The Reaction of Carbon Dioxide with Palladium Allyl Bonds

A family of palladium allyl complexes of the type bis(2-methylallyl)Pd(L) (L = PMe(3) (1), PEt(3) (2), PPh(3) (3) or NHC (4); NHC = 1,3-Bis(2,6-diisopropylphenyl)-1,3-dihydro-2H-imidazol-2-ylidene) have been prepared through the reaction of bis(2-methylallyl)Pd with the appropriate free ligand. Compounds 1-4 contain one η(1) and one η(3)-2-methylallyl ligand and 3 was characterized by X-ray crystallography. These complexes react rapidly with CO(2) at low temperature to form well defined unidentate palladium carboxylates of the type (η(3)-2-methylallyl)Pd(OC(O)C(4)H(7))(L) (L = PMe(3) (6), PEt(3) (7), PPh(3) (8) or NHC (9). The structure of 9 was elucidated using X-ray crystallography. The mechanism of the reaction of 1-4 with CO(2) was probed using a combination of experimental and theoretical (density functional theory) studies. The coordination mode of the allyl ligand is crucial and whereas nucleophilic η(1)-allyls react rapidly with CO(2), η(3)-allyls do not react. We propose that the reaction of η(1)-palladium allyls with CO(2) does not proceed via direct insertion of CO(2) into the Pd-C bond but through nucleophilic attack of the terminal olefin on electrophilic CO(2), followed by an associative substitution at palladium.     

Scope and Mechanistic Study of the Coupling Reaction of α, β-Unsaturated Carbonyl Compounds with Alkenes: Uncovering Electronic Effects on Alkene Insertion vs Oxidative Coupling Pathways

The cationic ruthenium-hydride complex [(C(6)H(6))(PCy(3))(CO)RuH](+)BF(4) (-) (1) was found to be a highly effective catalyst for the intermolecular conjugate addition of simple alkenes to α,β-unsaturated carbonyl compounds to give (Z)-selective tetrasubstituted olefin products. The analogous coupling reaction of cinnamides with electron-deficient olefins led to the oxidative coupling of two olefinic C-H bonds in forming (E)-selective diene products. The intramolecular version of the coupling reaction efficiently produced indene and bicyclic fulvene derivatives. The empirical rate law for the coupling reaction of ethyl cinnamate with propene was determined as: rate = k[1](1)[propene](0)[cinnamate](-1). A negligible deuterium kinetic isotope effect (k(H)/k(D) = 1.1±0.1) was measured from both (E)-C(6)H(5)CH=C(CH(3))CONHCH(3) and (E)-C(6)H(5)CD=C(CH(3))CONHCH(3) with styrene. In contrast, a significant normal isotope effect (k(H)/k(D) = 1.7±0.1) was observed from the reaction of (E)-C(6)H(5)CH=C(CH(3))CONHCH(3) with styrene and styrene-d(10). A pronounced carbon isotope effect was measured from the coupling reaction of (E)-C(6)H(5)CH=CHCO(2)Et with propene ((13)C(recovered)/(13)C(virgin) at C(β) = 1.019(6)), while a negligible carbon isotope effect ((13)C(recovered)/(13)C(virgin) at C(β) = 0.999(4)) was obtained from the reaction of (E)-C(6)H(5)CH=C(CH(3))CONHCH(3) with styrene. Hammett plots from the correlation of para-substituted p-X-C(6)H(4)CH=CHCO(2)Et (X = OCH(3), CH(3), H, F, Cl, CO(2)Me, CF(3)) with propene and from the treatment of (E)-C(6)H(5)CH=CHCO(2)Et with a series of para-substituted styrenes p-Y-C(6)H(4)CH=CH(2) (Y = OCH(3), CH(3), H, F, Cl, CF(3)) gave the positive slopes for both cases (ρ = +1.1±0.1 and +1.5±0.1, respectively). Eyring analysis of the coupling reaction led to the thermodynamic parameters, Δ H(?) = 20±2 kcal mol(-1) and S(?) = -42±5 e.u. Two separate mechanistic pathways for the coupling reaction have been proposed on the basis of these kinetic and spectroscopic studies.     

