Co-reporter:Andrei A. Patrascu;Sergiu Calancea;Matteo Briganti;Stéphane Soriano;Augustin M. Madalan;Rafael A. Allão Cassaro;Andrea Caneschi;Federico Totti;Maria G. F. Vaz;Marius Andruh
Chemical Communications 2017 vol. 53(Issue 48) pp:6504-6507
Publication Date(Web):2017/06/13
DOI:10.1039/C7CC03236F
End-off bicompartmental ligands bearing a nitronyl–nitroxide arm have been designed for synthesizing various heterospin molecular systems. These ligands can selectively interact with 3d and 4f metal ions, leading to 2p–4f, 2p–3d, and 2p–3d–4f complexes. The magnetic properties of the 2p–4f and 2p–3d–4f complexes have been investigated and rationalized by theoretical calculations.
Co-reporter:Samira G. Reis, Matteo Briganti, Stéphane Soriano, Guilherme P. Guedes, Sergiu Calancea, Carmen Tiseanu, Miguel A. Novak, Miguel A. del Águila-Sánchez, Federico Totti, Fernando Lopez-Ortiz, Marius Andruh, and Maria G. F. Vaz
Inorganic Chemistry 2016 Volume 55(Issue 22) pp:11676-11684
Publication Date(Web):November 4, 2016
DOI:10.1021/acs.inorgchem.6b01616
Binuclear complexes with general formula [Ln2(hfac)6(H2O)2(dppnTEMPO)] (LnIII = Gd, Tb, and Dy) have been obtained using the paramagnetic ligand 1-piperidinyl-4-[(diphenylphosphinyl)amino]-2,2,6,6-tetramethyl (dppnTEMPO) as a bridge. One of the lanthanide ions is ferromagnetically coupled with the TEMPO moiety. Two of the complexes (Dy and Tb) show slow relaxation of the magnetization, and the non-magneto-equivalence of the two LnIII ions was clearly observed. The ab initio CASSCF calculations were employed to confirm this behavior, as well as to rationalize the Ln–Rad interaction. The simulations of the magnetic properties were allowed by the insights given by the calculations. The inequivalence of the TbIII ions was also proved by emission spectroscopy.
Co-reporter:Samira G. Reis, Matteo Briganti, Daniel O. T. A. Martins, Handan Akpinar, Sergiu Calancea, Guilherme P. Guedes, Stéphane Soriano, Marius Andruh, Rafael A. A. Cassaro, Paul M. Lahti, Federico Totti and Maria G. F. Vaz
Dalton Transactions 2016 vol. 45(Issue 7) pp:2936-2944
Publication Date(Web):23 Dec 2015
DOI:10.1039/C5DT04469C
The synthesis, crystal structures and magnetic properties of two families of heterospin complexes containing lanthanide ions and a bis(imino nitroxide) biradical (IPhIN = 1-iodo-3,5-bis(4′,4′,5′,5′-tetramethyl-4′,5′-dihydro-1H-imidazole-1′-oxyl)benzene) are reported: in [Ln2(hfac)6(IPhIN)(H2O)2] compounds, two lanthanide ions [Ln = GdIII (1) and DyIII (2)] are coordinated to the biradical, and in [Ln(hfac)3(IPhIN)(H2O)] compounds, one lanthanide ion (Ln = TbIII (3), GdIII (4) or DyIII (5)) is coordinated to the biradical. Ferromagnetic intramolecular magnetic interactions between GdIII and the biradical were found for 1 and 4, while intramolecular magnetic interactions between the radicals were ferro- and antiferromagnetic, respectively. Compound 2 shows a field induced slow relaxation of magnetization, which (under an external applied field of 2 kOe) exhibits an activation energy barrier of ΔE/kB = 27 K and a pre-exponential factor of 1.4 × 10−8 s. To support the magnetic characterization of compound 3ab initio calculations were also performed.
