Naphthalene and anthracene complexes sandwiched by two {(Cp*)Fe(I)} fragments: strong electronic coupling between the Fe(I) centers.

The reactions of the half-sandwich iron(II) complex [FeCl(Cp*)(tmeda)] (1; Cp*=η(5)-C(5)Me(5), TMEDA=N,N,N',N'-tetramethylethylenediamine) with potassium naphthalenide or potassium anthracenide gave the diamagnetic complexes [(Cp*)Fe(µ-polyarene)Fe(Cp*)] (polyarene=naphthalene (2), anthracene (3a)), which have two {(Cp*)Fe} units bound to opposite faces of the polyarene. One of two {(Cp*)Fe} units in 3a is located over the central ring of anthracene while the other is positioned over an outer ring. The {(Cp*)Fe} unit bound to the central ring of 3a migrates to the outer ring upon heating in the solid state to give the isomer 3b. The electrochemical potential separations between successive one-electron redox events for complexes 2 and 3b are large. The mixed valence complexes [2](+) and [3b](+) were synthesized by chemical oxidation. The mixed-valence complex [3b](+) is charge delocalized on the Mössbauer timescale at 78 K, and its absorption spectrum shows an intervalence charge-transfer band. Complex [2](+) exhibits two absorption bands in the near-IR region and a slightly broadened doublet in the Mössbauer spectrum. DFT calculations were carried out to examine the electronic structures of these dinuclear iron(I) complexes to elucidate the factors responsible for their diamagnetism and to determine the degree of charge delocalization in the mixed-valence complexes.

Synthesis, structures, and electronic properties of [8Fe-7S] cluster complexes modeling the nitrogenase P-cluster.

High-yield synthesis of the iron-sulfur cluster [{N(SiMe(3))(2)}{SC(NMe(2))(2)}Fe(4)S(3)](2)(mu(6)-S) {mu-N(SiMe(3))(2)}(2) (1), which reproduces the [8Fe-7S] core structure of the nitrogenase P(N)-cluster, has been achieved via two pathways: (1) Fe{N(SiMe(3))(2)}(2) + HSTip (Tip = 2,4,6-(i)Pr(3)C(6)H(2)) + tetramethylthiourea (SC(NMe(2))(2)) + elemental sulfur (S(8)); and (2) Fe(3){N(SiMe(3))(2)}(2)(mu-STip)(4) (2) + HSTip + SC(NMe(2))(2) + S(8). The thiourea and terminal amide ligands of 1 were found to be replaceable by thiolate ligands upon treatment with thiolate anions and thiols at -40 degrees C, respectively, and a series of [8Fe-7S] clusters bearing two to four thiolate ligands have been synthesized and their structures were determined by X-ray analysis. The structures of these model [8Fe-7S] clusters all closely resemble that of the reduced form of P-cluster (P(N)) having 8Fe(II) centers, while their 6Fe(II)-2Fe(III) oxidation states correspond to the oxidized form of P-cluster (P(OX)). The cyclic voltammograms of the [8Fe-7S] clusters reveal two quasi-reversible one-electron reduction processes, leading to the 8Fe(II) state that is the same as the P(N)-cluster, and the synthetic models demonstrate the redox behavior between the two major oxidation states of the native P-cluster. Replacement of the SC(NMe(2))(2) ligands in 1 with thiolate anions led to more negative reduction potentials, while a slight positive shift occurred upon replacement of the terminal amide ligands with thiolates. The clusters 1, (NEt(4))(2)[{N(SiMe(3))(2)}(SC(6)H(4)-4-Me)Fe(4)S(3)](2)(mu(6)-S){mu-N(SiMe(3))(2)}(2) (3a), and [(SBtp){SC(NMe(2))(2)}Fe(4)S(3)](2)(mu(6)-S){mu-N(SiMe(3))(2)}(2) (5; Btp = 2,6-(SiMe(3))(2)C(6)H(3)) are EPR silent at 4-100 K, and their temperature-dependent magnetic moments indicate a singlet ground state with antiferromagnetic couplings among the iron centers. The (57)Fe Mössbauer spectra of these clusters are consistent with the 6Fe(II)-2Fe(III) oxidation state, each exhibiting two doublets with an intensity ratio of ca. 1:3, which are assignable to Fe(III) and Fe(II), respectively. Comparison of the quadrupole splittings for 1, 3a, and 5 has led to the conclusion that two Fe(III) sites of the clusters are the peripheral iron atoms.