Desymmetrized Diiron Azadithiolato Carbonyls: A Step Toward Modeling the Iron-Only Hydrogenases

Condensation of Fe(2)(SH)(2)(CO)(6), acetaldehyde, and (NH(4))(2)CO(3) affords the methyl-substituted azadithiolate Fe(2)[(SCHMe)(2)NH](CO)(6) (1). The complex exists mainly (~95%) as the meso diastereomer, but the d,l diastereoisomers could be detected. DFT calculations predict that the meso isomer would be 2.5 kcal/mol more stable than the d,l isomer due to conventional nonbonding interactions between the methyl groups and the ring hydrogen atoms. Crystallographic analysis of meso-1 confirms that the two methyl groups are equatorial, constraining the diferraazadithiolate bicycle to a conformation that desymmetrizes the diiron center. The lowered symmetry is confirmed by the observation of two (13)C NMR signals in the FeCO region under conditions of fast turnstile rotation at the Fe(CO)(3) groups. The pK(a) value of the amine in 1 is 7.89 (all pK(a)'s determined in MeCN solution), which is similar to a redetermined value for Fe(2)[(SCH(2))(2)NH](CO)(6) (2, pK(a) = 7.98) and only slightly less basic than the tertiary amine Fe(2)[(SCH(2))(2)NMe](CO)(6) (pK(a) = 8.14). Substitution of 1 with PMe(3) proceeded via the intermediacy of two isomers of Fe(2)[(SCHMe)(2)NH](CO)(5)(PMe(3)), affording Fe(2)[(SCHMe)(2)NH](CO)(4)(PMe(3))(2) (3). (31)P NMR spectra confirm that the two PMe(3) ligands in 3 are nonequivalent, consistent with the desymmetrizing effect of the dithiolate. The pK(a) value of the amine in 3 was found to be 11.3. Using triphenylphosphine, we prepared Fe(2)[(SCHMe)(2)NH](CO)(5)(PPh(3)) as a single regioisomer.     

Chelate-Assisted Oxidative Coupling Reaction of Arylamides and Unactivated Alkenes: Mechanistic Evidence for Vinyl C-H Bond Activation Promoted by an Electrophilic Ruthenium-Hydride Catalyst

The cationic ruthenium-hydride complex [(η(6)-C(6)H(6))(PCy(3))(CO)RuH](+)BF(4) (-) was found to be a highly regioselective catalyst for the oxidative C-H coupling reaction of aryl-substituted amides and unactivated alkenes to give ortho-alkenylamide products. The kinetic and spectroscopic analyses support a mechanism involving a rapid vinyl C-H activation followed by a rate-limiting C-C bond formation steps.     

Reaction of Aryl Diazonium Salts and Diiron(I) Dithiolato Carbonyls: Evidence for Radical Intermediates

Treatment of Fe(2)(pdt)(CO)(4)(dppv) (1) with aryldiazonium salts affords the 34e(-) adducts [Fe(2)(pdt)(μ-N(2)Ar)(CO)(4)(dppv)](+) (pdt(2-) = 1,3-propanedithiolate, dppv = cis-C(2)H(2)(PPh(2))(2)). Under some conditions, the same reaction gave substantial amounts of [1](+), the product of electron-transfer. Consistent with the influence of electron transfer in the reactions of some electrophiles with Fe(I)Fe(I) dithiolates, the reaction of [Me(3)S(2)](+) and Fe(2)(pdt)(CO)(4)(dppbz) was found to give [Fe(2)(pdt)(CO)(4)(dppbz)](+) as well as Me(2)S and Me(2)S(2) (dppbz = 1,2-bis(diphenylphosphino)benzene).     

Anticancer Activity of Self-Assembled Molecular Rectangles via Arene-Ruthenium Acceptors and a New Unsymmetrical Amide Ligand

Two new and large molecular rectangles 4 and 5 were synthesized from two different arene-ruthenium [Ru(2)(μ-η(4)-C(2)O(4))(MeOH)(2)(η(6)-p-Pr(i)C(6)H(4)Me)(2)][O(3)SCF(3)](2) (2), and [Ru(2) (p-cymene)(2) (donq) (OH(2))(2)] [O(3)SCF(3)](2) (donq = 5,8-dioxydo-1,4-naphthaquinonato) (3) acceptors and a new unsymmetrical N-(4-(pyridin-4-ylethynyl)phenyl) isonicotinamide (1) donor ligand. X-ray crystallography of 4 confirmed a molecular rectangle. The (1)H NMR spectra of both rectangles 4 and 5 showed a mixture of two structural, head-to-tail (HTL) and head-to-head (HTH) type, isomers in a 1:1 ratio. The cytotoxicities of both rectangles have been established against Colo320 (colorectal cancer), A549 (lung cancer), MCF-7(breast cancer) and H1299 (lung cancer) human cancer cell lines. The cytotoxicity of rectangle 5 was found to be considerably stronger against all cancer cell lines than that of the reference drug cisplatin.     

