Ferromagnetic Intermolecular Interactions Research Articles

Structural and Magnetic Analysis of a Family of Structurally Related Iron(III)-Oxo Clusters of Metal Nuclearity Fe8, Fe12Ca4, and Fe12La4

The synthesis, crystal structure, and magnetic characterization are reported for three new structurally related iron(III) compounds (NHEt3)[Fe8O5(OH)5(O2PPh2)10] (1), [Fe12 Ca4O10(O2CPh)10(hmp)4] (2), and [Fe12La4O10(OH)4(tbb)24] (3), where hmpH is 2-(hydroxymethyl)pyridine and tbbH is 4-tBu-benzoic acid. 1 was obtained from the reaction of Fe(NO3)3·9H2O, diphenylphosphinic acid (Ph2PO2H), and NEt3 in a 1:4:16 molar ratio in MeCN at 50 °C; 2 was obtained from the reaction of [Fe3O(O2CPh)6(H2O)3](NO3), Ca(NO3)2, and NEt3 in a 1:1:4:2 ratio at 130 °C; and 3 was obtained from the reaction of Fe(NO3)3·9H2O, La(NO3)3·6H2O, 4-tBu-benzoic acid, and NEt3 in a 1:1:4:4 ratio in PhCN at 140 °C. The core of 1 consists of two {Fe4(µ3-O)2}8+ butterfly units stacked on top of each other and bridged by O2− and HO− ions. The cores of 2 and 3 also contain two stacked butterfly units, plus four additional Fe atoms, two at each end, and four M atoms (M = Ca2+ (2); La3+ (3)) on the sides. Variable-temperature (T) and solid-state dc and ac magnetization (M) data collected in the 1.8–300 K range revealed that 1 has an S = 0 ground state, 2 has a χMT value at low T consistent with the central Fe8 in a local S = 0 ground state and the two Fe3+ ions in each end-pair to be non-interacting, whereas 3 has a χMT value at low T consistent with these end-pairs each being ferromagnetically coupled with S = 5 ground states, plus intermolecular ferromagnetic interactions. These conclusions were reached from complementing the experimental studies with the calculation of the various Fe2 pairwise Jij exchange couplings by DFT computations and by using a magnetostructural correlation (MSC) for polynuclear Fe3+/O complexes, as well as a structural analysis of the intermolecular contacts in the crystal packing of 3.

Air-Stable Dy(III)-Macrocycle Enantiomers: From Chiral to Polar Space Group

Air-Stable Dy(III)-Macrocycle Enantiomers: From Chiral to Polar Space Group

Magnetic and Structural Properties of Organic Radicals Based on Thienyl- and Furyl-Substituted Nitronyl Nitroxide

Magnetic properties of organic radicals based on thienyl- and furyl-substituted nitronyl nitroxide (NN) and iminonitroxide (IN) were investigated by measuring the temperature dependence of the magnetization. The magnetic behavior of 2-benzo[b]thienyl NN (2-BTHNN) is interpreted in terms of the two-magnetic-dimer model, in which one dimer exhibits ferromagnetic (FM) intermolecular interaction and the other dimer shows antiferromagnetic (AFM) interaction. The existence of two dimers in 2-BTHNN is supported by crystal structure analysis. The magnetic behaviors of 2-bithienyl NN, 4-(2′-thienyl)phenyl NN (2-THPNN), 2- and 3-furyl NN, 2-benzo[b]furyl NN, and 3-benzo[b]thienyl IN are also reported. The one-dimensional alternating AFM nature observed in 2-THPNN is consistent with its crystal structure.

Cocrystals of Li+ encapsulated fullerenes and Tb(iii) double-decker single molecule magnet in a quasi-kagome lattice.

Cocrystallization of a lithium ion encapsulated fullerene Li+@C60 with a terbium(iii) phthalocyaninato porphyrinato double-decker single-molecule magnet [Tb(Pc)(OEP)] is reported. The cocrystal, containing PF6- as a counter anion, packs in a quasi-kagome lattice, which leads to intermolecular ferromagnetic interactions as well as the modulation of the single-molecule magnet (SMM) properties.

A Ferromagnetically Coupled, Bell-Shaped [Ni4Gd5] Cage.