Co-reporter:Sergiu Calancea, Samira G. Reis, Guilherme P. Guedes, Rafael A. Allão Cassaro, Felipe Semaan, Fernando López-Ortiz, Maria G.F. Vaz
Inorganica Chimica Acta 2016 Volume 453() pp:104-114
Publication Date(Web):1 November 2016
DOI:10.1016/j.ica.2016.07.057
•Mixed-ligand copper(II) clusters with different nuclearities have been synthesized.•The magnetic studies revealed predominant antiferromagnetic interactions.•Catecholase-like activity of copper(II) complexes was studied.In this work we report a family of mixed-ligand copper(II) clusters obtained with different nuclearities: [Cu3(μ-OH)(μ-dppi)3(μ-hfac)3] (1), [Cu4(μ-dppi)4(Hdppi)2(hfac)4] (2), [Cu5(μ-O)2(μ-dppi)(μ-Hdppi)2(μ-hfac)3(hfac)2] (3) and [Cu6(μ-O)2(μ-dppi)2(μ-Hdppi)(μ-hfac)6] (4), where hfac = hexafluoroacetylacetonate, dppi = diphenylphosphinate and Hdppi = diphenylphosphinic acid. Complexes 3 and 4 are the first examples of copper(II) clusters containing a μ-oxo oxygen atom and hfac as bridging ligands. The magnetic properties of all compounds showed predominant antiferromagnetic interactions and the magnetic coupling constants were evaluated using an isotropic exchange model based on the spin topology. A spin frustration phenomena was observed for the equilateral cyclic trinuclear complex (1), thus an antisymmetric exchange term was also considered to fit the experimental magnetic data. The obtained J values are in the range from −89 cm−1 to 1.7 cm−1 and were interpreted based on structural features. The electrochemical properties and catalytic activity of complexes 1 and 2 were investigated and compared with the [Cu(hfac)2] precursor. Catecholase-like activity of copper(II) complexes via oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) to 3,5-di-tert-butylquinone (3,5-DTBQ) was performed.A new family of mixed-ligand copper(II) clusters with different nuclearities (Cu3Cu6) was obtained. The magnetic properties of all compounds showed predominant antiferromagnetic interactions. The electrochemical properties and catalytic activity of Cu3 and Cu4 compounds were investigated. Catecholase-like activity of Cu3 and Cu4 clusters via oxidation of 3,5-di-tert-butylcatechol to 3,5-di-tert-butylquinone was performed.
Co-reporter:Rafael A. Allão Cassaro; Samira G. Reis; Thamyres S. Araujo; Paul M. Lahti; Miguel A. Novak;Maria G. F. Vaz
Inorganic Chemistry 2015 Volume 54(Issue 19) pp:9381-9383
Publication Date(Web):September 14, 2015
DOI:10.1021/acs.inorgchem.5b01431
Two isostructural 1D complexes, [M(hfac)2NaphNN]n [M = MnII (1) or CoII (2); NaphNN = 1-naphthyl nitronylnitroxide], were synthesized and exhibit very strong antiferromagnetic metal–radical exchange coupling. Compound 2 shows slow magnetic relaxation behavior with a high blocking temperature (TB ≈ 13.2 K) and a very high coercive field of 49 kOe at 4.0 K.
Co-reporter:Guilherme P. Guedes, Igor F. Santos, Luiza A. Mercante, Nivaldo L. Speziali, Jackson A. L. C. Resende, Alice M. R. Bernardino, Marius Andruh, and Maria G. F. Vaz
Crystal Growth & Design 2015 Volume 15(Issue 3) pp:1027-1030
Publication Date(Web):February 13, 2015
DOI:10.1021/cg5018328
Two new coordination polymers, 1∞[Cu2(L)4(MeOH)]·MeOH (1) and 3∞[Cu(L)2]·5H2O (2), have been obtained exploring the potential of 5-amino-1-phenyl-1H-pyrazole-4-carboxylate (L–) to act as a spacer. The different architectures of these compounds arise from the versatility of this organic ligand. In compound 1, the carboxylato groups (syn-syn bridging mode) and the copper ions generate a binuclear paddle-wheel motif. Each binuclear entity coordinates to another one, through one out of the four pyrazole rings, resulting in double chains. In crystal 2, the organic ligand is coordinated to a copper ion through the carboxylato group (asymmetric chelating) and to another copper ion through the pyrazole nitrogen atom. Compound 2 crystallizes in the hexagonal system with the chiral space group P6122, featuring a quartz-like topology. The magnetic properties of both compounds have been investigated.
Co-reporter:Marguerite Kalisz, Rafael A. A. Cassaro, Miguel A. Novak, Marius Andruh, Helio S. Amorim and Maria G. F. Vaz
CrystEngComm 2015 vol. 17(Issue 38) pp:7423-7429
Publication Date(Web):19 Aug 2015
DOI:10.1039/C5CE01537E
In this work we describe the structure of a coordination polymer, which was solved by using synchrotron X-ray powder diffraction. The heterometallic CuII–MnII compound, [Cu2Mn2(bopba)(DMSO)7]·DMSO, was assembled from a binuclear oxamato copper(II) complex and manganese(II) ions, generating a Mn–Cu–Mn–Cu– chain motif. Each chain is connected to two others, resulting in a folded two-dimensional coordination network where the uncoordinated DMSO molecule is located in the space between the layers. The loss of the DMSO molecules leads to the loss of both crystallinity and long range magnetic order. The knowledge of the structure allowed the quantification of the intrachain magnetic interaction.
