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Oxidation of a blue ethanolic mixture containing Co(BF4)2·6H2O and PClPh2 by tetramethylthiuram disulfide afforded a red-colored complex having a cis-[CoIII(Me2dtc)2(P)2] environment (Me2dtc− = N,N-dimethyldithiocarbamate), although the yield was relatively low. Single-crystal X-ray crystallography revealed that the product was [Co(Me2dtc)2{(Ph2PO)2BF2}] (1), where bis(diphenylphosphinito)difluoroborate was probably formed by hydrolysis of PClPh2 followed by reaction with BF4− in ethanol. The same complex was also prepared by hydrolysis of cis-[Co(Me2dtc)2(PHPh2)2]BF4 in a mixture of acetonitrile, methanol and water. The molecular structure and spectroscopic properties of complex 1 were compared with those of the corresponding Ph2POMe complex, cis-[Co(Me2dtc)2(Ph2POMe)2]BF4.

Three iron(II) complexes with a linear symmetrical pentadentate ligand H 2 L 1 and a monodentate ligand X (X = N 3 − , NCS − , NCSe − ), [Fe II N 3 (H 2 L 1 )]BPh 4 ( 1 ), [Fe II NCS(H 2 L 1 )]BPh 4 ( 2 ), and [Fe II NCSe(H 2 L 1 )]BPh 4 ( 3 ), were synthesized and characterized, where H 2 L 1 denotes bis( N , N ′-2-methylimidazol-4-yl-methylideneaminopropyl)methylamine. Compounds 1 , 2 and 3 consist of a mononuclear complex-cation of [Fe II X(H 2 L 1 )] + (X = N 3 − , NCS − , NCSe − ) and a tetraphylborate (BPh 4 − ) anion. Each complex-cation has an octahedral coordination geometry with N 6 donor atoms of a linear pentadentate ligand of H 2 L 1 and a nitrogen atom of N 3 − , NCS − , or NCSe − , in which the linear pentadentate ligand is folded to coordinate to Fe II ion in a cis -form. One of two imidazole groups of a complex-cation is hydrogen bonded to N 3 − , NCS − , or NCSe − of the adjacent complex-cation to form a cyclic dimer structure for 1 and a zigzag-chain structure for 2 and 3 . The temperature dependence of the magnetic data revealed that 1 , 2 and 3 are high-spin (HS) complexes.

Four cobalt(III) complexes with the formula of [Co(Ln)2]− bearing tridentate amine-amidato-phenolato-type ligands (Ln: n = 1–4) were synthesized. All of the complexes were characterized by 1H NMR spectroscopy and X-ray analysis. The geometrical selectivity was found to depend on the flexibility of the amine-amidato chelate in combination with the planar 2-oxybenzamido 6-membered chelate; that is, the amine-amidato 5-membered chelate took the mer-type geometry, and the 6-membered chelate took the fac-type geometry. In most of the mer-type complexes, intermolecular double hydrogen bonds via amidato(O) and amino group were selectively formed between their enantiomeric pairs of mononuclear complexes. In the case of two chiral ligands {L22– = 2-amino-1-(2-oxybenzamido)propane; L32− = trans-1-amino-2-(2-oxybenzamido)cyclohexane}, [Co(L3)2]− showed diastereoselectivity while [Co(L2)2]− did not. Furthermore, PPh4[Co(L1)2] (L12− = 2-amino-1-(2-oxybenzamido)-2-methylpropane) showed an apparent solvatochromic behavior in several solvents. Although the molecular structures of [Co(L2 or L3)2]− are quite similar to that of [Co(L1)2]−, these complexes did not exhibit such a solvatochromic behavior.

A bidentate 2-methylimidazol-4-yl-methylideneaminobenzyl ligand (HLMe-Benz) reacts with FeIICl2·4H2O and NaPF6 at a 3:1:1 molar ratio to yield a tris(2-methylimidazol-4-yl-methylideneaminobenzyl)iron(II) chloride hexafluorophosphate solvate with the formula of [FeII(HLMe-Benz)3]Cl·PF6·solvent. Meridional and facial geometrical isomers, i.e., mer-[FeII (HLMe-Benz)3]Cl·PF6·1.5H2O (1·PF6·1.5H2O) and fac-[FeII(HLMe-Benz)3]Cl·PF6·EtOH·H2O (2·PF6·EtOH·H2O), were selectively crystallized from methanol and ethanol solutions, respectively. fac-[FeII(HLMe-Benz)3]Cl·SbF6·H2O (2·SbF6·H2O) and fac-[FeII(HLMe-Benz)3]Cl·ClO4·EtOH·H2O (2·ClO4·EtOH·H2O) are synthesized in ethanol, using the corresponding anions. Each FeII ion has an octahedral coordination geometry with N6 donor atoms from three bidentate ligands. All three imidazole groups in both the fac- and mer-[FeII(HLMe-Benz)3]2+ cations are hydrogen-bonded to neighboring three Cl− ions, and each Cl− ion is hydrogen-bonded to three imidazole groups of three neighboring complex cations; this results in the formation of hydrogen-bonded assembly structures. mer-Complex 1·PF6·1.5H2O forms a heterochiral two-dimensional (2D) network structure comprised of cyclic {mer-[FeII(HLMe-Benz)3]2+⋯Cl−}3 units with an ΔΔΛ or ΛΛΔ configuration; the PF6− ions occupy the spaces between the 2D layers. All the fac-complexes have isomorphous cubane-like tetrameric structures, i.e., {fac-[FeII(HLMe-Benz)3]2+⋯Cl−}4. The tetranuclear structure comprises four homo-chiral fac-Δ- or fac-Λ-[FeII(HLMe-Benz)3]2+ cations and four Cl− ions interconnected by twelve imidazole-chloride hydrogen bonds to form a chiral cubane supramolecule that encapsulates one counter anion. In the crystal lattice, the cubane-like tetramers with opposite chiralities are alternately arrayed. The temperature dependence of the magnetic susceptibilities and Mossbauer spectra reveal that the fac-complexes show incomplete spin crossover behavior, while the mer-complex shows a gradual spin crossover between high-spin (HS, S = 2) and low-spin (LS, S = 0) states.