Reaction between NiCl2·6H2O, 2-hydroxy-4-methyl-6-phenyl-pyridine-3-amidoxime (H2L), benzoic acid, and M(NO3)3·6H2O (M = Gd, Y) in MeCN under basic conditions yields the complexes [NiII4GdIII5(PhCOO)10(HL)4(HLzw)4(OH)2(NO3)2]Cl·13.6MeCN·H2O (1·13.6MeCN·H2O) and [NiII4YIII5(PhCOO)10(HL)4(HLzw)4(OH)2(NO3)1.5(H2O)0.5]0.5Cl(NO3)·3H2O (2·3H2O). Both clusters display similar structures, consisting of a bell-shaped {NiII4MIII5} unit, in which a linear "zigzag" {Ni4} subunit bisects the central {MIII5} "ring". Direct (dc) and alternating current (ac) magnetic susceptibility measurements carried out in the 2-300 K temperature range for complexes 1 and 2 revealed ferromagnetic intermolecular interactions, while heat-capacity measurements for the Gd analogue suggest that complex 1 lowers its temperature from T = 9.6 K down to 2.3 K by adiabatically demagnetizing from Bi = 7 T to Bf = 0.

Exploring orientationally aligned anisotropic large spin molecules with unusual long-distance intermolecular ferromagnetic interactions

Orientationally aligned anisotropic large-spin polyoxometalate clusters exhibited unusual long-distance intermolecular ferromagnetic interactions below 35 K under a small magnetic field.

Novel P,P-diphenylphosphinic amide-TEMPO radicals family: Synthesis, crystal structures, spectroscopic characterization, magnetic properties and DFT calculations

A new family of three P,P-diphenylphosphinic amide-TEMPO radicals with general formula (C6H5)2P(X)-NH-TEMPO, X = O (1), S (2) and Se (3) were obtained by reaction of chlorodiphenylphosphine with 4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl radical (NH2-TEMPO) and subsequent oxidation with H2O2 and elemental sulfur or selenium. These radicals were characterized by UV–Vis, FT-IR and 1H, 31P and 77Se nuclear magnetic resonance spectroscopy. The crystal structures of all radicals were determined by single-crystal X-ray diffraction. The magnetic study of all diphenylphosphinic amide-TEMPO radicals reveals very weak intermolecular ferromagnetic interactions. Density functional theory (DFT) calculations have been also performed to support the interpretation of magnetic properties and electronic structure.

Tyrosinase and catecholase-like activities of a dinuclear Cu(II) complex

A dinuclear Cu(II) complex was synthesized and crystallographically characterized. The compound was found to have antiferromagnetic interaction in between the Cu(II) centres in the molecule. It had weak intermolecular ferromagnetic interaction. The compound was found to be tyrosinase and catecholase active. In case of tyrosinase activity, the diphenol formed was isolated using thin layer chromatography (TLC) and characterized through 1H NMR as well as mass spectrometry. The o-quinone derivative formed in this reaction was characterized using GC–MS. The latter activity was monitored spectrophotometrically and the product o-quinone derivative was isolated (in MeOH and MeCN) column chromatographically and characterized using melting point determination. These were followed by Michealis–Menten kinetics with turnover numbers 4.95 × 103 and 1.58 × 103 h−1 in MeOH and MeCN, respectively.

Ferromagnetic Coupling in the Heterospin Bis-Catecholato-Manganese(IV) Complex with Pyridine Substituted by Nitronyl-nitroxide.

A new bis(3,6-di-tert-butyl-catecholato)manganese complex with two 4-NIT-Py ligands was synthesized and characterized [4-NIT-Py = pyridine substituted at position 4 with nitronyl-nitroxide radical, 2-(pyridin-4-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl]. X-ray diffraction indicated an octahedral environment of the manganese atom with a trans arrangement of ligands. Bonds lengths in the inner coordination core of the metal and in the chelate cycles that are representative of the charge distribution between the metal and ligands displayed a Mn(IV)(Cat2-)2 charge distribution. Variable-temperature magnetic susceptibility measurements detected intramolecular ferromagnetic coupling between the Mn(IV) S = 3/2 spins and spins of nitronyl-nitroxyls and intermolecular ferromagnetic interactions of spins of adjacent nitronyl-nitroxide fragments in a chain of molecules at low temperatures. The last phenomenon is revealed by short contacts between nitronyl-nitroxide radicals of adjacent complex molecules.