Co-reporter:Dr. Maria G. F. Vaz;Dr. Rafael A. Allão Cassaro;Dr. Han Akpinar;Dr. John A. Schlueter; Paul M. Lahti; Miguel A. Novak
Chemistry - A European Journal 2014 Volume 20( Issue 18) pp:5460-5467
Publication Date(Web):
DOI:10.1002/chem.201304852
Abstract
Coordination of a [Co(hfac)2] moiety (hfac=hexafluoroacetylacetonate) with a nitronylnitroxide radical linked to bulky, rigid pyrene (PyrNN) gives a helical 1:1 chain complex, in which both oxygen atoms of the radical NO. groups are bonded to CoII ions with strong antiferromagnetic exchange. The complex shows single-chain magnet (SCM) behavior with frequency-dependent magnetic susceptibility, field-cooled and zero-field-cooled susceptibility divergence with a high blocking temperature of around 14 K (a record among SCMs), and hysteresis with a very large coercivity of 32 kOe at 8 K. The magnetic behavior is partly related to good chain isolation induced by the large pyrene units. Two magnetic relaxation processes have been observed, a slower one attributable to longer, and a faster one attributable to short chains. No evidence of magnetic ordering has been found.
Co-reporter:Guilherme P. Guedes, Stéphane Soriano, Luiza A. Mercante, Nivaldo L. Speziali, Miguel A. Novak, Marius Andruh, and Maria G. F. Vaz
Inorganic Chemistry 2013 Volume 52(Issue 15) pp:8309-8311
Publication Date(Web):July 5, 2013
DOI:10.1021/ic401479d
Four tetranuclear heterometallic complexes, [CoII2Mn2III(dpm)4(MeO)6] (1) and [LnIII2MnIII2(dpm)6(MeO)6(MeOH)n], where Ln = Gd (2, n = 2), Tb (3, n = 2), and Dy (4, n = 0), have been obtained following the same general synthetic route, namely, the one-pot reaction between 2,2,6,6-tetrametil-3,5-heptanodione (Hdpm), MnCl2 and CoCl2 or Ln(NO3)3 in the presence of sodium methoxide. Within the four compounds, the metal ions bridged by methoxide ligands display a defect-diheterocubane core. Compounds 1, 3, and 4 show slow relaxation of the magnetization below 4 K.
Co-reporter:Rafael A. Allão Cassaro, Samuele Ciattini, Stephane Soriano, Hélio S. Amorim, Nivaldo L. Speziali, Marius Andruh, and Maria G. F. Vaz
Crystal Growth & Design 2013 Volume 13(Issue 7) pp:2711-2715
Publication Date(Web):May 29, 2013
DOI:10.1021/cg400547a
Two novel heterobimetallic three-dimensional coordination polymers, [Cu2Na4L2(CH3OH)2.3(H2O)5.2]·1.7H2O (1) and [CuNa2L(H2O)3.88]·H2O (2), have been obtained by assembling a bis-oxamate copper(II) complex with sodium ions (L = 4,4′-sulfonylbis(phenylene)bis(oxamate). Both coordination frameworks are constructed by connecting {Cu4L4} crosslike anionic units by sodium ions forming polymers with different topologies. The magnetic susceptibility data shows weak antiferromagnetic interaction for both compounds.
Co-reporter:Rafael A. Allão Cassaro, Jackson A. L. C. Resende, Sauli Santos Jr., Lorenzo Sorace, Marius Andruh and Maria G. F. Vaz
CrystEngComm 2013 vol. 15(Issue 42) pp:8422-8425
Publication Date(Web):14 Aug 2013
DOI:10.1039/C3CE41376D
The homometallic 3-D coordination intercatenated polymer, [Ca(H2L)(H2O)]·2H2O, has been obtained by assembling a dianionic ligand H2L2− = 4,4′-sulfonylbis(phenyl)bis(oxamate) with calcium(II) ions. We also describe the crystalline structure of the proligand, H4L, and the structure of its diethylester precursor, H2Et2L, and the importance of intermolecular interactions to the supramolecular architecture.
Co-reporter:Guilherme P. Guedes, Stéphane Soriano, Nadia M. Comerlato, Nivaldo L. Speziali, Miguel A. Novak, Maria G.F. Vaz
Inorganic Chemistry Communications 2013 Volume 37() pp:101-105
Publication Date(Web):November 2013
DOI:10.1016/j.inoche.2013.09.034
•Two heptanuclear cobalt(II) compounds were synthesized and characterized.•Crystal structures consist of two cubane-like units linked by one shared CoII vertex.•Compounds present single-molecule magnet behavior.The reaction between the tetranuclear compound [Co4(tta)4(OMe)4(MeOH)4] (tta = 4,4,4-trifluoro-1-thienoyl-2,4-butanedionate) and isopropanol or n-butanol leads to two heptanuclear compounds with general molecular formula [Co7(OH)8(tta)6(ROH)6]·ROH (R = isopropyl, for 1 or n-butyl, for 2). The crystal structures of both heptamers consist of two cubane-like units linked through one shared cobalt(II) ion vertex. The reaction leads to the replacement of precursor methoxide bridges by hydroxo in the heptanuclear compounds, which connect the internal metal ion to the six external ones. The magnetic properties revealed moderate ferromagnetic interactions among the cobalt(II) ions. Furthermore, ac magnetic susceptibility measurements confirm that these compounds are new examples of single-molecule magnets (SMM) containing cobalt(II) ions, with an energy barrier for magnetization reversal of 22 K and 21 K, respectively for 1 and 2.The reaction between isopropanol or n-butanol and the tetranuclear precursor [Co4(tta)4(OMe)4(MeOH)4] (tta = 4,4,4-trifluoro-1-thienoyl-2,4-butanedionate) leads to two heptanuclear compounds with general molecular formula [Co7(OH)8(tta)6(ROH)6]·ROH (R = isopropyl or n-butyl). Moderate ferromagnetic interactions are present in both compounds. Ac magnetic measurements revealed that these compounds behave as single-molecule magnets at low temperatures.