Synthesis, characterization, and electrochemical properties of mono-, di-, and trinuclear transition Metal [60]fullerene complexes containing diphosphine cis-Ph2PCH=CHPPh2 ligand

New transition metal fullerene complexes containing cis-Ph2PCH=CHPPh2 (dppet) ligand have been investigated. The mononuclear complexes (etau2-C60)M(cis-dppet) (1, 2; M = Pd, Pt) were prepared by reaction of C60 with M(dba)2 (dba = dibenzylideneacetone) followed by treatment with cis-dppet, while the in situ prepared 1 and 2 reacted with M1(PPh3)4 to afford dinuclear complexes (eta2 : eta2-C60)M(cis-dppet)M1 (PPh3)2 (3-6; M, M1 = Pd, Pt). Similarly, trinuclear complexes (eta2 : eta2-C60) M(cis-dppet)M1 (dppr) (7-10; M, M1 = Pd, Pt; dppr = (eta5-Ph2PC5H4)2Ru) could be synthesized by reaction of the in situ prepared 3-6 with dppr. 1-10 were characterized by elemental analysis and spectroscopy. Cyclic voltammetric studies on 2 (M = Pt), 3 (M = Pd, M1 = Pd) and 9 (M = Pt, M1 = Pd) provided further evidence for the eta2-coordination of C60 to one metal fragment or two metal fragments in these complexes.     

Ion-Pair Extraction of Metalloporphyrins into Acetonitrile for Determination of Copper(II)

Equilibrium study of ion-pair extraction of a cationic water-soluble porphyrin [5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphyrin, H(2)tmpyp(4+)] and its metalloporphyrins (MP) into the acetonitrile layer, separated by addition of sodium chloride (4.00 mol dm(-)(3)) to a 1:1 (v/v) acetonitrile-water mixed solvent, was carried out to develop a new and useful method for the determination of a subnanogram amount of copper(II). M denotes Zn(2+), Cu(2+), Co(3+), Fe(3+), and Mn(3+), and P(2)(-) is porphyrinate ion. The extraction and dissociation constants of the ion-pair complexes, defined by K(ex) = [MP(ClO(4))(4)](org)[MP(4+)](aq)(-)(1)[ClO(4)(-)](aq)(-)(4), K(dis,1) = [MP(ClO(4))(3)(+)](org)[ClO(4)(-)](org)[MP(ClO(4))(4)](org)(-)(1), and K(dis,2) = [MP(ClO(4))(2)(2+)](org)[ClO(4)(-)](org)[MP(ClO(4))(3)(+)](org)(-)(1), were determined by taking into account the partition constant of sodium perchlorate (K(D) = 1.82 ± 0.01). The equilibrium constants were found to be K(ex)K(dis,1) = (7.2 ± 1.3) × 10(4), (6.4 ± 0.9) × 10(4), (1.35 ± 0.13) × 10(5), (4.8 ± 0.6) × 10(3), (1.23 ± 0.05) × 10(4), and (1.42 ± 0.07) × 10(3) at 25 °C for the free base porphyrin (H(2)tmpyp(4+)) and the metalloporphyrins of zinc(II), copper(II), cobalt(III), iron(III), and manganese(III), respectively. The K(dis,2) values were (2.9 ± 1.4) × 10(-)(2), (3.1 ± 1.1) × 10(-)(2), (8.0 ± 4.9) × 10(-)(3), and (5.1 ± 2.2) × 10(-)(2) for the free base porphyrins and the metalloporphyrins of zinc(II), copper(II), and cobalt(III), respectively. The results were developed for determination of a trace amount of copper(II) (3 × 10(-)(8)-4 × 10(-)(6) mol dm(-)(3)) in natural water samples using H(2)tmpyp(4+) with a molar absorptivity of 3.1 × 10(5) mol(-)(1) dm(3) cm(-)(1) at a precision of 1.3% (RSD). The determination of copper(II) was not interfered by the presence of 10(-)(4) mol dm(-)(3) of Mn(2+), Co(2+), Ni(2+), Hg(2+), Cd(2+), Ag(+), Cr(3+), V(5+), Al(3+), Mg(2+), Ca(2+), Br(-), I(-), SCN(-), and S(2)O(3)(2)(-) and 10(-)(5) mol dm(-)(3) of Fe(3+), Zn(2+), and Pd(2+).     