Specific features of spin-variable properties of [Fe(acen)pic2]BPh4 · nH2O

The [Fe(acen)pic2]BPh4 · nH2O compound has been synthesized and studied in the temperature interval of 5–300 K by the methods of EPR and magnetic susceptibility. The existence of ferromagnetic interactions between Fe(III) complexes in this compound has been revealed, in contrast to unhydrated [Fe(acen)pic2]BPh4. The reduction in the integrated intensity of the magnetic resonance signal as the temperature decreases below 80 K has been explained by the transition of high-spin ions to the low-spin state. It has been shown that the phase transition temperature in the presence of intermolecular (ferromagnetic) interactions is lower than that in the case of noninteracting centers.

Trinuclear CuIIStructural Isomers: Coordination, Magnetism, Electrochemistry and Catalytic Activity towards the Oxidation of Alkanes

AbstractThe reaction of the Schiff base (3,5‐di‐tert‐butyl‐2‐hydroxybenzylidene)‐2‐hydroxybenzohydrazide (H3L) with copper(II) nitrate, acetate or metaborate has led to the isomeric complexes [Cu3(L)2(MeOH)4] (1), [Cu3(L)2(MeOH)2]·2MeOH (2) and [Cu3(L)2(MeOH)4] (3), respectively, in which the ligand L exhibits dianionic (HL2–, in1) or trianionic (L3–, in2and3) pentadentate 1κO,O′,N:2κN′,O″chelation modes. Complexes1–3were characterized by elemental analysis, IR spectroscopy, single‐crystal X‐ray crystallography, electrochemical methods and variable‐temperature magnetic susceptibility measurements, which indicated that the intratrimer antiferromagnetic coupling is strong in the three complexes and that there exists very weak ferromagnetic intermolecular interactions in1but weak antiferromagnetic intermolecular interactions in both2and3. Electrochemical experiments showed that in complexes1–3the CuIIions can be reduced, in distinct steps, to CuIand Cu0. All the complexes act as efficient catalyst precursors under mild conditions for the peroxidative oxidation of cyclohexane to cyclohexyl hydroperoxide, cyclohexanol and cyclohexanone, leading to overall yields (based on the alkane) of up to 31 % (TON = 1.55 × 103) after 6 h in the presence of pyrazinecarboxylic acid.

Unsymmetrical Chelation of N-Thioether-Functionalized Bis(diphenylphosphino)amine-Type Ligands and Substituent Effects on the Nuclearity of Iron(II) Complexes: Structures, Magnetism, and Bonding.

Starting from the short-bite ligands N-thioether-functionalized bis(diphenylphosphino)amine-type (Ph2P)2N(CH2)3SMe (1) and (Ph2P)2N(p-C6H4)SMe (2), the Fe(II) complexes [FeCl2(1)]n (3), [FeCl2(2)]2 (4), [Fe(OAc)(1)2]PF6 (5), and [Fe(OAc)(2)2]PF6 (6) were synthesized and characterized by Fourier transform IR, mass spectrometry, elemental analysis, and also by X-ray diffraction for 3, 4, and 6. Complex 3 is a coordination polymer in which 1 acts as a P,P-pseudochelate and a (P,P),S-bridge, whereas 4 has a chlorido-bridged dinuclear structure in which 2 acts only as a P,P-pseudochelate. Since these complexes were obtained under strictly similar synthetic and crystallization conditions, these unexpected differences were ascribed to the different spacer between the nitrogen atom and the −SMe group. In both compounds, one Fe–P bond was found to be unusually long, and a theoretical analysis was performed to unravel the electronic or steric reasons for this difference. Density functional theory calculations were performed for a set of complexes of general formula [FeCl2(SR2){R21PN(R2)P′R23}] (R = H, Me; R1, R2, and R3 = H, Me, Ph), to understand the reasons for the significant deviation of the iron coordination sphere away from tetrahedral as well as from trigonal bipyramidal and the varying degree of unsymmetry of the two Fe–P bonds involving pseudochelating PN(R)P ligands. Electronic factors nicely explain the observed structures, and steric reasons were further ruled out by the structural analysis in the solid-state of the bis-chelated complex 6, which displays usual and equivalent Fe–P bond lengths. Magnetic susceptibility studies were performed to examine how the structural differences between 3 and 4 would affect the interactions between the iron centers, and it was concluded that 3 behaves as an isolated high-spin Fe(II) mononuclear complex, while significant intra- and intermolecular ferromagnetic interactions were evidenced for 4 at low temperatures. Complexes 3 and 4 were also tested in catalytic ethylene oligomerization but did not exhibit any significant activity under the studied conditions.

