Structures and magnetic properties of tetranuclear nickel(II) complexes with unusual mu3-1,1,3 azido bridges

Pyrazolate-based dinucleating ligands with thioether-containing chelate arms have been used for the synthesis of a family of novel tetranuclear nickel(II) complexes [L2Ni4(N3)3(O2CR)](ClO4)2 that incorporate three azido bridges and one carboxylate (R = Me, Ph). Molecular structures have been elucidated by X-ray crystallography in four cases, revealing Ni4 cores with a unique topology in which two of the azido ligands adopt an unusual mu3-1,1,3 bridging mode. The compounds were further characterized by mass spectrometry, IR spectroscopy, and variable-temperature magnetic susceptibility measurements. Magnetic data analyses indicate a combination of significant intramolecular ferromagnetic and antiferromagnetic exchange interactions that give rise to an overall S(T) = 0 ground state. The sign and the magnitude of the individual couplings have been rationalized in the framework of the common magnetostructural correlations for end-to-end and end-on azido linkages, suggesting that these correlations also remain valid for the respective fragments of multiply bridging mu3-1,1,3 azido ligands.     

Synthesis, crystal structures, and magnetic properties of tetranuclear nickel(II) and copper(II) complexes with tridentate Schiff bases

Two cubane-type tetranuclear nickel(II) and copper(II) complexes, [Ni₄(L¹)₄(CH₃OH)₄] (1) and [Cu₄(L²)₄]·H₂O (2), where L¹ and L² are the dianionic forms of the tridentate Schiff bases 4-nitro-2-[(2-hydroxyethylimino)methyl]phenol (H₂L¹) and 5-methoxy-2-[(2-hydroxyethylimino)methyl]phenol (H₂L²), respectively, have been synthesized and characterized by physicochemical methods and single-crystal X-ray diffraction. The magnetic properties of the complexes show the presence of ferromagnetic interactions for complex 1 and antiferromagnetic interactions for complex 2, mediated by hydroxyl bridges.     

Structures and magnetic properties of imidazolate-bridged tetranuclear and polymeric copper(II) complexes

Eight kinds of imidazolate-bridged copper(II) complexes were found to be classified into two categories from the magnetic properties. The crystal structures of [Cu(L)(μ-im)]_n (Him = imidazole; L = nonane-4,6-dionate, 2,6-dimethylheptane-3,5-dionate) and [Cu(L)(μ-im)]₄ (L = nonane-4,6-dionate, 1-phenylbutane-1,3-dionate) were determined, to reveal that they consist of polymeric chains and tetranuclear cycles, respectively. Note that the nonane-4,6-dionate derivative gave the two phases. The Bonner–Fisher model (a one-dimensional antiferromagnetic chain model) was plausibly applied to [Cu(L)(μ-im)]_n for the best fit, while a square model was to [Cu(L)(μ-im)]₄. The complexes with unknown crystal structures were also subjected to magnetic measurements, and the tetra- and polymeric structures could be clearly distinguished from each other by fitting the magnetic data to appropriate models. The exchange parameters were comparable for both series (2J/k_B = ?78 to ?97 K) because the structurally common bridges Cu–N(eq)–N(eq)–Cu afford comparable magnitudes of couplings.     

Synthesis and magnetic properties of dithiooxamide-bridged nickel(II) complexes

Two novel nickel(II) dinuclear complexes [Ni2(cyclam)2- (DTA)](ClO4)2 (1) and [Ni2(TAA)2(DTA)] (ClO4)2 (2) (TAA=N(CH2CH2NH2)3 , cyclam = 1,4,8,11-tetraazacyclotetradecane, DTA=dithiooxamide) have been prepared and studied by elemental analyses, i.r. and electronic spectra and magnetic measurements. The magnetic susceptibility temperature dependence was measured over the 77–300K range and the observed data were successfully simulated by an equation based on the spin Hamiltonian operator (H=–2JS1S2) giving the exchange integral J=–23.09cm–1 for (1) and J= –26.0cm–1 for (2).     

Tetranuclear nickel(II) complexes with genuine mu3-1,1,3 and mu4-1,1,3,3 azide bridges

Unique tetranickel(II) complexes have been synthesized which incorporate genuine mu3-1,1,3 or mu4-1,1,3,3 bridging azido ligands. Identification of two distinct isomeric mu4-1,1,3,3 binding modes confirms the structural flexibility of the quadruply bridging azide.     

