Construction and commissioning of mid-infrared self-amplified spontaneous emission free-electron laser at compact energy recovery linac.

The mid-infrared range is an important spectrum range where materials exhibit a characteristic response corresponding to their molecular structure. A free-electron laser (FEL) is a promising candidate for a high-power light source with wavelength tunability to investigate the nonlinear response of materials. Although the self-amplification spontaneous emission (SASE) scheme is not usually adopted in the mid-infrared wavelength range, it may have advantages such as layout simplicity, the possibility of producing a single pulse, and scalability to a short-wavelength facility. To demonstrate the operation of a mid-infrared SASE FEL system in an energy recovery linac (ERL) layout, we constructed an SASE FEL setup in cERL, a test facility of the superconducting linac with the ERL configuration. Despite the adverse circumstance of space charge effects due to the given boundary condition of the facility, we successfully established the beam condition at the undulators and observed FEL emission at a wavelength of 20 µm. The results show that the layout of cERL has the potential for serving as a mid-infrared light source.

Ferromagnetic superexchange coupling through a diamagnetic iron(II) ion in a mixed-valent iron(III, II, III) meso-helicate.

meso-Helicates [Ni(3)(pzNTR)(6)].4CH(3)CN and [Fe(3)(pzNTR)(6)](ClO(4))(2).CH(3)OH were prepared (HpzNTR stands for N-tert-butyl-alpha-3-pyrazolylnitrone). The former showed antiferromagnetic coupling between neighboring ions with J/k(B) = -28.2(2) K, which can be reasonably interpreted in terms of the superexchange mechanism. On the other hand, the latter exhibited ferromagnetic coupling with J/k(B) = +0.292(8) K between the two terminal S = 5/2 Fe(3+) ions through the intervening diamagnetic Fe(2+) ion. The admixture of low-lying excited states with the ground state stabilizes the ferromagnetically coupled state, like the Prussian blue magnet.

Ferromagnetic Dy-Ni and antiferromagnetic Dy-Cu couplings in single-molecule magnets [Dy2Ni] and [Dy2Cu].

The exchange couplings in [{Dy(hfac)3}2Cu(dpk)2] and [{Dy(hfac)3}2Ni(dpk)2(py)2] (Hdpk = di-2-pyridyl ketoxime) were precisely evaluated by high-frequency electron paramagnetic resonance and pulsed-field magnetization studies, giving J(Dy-Cu)/kB = -0.126 K and J(Dy-Ni)/kB = +0.031 K.

Magneto-structure relationship in copper(II) and nickel(II) complexes chelated with stable tert-butyl 5-phenyl-2-pyridyl nitroxide and related radicals.

We have isolated and characterized a new paramagnetic bidentate ligand, tert-butyl 5-phenyl-2-pyridyl nitroxide (phpyNO). The spin distribution onto the pyridine ring was clarified from the Electron Spin Resonance spectrum. Complexation of phpyNO with nickel(II) and copper(II) ions gave ML 2-type chelated compounds. The magnetic measurements of [Ni(phpyNO) 2(H 2O) 2].(ClO 4) 2 and [Cu(phpyNO) 2(H 2O)].(ClO 4) 2.C 6H 4Cl 2 revealed that the metal-radical exchange couplings were ferromagnetic with 2 J/ k B = +409(10) and +434(12) K, respectively. The torsion angle (varphi) around M-O-N-C 2py can be regarded as a reliable indicator for the plane geometry of chelates; namely, highly planar chelates defined by small varphi exhibit ferromagnetic coupling. An approximate linear relation was found in the J versus varphi plot using the data of the present complexes and related known compounds. The critical angle of varphi, at which the sign of the metal-radical exchange changes from positive to negative, was 12.6(9) degrees . This finding could be almost reproduced by density-functional theory calculation on a model copper(II)-nitroxide dyad. The exchange couplings in equatorially coordinated copper(II)- and nickel(II)-nitroxide complexes are very strongly ferromagnetic by nature.

Giant coercivity in a one-dimensional cobalt-radical coordination magnet.

A metal-radical polymer [Co(hfac)2.BPNN] showed a very large coercive field of 52 kOe (4.1 MA m-1) at 6 K, indicating that it is the hardest magnet ever reported. Above 10 K, a soft character appeared, owing to the fast dynamics of magnetization reorientation.

Magnetic exchange coupling tunable by means of selective cation binding into poly(radical-armed) azacrowns.