Solid-state transition metal chemistry with imidazol-2-yl-methyl[N-(n-butyl)amino]-diphenylphosphine oxide (2-izmape). Crystal structure of the [Cu(2-izmape)2](ClO4)2 complex

The complexes of general formula [Cu(2-izmape)2](ClO4)2, [M(2-izmape)2(ClO4)2], M=Ni and Co, with imidazol-2-yl-methyl[N-(n-butyl)amino]-diphenylphosphine oxide (2-izmape) ligand have been synthesized and characterized. In particular, the crystal structure of copper complex has been determined. The complexes have been characterized by infrared, ligand field spectra and magnetic measurements. These mononuclear complexes are 4+2 coordinated (Cu) and 6-coordinated (Ni and Co). The ligand acts as N,N,O′-chelate (Cu) and N,N-chelate (Ni, Co). The results of the magnetic studies of complexes in the range of 1.8–300K indicate the copper centers are magnetically isolated. For Ni and Co complexes a very weak intermolecular ferromagnetic interaction is suggested. The magnetic behavior of cobalt and nickel complexes indicates an important orbital contribution in magnetic properties via spin-orbit.

A computational perspective on magnetic coupling, magneto-structural correlations and magneto-caloric effect of a ferromagnetically coupled {GdIII–GdIII} Pair

Density functional calculations have been performed on a dinuclear {GdIII–GdIII} complex [{Gd(OAc)3(H2O)2}2]·4H2O (1) which has recently been reported to have a very large MCE [M. Evangelisti, O. Roubeau, E. Palacios, A. Camon, T.N. Hooper, E.K. Brechin, J.J. Alonso, Angew. Chem., Int. Ed. 50 (2011) 6606]. The focus here is (i) to asses a suitable functional within DFT framework to compute good numerical estimate of J values (ii) to probe the mechanism of coupling between the two GdIII ions via computational means (iii) to develop magneto-structural correlations to relate the sign and strength of J to specific structural parameter and (iv) to conceive the origin of large magneto-caloric effect (MCE) observed. Testing a series of functionals and a set of basis sets, it is evident that the hybrid B3LYP functional behaves marginally well over others with a combination of SARC basis set incorporating ZORA (zeroth-order regular approximation) relativistic effect for the GdIII ions. The MO and NBO tools have been utilized to probe the mechanism of coupling and this reveals that there are two contributions. The first is charge transfer in nature leading to a ferromagnetic contribution due to the involvement of empty 6s/5d/6p orbitals of GdIII ions and the second contribution is due to 4f–4f orbital overlap and this adds to both ferro and antiferromagnetic part of the exchange. In 1, the ferromagnetic contribution prevails over the other leading to a net ferromagnetic J. The developed magneto-structural correlations reveal that the Gd–O–Gd angle is an important parameter as it switches the coupling from ferro to antiferro at lower angles. A weak intermolecular ferromagnetic interaction mediating via H-bonding interaction results in a ferromagnetic interaction at low temperatures and hence a large MCE.

Hydrothermal synthesis, structures, luminescence and magnetic properties of Zn(II) and Cu(II) complexes with new hydrazone ligand