Synthesis and magnetic properties of nickel(II) complexes with the nitronyl nitroxides

Four novel complexes of nickel(II), Ni(tfac)2(NITPa)2 (1), Ni(tfac)2(NITPhNO2)2 (2), Ni(pfpr)2(NITPa)2 (3) and Ni(pfpr)2(NITPhNO2)2 (4), [tfac=trifluoro- acetato, NITPa=2-(3,4-methylenedioxyphenyl)-4,4,5, 5-tetramethylimidazoline-1-oxy-3-oxid, NITPhNO2= 2-(3-nitrophenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxid, pfpr=pentafluoropropionato], have been prepared and characterized by elemental analysis, i.r., and electronic spectra, and molar conductances. The temperature dependence of the magnetic susceptibility for complexes (1) and (3) was measured (4–300K). The observed data were successfully simulated giving the exchange integral J=–1.48cm–1 for (1) and J=–1.25cm–1 for (3). These results indicate a weak antiferromagnetic spin exchange interaction between nickel(II) ion and the radicals.     

New tetranuclear Cu(II) complexes: synthesis, structure, and magnetic properties

The synthesis, structure, and magnetic properties of two new tetranuclear Cu(II) complexes containing N,N,N',N'-tetraethylpyridine-2,6-dithiocarboxamide (S-dept) of formula [Cu(2)Cl(2)(mu-S-dept)(2)][Cu(2)Cl(4)(mu-Cl)(2)] (1) and [Cu(2)(mu-Cl)(2)(S-dept)(2)][CuCl(3)(EtOH)](2) (2) are reported. Their X-ray crystal structures reveal that the complexes are composed of anionic and cationic dimers, that in both cases contain the metal centers which interact via Coulombic and/or hydrogen bonding interactions. In both cases, the Cu centers in the anionic moieties adopt a slightly distorted tetrahedral geometry whereas for the cationic moieties they adopt a square-pyramidal type of geometry. Magnetic susceptibility data show that compounds 1 and 2 present an overall antiferromagnetic behavior arising from the contribution of both anionic and cationic moieties. For 1, the best fit obtained gave J(1) = -2.62 +/- 0.19 cm(-1), J(2) = -19.54 +/- 0.47 cm(-1), and g(2) = 2.164 +/- 0.004 cm(-1) (R = 8.28 x 10(-5)) whereas for 2 it gave J(1) = 4.48 +/- 2.73 cm(-1), g(1) = 2.20 +/- 0.03, J(2) = -11.26 +/- 2.01 cm(-1), and g(2) = 2.10 +/- 0.03 (R = 1.15 x 10(-4)). The nature of the superexchange pathways in 1 and 2 is discussed on the basis of structural, magnetic, and molecular orbital considerations. Theoretical calculations are performed at the extended Huckel level in order to obtain their molecular orbitals and energies using their crystallographic data.     

Structural and magnetic properties of iron(II) complexes with 1,4,5,8,9,12-hexaazatriphenylene (HAT)

Reactions of Fe(II) salts with the ligand 1,4,5,8,9,12-hexaazatriphenylene (HAT) led to the isolation and characterization of four new compounds: [Fe3(HAT)(H2O)12](SO4)3.3.3H2O (1), [Fe2(HAT)(SO4)(H2O)5](SO4).2H2O.CH3OH (2), [Fe2(HAT)(SO4)(H2O)5](SO4).3H2O (3), and [Fe3Cl5(HAT)(CH3OH)4(H2O)]Cl (4). Compound 1 crystallizes as a trinuclear cluster in which HAT acts as a tris-chelating ligand. Compounds 2 and 3 are two polymorphs of an infinite one-dimensional structure in which the Fe atoms are coordinated to HAT and then connected into the chain through bridging sulfate anions. Compound 4 exhibits a similar chain structure, but with bridging chloride ligands. The magnetic behavior of the new compounds is indicative of weak antiferromagnetic coupling between the Fe(II) centers through the HAT ligand.     