A new time-resolved fluorometric microarray detection system using core-shell-type fluorescent nanosphere and its application to allergen microarray.

We have developed a new time-resolved fluorometric (TRF) microarray detection system consisting of fluorescent NH2 nanosphere, TRF microarray detector and gamma-irradiated polystyrene chip. Using the TRF microarray detector, we detected 500 particles of the fluorescent nanosphere in one channel. Cross-talk fluorescence from the adjacent channels was little observed in the TRF microarray detector (<0.0004 %). The TRF microarray detection system was further applied for serum allergen-specific immunoglobulin E (IgE) multi-analyses. As a labeled tag antibody, an anti-human IgE Fab' fragment-conjugated fluorescent nanosphere (Fab' nanosphere) was prepared as described previously. As a chip surface appropriate for allergen immobilization, the polystyrene chip surface was modified by gamma irradiation. The immunoassay reactivity using the gamma-irradiated polystyrene chip was approximately 2.5-times improved compared with that of the non-treated polystyrene chip. Non-specific adsorption of the Fab' nanosphere onto the gamma-irradiated polystyrene chip surface was very low level (<0.0009 %). In only 20 mul of serum, six allergen-specific IgEs could be simultaneously determined in one reaction well in fewer than 90 min. Good correlation curves were obtained between the microarray immunoassay and the CAP RAST fluoro-enzyme immunoassay (CAP/RAST FEIA) method (r > 0.961). Reproducibility (CVs) of the microarray immunoassay was 8.6 % to 19.0 % (n = 5).

A steep one-step [HS-HS] to [LS-LS] spin transition in a 4,4'-bipyridine linked one-dimensional coordination polymer constructed from a pyrazolato bridged Fe(II) dimer.

The variable temperature magnetic susceptibility, X-ray crystallography, and Mössbauer and Raman spectra of a new dinuclear complex-based one-dimensional coordination polymer [[Fe(II)2(NCS)2(mu-bpypz)2](micro-4,4'-bpy)].MeOH demonstrated a steep one-step [HS-HS] to [LS-LS] spin transition.

Synthesis of the P-cluster inorganic core of nitrogenases.

The [8Fe-7S] core of the P-clusters in nitrogenases is unique among the known [Fe-S] clusters which are essential to electron-transfer processes in nature. The [8Fe-7S] cluster has been thought unstable and to exist only in protein environments. We found that this unusual [8Fe-7S] structure can be self-assembled from the reaction of Fe(II) bis-amide, tetramethylthiourea, 2,4,6-triisopropylbenzenethiol, and elemental sulfur in a specific mole ratio. The structure of the complex isolated therefrom closely resembles that of the reduced form (PN) of the P-clusters, while the 6Fe(II)2Fe(III) oxidation state was manifested by the Mössbauer study.

Design of novel inorganic-organic hybrid materials based on iron-chloranilate mononuclear complexes: characteristics of hydrogen-bond-supported layers toward the intercalation of guests.

Novel intercalation compounds constructed from the common two-dimensional hydrogen-bond-supported layers and functional guests [(H(0.5)phz)(2)[Fe(CA)(2)(H(2)O)(2)].2H(2)O](n)(1), ([Fe(Cp)(2)][Fe(CA)(2)(H(2)O)(2)])(n)(2), ([Fe(Cp*)(2)][Fe(CA)(2)(H(2)O)(2)])(n)(3), and [(TTF)(2)[Fe(CA)(2)(H(2)O)(2)]](n)(4) (H(2)CA = chloranilic acid, phz = phenazine, [Fe(Cp)(2)] = ferrocene, [Fe(Cp*)(2)] = decamethylferrocene, TTF = tetrathiafulvalene) are described. The guest cations are introduced between the ([Fe(CA)(2)(H(2)O)(2)](m-))(l) layers by electrostatic (1-4) and pi-pi stacking (3, 4) interactions. [Fe(Cp*)(2)](+) cations in 3 are stacked on each other making tilted columns which are included in the channel created by the chlorine atoms of CA(2-) dianions. TTF cations in 4 are stacked face to face with two types of S...S distances (type A; 3.579(3) A, and type B; 3.618(3) A) making a columnar structure. The TTF cations in the stacked column have a head-to-tail arrangement with respect to the iron-chloranilate layer. Mössbauer spectroscopy suggests that [Fe(CA)(2)(H(2)O)(2)](m-) anion in 3 is consistent with high-spin (S = 5/2) iron(III) ions and [Fe(Cp*)(2)](+) in the low-spin (S = 1/2) iron(III) ions. In 4, Mössbauer spectroscopy shows high-spin iron(II) ions (IS = 1.10 mm.s(-1) and QS = 1.66 mm.s(-1) at 297 K) and high-spin iron(III) ions (IS = 0.42 mm.s(-1) and QS = 1.27 mm.s(-1) at 297 K), suggesting that the anionic layer of iron-chloranilate has a valence-trapped mixed-valence state. At the temperature range of 77-300 K, the compounds 1, 2, and 3 are EPR silent, whereas the EPR spectrum of 4 shows two types of signals with g = 2.008 indicating the radical form of TTF.