Studies on the Condensation Pathway to and Properties of Diiron Azadithiolate Carbonyls

Reaction of Fe(2)(SH)(2)(CO)(6) and HCHO, which gives Fe(2)[(SCH(2))(2)NH](CO)(6) in the presence of NH(3), affords the possible intermediate Fe(2)(SCH(2)OH)(2)(CO)(6), which has been characterized crystallographically as its axial-equatorial isomer. Fe(2)(SCH(2)OH)(2)(CO)(6) was shown to react with ammonia and amines to give Fe(2)[(SCH(2))(2)NR](CO)(6) (R = H, alkyl). Related hemithioacetal intermediates were generated by treatment of Fe(2)(SH)(2)(CO)(6) with RC(O)C(O)R (R = H, Ph, 4-F-C(6)H(4)) to give cycloadducts. The benzil derivative Fe(2)[S(2)C(2)(OH)(2)Ph(2)](CO)(6), a C(2)-symmetric species, was also characterized crystallographically. The acylated azadithiolate Fe(2)[(SCH(2))(2)NAc](CO)(6) was prepared by reaction of Li(2)Fe(2)S(2)(CO)(6) with (ClCH(2))(2)NC(O)Me. DNMR experiments show that the free energies of activation for rotation of the amide bond are the same for Fe(2)[(SCH(2))(2)NAc](CO)(6) and Fe(2)[(SCH(2))(2)NAc](CO)(4)(PMe(3))(2), which implies that the ligands on the iron centers do not strongly affect the basicity of the nitrogen. As a control, we showed that the thioamide Fe(2)[(SCH(2))(2)NC(S)Me](CO)(6) does exhibit a significantly higher barrier to rotation, attributable to the increased double-bond character of the N-C(S) bond.     

A photochemical procedure for determining reaction quantum efficiencies in systems with multicomponent inner filter absorbances

A kinetic procedure for measuring the photochemical quantum efficiencies of reactions in which several components have overlapping absorbances is fully described. This method has been found to be particularly suitable for photochemical determinations where inner filter effects are substantial, such as those typically observed in the ligand substitution and intermolecular C-H/Si-H bond activation mechanisms of metal complexes. The quantitative measurement of the Si-H bond activation photochemistry of (η(5)-C(5)H(5))Rh(CO)(2) in triethylsilane solution is demonstrated in detail, although the procedure has widespread application in photochemistry.     

Fourier transform infrared spectroscopic method for the quantitative trace analysis of transition-metal carbonyl-labeled bioligands.

A quantitative FT-IR spectroscopic method has been developed for the trace analysis in chlorinated organic solvents of transition-metal carbonyl-labeled bioligands. In order to illustrate the widespread analytical potential of the method, three derivatives of the female hormonal steroid 17 beta-estradiol, containing Cr(CO)3, Cp2Mo2(CO)4 (Cp = eta 5-C5H5), and Co2(CO)6 as labels, and the anticonvulsant drug phenobarbital, labeled with (eta 5-C5H4)Mn(CO)3, were examined. The cobalt carbonyl marker proved to be the best sulted for quantitative analysis purposes, and the minimum tracer quantity detectable for this particular marker (64 scans, 4-cm-1 resolution, 3.5 min) was optimized in CCl4 solution at about 300 fmol (or 0.3 pmol, 180 pg) by using an ultralow volume (23.0 microL), gold light-pipe IR solution cell and a liquid nitrogen cooled, InSb (indium antimonide) IR detector. The repeatability of this radically different analytical procedure over the concentration range 1.0 x 10(-6) to 5.0 x 10(-8) M was good (coefficient of variance less than or equal to 6%) and the method provides the basis for a new immunological test--carbonylmetalloimmunoassay (CMIA).     

Thermolysis of some transition metal nitrate complexes with 1,4-diamino butane ligand

Four complexes are prepared and characterized having molecular formula [Zn(dab)(2)](NO(3))(2), [Cu(dab)(2)](NO(3))(2).H(2)O, [Ni(dab)(2)](NO(3))(2).2H(2)O and [Mn(dab)(2)](NO(3))(2), where dab: 1,4-diaminobutane. Thermolyses of these complexes were investigated by simultaneous thermogravimetry (TG), derivatives thermogravimetry (DTG), differential thermal analysis (DTA) and differential scanning calorimetry (DSC). The kinetics of the thermolysis at early stages is investigated using isothermal TG by applying model-fitting and isoconversional method. Thermolytic process is slow in inert (N(2)) and is fast in air atmosphere due to oxidative nature. To investigate the response of these complexes under the condition of rapid heating, ignition delay (D(i)) has been measured. Thermal stability of the complexes was found to increase in the order Mn < Cu < Ni < Zn.     

