Crystal structure and magnetism of layered Ln2Ca2MnNiO8 (Ln=Pr,Nd, Sm,and Gd) compounds

We report the syntheses, crystal structure, and magnetic properties of a series of distorted K₂NiF₄-type oxides Ln₂Ca₂MnNiO₈ (Ln=Pr, Nd, Sm, and Gd) in which Ln/Ca and Mn/Ni atoms randomly occupy the K and Ni sites respectively. The Ln=La compound does not form. These compounds show systematic distortions from the ideal tetragonal K₂NiF₄ structure (space group I4/mmm) to an orthorhombic structure (space group Pccn) with buckled MO₂ (M=Mn/Ni) layers. The degree of distortion is increased as the size of Ln decreases. Based on the magnetic data and X-ray absorption near edge spectra, we assigned Mn^IV and Ni^II. The Curie–Weiss plots of the high temperature magnetic data suggest strong ferromagnetic interactions probably due to Mn^IV–O–Ni^II linkages, implying local ordering of Mn/Ni ions to form ferromangnetic clusters in the MO₂ layers. At low temperatures below 110–130 K, these compounds show antiferromagnetic behaviors because of Mn^IV–O–Mn^IV and/or Ni^II–O–Ni^II contacts between the ferromagnetic clusters. The Ln=Pr and Nd compounds show additional antiferromagnetic signals that we attribute to the interlayer interactions between the clusters mediated by the Pr³⁺ and Nd³⁺ ions in the interlayer spaces. The present compounds show many parallels with the previously reported Ln₂Sr₂MnNiO₈ compounds.     

Cyanido-bridged one-dimensional systems assembled from [ReIVCl4(CN)2]2? and [MII(cyclam)]2+ (M = Ni, Cu) precursors

Three new cyanido-bridged heterometallic Re^IVNi^II and Re^IVCu^II one-dimensional systems were synthesized and extensively characterized both structurally and magnetically. Single-crystal X-ray diffraction analysis revealed that these compounds display a common topology, with chains composed of alternating [Re^IVCl₄(CN)₂]^2? and [M^II(cyclam)]²⁺ (M = Ni in 1, Cu in 2) or [Cu^II(N,N??-dimethylcyclam)]²⁺ (in 3) building units. Two different chain orientations with a tilt angle of ca. 51° to 55° are present in the crystal packing of these compounds. The magnetic susceptibility measurements suggest the presence of intrachain ferromagnetic interactions between the S = 3/2 Re^IV centers and the 3d metal ions: S = 1 Ni^II or S = 1/2 Cu^II. At low temperature, a three-dimensional ordered magnetic phase induced by interchain antiferromagnetic interactions (antiferromagnetic for 1 and 2; canted antiferromagnetic for 3) is detected for the three compounds.     

Characterization of Mixed Crystals in the System Cu2MnxCo1−xGeS4 and Investigations of the Tetrahedra Volumes

In a series of investigations on normal tetrahedral compounds we present mixed crystals in the system Cu₂Mn_xCo_1?xGeS₄ (0 < x < 1) and an inspection of their tetrahedra volumes. Cu₂CoGeS₄ crystallizes tetragonal in a stannite type structure, Cu₂MnGeS₄ crystallizes orthorhombic in the wurtzstannite structure type. The crystal structures of Cu₂CoGeS₄ and Cu₂Mn_0.68Co_0.32GeS₄ were refined from single crystal diffraction data. The refinement of Cu₂CoGeS₄ converged to R = 0.0547 and wR2 = 0.0847 for 299 unique reflections. The refinement of Cu₂Mn_0.68Co_0.32GeS₄ converged to R = 0.0481 and wR2 = 0.0877 for 1556 unique reflections. From these data the tetrahedra volumes of the end members and of Cu₂Mn_0.68Co_0.32GeS₄ are calculated. In Cu₂CoGeS₄ tetrahedra [MS₄] are similar in size. In contrast, the differences of the volumes of the polyhedra [MS₄] in the orthorhombic wurtzite superstructure type compounds Cu₂MnGeS₄ and Cu₂Mn_0.68Co_0.32GeS₄ are significant (M = Cu, Mn, (Mn_0.68Co_0.32), Co, Ge). From x = 0 to x = 0.5 the tetragonal structure type dominates while from x = 0.7 to the Cu₂MnGeS₄ end member the products crystallize in the orthorhombic structure type. Melting points of the mixed crystals decrease linearly with increasing manganese content.     