Co-reporter:Guilherme P. Guedes, Antonio S. Florencio, José Walkimar de M. Carneiro, Maria G.F. Vaz
Solid State Sciences 2013 Volume 18() pp:10-16
Publication Date(Web):April 2013
DOI:10.1016/j.solidstatesciences.2012.12.014
The synthesis, crystal structure, magnetic properties and DFT calculations of two low-nuclearity Fe(III) compounds based on β-diketonate ligand, [Fe(OMe)(BTA)2]2 (1) and Fe(BTA)3 (2) (BTA = 4,4,4-trifluoro-1-phenyl-2,4-butanedione) are reported. Compound (1) is a molecular dimer in which Fe(III) ions are coordinated to two BTA ligands and bridged by two methoxide anions, while compound (2) is a trischelated Fe(III) monomer. Magnetic measurements revealed antiferromagnetic interactions in both compounds. In (1) the magnetic coupling is intramolecular, whereas in (2) it occurs via intermolecular interactions as a result of π–π stacking between the phenyl rings. DFT calculations using the broken symmetry approach were carried out to obtain the theoretical coupling constant value for both compounds and to rationalize the pathway for magnetic interactions in (2).Graphical abstractHighlights► Compounds with different nuclearities were obtained depending on the order of the reagent addition. ► Intermolecular π–π stacking plays a key role to the magnetic behavior of the mononuclear compound. ► DFT calculations rationalize the pathway for the magnetic interactions.
Co-reporter:Maria G. F. Vaz ; Rafael A. Allão ; Handan Akpinar ; John A. Schlueter ; Sauli Santos ; Jr.; Paul M. Lahti ;Miguel A. Novak
Inorganic Chemistry 2012 Volume 51(Issue 5) pp:3138-3145
Publication Date(Web):February 22, 2012
DOI:10.1021/ic202623p
2-(1′-Pyrenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (PyrNN) was reacted with M(hfac)2 (M = Mn(II) and Co(II), hfac = hexafluoracetylacetonate) to give two isostructural ML2 stoichiometry M(hfac)2(PyrNN)2 complexes and a ML stoichiometry one-dimensional (1-D) polymer chain complex [Mn(hfac)2(PyrNN)]. The ML2 complexes have similar crystal structures with monoclinic unit cells, in which one NO unit from each PyrNN ligand is bonded to the transition metal on cis vertices of a distorted octahedron. The major magnetic interactions are intracomplex metal-to-radical exchange (J), and intermolecular exchange across a close contact between the uncoordinated NO units (J′). For M = Mn(II) an approximate chain model fit gives g = 2.0, J = (−)125 cm–1 and J′ = (−)49 cm–1; for M = Co(II), g = 2.4, J = (−)180 cm–1, and J′ = (−)70 cm–1. Hybrid density functional theory (DFT) computations modeling the intermolecular exchange by using only the radical units across the close contact are in good accord with the estimated values of J′. The chain type complex structure shows solvent incorporation for overall structure [Mn(hfac)2(PyrNN)]n·0.5(CHCl3)·0.5(C7H16). Both NO groups of the PyrNN ligand are complexed to form helical chains, with very strong metal to radical antiferromagnetic exchange that gives overall ferrimagnetic behavior.
Co-reporter:Guilherme P. Guedes;Stéphane Soriano;Nadia M. Comerlato;Nivaldo L. Speziali;Paul M. Lahti;Miguel A. Novak;Maria G. F. Vaz
European Journal of Inorganic Chemistry 2012 Volume 2012( Issue 34) pp:5642-5648
Publication Date(Web):
DOI:10.1002/ejic.201200615
Abstract
The synthesis and the structural and magnetic characterization of two new cobalt(II) compounds [Co4(TTA)4(OMe)4(EtOH)4] (1) and [Co4(TTA)4(OMe)4(MeOH)4] (2) (TTA = 4,4,4-trifluoro-1-thienoyl-2,4-butanedione) are reported. The structures consist of a tetranuclear Co4O4 core in a cubane framework. Both systems were modeled by a spin Hamiltonian with two isotropic exchange interactions and local orthogonal anisotropy axis configuration. The temperature-dependent susceptibility was successfully simulated yielding many low-lying mixed eingenstates that cannot be approximated by a giant spin model. A surprising fact is that despite the structural similarities there are striking differences between their magnetic properties. DC magnetic susceptibilities showed only ferromagnetic interactions between cobalt(II) ions for 2, whereas 1 has ferromagnetic and weaker antiferromagnetic interactions among their ions. In addition, compound 1 presented split zero-field-cooled and field-cooled susceptibility around 6 K and a frequency dependent ac susceptibility typical of slow magnetization not observed in 2. The temperature dependence of this relaxation is similar to what is observed for cluster-glass systems and may be related to a complex process involving many low-level mixed states.