Host-guest complexes of tris(NN-CH2)-substituted 1,4,7-triazacyclononane and tetrakis(NN-CH2)-substituted 1,4,7,10-tetraazacyclododecane afforded the folded structures of the hosts where the NN radical oxygen atoms were coordinated to the guest metal ion, leading to enhanced antiferromagnetic couplings in the solid state and an ESR line broadening in the solution phase (NN = 4,4,5,5-tetramethylimidazolin-1-oxyl 3-oxide).

Strong ferromagnetic exchange couplings in copper(II) and nickel(II) complexes with a paramagnetic tridentate chelate ligand, 2,2'-bipyridin-6-yl tert-butyl nitroxide.

A paramagnetic ligand 6bpyNO (2,2'-bipyridin-6-yl tert-butyl nitroxide) is a newcomer in the field of metal-radical hybrid magnetic materials. Complexes [CuII(6bpyNO)Cl2] and [NiII(6bpyNO)2](PF6)2 having highly planar chelate rings showed considerably strong ferromagnetic exchange couplings J/kB = 202 and 192 K, respectively, across the direct radical oxygen coordination bonds (the spin Hamiltonian is defined as -2JSi.Sj).

Double half-cubane copper(II) complexes available from copper(II) 1,1,1,5,5,5-hexafluoropentane-2,4-dionate dissolved in formamides.

Tetranuclear copper(II) complexes were obtained after simply dissolving [Cu(hfac)2] in formamide-methanol mixed solvents (Hhfac=1,1,1,5,5,5-hexafluoropentane-2,4-dione). X-Ray diffraction studies revealed that they possessed a tetranuclear double half-cubane core sandwiched with two trianionic ligands from 2,4,6-tris(trifluoromethyl)tetrahydropyran-2,4,6-triol (H3ttpt). Complexes [Cu4(ttpt)2(hfac)2(dmf)2.5], [Cu4(ttpt)2(tfa)2(def)4], and [Cu4(ttpt)2(hfac)2(H2O)4](fa) were prepared from N,N-dimethylformamide(dmf)-MeOH, N,N-diethylformamide (def)-MeOH, and formamide(fa)-MeOH (Htfa=trifluoroacetic acid), respectively. A possible mechanism is proposed where a templated aldol-type reaction takes place between hfac and 1,1,1-trifluoroacetonate. Magnetic measurements revealed the presence of antiferromagnetic interaction in the Cu4O6 core.

Polymorphic alternating HNN-cobalt(II) chains both behaving as single-chain magnets (HNN = 4,4,5,5-tetramethylimidazolin-1-oxyl 3-oxide).

Metal-radical alternating chains [Co(hfac)2HNN]n crystallized in two morphs containing repeating all-cis (alpha) and cis,cis,trans (beta) configurations with respect to the O(HNN)-Co-O(HNN) geometry (HNN = 4,4,5,5-tetramethylimidazolin-1-oxyl 3-oxide). Both phases showed magnetization jumps with hysteresis at 2 K. The alpha phase has a relatively high activation energy of magnetization reorientation (193 K).

Self-assembled meso-helicates of linear trinuclear nickel(II)-radical complexes with triple pyrazolate bridges.

Complexation of 3-nitronyl-nitroxide-substituted pyrazolate (pzNN) and 3-imino-nitroxide-substituted pyrazolate (pzIN) with nickel(II) gave [Ni3(pzNN)6] and [Ni3(pzIN)6], respectively. They were practically isomorphous and characterized as a linear trinuclear structure with neighboring nickel ions triply bridged by pyrazolate moieties. The space groups were P2(1)/n but the molecules have a pseudo three-fold axis. We found polymorphs in the crystals of [Ni3(pzIN)6] depending on the solvate molecules; another space group was a cubic Pa3[combining macron]. The opposite chirality around the inversion center at the central nickel(II) ion leads to a meso-helical symmetry in the whole molecule. The radical oxygen atoms participate in the 6-membered chelation at the terminal nickel(II) ions. Antiferromagnetic couplings were observed in both complexes, which are ascribable to interactions between the nickel and radical spins and between the nickel spins across the pyrazolate bridges.

Oximate-bridged trinuclear Dy-Cu-Dy complex behaving as a single-molecule magnet and its mechanistic investigation.