Synthesis,Structures, and Properties of Crystalline Salts with Radical Anions of Metal‐Containing and Metal‐Free Phthalocyanines

Radical anion salts of metal‐containing and metal‐free phthalocyanines [MPc(3?)]^.?, where M=Cu^II, Ni^II, H₂, Sn^II, Pb^II, Ti^IVO, and V^IVO ( 1 – 10 ) with tetraalkylammonium cations have been obtained as single crystals by phthalocyanine reduction with sodium fluorenone ketyl. Their formation is accompanied by the Pc ligand reduction and affects the molecular structure of metal phthalocyanine radical anions as well as their optical and magnetic properties. Radical anions are characterized by the alternation of short and long C?N_imine bonds in the Pc ligand owing to the disruption of its aromaticity. Salts 1 – 10 show new bands at 833–1041 nm in the NIR range, whereas the Q‐ and Soret bands are blue‐shifted by 0.13–0.25 eV (38‐92 nm) and 0.04–0.07 eV (4–13 nm), respectively. Radical anions with Ni^II, Sn^II, Pb^II, and Ti^IVO have S=1/2 spin state, whereas [Cu^IIPc(3?)]^.? and [V^IVOPc(3?)]^.? containing paramagnetic Cu^II and V^IVO have two S=1/2 spins per radical anion. Central metal atoms strongly affect EPR spectra of phthalocyanine radical anions. Instead of narrow EPR signals characteristic of metal‐free phthalocyanine radical anions [H₂Pc(3?)]^.? (linewidth of 0.08–0.24 mT), broad EPR signals are manifested (linewidth of 2–70 mT) with g‐factors and linewidths that are strongly temperature‐dependent. Salt 11 containing the [Na^IPc(2?)]^? anions as well as previously studied [Fe^IPc(2?)]^? and [Co^IPc(2?)]^? anions that are formed without reduction of the Pc ligand do not show changes in molecular structure or optical and magnetic properties characteristic of [MPc(3?)]^.? in 1 – 10 .     

A chiral Mn(IV) complex and its supramolecular assembly: Synthesis, characterization and properties

The open air reaction of the chiral Schiff base ligand H₂L, prepared by the condensation of L-phenylalaninol and 5-bromosalicylaldehyde, with Mn^II(CH₃COO)₂.4H₂O yielded dark brown complex [Mn^IV L₂]·0·5 DMF (1). Compound 1 was characterized by elemental analysis, IR, UV-visible, CD and EPR spectroscopy, cyclic voltammetry and room temperature magnetic moment determination. Single-crystal X-ray analysis revealed that compound 1 crystallises in the monoclinicP2 ₁ space group with six mononuclear [Mn^IV L₂] units in the asymmetric unit along with three solvent DMF molecules. In the crystal structure, each Mn(IV) complex, acting as the building unit, undergoes supramolecular linking through C-H...0 bonds leading to an intricate hydrogen bonding network.     

Studies on 4-(2-thiazolyl)-1-(2-acetylpyridine)thiosemicarbazone complexes of some bivalent metal ions

Summary Complexes [VO(Htaptsc)SO₄] and [M(Htaptsc)₂Cl₂] [M=Mn^II, Ni^II, Cd^II or Hg^II], Cu(Htaptsc)Cl₂ and [M(Htaptsc)Cl₂] [M=Co^II or Zn^II], and deprotonated compounds Co(taptsc)₂ and [M(taptsc)₂] [M=V^IVO, Mn^II, Ni^II, Cu^II or Zn^II] [Htaptsc=4-(2-thiazolyl)-1-(2-acetylpyridine)thiosemicarbazone] have been characterized by elemental analyses, electrical conductivity and magnetic susceptibility measurements and electronic, e.s.r. and i.r. spectroscopy. The bonding sites of Htaptsc and the bonding and stereochemistry of the complexes are discussed.     