A iron(II) complex of the linear hexadentate N6 ligand H2L2-3-2, [Fe(H2L2-3-2)](ClO4)2, was synthesized and the spin crossover properties were investigated, where H2L2-3-2 denotes bis[N-(2-methylimidazol-4-yl)methylidene-2-aminoethyl]propanediamine. The complex showed a gradual and reversible one-step spin crossover (SCO) between the high-spin (S = 2) and low-spin (S = 0) states at T1/2 = 208 K without hysteresis. The crystal structures were determined at 296 and 250 K (HS state), 230, 210, and 200 K (intermediate between the HS and LS states) and 150 and 110 K (LS state). The spin transition from 296 to 150 K accompanies with the conformation change of the chelate rings at the triamine moiety and the formation of the hydrogen bond network in the same space group of orthorhombic Pbcn (no. 60). However, in the LS state at 110 K, the space group changed from orthorhombic Pbcn at 150 K (Pcan when the same axial setting to 110 K was used) to monoclinic P21/a (no. 14) at 110 K, although no spin transition and no change of assembly structure between 150 and 110 K were observed. It give us an idea that the space group transformation is mainly related to the conformational thermodynamic stability of the chelate rings at the triamine moiety and is not directly correlated with the spin transition.

A series of compounds [FeIIH3LMe]Br·Y·nMeOH ( Y = PF 6 - (1), AsF 6 - (2), SbF 6 - (3), CF 3 SO 3 - (4); n = 0 or 1) were synthesized, where H3LMe is a hexadentate N6 tripodal ligand of the neutral form, tris[2-(((2-methylimidazol-4-yl)methylidene)amino)ethyl]amine, and their structures and magnetic properties were investigated. The compounds 1−3 with counter anions Y = PF 6 - , AsF 6 - , and SbF 6 - contain methanol as a crystal solvent, and show no SCO behaviors, while the corresponding Cl− compounds have no crystal solvent and show a variety of SCO behaviors. The compound [FeIIH3LMe]Br·CF3SO3 (4) has no crystal solvent and has isomorphous structure to the Cl− compounds, and shows an abrupt spin transition between the HS (S = 2) and LS (S = 0) states with a hysteresis about 2 K and large frozen-in effect below 72 K. The T1/2↑ and T1/2↓ values are 98 and 96 K, whose values are higher than those of corresponding Cl− compound about 15 K and the width of hysteresis is narrower than that of corresponding Cl− compound about 2 K. The crystal structures of 4 were determined at 296 and 93 K, where the crystal system and space group showed no change between these temperatures. The structures at both temperatures have a same 2D layered structure, which is composed of NH⋯Br− hydrogen bonds between the Br− ion and the imidazole NH groups of three neighboring cations [FeIIH3LMe]2+. This network structure is the same as that of corresponding Cl− compound. The 600 nm light irradiation at 5 K induced the LIESST effect.

Mononuclear [Fe(H2LR)2]X2 (R = H, 2-Me, 5-Me, 2-Et-5-Me; X = ClO4, BF4) and dinuclear [Fe2(H2LR)3]X4 complexes containing imidazole-4-carbaldehyde azine (H2LH) and its derivatives prepared by condensation of 4-formylimidazole, 2-methyl- or 5-methyl-4-formylimidazole, or 2-ethyl-4-methyl-5-formylimidazole, with hydrazine in a 2:1 mole ratio in methanol, were prepared and their magnetostructural relationships were studied. In the mononuclear complexes, H2LR acts as an unsymmetrical tridentate ligand with two imidazole nitrogen atoms and one azine nitrogen atom, while in the dinuclear complexes, H2LR acts as a dinucleating ligand employing four nitrogen atoms to form a triple helicate structure. At room temperature, [Fe2(H2LH)3](ClO4)4 and [Fe2(H2L2-Me)3](ClO4)4 were in the high-spin (HS) and low-spin (LS) states, respectively. The results are in accordance with the ligand field strength of H2L2-Me with electron-donating methyl groups being stronger than H2LH, with the order of the ligand field strengths being H2L2-Me > H2LH. However, in the mononuclear [Fe(H2LH)2](ClO4)2 and [Fe(H2L2-Me)2](ClO4)2 complexes, a different order of ligand field strengths, H2LH > H2L2-Me, was observed because [Fe(H2LH)2](ClO4)2 was in the LS state while [Fe(H2L2-Me)2](ClO4)2 was in the HS state at room temperature. X-ray structural studies revealed that the interligand steric repulsion between a methyl group of an H2L2-Me ligand and the other ligand in [Fe(H2L2-Me)2](ClO4)2 is responsible for the observed change in the spin state. The same is true for [Fe(H2L2-Et-5-Me)2](ClO4)2, while [Fe(H2L5-Me)2](ClO4)2 does not involve such a steric congestion and stays in the LS state over the temperature range 5–300 K. Two kinds of crystals (polymorphs) were isolated for [Fe2(H2LH)3](BF4)4 and [Fe2(H2L2-Et-5-Me)3](ClO4)4, and they exhibited different magnetic behaviors.

Scission of sulfide linkages in vulcanized rubber has been a major concern since the early 20th century, because devulcanization is a key process for recycling waste rubber products as polymer materials that pose low environmental risks. We herein demonstrate that lipid peroxidation (LPO) of linoleic acid by manganese peroxidase (MnP), a proposed lignin-degradation system in the early stage of selective white rot fungi, cleaves sulfide bond in a model rubber compound, di(2-methylpent-2-enyl) sulfide, to 2,4-dimethylthiophene and 2-methyl-2-pentenal. The major intermediate of the LPO process, 2,4-decadienal was directly oxidized by MnP to cleave the sulfur-carbon bond. We propose that electrophilic radicals from 2,4-decadienal abstract one electron from a sulfur atom of the model compound to produce the sulfur radical cation intermediate, which in turn reacts with molecular oxygen to cleave the sulfur-carbon bond. The discovery of free radical-mediated scission of sulfide bond coupled with Mn oxidation provides a novel strategy for recycling vulcanized rubber wastes.