Lanthanide ions are supposed to be promising candidates for the elements of single-molecule magnets (SMMs) because of the large magnetic momentum and anisotropy. We have established the [Dy2Cu] complex as a new SMM. A plausible mechanism for quantum tunneling of magnetization is proposed for the first time among the 4f-3d heterometallic SMMs. The magnetic coupling parameter between Dy and Cu ions was well-defined as -0.155 K.

A peptide sequence controls the physical properties of nanoparticles formed by peptide-polymer conjugates that respond to a protein kinase a signal.

We previously reported that poly(N-isopropylacrylamide) grafted with Peptide 1 (-GLRRASLG) and poly(ethylene glycol) changed its physical properties in response to an intracellular protein phosphorylation signal, protein kinase A (PKA) (Katayama, Y. et al. (2001) Macromolecules 34, 905). In this study, we investigated the effect of changing peptide structure on the lower critical solution temperature (LCST) of peptide-polymer conjugates, before and after phosphorylation with PKA. For Peptide 2 (Ac-LRRASL-), which has a formal net charge of +2 at physiological pH, the LCST of the conjugate decreased on phosphorylation. In contrast, the LCSTs of the conjugates with Peptide 3 (-ALRRASLE) and Peptide 4 (Ac-DWDALRRASL-), which have neutral net charges, were greatly increased. This suggests that the LCST of the polymer was mainly governed by two factors: the change in hydration around the polymer chain and the interpeptide electrostatic repulsion, resulting from phosphorylation. These polymers have potential for use as drug capsules that respond to cellular conditions.

Trans-fused macrobicycle "betweenanene" around a planar Cu2(mu-CH3O)2 core showing remarkable antiferromagnetic interaction.

Complexation of 4,6-bis{3-(2-pyridyl)-1H-pyrazol-1-yl}pyrimidine (bppp) and copper(II) tetrafluoroborate in methanol gave a self-assembled [Cu2(CH3O)2(bppp)2]2+ ion having a betweenanene-type structure. Each bppp spans across the common Cu2O2 plane in a trans fashion to ligate each copper center. The antiferromagnetic interaction observed in the Cu2O2 core is ascribable to the superexchange along the Cu-O-Cu linkage and found to be one of the largest among the analogous compounds, owing to the large Cu-O-Cu angle perturbed with the two bppp molecular tweezers.

The first A2B2-heterometal ferrimagnetic chain. Structures and magnetic properties of polymeric [Gd2Cu2]n and the corresponding monomer.

One-dimensional polymeric complexes consisting of alternating dicopper(II) and digadolinium(III) units exhibited ferrimagnetic behavior which was ascribable to antiferromagnetic coupling across the oximate N-O bridges between the high-spin homodinuclear units.

Synthesis and characterization of dibenzodioxadiselenafulvalene.

Dibenzodioxadiselenafulvalene (DBOSF) was prepared and the cis and trans isomers were separated. X-ray crystallographic analysis revealed the presence of Se- - -H and O- - -H hydrogen bonds in both crystals. The electrochemical properties of cis- and trans-DBOSFs together with dibenzotetraoxafulvalene (DBTOF) and cis- and trans-dibenzodioxadithiafulvalenes were investigated by means of cyclic voltammetry and DFT calculation. The electron-donating ability and the stability of oxidized forms of DBOSFs are improved compared with those of DBTOF.

Supramolecular triangular and linear arrays of metal-radical solids using pyrazolato-silver(I) motifs.

New chelating radical ligands pzNNH, pzINH, and pzbisINH (3-pyrazolyl nitronyl nitroxide, 3-pyrazolyl imino nitroxide, and pyrazole-3,5-diyl bis(imino nitroxide), respectively) were prepared. Complexation of these ligands with Ag+ gave [Ag(pzNN)]n, [Ag(pzIN)]6, and [Ag(pzbisIN)]n containing the corresponding anionic forms of the ligands. From the X-ray crystal structure analysis, [Ag(pzIN)]6 was characterized as a dimer of almost planar triangular moieties where the pyrazolate worked as a bridge, and metal-metal bonds brought about dimerization of triangles. [Ag(pzbisIN)]n was characterized as a uniform zigzag chain consisting of pyrazolate bridges and Ag ions with a cis-Npz-Ag-Npz coordination structure. Antiferromagnetic interactions observed could be analyzed based on the structures determined for both compounds. Ferromagnetic coupling was observed in [Ag(pzNN)]n, and a polymeric structure was assumed although the crystal structure could not be determined. Novel supramolecular architectures using pyrazolate-substituted imino nitroxides have been developed, using the unique coordinative versatility of the pyrazolate derivatives

Molecular metamagnet [Ni(4ImNNH)(2)(NO(3))(2)] (4ImNNH = 4-imidazolyl nitronyl nitroxide) and the related compounds showing supramolecular H-bonding interactions.