Abstract Two new complexes [Zn(HL)2(py)2] (1) and [Cu(HL)]2 (2) have been synthesised from a bidentate Schiff base ligand HL (benzylidene acetophenone benzoyl hydrazone). The crystal structures of complex 1 and complex 2 were determined by single-crystal X-ray diffraction. The data indicate that: the complex 1 crystallizes in the monoclinic space group P2(1)/n, with a (nm) = 1.35816(8), b (nm) = 2.39486(13), c (nm) = 1.41368(8), α (°) = 90, β (°) = 96.0840(10), γ (°) = 90, Z = 4. The complex 2 crystallizes in the triclinic space group P−1, with a (nm) = 1.02483(8), b (nm) = 1.35797(11), c (nm) = 1.38271(11), α (°) = 71.5020(10), β (°) = 78.5850(10), γ (°) = 74.3110(10), Z = 1. Moreover, the unsaturated coordination site of metal ion is occupied by secondary ligand of pyridine. The mononuclear units in 1 and 2 are packed through weak C H⋯π and π–π interactions respectively. The results of analytical, IR and TG analysis studies are presented in this paper. Both the ligand and complex 1 show fluorescence in DMF solutions at room temperature. The complex 2 variable-temperature (300–1.8 K) magnetic test show that there is ferromagnetic intramolecular interaction and weak antiferromagnetic intermolecular interaction.

Theoretical Study of Magnetic Properties of Oxovanadium(IV) Complex Self-Assemblies with Tetradentate Schiff Base Ligands

The theoretical study of the magnetic properties of oxovanadium(IV) complex self-assemblies with tetradentate Schiff base ligands is discussed on the basis of DFT calculations. Large negative spin densities are found on the axial oxygens of the various oxovanadium(IV) complexes. The relationship between the effective exchange parameters J(ab) and the geometrical parameters for these complexes was studied by changing the position of the neighboring molecules for the purpose of clarifying the mechanism of the ferromagnetic coupling. The intermolecular ferromagnetic interaction of the oxovanadium(IV) complexes with tetradentate Schiff base ligands is significantly affected by the formation of polymeric octahedral structures in the solid state. The overlap between the 2p orbitals of the axial oxygen and the 3d orbitals of the adjacent vanadium is effective for the ferromagnetic coupling. On the other hand, the effect of overlap between the vanadium 3d(xy) orbitals is too small to lead to magnetic coupling. It was revealed that the intermolecular ferromagnetic interaction of the polynuclear oxovanadium(IV) complexes is significantly affected by the spin polarization on the axial oxygen.

A New Family of 1D Exchange Biased Heterometal Single-Molecule Magnets: Observation of Pronounced Quantum Tunneling Steps in the Hysteresis Loops of Quasi-Linear {Mn2Ni3} Clusters

First members of a new family of heterometallic Mn/Ni complexes [Mn(2)Ni(3)X(2)L(4)(LH)(2)(H(2)O)(2)] (X = Cl: 1; X = Br: 2) with the new ligand 2-{3-(2-hydroxyphenyl)-1H-pyrazol-1-yl}ethanol (H(2)L) have been synthesized, and single crystals obtained from CH(2)Cl(2) solutions have been characterized crystallographically. The molecular structures feature a quasi-linear Mn(III)-Ni(II)-Ni(II)-Ni(II)-Mn(III) core with six-coordinate metal ions, where elongated axes of all the distorted octahedral coordination polyhedra are aligned parallel and are fixed with respect to each other by intramolecular hydrogen bonds. 1 and 2 exhibit quite strong ferromagnetic exchange interactions throughout (J(Mn-Ni) ≈ 40 K (1) or 42 K (2); J(Ni-Ni) ≈ 22 K (1) or 18 K (2)) that lead to an S(tot) = 7 ground state, and a sizable uniaxial magnetoanisotropy with D(mol) values -0.55 K (1) and -0.45 K (2). These values are directly derived also from frequency- and temperature-dependent high-field EPR spectra. Slow relaxation of the magnetization at low temperatures and single-molecule magnet (SMM) behavior are evident from frequency-dependent peaks in the out-of-phase ac susceptibilities and magnetization versus dc field measurements, with significant energy barriers to spin reversal U(eff) = 27 K (1) and 22 K (2). Pronounced quantum tunnelling steps are observed in the hysteresis loops of the temperature- and scan rate-dependent magnetization data, but with the first relaxation step shifted above (1) or below (2) the zero crossing of the magnetic field, despite the very similar molecular structures. The different behavior of 1 and 2 is interpreted in terms of antiferromagnetic (1) or ferromagnetic (2) intermolecular interactions, which are discussed in view of the subtle differences of intermolecular contacts within the crystal lattice.