Tetrathiapentalene-based organic conductors

The synthesis, structure and properties of tetrathiapentalene-based (TTP) organic conductors are reviewed. Among various TTP-type donors, bis-fused tetrathiafulvalene, 2,5-bis(1,3-dithiol-2-ylidene)-1,3,4,6-tetrathiapentalene (BDT-TTP) and its derivatives afford many metallic radical cation salts stable down to low temperatures, regardless of the size and shape of the counter anions. Most BDT-TTP conductors have a β-type donor arrangement with almost uniform stacks. Introduction of appropriate substituents results in molecular packing that differs from the β-type. A vinylogous TTP, 2-(1,3-dithiol-2-ylidene)-5-(2-ethanediylidene-1,3-dithiole)-1,3,4,6-tetrathiapentalene (DTEDT) has yielded an organic superconductor (DTEDT)₃Au(CN)₂ as well as metallic radical cation salts, regardless of the counter anions. (Thio)pyran analogs of TTP, namely (T)PDT-TTP and its derivatives produce molecular conductors with novel molecular arrangements. A TTP analog with reduced π-electron system 2,5-bis(1,3-dithian-2-ylidene)-1,3,4,6-tetrathiapentalene (BDA-TTP) has afforded several organic superconductors. Highly conducting molecular metals with unusual oxidation states (+1, +5/3 and neutral) have been developed on the basis of 2,5-bis(1,3-dithiol-2-ylidene)-1,3,4,6-tetrathiapentalene (BDT-TTP) derivatives and analogous metal derivatives M(dt)₂ (M = Ni, Au).     

From cobalt nitrate carbonate hydroxide hydrate nanowires to porous Co(3)O(4) nanorods for high performance lithium-ion battery electrodes

We have developed a simple approach for the large-scale synthesis of cobalt nitrate carbonate hydroxide hydrate (Co(CO(3))(0.35)(NO(3))(0.2)(OH)(1.1)·1.74H(2)O) nanowires via the hydrothermal process using sodium hydroxide and formaldehyde as mineralizers at 120?°C. The porous Co(3)O(4) nanorods 10-30?nm in diameter and hundreds of nanometres in length have been fabricated from the above-mentioned multicomponent nanowires by calcination at 400?°C. The morphology and structure of cobalt nitrate carbonate hydroxide hydrate nanowires and Co(3)O(4) nanorods have been characterized by transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM) and x-ray powder diffraction (XRD). Moreover, the porous Co(3)O(4) nanorods have been applied in the negative electrode materials for lithium ion batteries, which exhibit high electrochemical performance.     

Preparation, characterization and mechanical performance of dense β-TCP ceramics with/without magnesium substitution

Beta-tricalcium phosphate (beta-TCP) powder was prepared by a two-step process: wet precipitation of apatitic tricalcium phosphate [Ca(9)(HPO(4))(PO(4))(5)(OH)] (beta-TCP 'precursor') and calcination of the precursor at 800 degrees C for 3 h to produce beta-TCP. Magnesium-substituted tricalcium phosphate (beta-TCMP) was produced by adding Mg(NO(3))(2) . 6H(2)O into Ca(NO(3))(2) solution as Mg(2+) source before the precipitation step. The transition temperature from beta-TCP to alpha-TCP increases with the increase of Mg(2+) content in beta-TCMP. beta-TCMP with 3 mol.% Mg(2+) has beta-TCP to alpha-TCP transition temperature above 1,300 degrees C. Dense beta-TCMP (3 mol.% Mg(2+)) ceramics ( approximately 99.4% relative density) were produced by pressing the green bodies at 100 MPa and further sintering at 1,250 degrees C for 2 h. The average compressive strength of dense beta-TCP ceramics sintered at 1,100 degrees C is approximately 540 MPa, while that of beta-TCMP (3 mol.% Mg(2+)) ceramics is approximately 430 MPa.     