A new chelating radical ligand 4ImNNH (2-(4-imidazolyl)-4,4,5,5-tetramethylimidazolin-1-oxyl 3-oxide) was prepared, and complexation with divalent transition metal salts gave complexes, [M(4ImNNH)(2)X(2)], which showed intermolecular ferromagnetic interaction in high probability (7 out of 10 paramagnetic compounds investigated here). The nitrate complexes (X = NO(3); M = Mn (1), Co (2), Ni (3), Cu (4)) crystallize isomorphously in monoclinic space group P2(1)/a. The equatorial positions are occupied with two 4ImNNH chelates and the nitrate oxygen atoms are located at the axial positions. Magnetic measurements revealed that the intramolecular exchange couplings in 1, 2, and 4 were antiferromagnetic, while that in 3 was ferromagnetic with 2J/k(B) = +85 K, where the spin Hamiltonian is defined as H = -2J(S(1).S(2) + S(2).S(3)) based on the molecular structures determined as the linear radical-metal-radical triads. The intramolecular ferromagnetic interaction in 3 is interpreted in terms of orthogonality between the radical pi and metal dsigma orbitals. Compounds 1-3 exhibited intermolecular ferromagnetic interaction ascribable to a two-dimensional hydrogen bond network parallel to the crystallographic ab plane. Complex 3 became an antiferromagnet below 3.4 K and exhibited a metamagnetic transition on applying a magnetic field of 5.5 kOe at 1.8 K. The complexes prepared from metal halides, [M(4ImNNH)(2)X(2)] (X = Cl, Br; M = Mn, Co, Ni, Cu), showed intramolecular antiferromagnetic interactions, which are successfully analyzed based on the radical-metal-radical system. The crystal structures determined here on 1-4, [Mn(4ImNNH)(2)Cl(2)], and [Cu(4ImNNH)(2)Br(2)] always have intermolecular hydrogen bonds of H(imidazole).X(axial ligand)-M, where X = NO(3), Cl, Br. This interaction seems to play an important role in molecular packing and presumably also in magnetic coupling.

Ferro- and ferrimagnetic chains of hin-bridged copper(II) and manganese(II) and hnn-bridged manganese(II) complexes (hin = 4,4,5,5-tetramethylimidazolin-1-oxyl; hnn = 4,4,5,5-tetramethylimidazolin-1-oxyl 3-oxide).

We have exploited potential utility of 4,4,5,5-tetramethylimidazolin-1-oxyl (hin) and 4,4,5,5-tetramethylimidazolin-1-oxyl 3-oxide (hnn) as mu-1,4 and mu-1,5 bridging ligands, respectively, carrying an unpaired electron in development of metal-radical hybrid magnets. X-ray diffraction measurements of [Cu(hfac)(2)hin] (1), [Mn(hfac)(2)hin] (2), and [Mn(hfac)(2)hnn] (3) revealed one-dimensional metal-radical alternating chain structures, where hfac denotes 1,1,1,5,5,5-hexafluoropentane-2,4-dionate. Magnetic measurements of 1 indicate the presence of intrachain ferromagnetic coupling between copper and radical spins. The magnetic exchange parameter was estimated as 2J/k = 56.8 K based on an S = 1/2 equally spaced ferromagnetic chain model (H = -2J summation operator S(i).S(i+1)). This ferromagnetic interaction can be explained in terms of the axial coordination of the hin nitrogen or oxygen to Cu(II). The chi(m)T value of 2 and 3 increased on cooling, and the magnetic data could be analyzed by Seiden's ferrimagnetic chain model, giving 2J/k = -325 and -740 K, respectively. The antiferromagnetic interaction of 2 and 3 can be attributed to orbital overlap between the manganese and the oxygen or nitrogen magnetic orbitals. The exchange interactions between Cu-hin and Mn-hnn are larger than those of typical Cu- and Mn-nitronyl nitroxide complexes, indicating that the choice of small ligands is a promising strategy to bestow strong exchange interaction. Compound 3 became a ferrimagnet below 4.4 K, owing to ferromagnetic coupling among the ferrimagnetic chains.