Synthesis,characterization and antimicrobial studies on 13-membered-N6-macrocyclic transition metal complexes containing trimethoprim

Asymmetrical macrocyclic complexes of Mn^II, Co^II, Ni^II, Cu^II and Zn^II have been synthesized by the template process using bis(benzil)ethylenediamine as precursor. Bis(benzil)ethylenediamine reacts with transition metal chlorides and trimethoprim in a 1:1:1 molar ratio in methanol to give several solid metal complexes of the general composition [M(L)X₂] (M = Mn^II, Co^II, Ni^II, Cu^II and Zn^II, L = ligand and X = Cl^?). They were characterized by physicochemical and spectroscopic techniques. Based on analytical, spectral and magnetic moments, all the complexes are identified as distorted octahedral structures. All the complexes are of the [M(L)X₂] type. The shifts of the ν(CN) (azomethine) stretches have been monitored. To find out the donor sites of the ligands, the activity data show that the metal complexes are more potent than the parent ligand. The [M(L)X₂] complexes showed a broad spectrum of antimicrobial activity in vitro against both gram-positive and gram-negative human pathogenic bacterial isolates and the antimicrobial spectrum enhanced only with a combination of metal chlorides and trimethoprim complex. From the results it is imperative that the synthesized macrocyclic [M(L)X₂] complexes exhibit potent broad spectrum antibacterial activity.     

Dioxygen Reactivity of Copper(I)/Manganese(II)-Porphyrin Assemblies: Mechanistic Studies and Cooperative Activation of O2

The oxidation of transition metals such as manganese and copper by dioxygen (O₂) is of great interest to chemists and biochemists for fundamental and practical reasons. In this report, the O₂ reactivities of 1:1 and 1:2 mixtures of [(TPP)Mn^II] (1; TPP: Tetraphenylporphyrin) and [(tmpa)Cu^I(MeCN)]⁺ (2; TMPA: Tris(2-pyridylmethyl)amine) in 2-methyltetrahydrofuran (MeTHF) are described. Variable-temperature (−110 °C to room temperature) absorption spectroscopic measurements support that, at low temperature, oxygenation of the (TPP)Mn/Cu mixtures leads to rapid formation of a cupric superoxo intermediate, [(tmpa)Cu^II(O₂^•–)]⁺ (3), independent of the presence of the manganese porphyrin complex (1). Complex 3 subsequently reacts with 1 to form a heterobinuclear μ-peroxo species, [(tmpa)Cu^II–(O₂^2–)–Mn^III(TPP)]⁺ (4; λ_max = 443 nm), which thermally converts to a μ-oxo complex, [(tmpa)Cu^II–O–Mn^III(TPP)]⁺ (5; λ_max = 434 and 466 nm), confirmed by electrospray ionization mass spectrometry and nuclear magnetic resonance spectroscopy. In the 1:2 (TPP)Mn/Cu mixture, 4 is subsequently attacked by a second equivalent of 3, giving a bis-μ-peroxo species, i.e., [(tmpa)Cu^II−(O₂²⁻)−Mn^IV(TPP)−(O₂²⁻)−Cu^II(tmpa)]²⁺ (7; λ_max = 420 nm and δ_pyrrolic = −44.90 ppm). The final decomposition product of the (TPP)Mn/Cu/O₂ chemistry in MeTHF is [(TPP)Mn^III(MeTHF)₂]⁺ (6), whose X-ray structure is also presented and compared to literature analogs.     

Synthesis and spectral studies on mononuclear complexes of chromium(III) and manganese(II) with 12-membered tetradentate N2O2, N2S2 and N4 donor macrocyclic ligands

Complexes of Cr^III and Mn^II of general formula [Cr(L)X₂] X and [Mn(L)X₂] respectively were prepared from N₂O₂, N₂S₂ and N₄ donor macrocyclic ligands. The complexes have been characterized by elemental analysis, molar conductance measurements, spectral methods (i.r, mass, ¹H-n.m.r, electronic spectra and e.p.r.) and magnetic measurements. The macrocyclic ligands have three different donating atom cavities, one with two unsaturated nitrogens and the other two have saturated nitrogen, oxygen and sulphur atoms. The effect of different donor atoms on the spectra and ligand field parameters is discussed. All the complexes show magnetic moments corresponding to a high-spin configuration. On the basis of spectral studies a six coordinated octahedral geometry may be assigned to these complexes.     