ChemInform Abstract: Synthesis and Magnetic Behavior of Paramagnetic Phosphorus-Containing Ligands and Their Metal Complexes

Abstract The synthesis of new paramagnetic phosphorus-containing compounds, (para-RAD-phenyl)diphenylphosphine and phosphine oxide (RAD = nitronylnitroxide. tBuNO), is described. Complexation of these phosphines with diamagnetic metal centres yields, for example, intermolecular ferromagnetic interactions with {Mo(CO)5(phosphine)}, antiferromagnetic interactions with {AuCl(phosphine)} and {PdCl2(phosphine)2}, a complex with multiple paramagnetic ligands. Ligation of nitronylnitroxide-containing phosphines to paramagnetic metals is hindered by catalytic nitrogen to phosphorus oxo-transfer to form the corresponding iminonitroxide-substituted phosphine oxide. A molecular square containing two nitronylnitroxide-substituted phosphine oxide ligands and two Mn(hfac)2 units is also described.

Coordination compounds of tetrazolate-5-carboxylate with cobalt(II): Synthesis, structure and magnetic properties

Four coordination compounds of tetrazolate-5-carboxylate (tzc) with cobalt(II), [Co 2(tzc) 2(H 2O) 6]·2H 2O ( 1), [Co 2(tzc) 2(phen) 2(H 2O) 2]·2H 2O ( 2), [Co 2(tzc) 2(2,2′-bpy) 2(H 2O) 2]·H 2O ( 3), and [Co(tzc)(4,4′-bpy)] ( 4), where phen = 1,10-phenanthroline, 2,2′-bpy = 2,2′-bipyridyl, and 4,4′-bpy = 4,4′-bipyridyl, have been synthesized by the hydrothermal methods involving the in situ generation of the ligand from sodium ethyl tetrazolate-5-carboxylate. Compounds 1, 2 and 3 all contain dinuclear molecules in which metal ions are linked by the double N–N bridges from two tzc ligands in the μ 2-N 1,O 1:N 2 mode, and the dinuclear molecules are associated into 3D architecture through extensive hydrogen bonding and π–π stacking interactions in various fashions. Compound 4 exhibits a two-dimensional layer structure in which Co(tzc) chains with μ 3-N 1,O 1:O 1:N 2 tzc are cross-linked by 4,4′-bpy. Magnetic investigations on 1– 3 revealed intramolecular ferromagnetic coupling through the double N–N bridges with intermolecular ferromagnetic or antiferromagnetic interactions. The interaction through the mixed N–N and μ 2-O carboxylate bridges in 4 is antiferromagnetic.

Unprecedented formation of binuclear copper(II) complex with a perylene derived ligand by the oxidative reaction

A new perylene-pendent tridentate ligand, N-(3-perylenylmethyl)- N, N-bis(2-pyridylmethyl)amine (perbpa) 1 and its Cu(II) complex, [Cu(perbpa)Cl 2] ( 2) were prepared and structurally characterized by the X-ray diffraction method. In the packing structure of ligand 1, perylene groups were aggregated to form a π–π stacked layer of dimerized pelylene moieties similar to the packing of pristine perylene. This result suggests both that the π–π interactions among the perylene moieties predominate for the arrangement of perbpa molecules in the crystal and that this ligand is a good candidate for constructing electron conducting path. A complex 2 was prepared from the ligand 1 and a copper(II) chloride dehydrate. Complex 2 had a mononuclear and 5-coordinate distorted square pyramidal structure with a perbpa and two coordinated chloride ions. The chemical oxidation of 2 by iodine resulted in the unprecedented binuclear Cu(II) species, [Cu 2( μ-Cl) 2(perbpa) 2](I 3) 2, 3·(I 3) 2. An X-ray crystal structure analysis of 3·(I 3) 2 revealed the binuclear structure bridged by the chloride ions. A temperature dependent magnetic susceptibility measurement of 3 showed a weak ferromagnetic exchange interaction with S = 1 ground state, g = 2.12 and J = +1.17 cm −1, based on H = −2 J S 1 · S 2 . The UV–Vis absorption and the EPR spectra of 3 showed that the perylene groups are not oxidized. These results indicate a couple of Cu(II) constructed S = 1 ground state with intermolecular ferromagnetic interaction. The electrochemical study suggested that the crystallization of 3·(I 3) 2 was initiated by the oxidation of the N, N-bis-(2-pyridylmethyl)amino (bpa) groups of 2 by I 2.