Synthesis and magnetic properties of new nickel(II)-copper(II)-nickel(II) trinuclear complexes with irregular spin-state structure

Summary Four novel heterotrinuclear complexes were prepared, namely {[Ni(L)₂]₂[Cu(pba)]}(ClO₄)₂, where pba = pro-pylene-1,3-bis(oxamato) and L = 1,10-phenanthroline (phen), 5-nitro-1,10-phenanthroline (NO₂-phen), 2,2-bipyridyl (bpy), 4,4-dimethyl-2,2-bipyridyl (Me₂bpy). Based on i.r., elemental analyses, conductivity measurements and electronic spectra oxamato-bridged structures are proposed for these complexes, consisting of two nickel(II) ions, each in a distorted octahedral environment, and a copper(II) ion in a square planar environment, respectively. The temperature dependence of the magnetic susceptibility of {[Ni(phen)₂]₂[Cu(pba)]}(ClO₄)₂·H₂O was studied in the 4–300 K range, giving the exchange integral J = - 106 cm^–1. TheX _scm T versusT plot exhibited a minimum at ca. 98 K, characteristic of this kind of coupled polymetallic complex with an irregular spin-state structure. E.s.r. spectra of these complexes clearly indicated a strong rhombicity withg ₁ = 5.20,g ₂ = 2.29 andg ₃ = 2.02 (approximately), which agrees with an anisotropicS = ±1/2 Kramer doublet in the ground state.     

Synthesis,characterization, structure and magnetic properties of azido-bridged nickel(II) and copper(II) complexes with a pyridylpyrazole-based ligand

A new pyridylpyrazole-containing tetradentate ligand, namely N,N-bis(3,5-dimethylpyrazol-1-ylmethyl)aminomethylpyridine (L), and two of its binuclear azido-bridged complexes, [Ni₂(L)₂(N₃)₂](ClO₄)₂·2EtOH (1) and [Cu₂(L)₂(N₃)₂](ClO₄)₂ (2), have been synthesized and characterized by physico-chemical and spectroscopic methods. The crystal structures of both complexes are reported. Each metal atom in the complexes has a MN₆ coordination environment with distorted octahedral geometry. Variable-temperature magnetic susceptibility measurements for complex (1) show typical antiferromagnetic behavior with J value −84.5 ± 1.3 cm⁻¹, whereas complex (2) has no magnetic interactions.     

Low-temperature field dependence of the magnetic moment of ferromagnetic tetranuclear nickel(II) clusters

We examine the characteristics of the low-temperature behavior of the magnetic moment of tetranuclear methoxo complexes of nickel(II) of the type [Ni(OCH₃L· (CH₃OH)]₄ (L is the residue of 2,4-dinitrophenol (I), 2,4,6-trichlorophenol (II) and acetylacetone (III)), having the cubane structure. Within the model taking into account the isotropic Heisenberg interaction (J₁₂=J₂₃=J₃₄=J₄₁=J, J₁₃=J₂₄=J_iso), the local anisotropy (parameters D and g_i), intercluster exchange (parameter J_ic), we could interpret both the field dependence (=0.4-0.8 T) and the temperature dependence of the magnetic moment. We have established that the nature of the ligand L exerts a substantial effect on the magnetic proper ties of the considered compounds.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 3, pp. 339–344, May–June, 1989.     

Structure and magnetic properties of carbonate-bridged five-coordinate nickel(II) complexes controlled by solvent effect

CO2 and HCO3- react with the dinuclear hydroxo-complex [Ni(mcN3)(mu-OH)]2(PF6)2 (mcN3 = 2,4,4,9-tetramethyl-1,5,9-triazacyclododec-1-ene) to form micro-CO3 bridged nickel(II) complexes, [{Ni(mcN3)}2(mu-CO3)](PF6)2 (1a) with a symmetric core in which both nickel atoms are five-coordinate and [Ni(mcN3)(mu-CO3)Ni(mcN3)(MeCN)](PF6)2 (1b) with an asymmetric dinuclear core containing five- and six-coordinate nickel atoms. The magnetic behaviour indicates the existence of antiferromagnetic coupling between the metallic centres. A substantial increase in the value of J occurs when the symmetric five-coordinate nickel species transforms to an asymmetric five- and six-coordinate species by axial coordination of acetonitrile.     