Synthesis,Crystal Structure,and Characterization of Two Oxamido‐bridged NiIICuIINiII Heteronuclear Complexes

Two new trinuclear complexes [Cu^II(Ni^IIX₁)₂(C₂H₅OH)₂]· (ClO₄)₂·2(CH₃OH) ( 1 ) and [Cu^II(Ni^IIX₂)₂(H₂O)]·(ClO₄)₂· 0.75(H₂O) ( 2 ) (X₁ = dianion of 5,6;13,14‐dibenzo‐7,12‐bis(ethoxycarboxyl)‐9‐methyl‐2,3‐dioxo‐1,4,8,11‐tetraazacyclotetradeca‐7,11‐diene. X₂ = dianion of 5,6;13,14‐dibenzo‐9,10‐cyclohexano‐7,12‐bis(ethoxycarboxyl)‐2,3‐dioxo‐1,4,8,11‐tetraazacyclotetradeca7,11‐diene.) have been synthesized and characterized by single crystal X‐ray analysis, elemental analysis, IR, UV and EPR spectroscopies. The complexes consist of Ni^IICu^IINi^II heteronuclear cationic entities. The central Cu^II atom of 1 lies in an octahedral coordination environment, while that of 2 resides in a square‐pyramidal coordination sphere. The adjacent trinuclear units of 1 are linked together through π‐π stacking interactions resulting in a 1D supramolecular chain, whereas the π‐π stacking interactions between the contiguous units of 2 lead to a 2D structure. The EPR spectra of the two complexes show a signal of an axially elongated octahedral Cu^II system in 1 and an axially elongated square‐pyramidal Cu^II system in 2 , respectively. The hyperfine splitting of the Cu^II atoms (I^Cu = 3/2) has also been observed in the EPR spectra.     

Two new clusters with MnII-MnIV magnetic exchange from the use of polyalcohol ligands

Two mixed-valence Mn(II,IV) complexes, [Mn^II₄Mn^IV₃(teaH)₃(tea)(thmeH)₃(thme)](ClO₄)₂·3MeCN (1) and [Mn^II₂Mn^IV₂(edteH)₂(peolH)₂]·4MeOH (2), where H₄edte = N,N,N′,N′-tetrakis(2-hydroxyethyl)ethylenediamine, teaH₃ = tris(2-hydroxyethyl)amine, H₄peol = pentaerythritol, and H₃thme = 1,1,1-tris(hydroxymethyl)ethane, were prepared from the corresponding manganese salts and mixed ligands with polyalcohols. The two clusters consist of a trapped-valence polynuclear core comprising 4Mn^II and 3Mn^IV for 1, 2Mn^II and 2Mn^IV ions for 2. Complex 1 crystallizes in the rhombohedral space group R3c, while 2 crystallizes in the monoclinic space group P2₁/c. Complex 1 consists of a near-planar Mn₇ unit that comprises a Mn₆ hexagon of alternating Mn^II and Mn^IV ions surrounding a central Mn^II ion. The remaining coordinated sites are occupied by eight different deprotonation degrees of H₃tea or H₃thme. The tetranuclear cluster of 2 consists of a fused defective dicubane Mn₄O₆ core, and the four Mn ions are coordinated by oxygens from edteH^3? and peolH^3? into an unusual butterfly-like [Mn^II₂Mn^IV₂] topology. The two clusters are also characterized by mass spectra and X-ray photoelectron spectroscopy. Direct current magnetization studies reveal ferromagnetic interactions within both Mn clusters.     

Magnetic properties of the mixed-valence compounds CaMn3O6 and CaMn4O8

The preparation of two new mixed-valence compounds, CaMn₃O₆ and CaMn₄O₈, are described and their magntic and EPR behavior investigated. The Mn moments in both compounds have nearly spinonly values. CaMn₃O₆ and CaMn₄O₈ order ferrimagnetically near 3 and 89 K, respectively. The broad, Lorentzian EPR lines indicate a significant exchange interaction between Mn³⁺ and Mn⁴⁺ ions. The magnetic and EPR results suggest a strong ferromagnetic interaction between Mn³⁺ and Mn⁴⁺ ions and a comparable antiferromagnetic Mn³⁺Mn³⁺ and/or Mn⁺Mn⁴⁺ interaction.     

Transition metal complexes with tridentate salicylaldimine derived from 3,5-di-t-butylsalicylaldehyde

Several new binuclear Cu^II, Ni^II, OV^IV and Mn^II complexes of tridentate salicylaldimine (H₂L), obtained from 3,5-di-t-butylsalicylaldehyde and o-aminophenol, have been prepared and characterized by analytical, spectroscopic (i.r., u.v.–vis., e.s.r.) techniques, magnetic and thermal measurements. The adduct formation or dissociation of these complexes in the presence of strongly coordinating solvents like pyridine and DMSO did not take place. The complexation of Co^II with H₂L is accompanied by intramolecular electron transfer from the metal to the coordinated ligand yielding the radical ligand Co^III complex (g = 2.003, A ^Co = 10 G). The e.s.r. spectra of the Cu^II, OV^IV and Mn^II complexes in the solid state and in solution are very broad due to intramolecular dipolar antiferromagnetic interactions.     