The Valence-Detrapping Phase Transition in a Crystal of the Mixed-Valence Trinuclear Iron Cyanoacetate Complex [Fe(3)O(O(2)CCH(2)CN)(6)(H(2)O)(3)].

A mixed-valence trinuclear iron cyanoacetate complex, [Fe(3)O(O(2)CCH(2)CN)(6)(H(2)O)(3)] (1), was prepared, and the nature of the electron-detrapping phase transition was studied by a multitemperature single-crystal X-ray structure determination (296, 135, and 100 K) and calorimetry by comparison with an isostructural mixed-metal complex, [CoFe(2)O(O(2)CCH(2)CN)(6)(H(2)O)(3)] (2). The mixed-valence states at various temperatures were also determined by (57)Fe Mössbauer spectroscopy. The Mössbauer spectrum of 1 showed a valence-detrapped state at room temperature. With decreasing temperature the spectrum was abruptly transformed into a valence-trapped state around 129 K, well corresponding to the heat-capacity anomaly due to the phase transition (T(trs) = 128.2 K) observed in the calorimetry. The single-crystal X-ray structure determination revealed that 1 has an equilateral structure at 296 and 135 K, and that the structure changes into an isosceles one at 100 K due to the electron trapping. The crystal system of 1 at 296 K is rhombohedral, space group R&thremacr; with Z = 6 and a = 20.026(1) Å, c = 12.292(2) Å; at 135 K, a = 19.965(3) Å, c = 12.145(4) Å; and at 100 K, the crystal system changes into triclinic system, space group P&onemacr;, with Z = 2 and a = 12.094(2) Å, b = 12.182(3) Å, c = 12.208(3) Å, alpha = 110.04(2) degrees, beta = 108.71(2) degrees, gamma = 109.59(2) degrees. The X-ray structure determination at 100 K suggests that the electronically trapped phase of 1 at low temperature is an antiferroelectrically ordered phase, because the distorted Fe(3)O molecules, which are expected to possess a nonzero electronic dipole moment, oriented alternatively in the opposite direction with respect to the center of symmetry. On the other hand, no heat-capacity anomaly was observed in 2 between 7 and 300 K, and X-ray structure determination indicated that 2 shows no structure change when the temperature is decreased from 296 K down to 102 K. The crystal system of 2 at 296 K is rhombohedral, space group R&thremacr; with Z = 6 and a = 19.999(1) Å, c = 12.259(1) Å; at 102 K, a = 19.915(2) Å, c = 12.061(1) Å. Even at 102 K the CoFe(2)O complex still has a C(3) axis, and the three metal ion sites are crystallographically equivalent because of a static positional disorder of two Fe(III) ions and one Co(II) ion. The activation energy of intramolecular electron transfer of 1 in the high-temperature disordered phase was estimated to be 3.99 kJ mol(-)(1) from the temperature dependence of the Mössbauer spectra with the aid of the spectral simulation including the relaxation effect of intramolecular electron transfer. Finally the phase-transition mechanism of 1 was discussed in connection with the intermolecular dielectric interaction.

Rational Design of a Novel Intercalation System. Layer-Gap Control of Crystalline Coordination Polymers, {[Cu(CA)(H(2)O)(m)()](G)}(n)() (m = 2, G = 2,5-Dimethylpyrazine and Phenazine; m = 1, G = 1,2,3,4,6,7,8,9-Octahydrophenazine).