Co-reporter:Guilherme P. Guedes, Rafael G. Zorzanelli, Nadia M. Comerlato, Nivaldo L. Speziali, Sauli Santos-Jr, Maria G.F. Vaz
Inorganic Chemistry Communications 2012 Volume 23() pp:59-62
Publication Date(Web):September 2012
DOI:10.1016/j.inoche.2012.06.006
Two copper(II) compounds with pyridyl substituted nitronyl nitroxide radicals were synthesized and magnetically characterized: [Cu(FOD)2(NITpPy)] (1) and [Cu(FOD)2(NIToPy)] (2) (FOD = 1,1,1,2,2,3,3-heptafluoro-7,7-dimethyloctane-4,6-dione, NITpPy = 4-pyridyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide and NIToPy = 2-pyridyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide). The crystal structures of both compounds were solved and showed that (1) is the first magnetic dimer in which the NITpPy radical is coordinated to a [Cu(β-diketonate)2] building block only by the pyridinic nitrogen atom, whereas in (2) the NIToPy radical is coordinated to metal ion through nitroxide and pyridyl groups. The magnetic coupling between the spin carriers in compound (1) is of antiferromagnetic nature while in (2) is ferromagnetic.[Cu(FOD)2NITpPy] (1) is the first dimer in which the NITpPy radical is coordinating the metal through the pyridinic nitrogen, whereas for [Cu(FOD)2(NIToPy)] (2) both nitroxide and pyridinic nitrogen are bonded to Cu(II). Magnetic coupling between copper(II) ion and NITpPy in (1) is of antiferromagnetic whereas in (2) is ferromagnetic.Highlights► Crystal structure of two pyridyl nitronyl substituted nitroxide copper(II) complexes. ► Bulky groups in the β-diketonate ligand ► Two coordination modes of the pyridyl substituted nitronyl nitroxide radical to copper(II) ion. ► Antiferro- and ferromagnetic interactions between copper(II) and organic radical
Co-reporter:Igor F. Santos, Guilherme P. Guedes, Luiza A. Mercante, Alice M.R. Bernardino, Maria G.F. Vaz
Journal of Molecular Structure 2012 1011() pp: 99-104
Publication Date(Web):
DOI:10.1016/j.molstruc.2011.12.036
Co-reporter:R. A. Allão, A. K. Jordão, J. A. L. C. Resende, A. C. Cunha, V. F. Ferreira, M. A. Novak, C. Sangregorio, L. Sorace and M. G. F. Vaz
Dalton Transactions 2011 vol. 40(Issue 41) pp:10843-10850
Publication Date(Web):23 Aug 2011
DOI:10.1039/C1DT10780A
A new one-dimensional copper(II) complex with formula [Cu(hfac)2(N3TEMPO)]n (hfac = hexafluoroacetylacetonate and N3TEMPO = 4-azido-2,2,6,6-tetramethylpiperidine-1-oxyl) has been synthesized and investigated by X-ray crystallography, magnetometry and multifrequency single crystal EPR. The system crystallizes in the P space group with two non equivalent copper(II) ions in the unit cell, the two nitroxide radicals being coordinated to Cu(1) in axial positions. The copper(II) ions are bridged by N3TEMPO radicals resulting in a zig-zag chain structure. The magnetic susceptibility data were at first satisfactorily modeled assuming an alternating spin chain along the monodimensional covalent skeleton, with a ferromagnetic interaction between Cu(1) and the nitroxide moieties and a weaker antiferromagnetic interaction between these and Cu(2) (J1 = −13.8 cm−1, J2 = +2.4 cm−1). However, single crystal EPR studies performed at the X- and W-band clearly demonstrate that the observed magnetic monodimensional character of the complex is actually due to the intermolecular contacts involving N3TEMPO ligands. This prompted us to fit the magnetic data using a consistent model, pointing out the fundamental role of single crystal EPR data in defining a correct model to describe the magnetic properties of molecular low dimensional systems.