Zero-Field Splittings and Redox Potentials in an Isostructural Series of Dinuclear FeIITiIV,FeIIITiIV, and MnIITiIV Complexes with a Face-Sharing Bridging Motive

The ligand H₆ioan has been used to synthesize the three dinuclear complexes [(ioan)Mn^IITi^IV], [(ioan)Fe^IITi^IV], and [(ioan)Fe^IIITi^IV]⁺. The face-sharing bridging mode of the three phenolates provides short M-Ti^IV distances of ≈3.0 Å. Mössbauer spectra of [(ioan)Fe^IIITi^IV]⁺ show a magnetically split six-line spectrum at 3 K in zero magnetic field demonstrating a slow magnetic relaxation. Magnetic measurements provide a zero-field splitting of |D|=5 cm⁻¹ in [(ioan)Fe^IITi^IV]. EPR spectroscopy demonstrates sizable zero-field splittings of the S=5/2 spin systems of [(ioan)Mn^IITi^IV] (D=0.246 cm⁻¹) and [(ioan)Fe^IIITi^IV]⁺ (D<−1 cm⁻¹) that can be related to enforced covalency of the M-O^ph bonds. [(ioan)Fe^IIITi^IV]⁺ exhibits a reversible reduction at −0.26 V vs. Fc⁺/Fc demonstrating the facile accessibility of Fe^III and Fe^II. In contrast to an irreversible oxidation in [(ioan)Ni^IITi^IV] at 0.78 V vs. Fc⁺/Fc, the reversible oxidation at 0.25 V vs. Fc⁺/Fc in [(ioan)Mn^IITi^IV] indicates even the access of Mn^III. These results indicate that pentanuclear complexes [(ioan)FeM¹M²M¹Fe(ioan)]ⁿ⁺ are meaningful targets to access electron delocalization in mixed-valence systems over five ions due to the facile accessibility of both Fe^II and Fe^III in the terminal positions. This study provides important local spin-Hamiltonian and Mössbauer parameters that will be essential for the understanding of the potentially complicated electronic structure in the anticipated pentanuclear complexes.     

Synthetic routes to a family of Mn–Ce heterometallic clusters

Synthetic methods are described that have resulted in the preparation of several mixed-metal Mn–Ce clusters. The methods involve the reaction of Mn^II salts or preformed Mn clusters with Ce^IV reagents. The products may be divided into three general classes on the basis of the Mn and Ce oxidation states, Mn^IV–Ce^IV, Mn^III–Ce^IV, and Mn^III–Ce^III/IV. All Mn^IV–Ce^IV compounds were prepared by addition of Ce^IV to Mn^II salts, whereas all Mn^III–Ce^IV and Mn^III–Ce^III/IV clusters were prepared by addition of Ce^IV to Mn^III-containing clusters. All the mixed Mn–Ce clusters have aesthetically pleasing structures and some of them also have interesting magnetic properties.     

Large breathing effect induced by water sorption in a remarkably stable nonporous cyanide-bridged coordination polymer

While metal–organic frameworks (MOFs) are at the forefront of cutting-edge porous materials, extraordinary sorption properties can also be observed in Prussian Blue Analogs (PBAs) and related materials comprising extremely short bridging ligands. Herein, we present a bimetallic nonporous cyanide-bridged coordination polymer (CP) {[Mn(imH)]₂[Mo(CN)₈]}_n (1Mn; imH = imidazole) that can efficiently and reversibly capture and release water molecules over tens of cycles without any fatigue despite being based on one of the shortest bridging ligands known – the cyanide. The sorption performance of {[Mn(imH)]₂[Mo(CN)₈]}_n matches or even outperforms MOFs that are typically selected for water harvesting applications with perfect sorption reversibility and very low desorption temperatures. Water sorption in 1Mn is possible due to the breathing effect (accompanied by a dramatic cyanide-framework transformation) occurring in three well-defined steps between four different crystal phases studied structurally by X-ray diffraction structural analysis. Moreover, the capture of H₂O by 1Mn switches the EPR signal intensity of the Mn^II centres, which has been demonstrated by in situ EPR measurements and enables monitoring of the hydration level of 1Mn by EPR. The sorption of water in 1Mn controls also its photomagnetic behavior at the cryogenic regime, thanks to the presence of the [Mo^IV(CN)₈]⁴⁻ photomagnetic chromophore in the structure. These observations demonstrate the extraordinary sorption potential of cyanide-bridged CPs and the possibility to merge it with the unique physical properties of this class of compounds arising from their bimetallic character (e.g. photomagnetism and long-range magnetic ordering).