New copper(II) intercalation compounds, {[Cu(CA)(H(2)O)(2)](G)}(n)() (H(2)CA = chloranilic acid; G = 2,5-dimethylpyrazine (dmpyz) (1a and 1b) and phenazine (phz) (2)) have been synthesized and characterized. 1acrystallizes in the triclinic space group P&onemacr;, with a = 8.028(2) Å, b = 10.269(1) Å, c = 4.780(2) Å, alpha = 93.85(3) degrees, beta = 101.01(2) degrees, gamma = 90.04(3) degrees, and Z = 1. 1b crystallizes in the triclinic space group P&onemacr;, with a = 8.010(1) Å, b = 10.117(1) Å, c = 5.162(1) Å, alpha = 94.40(1) degrees, beta = 97.49(1) degrees, gamma = 112.64(1) degrees, and Z = 1. 2crystallizes in the triclinic space group P&onemacr;, with a = 8.071(1) Å, b = 11.266(1) Å, c = 4.991(1) Å, alpha = 97.80(1) degrees, beta = 99.58(1) degrees, gamma = 83.02(1) degrees, and Z = 1. For all the compounds, the crystal structures consist of one dimensional [Cu(CA)(H(2)O)(2)](m)() chains and uncoordinated guest molecules (G). Each copper atom for 1a, 1b, and 2 displays a six-coordinate geometry with the two bis-chelating CA(2)(-) anions and water molecules, providing an infinite, nearly coplanar linear chains running along the a-direction. Theses chains are linked by hydrogen bonds between the coordinated water and the oxygen atoms of CA(2)(-) on the adjacent chain, forming extended layers, which spread out along the ac-plane. The guest molecules are intercalated in between the {[Cu(CA)(H(2)O)(2)](k)()}(l)() layers, just like pillars, which are supported with N.H(2)O hydrogen bonding. The guest molecules are stacked each other with an interplanar distance of ca. 3.2 Å along the c-axis perpendicular to the [Cu(CA)(H(2)O)(2)](m)() chain. The EHMO band calculations of intercalated dmpyz and phz columns show an appreciable band dispersion of phz pi (b(2g) and b(3g)) and dmpyz pi (b(g)), indicative of the importance of planar pi structure for the formation of the intercalated structure. The distances of O-H---N (guest molecules) fall within the range 2.74-2.80 Å, insensitive to the guest, whereas the interlayer distances increase in the order 9.25 Å (1b), 10.24 Å (1a), and 11.03 Å (2). The degree in lengthening the distance correlates well with the size of a molecule, indicative of the stability of the 2-D sheet structure and the flexibility of the sheet packing. The magnetic susceptibilities were measured from 2 to 300 K and analyzed by a one-dimensional Heisenberg-exchange model to yield J = -1.83 cm(-)(1), g = 2.18 (1a), J = -0.39 cm(-)(1), g = 2.14 (1b), and J = -1.84 cm(-)(1), g = 2.18 (2). The absolute value of J is smaller than that value for [Cu(CA)](n)(), which has a planar ribbon structure suggesting that the magnetic orbital d(x)()()2(-)(y)()()2 is not parallel to the chloranilate plane. For comparison with phz another type of copper(II) coordination compound, {[Cu(CA)(H(2)O)](ohphz)}(n)() (ohphz = 1,2,3,4,6,7,8,9-octahydrophenazine (7)) has also been obtained. 7 crystallizes in the orthorhombic space group Cmcm with a = 7.601(2) Å, b = 13.884(2) Å, c = 17.676(4) Å, and Z = 4. Nonplanar ohphz molecules are in between [Cu(CA)(H(2)O)(2)](m)() chains with the N.H(2)O hydrogen bonding in a fashion parallel to the chain direction. The copper atom shows a five-coordinate square-pyramidal configuration with two CA and one water molecule, thus affording no hydrogen bonding links between chains, dissimilar to 1a, 1b, and 2. The magnetic susceptibilities yield J = -10.93 cm(-)(1) and g = 2.00, comparable to that of the four-coordinate [Cu(CA)](n)(). On this basis both hydrogen bonding and stack capability of a guest molecule is responsible for building the unique intercalated structure such as is seen in 1a, 1b, and 2.