Co-reporter:Guilherme P. Guedes, Fernanda F. Farias, Miguel A. Novak, Fernando L. de A. Machado, Maria G.F. Vaz
Inorganica Chimica Acta 2011 Volume 378(Issue 1) pp:134-139
Publication Date(Web):30 November 2011
DOI:10.1016/j.ica.2011.08.035
In this work we present the synthesis, crystal structure, magnetic and specific heat measurements of a new monomeric copper(II) compound, in which the metal ion is coordinated to two p-aminobenzoic acid (PABA) molecules and two chloride ions. This compound with formula [CuCl2(C7H7NO2)2] presents a peculiar crystalline structure packing, showing hydrogen-bonds between carboxylic acid groups and short N–H⋯Cl contacts resulting in a polymeric character in two dimensions. In the third direction, Cu⋯Cl close contacts between neighboring molecules are responsible for a chain-like magnetic behavior. Considering the simplicity of the molecular unit, the magnetic properties show surprising results: below 6.4 K a hysteresis cycle appears in the magnetization curves as well as a splitting between low field ZFC–FC measurements. No phase transition to a long-range order was observed by specific heat measurement.Graphical abstractA new copper(II) complex with p-aminobenzoic acid was synthesized. In the crystalline structure, a network of H-bonds and short N–H⋯Cl contacts lead to a polymeric character in two dimensions. The magnetic properties show surprising results: below 6.4 K a hysteresis cycle appears in the magnetization curve.Highlights► Monomeric copper(II) complex with p-aminobenzoic acid. ► Short contacts N–H⋯Cl give rise to ferromagnetic interactions. ► The compound presents ZFC–FC splitting and hysteresis. ► No long range order was observed in specific heat measurement.
Co-reporter:Denise A. Souza, Yanko Moreno, Eduardo A. Ponzio, Jackson A.L.C. Resende, Alessandro K. Jordão, Anna C. Cunha, Vitor F. Ferreira, Miguel A. Novak, Maria G.F. Vaz
Inorganica Chimica Acta 2011 370(1) pp: 469-473
Publication Date(Web):
DOI:10.1016/j.ica.2011.02.026
Co-reporter:Denise A. Souza, Antonio S. Florencio, Stéphane Soriano, Rafael Calvo, Rosana P. Sartoris, José Walkimar de M. Carneiro, Claudio Sangregorio, Miguel A. Novak and Maria G. F. Vaz
Dalton Transactions 2009 (Issue 34) pp:6816-6824
Publication Date(Web):15 Jul 2009
DOI:10.1039/B902967B
The novel chain compound [Cu(Phtfac)2(NITpPy)]n (where NITpPy = 4-pyridyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide and Phtfac = 4,4,4-trifluoro-1-phenylbutane-1,3-dione) was synthesized and characterized structurally, magnetically and by EPR. The compound contains two non equivalent Cu(II) ions, Cu1 and Cu2, located at inversion centers and bridged by a NITpPy ligand coordinating Cu1 through the pyridine donor atom, and Cu2 through a N–O group, resulting in a head-to-head chain structure. The chain exhibits an unusual spin topology with two alternating pairs of magnetic coupling constants. The magnetic behavior was modeled considering a 16-membered ring with alternating exchange couplings. The best fit parameters indicate a ferromagnetic (J1 = 29.4 cm−1), and antiferromagnetic (J2 = −4.6 cm−1) couplings and an average g = 2.05, corresponding to a ground state with three parallel and one anti-parallel spin for each Cu2NITpPy2 unit. DFT calculations allowed assigning the ferromagnetic coupling to Cu-O-NITpPy and the antiferromagnetic coupling to Cu-NPy-NITpPy. Single crystal EPR spectra display only one resonance for most field orientations, as a consequence of the collapse of the signals of the different spins produced by the exchange interactions. The observed g-tensor of this resonance is related to those expected for the Cu(II) and radical ions. Comparison of this compound with other Cu-NIT radicals chains bearing different substituents in the organic radicals, highlights that the β-diketonate ligand plays an important role in determining the final architecture. Moreover, we show how a knowledge of the spin density distribution in the initial building blocks is essential to rationalize the magnetic behavior of the resulting product.
Co-reporter:Rafael A. Allão, Jackeline S. Martins, Antonio S. Florencio, Guilherme P. Guedes, José Walkimar de M. Carneiro, Mauricio Lanznaster, Sauli Santos Jr, Maria G.F. Vaz
Polyhedron 2009 28(9–10) pp: 2026-2028
Publication Date(Web):
DOI:10.1016/j.poly.2008.12.021
Co-reporter:Denise A. Souza, Antonio S. Florencio, José Walkimar de M. Carneiro, Stéphane S. Soriano, Carlos B. Pinheiro, Miguel A. Novak, Maria G.F. Vaz
Inorganica Chimica Acta 2008 Volume 361(14–15) pp:4024-4030
Publication Date(Web):1 October 2008
DOI:10.1016/j.ica.2008.03.043
Two new magnetic compounds were obtained by using β-diketonate 1,3-butanedione, 4,4,4-trifluoro-1-phenyl (Phtfac) as ligand. The complexes with formula [M(Phtfac)2(NITpPy)2 [M = Co(II) 1, Mn(II) 2; NITpPy = 4-pyridyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide] were characterized structurally and magnetically. Both structures consist of [M(II)(Phtfac)2(NITpPy)2] units, where the metal ion is in an octahedral environment bound to two NITpPy through the nitrogen atom of the pyridine ring. Compound 1 is the first case where a nitronyl nitroxide radical is coordinated to cobalt linked by the β-diketonate by the nitrogen atom of the pyridine ring. The magnetic behavior of this compound indicates that the cobalt ion and the NITpPy ligand are antiferromagnetically coupled with a coupling constant of −4.3 cm−1. The manganese derivative shows a ferromagnetic behavior with a coupling constant of 3.0 cm−1. The discussion of the electronic structure based on DFT calculations allows the rationalization of the ferromagnetic behavior.Synthesis and characterization of the compounds [M(II)(Phtfac)2(NITpPy)2], where M = Co(II) and Mn(II), were described. The use of the group Phtfac allows to modulation the acidity of the cobalt ion leading to the coordination of the NITpPy by the nitrogen atom of the pyridine ring. DFT electronic calculations were used to rationalize the observed magnetic behavior of the manganese derivative.