Reaction of vanadium(III) chloride with 8-quinolinol (Hqn) gave a mononuclear vanadium(IV) complex, [VOCl2(H2O)2] 1) · 2H2qn · 2Cl · CH3CN, and three dinuclear vanadium(IV) complexes: [V2O2Cl2(qn)2(H2O)2] (2) · Hqn, [V2O2Cl2(qn)2(C3H7OH)2] (3), and [V2O2Cl2(qn)2(C4H9OH)2] (4). Reaction of vanadium(III) chloride with 5-chloro-8-quinolinol (HClqn) gave four dinuclear vanadium(IV) complexes: [V2O2Cl2(Clqn)2(H2O)2] (5) · 2HClqn, [V2O2Cl2(Clqn)2(C3H7OH)2] (6), [V2O2Cl2(Clqn)2(C6H5CH2OH)2] (7), and [V2O2Cl2(Clqn)2(C4H9OH)2] (8) · 2C4H9OH. Reaction of vanadium(III) chloride with 5-fluoro-8-quinolinol (HFqn) gave two dinuclear vanadium(IV) complexes: [V2O2Cl2(Fqn)2(H2O)2] (9) · HFqn · 2H2O and V2O2Cl2(Fqn)2(C3H7OH)2] (10). X-ray structures of 1 · 2H2qn · 2Cl · CH3CN, 3, 4, 6, 7, 8 · 2 t-BuOH, and 10 have been determined. As to the mononuclear species 1 · 2H2qn · 2Cl · CH3CN, coordination of Hqn to vanadium does not occur, but protonation to Hqn occurs to give H2qn+, which links 1’s through hydrogen bonding, while each of the dinuclear species has a terminal and a bridging qn (or Clqn, Fqn) ligand, giving rise to a (V–O)2 ring. Magnetic measurements of 3, 4, 6, 7, and 10 in solid form show very weak antiferromagnetic behavior, and the effective magnetic moments are close to spin only value (2.44) of d1–d1 system, while ESR of 3 in THF shows dissociation to monomeric species. Change from mononuclear, 1, to dinuclear, 2, species was followed by the change of electronic spectrum.

Several (azido)iridium(III) complexes having a pentamethylcyclopentadienyl (Cp∗) group, [Cp∗Ir(N3)2(Ph2Ppy-κP)] (1: Ph2Ppy = 2-diphenylphosphinopyridine), [Cp∗Ir(N3)(Ph2Ppy-κP,κN)]CF3SO3 (2), [Cp∗Ir(N3)(dmpm)]PF6 (3: dmpm = bis(dimethylphosphino)methane), [Cp∗Ir(N3)(Ph2Pqn)]PF6 · CH3OH (4 · CH3OH: Ph2Pqn = 8-diphenylphosphinoquinoline), and [Cp∗Ir(N3)(pybim)] (5: Hpybim = 2-(2-pyridyl)benzimidazole) have been prepared and their crystal structures have been analyzed by X-ray diffraction. In complex 1, the Ph2Ppy ligand is only coordinated via the P atom (-κP), while in 2 it acts as a bidentate ligand through the P and N atoms (-κP,κN) to form a four-membered chelate ring. Comparing the structural parameters of the chelate ring in 2 with those of a similar five-membered chelate ring formed by Ph2Pqn in 4, it became apparent that the angular distortion in the Ph2Ppy-κP,κN ring was remarkable, although the Ir–P and Ir–N bonds in the Ph2Ppy-κP,κN ring were not elongated very much from the corresponding bonds in the Ph2Pqn-κP,κN ring. In the pybim complex 5, the five-membered chelate ring was coplanar with the pyridine and benzimidazolyl rings. With the related (azido)iridium(III) complexes analyzed previously, comparison of the structural parameters of the Ir–N3 moiety in [Cp∗IrIII(N3)(L–L′)]+/0 complexes reveals an anomalous feature of the 2,2′-bipyridyl (bpy) complex, [Cp∗Ir(N3)(bpy)]PF6.

A Pd(II) complex containing didentate triazine ligand L1 (2-(2-methylphenyl)-3-(2-pyridyl)-2,3-dihydronaphtho[2,1-e][1,2,4]triazine) [PdCl2(L1)] (1) was prepared, and the structure was determined by X-ray crystallography. The absorption spectrum of complex 1 in dichloromethane changed gradually with isosbestic points when methanol was added to the solution, and [PdCl(L2)] (2) (L2 = N-[methoxy(2-pyridyl)methyl]-1-(2-methylphenylazo)-2-naphthylamide) was obtained from the resulting solution after the reaction was completed. Addition of hydrogen chloride to the solution of complex 2 led to the recovery of complex 1. Thus, a reversible ring opening and closure reaction of the triazine ligand was observed. The progress of the ring opening reaction was monitored by observing the absorbance changes at several wavelengths of the visible spectra as a function of the concentration of methanol. The absorbance plots were fitted successfully with a mechanism that includes the consumption of two methanol molecules and the release of HCl, whose concentration is equivalent to that of the produced Pd complex ( [ PdCl 2 ( L 1 ) ] + 2 CH 3 OH ⇌ [ PdCl ( L 2 ) ] + CH 3 OH 2 + · Cl - ) . In dichloromethane with a low dielectric constant, the polar HCl molecule will be stabilized by forming an adduct with methanol. The equilibrium constant was determined as K = [ PdCl ( L 2 ) ] [ CH 3 OH 2 + · Cl - ] [ PdCl 2 ( L 1 ) ] - 1 [ CH 3 OH ] - 2 = ( 2.2 ± 0.4 ) × 10 - 4 M - 1 at T = 25.0 °C. The kinetics of the reaction of [PdCl2(L1)] with methanol was investigated by monitoring the absorbance change of the reacting solution with time. We obtained rate constant values of k1 = (2.40 ± 0.07) × 10−3 s−1 and k2 = (5.8 ± 0.1) × 10−3 M−1 s−1 at T = 25.0 °C on the observed pseudo-first-order rate constant of the forward reaction, kf = k1 + k2 [CH3OH].