Phase Transformation and Magnetostriction of (R-Pr)(Fe-T)_2 (R=Dy Tb; T=Co, Ni)

1. IntroductionMuch attention has been focused onmagnetostrictive materials RFe2, particularly,Tbo.zv~o.sDyo.vs~o.vFez (Terfenol-D), due to theirexcellellt magnetoelastic properties for the transducer deviceslll. Clark et al. firstly suggestedthat the pseudobinary compounds combined byTb, Dy and Fe could be constructed in an effortto reduce the anisotropy while maintaining largemagnetostrictionlZ]. Clark et al. also found in thecompensated system Tbl--.Pr.FeZ that (Tb, Pr)Fe3phase appea…     

Highly Cooperative Tetrametallic Ruthenium-mu-Oxo-mu-Hydroxo Catalyst for the Alcohol Oxidation Reaction

The tetrametallic ruthenium-oxo-hydroxo-hydride complex {[(PCy(3))(CO)RuH](4)(mu(4)-O)(mu(3)-OH)(mu(2)-OH)} (1) was synthesized in two steps from the monomeric complex (PCy(3))(CO)RuHCl (2). The tetrameric complex 1 was found to be a highly effective catalyst for the transfer dehydrogenation of alcohols. Complex 1 showed a different catalytic activity pattern towards primary and secondary benzyl alcohols, as indicated by the Hammett correlation for the oxidation reaction of p-X-C(6)H(4)CH(2)OH (rho = -0.45) and p-X-C(6)H(4)CH(OH)CH(3) (rho = +0.22) (X = OMe, CH(3), H, Cl, CF(3)). Both a sigmoidal curve from the plot of initial rate vs [PhCH(OH)CH(3)] (K(0.5) = 0.34 M; Hill coefficient, n = 4.2+/-0.1) and the phosphine inhibition kinetics revealed the highly cooperative nature of the complex for the oxidation of secondary alcohols.     

Tetrathiapentalene-based organic conductors

Abstract

The synthesis, structure and properties of tetrathiapentalene-based (TTP) organic conductors are reviewed. Among various TTP-type donors, bis-fused tetrathiafulvalene, 2,5-bis(1,3-dithiol-2-ylidene)-1,3,4,6-tetrathiapentalene (BDT-TTP) and its derivatives afford many metallic radical cation salts stable down to low temperatures, regardless of the size and shape of the counter anions. Most BDT-TTP conductors have a β-type donor arrangement with almost uniform stacks. Introduction of appropriate substituents results in molecular packing that differs from the β-type. A vinylogous TTP, 2-(1,3-dithiol-2-ylidene)-5-(2-ethanediylidene-1,3-dithiole)-1,3,4,6-tetrathiapentalene (DTEDT) has yielded an organic superconductor (DTEDT)₃Au(CN)₂ as well as metallic radical cation salts, regardless of the counter anions. (Thio)pyran analogs of TTP, namely (T)PDT-TTP and its derivatives produce molecular conductors with novel molecular arrangements. A TTP analog with reduced π-electron system 2,5-bis(1,3-dithian-2-ylidene)-1,3,4,6-tetrathiapentalene (BDA-TTP) has afforded several organic superconductors. Highly conducting molecular metals with unusual oxidation states (+1, +5/3 and neutral) have been developed on the basis of 2,5-bis(1,3-dithiol-2-ylidene)-1,3,4,6-tetrathiapentalene (BDT-TTP) derivatives and analogous metal derivatives M(dt)₂ (M = Ni, Au).     

Phase Transformation and Magnetic Properties of Mechanically Alloyed PrCo5-based Magnets

PrCo5-based nanograin Pr=CO100-x （x=14-22） alloys with high coercivity were synthesized by mechanical alloying and subsequent annealing. The crystallization, phase components and magnetic properties of the alloys were investigated systematically. The main phase of the alloy for x=14 is Pr2CO17 with rhombohedral Th2Zn17-type. The amount of the Pr2CO17 phase decreases with increasing Pr content, and a nearly single phase PrCo5 with hexagonal CaCu5-type is formed in Pr18Co81 alloy. Further increase in the Pr content leads to the formation of another magnetically hard Pr2Co7 phase with its Curie temperature about 350℃. Remanences decrease monotonously with increasing Pr content, whereas the coercivities increase, reaching a maximum of 2040 kA/m （25.6 kOe） in Pr19CO81 powders milled for 5 h and annealed at 973 K for 2 min, and then decrease for higher Pr content. The high coercivity is attributed to the high anisotropy field of the PrCo~ phase and its nanoscale grain size.