Spectral and magnetic studies of tin(IV) complexes with nickel(II) thiocarbohydrazones

Tin(IV) chloride derivatives of nickel(II) thiocarbohydrazones were obtained by reacting tin(IV) chloride with nickel(II) thiocarbohydrazones in chloroform medium. All the complexes are greenish coloured solids and appear to be non-electrolytes in DMF. Elemental analyses conform to the 1:1 stoichiometry. Magnetic, electronic and IR spectral information suggest that square planar nickel(II) thiocarbohydrazones have changed their configuration to octahedral as a result of reaction with tin (IV) chloride.     

Synthesis and magnetic properties of binuclear cobalt(Ⅱ), nickel(Ⅱ) and copper(Ⅱ) complexes bridged by oxamidate group

Four binuclear Co(Ⅱ), Ni(Ⅱ) and Cu(Ⅱ) complexes bridged by oxamidate (oxd) group have been synthesized, namely Co2(byp)2(oxd)(ClO4)2 (1), Co2(Me2bpy)2(oxd)(ClO4)2.H2O (2), Ni2(bpy)2(oxd)(ClO4)2.2H2O (3) and Cu2(Me2bpy)2(oxd)(NO3)2 (4). (bpy=2,2'-bipyridyl, Me2-bpy=4,4'-dimethylbipyridyl, oxd=oxamidate) The complexes are characterized by IR, UV spectra, EPR and variable-temperature magnetic susceptibility (4-300 K). The susceptibility data for. complexes 1 and 3 were least-squares fit to the susceptibility equation derived from the spin Hamiltonian H=-2J . S1 . S2. The exchange integral, J, was found to be equal to -3.62 cm-1 in 1 and -1.82 cm-1 in 3. This indicates a weak antiferromagnetic spin exchange interaction between the metal ions.     

Synthesis,magnetic and spectral studies of nickel(II) and zinc(II) complexes of 4-formylantipyrine N(4)-substituted thiosemicarbazones

The synthesis and characterization of nickel(II) and zinc-(II) complexes with 4-formylantipyrine N(4)-methyl-, N(4)-dimethyl- and 3-piperidylthiosemicarbazones are reported. Elemental analyses, molar conductivities, magnetic measurements and spectral (i.r., electronic and n.m.r.) studies have been used to characterize the complexes. The i.r. spectra show that the thiosemicarbazones behave as bidentate or tridentate ligands, either in the thione or thiolato form. Stereochemistries are proposed for the complexes on the basis of spectral and magnetic studies.     

Self-assembly and interconversion of tetranuclear copper(II) complexes

The ligand 1,2-bis(benzimidazol-2-yl)-1,2-ethanediol (H2bzimed, 1) and its N-methylated analogue (H2mbzimed, 2) form a variety of polynuclear complexes with copper(II), all of which contain a planar Cu2O2 lozenge as a central element and in which the bridging oxygen belongs to an alkoxo group of the ligand. Syntheses are reported for dinuclear [Cu2(Hmbzimed)2](ClO4)2 x 1.5H2O, Cu(2)2(2), and the tetranuclear species [Cu4(Hbzimed)4(ClO4)2](NO3)2 x 4H2O, Cu(4)1(4), [Cu4(Hmbzimed)2(mbzimed)Cl2](ClO4)2 x 2H2O x C2H5OH, Cu(4)2(3), and rac-[Cu4(H2bzimed)4(bzimed)(ClO4)2](ClO4)4 x 1.5H2O x 3.5C2H5OH, Cu(4)1(5). Crystal structures are reported for the tetranuclear species. Cu(4)1(4) shows a cubane structure, Cu(4)2(3) a stepped cubane structure, and rac-Cu(4)1(5) a novel structure in which one doubly deprotonated ligand lies between the two Cu2O2 units. Magnetic susceptibility measurements indicate that all complexes show antiferromagnetic coupling in the solid state. Studies in solution (ESI-MS, CD, NMR) show that Cu(2)2(2) and Cu(4)2(3) persist in solution but that Cu(4)1(4) dissociates partially and rac-Cu(4)1(5) completely. The six coordination modes of the ligands are discussed together with the effect of the N-methylation on the ligand conformation.