New ligands containing a heterocyclic ring, L1 (1-anilino-2-(2-pyridyl)-naphth[1,2-d]imidazol-1-io-3-ide), L2 (2-phenyl-3-(2-pyridyl)-3,4-dihydro-naphtho[2,1-e][1,2,4]triazin-1-io-4-ide), and L3 (1-anilino-2-(2-quinolyl)-naphth[1,2-d]imidazol-1-io-3-ide), and their palladium (II) complexes have been prepared. Structures of the ligands and the complexes were determined by X-ray crystallography. The mononuclear square-planar complexes of [PdCl2(Ln)] (n = 1 (1), n = 2 (2) and n = 3 (3)) had didentate Ln (n = 1–3) ligands. The Ln (n = 1–3) ligands were stable and their absorption spectra did not change in dichloromethane and methanol. On the other hand, the absorption spectrum of [PdCl2(L2)] (2) in dichloromethane changed rapidly when methanol was added to the solution, and [PdCl(L4b)] (5) (L4b = N-[methoxy(2-pyridyl)methyl]-1-(phenylazo)-2-naphthylamide) was obtained from the concentrated reaction mixture. In this reaction, the dihydrotriazine ring of the didentate L2 ligand in complex 2 opened and the resulting tridentate L4b ligand coordinated to the Pd atom in complex 5. When an excess amount of (nBu)4NCl was added to complex 5 in dichloromethane, the absorption spectrum reverted to that of complex 2. Thus, the reversible ring opening and closure reactions of the coordinating dihydrotriazine ligand were observed. We also prepared [PdCl2(L5)] (9) (L5 = 1-(phenylazo)-N-[1-(2-pyridyl)ethylidene]-2-naphthylamine) and determined the structure. It is noted that neither the ring closure reaction nor the coordination of the azo nitrogen atom of the L5 ligand occurred in complex 9.

Apolipoprotein B-48 (apoB-48) is produced by the small intestine, as a part of chylomicrons (CMs), and appears to be a suitable marker for clinical studies of postprandial lipoproteins and related cardiovascular risk factors. We have developed an assay for routine analysis to quantify apoB-48 in serum or plasma.A microtiter plate was coated with monoclonal antibody (4C8) raised against apoB-48 C-terminal specific decapeptide. Serum samples were diluted 100-fold with 0.05 mol/l Tris-HCl buffer (with or without 0.1% Triton X-100). Appropriate calibration curves were obtained in the ELISA by using apoB-48 recombinant antigen.No cross-reactivity (0.001%) was found with apoB-100, as verified by ELISA and Western blot analyses. Intra- and inter-assay CVs were 4.8% and 5.4%, respectively. Recovery of added recombinant apoB-48 in serum was within 94-105%. The assay linearity was intact5-fold dilution of serum by dilution buffer. ApoB-48 levels in healthy controls (n=18) at fasting were within the range of 2.69-6.56 microg/ml (mean+/-S.D.: 4.60+/-1.54 microg/ml). In healthy subjects, serum apoB-48 concentrations markedly increased in the postprandial state, in parallel with serum triglycerides.This method for measuring apoB-48 using the monoclonal antibody 4C8 is simple, reliable and suitable for routine analyses.

New palladium(II) and platinum(II) complexes with didentate ligands derived from 1-phenylazo-2-naphthylamine and 2-(diphenylphosphino)benzaldehyde or 2-(tert-butylthio)benzaldehyde have been prepared and their structures are determined by X-ray crystallography. The palladium(II) and platinum(II) complexes containing a phosphorus donor atom ([MCl2(L1)] (M=Pd2+ (1), Pt2+ (2))) are mononuclear, whereas the complex containing a sulfur donor atom ([PdCl(L2)]3 (3)) has a trinuclear structure. The three palladium atoms of complex 3 are bound to each other through bridging sulfur (thiolato) donor atoms and a six-membered ring (Pd3S3) is formed. Complex 3 reacts with potassium iodide in acetonitrile to yield a dinuclear complex, [PdI(L2)]2 (4), which has a bent structure. The short PdPd distance (2.8855(7) A) of complex 4 suggests a PdPd bonding interaction. The coordinated ligands (L1 and L2) contain a six-membered heterocyclic ring, whose bond and electronic structures are also discussed.

Tetradentate chiral Schiff base-Ln(III) complexes (where Ln represents a lanthanide series element) have been prepared from the reaction of N,N′-bis(2-pyridylmethylidene)-1,2-(R,R)-cyclohexanediamine with Ln(NO3)3·nH2O (Ln=La, Ce, Pr, Nd, Sm, Eu (for n=6), Gd (for n=5), and Yb (for n=3)), LnCl3·nH2O (Ln=Ce, Pr (for n=7), Nd, Er, and Yb (for n=6)), and Yb(CF3SO3)3. The structures of the complexes were determined using X-ray crystallography, and an effect of the ionic radius on the structure of the complexes was studied. The chiral Schiff base-Ln(III) complexes prepared in situ in acetonitrile displayed catalytic activity for the asymmetric Diels–Alder reaction of 3-(2-propenoyl)-2-oxazolidinone with cyclopentadiene. The (R)-endo isomer of the cyclo adduct was obtained with high diastereoselectivity and moderate enantioselectivity. The enantioselectivity was sensitive to the ionic radius of the Ln(III) ion, and the enantiomeric excess values increased monotonically in the order: La