A cyanide-bridged coordination polymer {[Mn(imH)]₂[Mo(CN)₈]}_n shows exceptional water sorption properties, very large breathing effect and outstanding stability – properties that are unique for this class of compounds – Prussian blue analogs.     

Kinetics and mechanism of oxidation of 2‐mercaptosuccinic acid by bis(μ‐oxo)‐ manganese(III,IV)‐cyclam complex in aqueous medium: Influence of externally added copper(II)

Kinetic studies on the oxidation of 2‐mercaptosuccinic acid by dinuclear [Mn₂^III/IV(μ‐O)₂(cyclam)₂](ClO₄)₃] ( 1 ) (abbreviated as Mn^III–Mn^IV) (cyclam = 1,4,8,11‐tetraaza‐cyclotetradecane) have been carried out in aqueous medium in the pH range of 4.0–6.0, in the presence of acetate buffer at 30°C by UV–vis spectrophotometry. In the pH region, two species of complex 1 (Mn^III–Mn^IV and Mn^III–Mn^IVH, the later being μ‐O protonated form) were found to be kinetically significant. The first‐order dependence of the rate of the reactions on [Thiol] both in presence and absence of externally added copper(II) ions, first‐order dependence on [Cu²⁺] and a decrease of rate of the reactions with increase in pH have been rationalized by suitable sequence of reactions. Protonation of μ‐O bridge of 1 is evidenced by the perchloric acid catalyzed decomposition of 1 to mononuclear Mn(III) and Mn(IV) complex observed by UV–vis and EPR spectroscopy. The kinetic features have been rationalized considering Cu(RSH) as the reactive intermediate. EPR spectroscopy lends support for this. The formation of a hydrogen bonded outer‐sphere adduct between the reductant and the complex in the lower pH range prior to electron transfer reactions is most likely to occur. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 170–177 2004     

N-benzamidosalicylaldimine complexes of copper(II), nickel(II), cobalt(II), iron(II), manganese(II), oxyvanadium(IV) and oxytitanium(IV)

Summary N-benzamidosalicylaldimine (H₂L) complexes of Cu^II, Ni^II, Co^II, Fe^II, Mn^II. VO_IV and TiO_IV have been prepared. The ligand probably coordinates to the metal from the hydroxyl, carbonyl and imino groups.     

Synthesis and characterization of complexes of the first transition series cations with 2,2′-biimidazole and 2,2′-biimidazolate

Mononuclear [M(hfacac)₂(H₂biim)] complexes, where M = Mn^II, Fe^II, Co^II, Ni^II, Cu^II or Zn^II, hfacac = hexafluoroacetylacetonate, H₂biim = 2,2-biimidazole; dinuclear K₂[M₂(acac)₄(-biim)] (M = Cu^II or Zn^II) and tetranuclear K₂[M₄(acac)₈( ₄-biim)] (M = Co^II or Ni^II) complexes have been prepared and characterized by chemical analysis, conductance measurements, i.r., electronic and e.p.r. spectroscopies and by magnetic susceptibility measurements (in the 2–300 K range). Mn^II, Fe^II and Co^II are in a high spin state. The e.p.r. spectra of Cu^II and Mn^II compounds have been recorded.     

Magnetic properties of transition metal complexes with 2,2′-bipyridin-5-yl t-butyl nitroxide

Complexes [Mn^II(5bpno)₃(ClO₄)₂], [Mn^II(5bpno)(CH₃OH)₂Cl₂], [Cu^II(5bpno)₂(ClO₄)₂], and [Cu^II(5bpno)Cl₂] were prepared, where 5bpno stands for 2,2′-bipyridin-5-yl t-butyl nitroxide. X-ray crystallographic analysis clarified that the Cu ion in [Cu(5bpno)₂(ClO₄)₂] was tetra-coordinate with four nitrogen atoms forming two chelate rings. Magnetic measurements revealed the presence of ferromagnetic couplings in the Mn complexes, whereas the Cu complexes showed antiferromagnetic couplings. Magnetic exchange couplings between the metal and radical spins through the intervening pyridine ring can be explained in terms of the spin-polarization mechanism.