Co-reporter:A.M. Gomes, M.A. Novak, W.C. Nunes, R.E. Rapp
Inorganica Chimica Acta 2008 Volume 361(14–15) pp:3975-3979
Publication Date(Web):1 October 2008
DOI:10.1016/j.ica.2008.03.032
We present low temperature specific heat and ac-susceptibility measurements of Fe8 powdered sample. Below 1.3 K, super-paramagnetic blocking effects and an excess specific heat contribution are observed. The latter is attributed to a splitting of the ground state doublet in an inhomogeneous local field of hyperfine and dipolar origin. The local field contributions are evident at the resonances observed in the field dependent ac-susceptibility and specific heat below 0.5 K. The low temperature Schottky contribution is in agreement with known crystal field parameters of effective spin Hamiltonians proposed to simulate EPR and inelastic neutron scattering experiments.Low temperature specific heat of Fe8 results are presented and explained as a low temperature Schottky contribution, splitting of the ground state doublet in the local field of hyper-fine and dipolar origin and superparamagnetic blocking effect.
Co-reporter:Andrei A. Patrascu, Sergiu Calancea, Matteo Briganti, Stéphane Soriano, Augustin M. Madalan, Rafael A. Allão Cassaro, Andrea Caneschi, Federico Totti, Maria G. F. Vaz and Marius Andruh
Chemical Communications 2017 - vol. 53(Issue 48) pp:NaN6507-6507
Publication Date(Web):2017/05/23
DOI:10.1039/C7CC03236F
End-off bicompartmental ligands bearing a nitronyl–nitroxide arm have been designed for synthesizing various heterospin molecular systems. These ligands can selectively interact with 3d and 4f metal ions, leading to 2p–4f, 2p–3d, and 2p–3d–4f complexes. The magnetic properties of the 2p–4f and 2p–3d–4f complexes have been investigated and rationalized by theoretical calculations.
Co-reporter:Denise A. Souza, Antonio S. Florencio, Stéphane Soriano, Rafael Calvo, Rosana P. Sartoris, José Walkimar de M. Carneiro, Claudio Sangregorio, Miguel A. Novak and Maria G. F. Vaz
Dalton Transactions 2009(Issue 34) pp:NaN6824-6824
Publication Date(Web):2009/07/15
DOI:10.1039/B902967B
The novel chain compound [Cu(Phtfac)2(NITpPy)]n (where NITpPy = 4-pyridyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide and Phtfac = 4,4,4-trifluoro-1-phenylbutane-1,3-dione) was synthesized and characterized structurally, magnetically and by EPR. The compound contains two non equivalent Cu(II) ions, Cu1 and Cu2, located at inversion centers and bridged by a NITpPy ligand coordinating Cu1 through the pyridine donor atom, and Cu2 through a N–O group, resulting in a head-to-head chain structure. The chain exhibits an unusual spin topology with two alternating pairs of magnetic coupling constants. The magnetic behavior was modeled considering a 16-membered ring with alternating exchange couplings. The best fit parameters indicate a ferromagnetic (J1 = 29.4 cm−1), and antiferromagnetic (J2 = −4.6 cm−1) couplings and an average g = 2.05, corresponding to a ground state with three parallel and one anti-parallel spin for each Cu2NITpPy2 unit. DFT calculations allowed assigning the ferromagnetic coupling to Cu-O-NITpPy and the antiferromagnetic coupling to Cu-NPy-NITpPy. Single crystal EPR spectra display only one resonance for most field orientations, as a consequence of the collapse of the signals of the different spins produced by the exchange interactions. The observed g-tensor of this resonance is related to those expected for the Cu(II) and radical ions. Comparison of this compound with other Cu-NIT radicals chains bearing different substituents in the organic radicals, highlights that the β-diketonate ligand plays an important role in determining the final architecture. Moreover, we show how a knowledge of the spin density distribution in the initial building blocks is essential to rationalize the magnetic behavior of the resulting product.