This article describes the crystal structures of several vanadium complexes containing tetradentate Schiff base ligands, and their properties and reactivities in the solid state. [VO{sal-(R,R)-stien}] (H2sal-(R,R)-stien=N,N′-disalicylidene-(R,R)-1,2-diphenyl-1,2-ethanediamine) crystallized in two different forms, green (from dichloromethane and chloroform) and orange (from acetonitrile). X-ray structure analysis revealed that the green form contains mononuclear square-pyramidal molecules of the complex, whereas the orange form has a polynuclear linear chain structure. The green crystals turn orange when heated at 120 °C for a few minutes (thermochromism). Both forms are vapochromic, the orange crystals turning green on exposure to chloroform vapor, and the green crystals turning orange on exposure to acetonitrile vapor. The color of the orange complex changes to green on grinding (mechanochromism). [VO{3-EtOsal-(R,R)-2,4-ptn}] (H23-EtOsal-(R,R)-2,4-ptn=N,N′-di-3-ethoxysalicylidene-(R,R)-2,4-pentanediamine) also crystallizes in two different forms, green and orange. The polymeric orange crystals turn into the monomeric green form upon heating at 170 °C for 10 min. The mechanism of this conversion was studied using X-ray structure analysis and thermal analysis. Thermal isomerization in the solid state between a pair of diastereomers, I and II, of the oxovanadium(IV) complex with an unsymmetrical tetradentate Schiff base ligand, [VO{3-EtOsal,sal-(R,R)-chxn}] (H23-EtOsal,sal-(R,R)-chxn=N-salicylidene-N′-3-ethoxysalicylidene-(R,R)-1,2-cyclohexanediamine), was studied at 195 °C. The two diastereomers were separated using column chromatography, and each crystallized in two different colors: green (monomeric) and orange (polymeric). The orange complexes, I (orange) and II (orange), turned green on heating at 195 °C for a few minutes. All four complexes, I (green), II (green), I (orange), and II (orange), undergo isomerization at 195 °C to yield an equilibrium mixture, I:II≈1:1. On heating [VO(3-EtOsal-meso-stien)] (H23-EtOsal-meso-stien=N,N′-di-3-ethoxysalicylidene-(R,S)(S,R)-1,2-diphenyl-1,2-ethanediamine) at 190 °C for 8 h, dehydrogenation took place at the two benzylic carbon atom sites to form a C=C double bond in the five-membered N–N chelate ring moiety. A vanadium(V) species formed on heating the starting complex in the air will be the oxidant of the thermal dehydrogenation reaction.

The chiral and racemic oxovanadium(IV) salmmen complexes, [VO( X )-(C16-salmmen)] ( X = R ( 1 ), S ( 2 ), and rac ( 3 ); C16-salmmen = N , N ′-monomethylenebis(5-hexadecyloxysalicylideneimine)) containing 5-substituted alkoxy chains on aromatic rings were synthesized, and their mesomorphic behaviors and ferroelectric properties were also investigated. All complexes exhibited both smectic A and chiral smectic C mesophases above 360 K, and they showed ferroelectric properties in the chiral smectic C mesophase.

Tridentate Schiff base–ruthenium(II) complexes containing soft phosphorus or sulfur donor atoms were prepared, and their bidirectional thermal and photo substitution reactions were investigated. In acetonitrile, the chloro ligands of trans(Cl,Cl)[RuCl2(ppb-etol)(PPh3)] (1, ppb-etol=2-(Ph2P)C6H4CHN(CH2)2OH) were substituted by acetonitrile molecules stepwise to yield [RuCl(CH3CN)(ppb-etol)(PPh3)]Cl (2) (first step) and [Ru(CH3CN)2(ppb-etol)(PPh3)]Cl2 (3) (second step). Complexes 2 and 3 reverted to complex 1 in acetonitrile upon irradiation with UV–Vis light. Similar thermal and photo substitution reactions were also observed for trans(Cl,Cl)[RuCl2(btb-etol)(PPh3)] (4, btb-etol=2-(tBuS)C6H4CHN(CH2)2OH). The substitution rates were measured for the first-step reactions of complexes 1 and 4 over the temperature range of 19.5–29.5 °C in acetonitrile. Kinetic parameters were determined to be kobsd=(1.13±0.04)×10−4 s−1 (25.0 °C), ΔH‡=83.1±1.7 kJ mol−1, and ΔS‡=−41.9±5.6 kJ mol−1 for complex 1, and kobsd=(1.57±0.06)×10−3 s−1 (25.0 °C), ΔH‡=88.8±1.9 kJ mol−1, and ΔS‡=−0.9±6.5 kJ mol−1 for complex 4. Accordingly, the substitution reaction of complex 4 proceeded faster than that of complex 1. The structures of [RuCl2{ppb-(1R,2S)-ephe}(PPh3)] (5, ppb-(1R,2S)-ephe=2-(Ph2P)C6H4CHNCH(Me)CH(Ph)OH), complex 2, and [Ru(CH3CN)2{ppb-(R)-btol}(PPh3)](BF4)2 (6, ppb-(R)-btol=2-(Ph2P)C6H4CHNCH(Et)CH2OH) were determined by X-ray analyses. In each complex, the geometry around the ruthenium atom is distorted octahedral, and the tridentate Schiff base and triphenylphosphine ligands occupy the equatorial positions.

A series of mixed cobalt(III) complexes [Co(pySe)3−n(NN)n]n+ [pySe=pyridine-2-selenolato (1−); NN=1,2-ethanediamine (en) and 2,2′-bipyridine (bpy); n=0, 1 and 2] was prepared. The geometrical preference and trans influence of pySe are fairly different from those of pyridine-2-thiolate. These selenolato complexes were oxidized by peracetic acid to give the corresponding pyridine-2-seleninato (pySeO2) and pyridine-2-selenonato (pySeO3) complexes. The crystal structures of the pySeO2 and pySeO3 complexes revealed that the coordination mode change from an original N,Se-four-membered to the N,O-five-membered chelate ring occurred during oxidation and intramolecular hydrogen bonds between the non-coordinated oxygen of pySeO2 or pySeO3 and the amine protons of en stabilize the N,O-coordination mode.

