II) complexes 1-3 (IC₅₀ = 0.43-2.25 μM) showed potent inhibitory activity against jack bean urease, comparable with acetohydroxamicacid (IC₅₀ = 42.12 μM), which is a positive reference. And these copper(II) complexes (IC₅₀ = 10.26-15.82 μM) also exhibited strong ability to inhibit activity of XO, comparable to allopurinol (IC₅₀ = 10.37 μM), which was used as a positive reference. Nickel(II) and manganese(III) complexes 4-6 showed weak inhibitory activity to jack bean urease (IC₅₀ = 4.36-8.25 μM) and no ability to inhibit XO (IC₅₀ > 100 μM).     

Hydrothermal synthesis, crystal structure and magnetic characterization of three hexa-M substituted tungstoarsenates (M = Ni, Zn and Mn)

Three novel hexa-transition-metal complexes substituted tungstoarsenates, [Ni₆(imi)₆(B-α-H₃AsW₉O₃₃)₂]·2H₂O (1), [Zn₆(imi)₆(B-α-H₃AsW₉O₃₃)₂]·2H₂O (2) and [Mn₆(imi)₆(B-α-H₃AsW₉O₃₃)₂]·4H₂O (3) (imi = imidazole), have been synthesized hydrothermally without using any polyoxoanion as precursor and characterized by elemental analyses, IR, TG and X-ray single-crystal diffraction. Compounds 1-3 are isostructural, composed of [B-α-H₃AsW₉O₃₃]¹²⁻ anions and [M₆(imi)₆]¹²⁺ complex cations (M = Ni, Zn and Mn), all M atoms are square pyramidal geometry, and held together to form hexagonal metallocycles by edge-sharing oxygen atoms. In compounds 2 and 3, [M₆(imi)₆(B-α-AsW₉O₃₃)₂] (M = Zn, Mn) segments act as 12-connected nodes to form complicated 3D network via hydrogen-bonding interactions, respectively. Magnetic measurements for 1 show the presence of ferromagnetic interactions within the hexanuclear Ni²⁺ cations.     

Searching for switchable molecular conductors: Salts of [M(dcbdt)2] (M = Ni, Au) anions with [Fe(sal2-trien)] and [Fe(phen)3]

Salts of [Fe^III(sal₂-trien)]⁺and [Fe^II(phen)₃]²⁺ cations and M[(dcbdt)₂]⁻ anions with M = Ni and Au (dcbdt = dicyanobenzenedithiolate) with formula [Fe(sal₂-trien)] [M(dcbdt)₂] and [Fe(phen)₃] [M(dcbdt)₂]₂ were obtained and characterized by single X-ray diffraction and magnetic measurements. None of these salts shows a clear spin crossover behaviour and their magnetic properties are due essentially to the cations in a high spin S = 5/2 and low spin states for the Fe^III and Fe^II salts respectively. The magnetic Ni sublattices in both compounds appear to have a negligible direct contribution to the magnetization but enhance the AF interactions in the cation sublattice.     

Two cyano-bridged heterotrinuclear complexes built from [(Tp)Fe(CN)3] (Tp = hydrotris(pyrazolyl)borate): synthesis, crystal structures and magnetic properties

Using an anionic precursor [(Tp)Fe^III(CN)₃]⁻ (1) as a building block, two cyano-bridged centrosymmetric heterotrinuclear complexes, (2) and (3) (en = ethylenediamine), have been synthesized and structurally characterized. In each complex, [TpFe(CN)₃]⁻ acts as a monodentate ligand toward a central [Mn(C₂H₅OH)₄]²⁺ or [Ni(en)₂]²⁺ core through one of its three cyanide groups, the other two cyanides remaining terminal. The intramolecular Fe-Mn and Fe-Ni distances are 5.2354(4) and 5.0669(11) Å, respectively. The magnetic properties of complexes 2 and 3 have been investigated in the temperature range of 2.0-300 K. A weak antiferromagnetic interaction between the Mn(II) and Fe(III) ions has been found in complex 2. The magnetic data of 2 can be fitted with the isotropic Hamiltonian: where J and J′ are the intramolecular exchange coupling parameters between adjacent and peripheral spin carriers, respectively. This leads to values of J = −1.37 cm⁻¹ and g = 2.05. The same fitting method is applied to complex 3 to give values of J = 1.2 cm⁻¹ and g = 2.25, showing that there is a ferromagnetic interaction between the Fe(III) and Ni(II) ions.