Co-reporter:R. A. Allão, A. K. Jordão, J. A. L. C. Resende, A. C. Cunha, V. F. Ferreira, M. A. Novak, C. Sangregorio, L. Sorace and M. G. F. Vaz
Dalton Transactions 2011 - vol. 40(Issue 41) pp:NaN10850-10850
Publication Date(Web):2011/08/23
DOI:10.1039/C1DT10780A
A new one-dimensional copper(II) complex with formula [Cu(hfac)2(N3TEMPO)]n (hfac = hexafluoroacetylacetonate and N3TEMPO = 4-azido-2,2,6,6-tetramethylpiperidine-1-oxyl) has been synthesized and investigated by X-ray crystallography, magnetometry and multifrequency single crystal EPR. The system crystallizes in the P space group with two non equivalent copper(II) ions in the unit cell, the two nitroxide radicals being coordinated to Cu(1) in axial positions. The copper(II) ions are bridged by N3TEMPO radicals resulting in a zig-zag chain structure. The magnetic susceptibility data were at first satisfactorily modeled assuming an alternating spin chain along the monodimensional covalent skeleton, with a ferromagnetic interaction between Cu(1) and the nitroxide moieties and a weaker antiferromagnetic interaction between these and Cu(2) (J1 = −13.8 cm−1, J2 = +2.4 cm−1). However, single crystal EPR studies performed at the X- and W-band clearly demonstrate that the observed magnetic monodimensional character of the complex is actually due to the intermolecular contacts involving N3TEMPO ligands. This prompted us to fit the magnetic data using a consistent model, pointing out the fundamental role of single crystal EPR data in defining a correct model to describe the magnetic properties of molecular low dimensional systems.
Co-reporter:Samira G. Reis, Matteo Briganti, Daniel O. T. A. Martins, Handan Akpinar, Sergiu Calancea, Guilherme P. Guedes, Stéphane Soriano, Marius Andruh, Rafael A. A. Cassaro, Paul M. Lahti, Federico Totti and Maria G. F. Vaz
Dalton Transactions 2016 - vol. 45(Issue 7) pp:NaN2944-2944
Publication Date(Web):2015/12/23
DOI:10.1039/C5DT04469C
The synthesis, crystal structures and magnetic properties of two families of heterospin complexes containing lanthanide ions and a bis(imino nitroxide) biradical (IPhIN = 1-iodo-3,5-bis(4′,4′,5′,5′-tetramethyl-4′,5′-dihydro-1H-imidazole-1′-oxyl)benzene) are reported: in [Ln2(hfac)6(IPhIN)(H2O)2] compounds, two lanthanide ions [Ln = GdIII (1) and DyIII (2)] are coordinated to the biradical, and in [Ln(hfac)3(IPhIN)(H2O)] compounds, one lanthanide ion (Ln = TbIII (3), GdIII (4) or DyIII (5)) is coordinated to the biradical. Ferromagnetic intramolecular magnetic interactions between GdIII and the biradical were found for 1 and 4, while intramolecular magnetic interactions between the radicals were ferro- and antiferromagnetic, respectively. Compound 2 shows a field induced slow relaxation of magnetization, which (under an external applied field of 2 kOe) exhibits an activation energy barrier of ΔE/kB = 27 K and a pre-exponential factor of 1.4 × 10−8 s. To support the magnetic characterization of compound 3ab initio calculations were also performed.
Co-reporter:Samira G. Reis, Miguel A. del Águila-Sánchez, Guilherme P. Guedes, Glaucio B. Ferreira, Miguel A. Novak, Nivaldo L. Speziali, Fernando López-Ortiz and Maria G. F. Vaz
Dalton Transactions 2014 - vol. 43(Issue 39) pp:NaN14901-14901
Publication Date(Web):2014/08/12
DOI:10.1039/C4DT01444H
In the present work we describe the synthesis, crystal structures and magnetic properties of four coordination compounds obtained by assembling a new phosphinic amide containing the TEMPO moiety, 1-piperidinyloxy-4-[(diphenylphosphinyl)amino]-2,2,6,6-tetramethyl radical (dppnTEMPO), with [M(hfac)2] building blocks (M = CuII, CoII, MnII). The crystal structures of the coordination compounds revealed the usefulness of the functionalized radical to provide discrete or extended architectures. In the copper compound (1) the ligand is coordinated through the oxygen atom of the NPO linkage to the metal, which exists in a square pyramidal or octahedral geometry. For the cobalt and manganese complexes (2–4), both the phosphinic amide and the nitroxide oxygen atoms are involved in the coordination to the metal leading to one dimensional systems. In the cobalt complex (2) an interesting spin topology in the zig-zag chain was obtained due to the oxygen atom of the phosphinic amide group being μ2 coordinated to two cobalt(II) ions. The magnetic behaviour of the coordination compounds shows overall antiferromagnetic interactions involving the metal ion and the organic radical. DFT calculations were performed in order to assign the main path for the magnetic interactions.
![N-[3-(hydroxyamino)-2,3-dimethyl-butan-2-yl]hydroxylamine](/data/chemimg/521200/14538-51-3.png)
![N-[3-(hydroxyamino)-2,3-dimethyl-butan-2-yl]hydroxylamine](/data/chemimg/521200/14538-51-3_b.png)