Palladium(II) and platinum(II) complexes, [PdX(NS3 1Bu)]BPh4 (X=Cl, Br, I; NS3 1Bu=tris[2-(tert-butylthio)ethyl]amine) and [PtCl(NS3 1Bu)]BPh4, were prepared, and their structures were determined by X-ray analyses. The geometry around the palladium and platinum atoms is square planar. The NS3 1Bu ligand functions as a tridentate ligand and one sulfur atom is not coordinated to the metal. The 1H NMR spectrum of [PdCl(NS3 1Bu)]BPh4 in acetone-d6 exhibited a dynamic behavior. At 20°C the spectrum showed a singlet signal at 1.60 ppm that can be assigned to tert-butyl protons, whereas at −70°C three singlet signals were observed at 1.36, 1.61, and 1.70 ppm with an intensity ratio of 1: 0.25: 2. The signals at 1.36 and 1.70 ppm are assigned to the tert-butyl protons in the square-planar structure, and these signals are consistent with the X-ray structure. The signal at 1.61 ppm can be assigned to the tert-butyl protons in a trigonal-bipyramidal structure where the three tert-butyl groups are magnetically equivalent. Thus, we concluded that the coordination-site exchange occurred via a trigonal-bipyramidal intermediate. The square-planar and trigonal-bipyramidal species of [PdCl(NS3 1Bu)]BPh4 are in equilibrium in acetone-d6. The equilibrium was shifted toward the square-planar species on decreasing the temperature. The 1H NMR spectra for [PdX(NS3 1Bu)]BPh4 (X=Cl, Br, and I) were similar to one another at the same temperature, suggesting that the site-exchange process is insensitive to the kind of coexisting halogen ligand. The site exchange reaction of [PtCl(NS3 1Bu)]BPh4 seems to occur more slowly than that of the palladium(II) analogue.

Two optically-active O , O ′-dialkyl dithiophosphate ligands, (Bor) 2 PS 2 − and (Men) 2 PS 2 − , were prepared from P 2 S 5 and the monoterpene alcohols, d -borneol and l -menthol. The chromium(III) complexes, [Cr{(Bor) 2 PS 2 } 3 ] and [Cr{(Men) 2 PS 2 } 3 ], were prepared by reaction with Cr(NO 3 ) 3 ·9H 2 O in acetone. The diastereoisomers (Δ and Λ) were separated by fractional crystallization of the complexes from toluene ([Cr{(Bor) 2 PS 2 } 3 ]) or acetone ([Cr{(Men) 2 PS 2 } 3 ]). The (−) 680 CD -Δ-[Cr{(Bor) 2 PS 2 } 3 ] isomer was obtained from the less soluble part. This isomer shows extremely strong CD, Δ e (680 nm, toluene)=−15.0 M −1 cm −1 . The Δ-[Cr{(Men) 2 PS 2 } 3 ] isomer could not be obtained in the optically-pure state, since the complex inverts appreciably during the recrystallization procedure. Activation parameters for isomerization (epimerization), Δ→Λ and Λ→Δ were determined for both complexes, [Cr{(Bor) 2 PS 2 } 3 ] and [Cr{(Men) 2 PS 2 } 3 ]. [Cr{(Men) 2 PS 2 } 3 ] isomerizes much faster than [Cr{(Bor) 2 PS 2 } 3 ].

Preparation and properties of dinuclear cis- dioxomolybdenum(VI) complexes containing ONO–ONO-type hexadentate Schiff bases derived from 2,5-dihydroxyterephthalaldehyde and aminoalcohols in a 1:2 molar ratio are reported. When 2-amino-2-methyl-1,3-propanediol was used as the aminoalcohol, the 1 H NMR spectrum of the complex showed two sets of resonances, indicating the presence of two isomers. The origin of the isomerism was elucidated by variable-temperature 1 H NMR spectroscopy and by comparing the 1 H NMR spectrum with those of the analogous dinuclear complexes derived from (1 R ,2 S )- and (1 S ,2 R )-norephedrine and with those of the corresponding mononuclear complexes. The Schiff base ligand derived from 2,5-dihydroxyterephthalaldehyde and 2-amino-2-methyl-1,3-propanediol contains two prochiral carbon atoms, which become chiral ( R and S ) upon coordination. The combination of these two chiral centers generates three stereoisomers, RR , SS , and RS (= SR ), and the NMR characteristics were accounted for by these isomers.

Light brown [VO(5-NO2salen)]·2H2O (1; H2(5-NO2 salen)=N,N′-di-5-nitrosalicylidene-1,2-ethanediamine) and orange [VO(5-NO2sal-meso-stien)]·0.5H2O (2; H2(5-NO2sal-meso-stien)=N,N′-di-5-nitrosalicylidene-(R,S)(S,R)-1,2-diphenyl-1,2-ethanediamine) which have linear chain structures in the solid state turn dark brown and yellow-brown, respectively, when ground thoroughly in mortars. The IR spectra of 1 and 2 in Nujol mulls show strong V=O stretching bands at 875 and 905 cm−1, respectively. On the other hand, the spectra of the finely ground complexes in Nujol mulls show very weak V=O stretching bands. X-ray powder diffraction patterns of the ground complexes scarcely show diffraction peaks. The spectroscopic and magnetic data suggest that the linear chain structures in the crystals of 1 and 2 are destroyed on grinding to yield the fragments of the polymeric chains.

New tetradentate Schiff base–oxovanadium(IV) complexes which have electron donating or withdrawing groups at the 5-position of the salicylaldehyde moieties, [VO{Xsal-(R,R)-2,4-ptn}] (H2{Xsal-(R,R)-2,4-ptn}: N,N′-di-Xsalicylidene-(R,R)-2,4-pentanediamine; X=5-MeO (methoxy), 5-Br, and 5-NO2) were prepared. The structures and redox potentials for the V(V)/V(IV) couple of the complexes were compared with those of other [VO{Xsal-(R,R)-2,4-ptn}] (X=3-EtO (ethoxy), 3-MeO, and H). The 5-MeO substituted complex which has electron donating groups at the 5-position of the salicylaldehyde moieties forms a monomeric structure in the solid state. The 3-EtO substituted complex has both monomeric and polymeric structures. On the other hand, the other [VO{Xsal-(R,R)-2,4-ptn}] (X=H, 3-MeO, 5-Br, 5-NO2) complexes have only polymeric structures. X-ray crystal structure analysis of [VO{5-MeOsal-(R,R)-2,4-ptn}]⋅CH3OH (1) was carried out. Complex 1 has a monomeric five-coordinate square–pyramidal structure. The six-membered N–N chelate ring forms a distorted flattened boat form with two methyl groups in the axial positions.

Dioxomolybdenum(VI)-tridentate Schiff base complexes, [MoO2{nap-(R)-btol}(py)], (1), [{MoO2{nap-(R)-btol}}2(4,4′-bpy)] (2), and [MoO2{nap-(R)-btol}] · CH2Cl2 (3) (H2nap-(R)-btol= (R)-2-[(2-hydroxy-1-naphthyl)methylideneamino]butanol, py = pyridine, 4,4′-bpy = bipyridine) were prepared and their structures determined by the X-ray method. In 1–3, the geometry around molybdenum is a distorted octahedron with one oxide ligand and the Schiff base ligand in the equatorial position. The oxide ligand occupies the axial position and the nitrogen atom of pyridine or 4,4′-bipyridine coordinates at the sixth site of the molybdenum center for1 or2 respectively. In3, the axial oxide ligand of one molecule coordinates to the sixth site of the molybdenum atom in an adjacent molecule to give an infinite linear Mo O...Mo O... chain,1 contains only one of the four possible isomers, while2 and3 are composed of two isomers. The 1H NMR spectra suggest rapid isomerization between the isomers in CD2Cl2 even at low temperatures. The isomers would proceed via a five-coordinate intermediate where rotation of the cis-MoO2 moiety takes place.

The H2O2 oxidation of [Co(pyt)(en)2]2+ [1, pyt=2-pyridinethiolate(1−) ion, en=ethylenediamine] afforded the orange [Co(pyse-N,S)(en)2]2+ [2, pyse=2-pyridinesulfenate(1−) ion] complex. Irradiation of this orange complex in the solid state yielded a green complex. The molecular structure of the green complex perchlorate was determined by X-ray diffraction to be [Co(pyse-N,O)(en)2](ClO4)2 (4); linkage isomerization took place upon photolysis. The crystal data and final R value for the cocrystal (3/5) are: triclinic, P 1 , a=9.374(4) A, b=11.248(4) A, c=9.238(8) A, α=95.26(4)°, β=95.14(5)°, γ=75.75(3)°, V=938(2) A3, Z=2 and R=0.040 for 2757 unique reflections. The pyse-N,O complex has an anomalous feature in the UV–vis spectrum. It has an extra band (16 400 cm−1) on the low-energy side of the first d–d absorption band (22 200 cm−1). This band can be rationalized as a splitting component of the first d–d band generated by the anisotropic interaction of the antibonding π* orbital of the coordinating oxygen with the t2g orbitals on the cobalt center. Treatment of [Co(pyt)(en)2]2+ with excess H2O2 afforded the yellow-orange sulfinato-N,S complex, [Co(pysi-N,S)(en)2]2+ [3, pysi=2-pyridinesulfinate(1−) ion]. The molecular structure of the pysi-N,S complex was determined by X-ray diffraction to be [Co(pysi-N,S)(en)2](ClO4)2 (3), which cocrystallized with the pysi-N,O complex (5). The crystal data and final R value are: monoclinic, C2, a=28.559(8) A, b=6.960(2) A, c=10.406(3) A, β=99.90(2)°, V=2038(2) A3, Z=4 and R=0.040 for 2391 unique reflections. The pysi-N,S complex was unstable and was easily converted photochemically or thermally to the linkage-isomerized orange pysi-N,O complex (5). The sulfur atom becomes chiral (R and S) upon linkage isomerization, and two kinds of racemic salt, Λ(R)Δ(S) and Λ(S)Δ(R), were separated by fractional crystallization of the complex perchlorate. The molecular structure of the less soluble isomer (Λ(S)Δ(R)-5) of the perchlorate was determined by X-ray diffraction to be Λ(S)Δ(R)-[Co(pysi-N,O)(en)2](ClO4)2. The crystal data and final R value are: triclinic, P 1 , a=9.384(4) A, b=11.807(8) A, c=8.640(5) A, α=98.54(5)°, β=94.40(4)°, γ=96.65(5)°, V=936(2) A3, Z=2 and R=0.038 for 3061 unique reflections. The two diastereomers of Λ-[Co(pysi-N,O)(en)2]2+ were separated by SP-Sephadex column chromatography, and one of them (Λ(R)-5) was structurally characterized by X-ray crystallography. Λ(R)-[Co(pysi-N,O)(en)2](ClO4)2, which crystallizes as orthorhombic in space group P212121 with Z=4, has the cell parameters a=9.896(2) A, b=20.758(6) A, c=9.494(4) A, V=1950(2) A3. The final R value was 0.041 for 1543 unique reflections. Kinetic studies of reversible isomerization (epimerization) between Λ(R)- and Λ(S)-[Co(pysi-N,O)(en)2]2+ were performed in aqueous solutions at 60 °C. The rate constants were kΛ(R)→Λ(S)=5.5×10−6 s−1 and kΛ(S)→Λ(R)=1.7×10−6 s−1. The orange-red [Co(pyso-N,O)(en)2]2+ [6, pyso=2-pyridinesulfonate(1−) ion] complex was prepared by the reaction of cis-[Co{OS(O)2CF3}2(en)2]+ with the 2-pyridinesulfonate ligand or by the oxidation of [Co(pyse-N,O)(en)2]2+ (4) with H2O2. The molecular structure of the trifluoromethanesulfonate salt of complex 6 was determined by X-ray diffraction. [Co(pyso-N,O)(en)2](CF3SO3)2 crystallizes as monoclinic in space group P21/a with Z=4. The cell parameters are a=19.079(8) A, b=16.699(6) A, c=7.462(4) A, β=100.51(4)°, V=2338(2) A3. The final R value was 0.050 for 3966 unique reflections. The pyso ligand has the strongest ligand field strength among the ligands studied here. A series of sulfur oxidation from [Co(pyt)(en)2]2+ to [Co(pyso-N,O)(en)2]2+ is established.

New tetradentate (O2N2, S2N2, and P2N2) Schiff base—ruthenium(II)(III) complexes were prepared and their properties were investigated. The Schiff base—ruthenium(II) complexes containing soft sulfur donor atoms cause photosubstitution of the axial ligands under room light. Thus, [RuCl2(btb-en)] (btb-en = N,N′-bis(2-tert-butylthiobenzilidene)-1,2-ethanediamine) in acetonitrile under room light yields [RuCl-(CH3CN)(btb-en)]Cl. The analogous photosubstitution reaction of [RuCl2{ppb-(RR)-chxn}] (ppb-(RR)-chxn = N,N′-bis(2-diphenyl-phosphinobenzilidene)-1,2-cyclohexanediamine) was also observed in acetonitrile. On the other hand, the photosubstitution reaction of [RuCl(PPh3){sal-(RR)-chxn}] (H2sal-(RR)-chxn = N,N′-disalicylidene-(R,R)-1,2-cyclohexanediamine) did not occur under the same conditions. The single-crystal diffraction studies afforded the following crystal data: monoclinic, C2/c, a = 16.092(4), b = 9.699(2), c = 20.618 (4) A, β = 109.20(2)°, Z = 4 for [RuCl2(btb-tn)] (btb-tn = N,N′-bis(2-tert-butylthiobenzilidene)-1,3-propanediamine); monoclinic, P21/n, a = 9.688(3), b = 16.795(3), c = 18.086(3) A, β = 101.10(2)°, Z = 4 for [RuCl(CH3CN)(btb-en)]Cl.

The six-coordinated octahedral silicon(IV) complex [Si(ht)3]+, where ht denotes the unsymmetrical didentate 4-isopropyltropolonate(1−) (≡ hinokitiolate(1−), C10H11O2) ligand, was prepared. The complex was resolved partially by fractional crystallization of the diastereomer with d-tartratoantimonate(III), [Sb2(d-tart)2]2−. The enantiomer obtained from the less soluble part was assigned to Λ on the basis of the exciton theory. The two geometrical isomers, mer (meridional) and fac (facial), were separated by high-performance ion-pair liquid chromatography. Kinetics of racemization and geometrical isomerization of mer-Λ- and fac-Λ-[Si(ht)3]+ were followed spectropolarimetrically and chromatographically respectively in methanol, 1,1,2,2-tetrachloroethane, and chloroform at 30–50°C. The first-order rate constants and activation energies for both reactions are similar to each other. The results are interpreted in terms of a common reaction pathway; they proceed by a bond-rupture mechanism through a five-coordinated intermediate.

The product of photolysis of K 3 (+)-[Co( l -cysi-N,S) 3 ] ( 1 , l -cysi= l -cysteinesulfinate(2−) ion, cysi=NH 2 CH(COO − )CH 2 SO 2 − ) was separated by column chromatography on DEAE-Sephadex A-25. The main band contained [Co( l -cysi-N,S) 2 ( l -cysi-N,O)] 3− ( 2 ); linkage isomerization from sulfinato- S to sulfinato- O took place. This complex ( 2 ) is thermally unstable and reverts to the starting complex ( 1 ). An anion-exchange high-performance liquid chromatographic (HPLC) method was successfully applied to the kinetic study of this linkage isomerization reaction from 2 to 1 .

The [Co(acac) 2 ( N -phenylethylenediamine)] + (acac= 2,4-pentanedionate ion)and[Co(acac) 2 ( N,N′ -diphenylethylenediamine)] + complexes were separated into two and three racemic pairs of the diastereomers, respectively, by means of column chromatography and the diastereomers were resolved by the chemical method. The diastereomers are stable in acidic water pH (2.5), but easily epimerize in neutral or basic water. The isomer distributions at equilibrium were determined and the results compared with those of the corresponding N -methyl-substituted ethylenediamine complexes.

The rates of the base-catalyzed proton exchange and inversion (epimerization) at chiral nitrogen centers of [Co(acac) 2 (Ph-en)] + (acac=2,4-pentanedionate ion; Ph-en= N -phenylethylenediamine) and [Co(acac) 2 (Me-en)] + (Me-en= N -methylethylenediamine) in aqueous solutions have been measured at 34.0 °C. The Ph-en complex, which has an electron-withdrawing phenyl group on the nitrogen atom undergoes proton exchange about 10 4 times faster than the Me-en complex which has an electron-repelling methyl group. The proton-exchange rates are ca . 10 2 and 10 5 times greater than the inversion rates for the Ph-en and Me-en complexes, respectively. The faster rate of inversion for the Ph-en complex was explained by the lower barrier of inversion; an increased stabilization of the intermediate was due to (p-p) π conjugation between the amide nitrogen atom and the phenyl group.

A high-performance liquid chromatographic (HPLC) method was successfully applied to kinetic studies of the inversion at the selenium atom of [Co(acac)2-(CH3SeCH2CH2NH2)]+ (acac — 2,4-pentanedionate ion). The complex was separated into two racemic pairs, Δ(R), Λ(S) and Δ(S), Λ(R), by column chromatography on sulphoethyl (SE)-Toyopearl. The racemate, Δ(R), Λ(S) or Δ(S), Λ(R), was epimerized in 0.05 mol dm-3 Na2SO4, and then the products, Δ(R), Λ(S) and Δ(S), Λ(R), were separated on SE-Toyopearl packed in an HPLC column. The activation enthalpy obtained, ΔH* — 113 kJ mol-1, is the highest reported so far for inversion of coordinated selenide.

By reaction of [RhCl2(tren)]+ (tren = tris(2-aminoethyl)amine) with CH3SeCH2CH2NH2 in water in the presence of NaBH4, or in its absence in ethanol, only one of the two geometrical isomers of [Rh(SeCH2CH2NH2)(tren)]2+ was formed. Both of the two geometrical isomers of the corresponding CoIII complex were formed by the reaction of CoII-tren species with (NH2CH2CH2Se–)2. The structure of the RhIII complex was determined by the X-ray method. Crystal data [Rh(C2H6NSe)(C6H18N4)](ClO4)2, monoclinic, space group P21/c, a = 9.012(1), b = 14.438(1), c = 14.550(4) A, β = 104.81(1)°, and Z = 4. The final R value was 0.026. The complex ion has a distorted octahedral structure with cis(tertiary amine nitrogen, Se) configuration. The RhN bond length for the amine nitrogen bonded trans to the selenium atom is longer by 0.039(6) A than the average cis RhN distance for the two other primary amine nitrogen of the tren ligand, indicating rans influence of the selenium atom.

Cinetique de l'inversion sur l'atome de Se de [Co(Clacac ou Meacac) 2 (CH 3 SeCH 2 CH 2 NH 2 )] + . L'ordre des cinetiques est Clacac