Mikio Yamasaki

Bidirectional Chemo‐Switching of Spin State in a Microporous Framework

The ins and outs of spin: Using the microporous coordination polymer {Fe(pz)[Pt(CN)(4)]} (1, pz=pyrazine), incorporating spin-crossover subunits, two-directional magnetic chemo-switching is achieved at room temperature. In situ magnetic measurements following guest vapor injection show that most guest molecules transform 1 from the low-spin (LS) state to the high-spin (HS) state, whereas CS(2) uniquely causes the reverse HS-to-LS transition.

Dinuclear Cobalt(II) Complexes of an Acyclic Phenol‐Based Dinucleating Ligand with Four Methoxyethyl Chelating Arms − First Magnetic Analyses in an Axially Distorted Octahedral Field

An end-off type acyclic ligand with four methoxyethyl chelating arms, 2,6-bis[bis(2-methoxyethyl)aminomethyl]-4-methylphenol [H(bomp)], formed dinuclear cobalt(II) complexes [Co2(bomp)(MeCO2)2]BPh4 (1) and [Co2(bomp)(PhCO2)2]BPh4 (2). X-ray analysis revealed that complex 1·CHCl3 contains two cobalt ions bridged by a phenolic oxygen and two acetate groups, forming a μ-phenoxo-bis(μ-acetato)dicobalt(II) core. Magnetic susceptibility was measured for 1 and 2 over the temperature range 1.8−300xa0K. The data were successfully analyzed using a new theoretical method assuming an axially distorted octahedral field (Δ = 753 and 775 cm−1, respectively) for each cobalt(II) ion to reveal weak antiferromagnetic interactions (J = −0.96 and −1.74 cm−1, respectively).

Synthesis, structure, and magnetic properties of dinuclear nickel(II) complexes with a phenol-based dinucleating ligand with four methoxyethyl chelating arms

Dinuclear nickel(II) complexes [Ni2(bomp)(MeCO2)2]BPh4 (1) and [Ni2(bomp)(PhCO2)2]BPh4 (2) were synthesized with the dinucleating ligand 2,6-bis[bis(2-methoxyethyl)aminomethyl]-4-methylphenol [H(bomp)]. X-Ray analysis revealed that the complex 1xa0·xa00.5CHCl3 contains two nickel(II) ions bridged by phenolic oxygen and two acetate groups, forming a μ-phenoxo-bis(μ-acetato)dinickel(II) core. Electronic spectra were investigated for 1 and 2 in the range of 400–1800 nm, and the data were typical for the octahedral high-spin nickel(II) complexes. Obtained spectral components were well simulated based on the angular overlap model assuming the trigonally distorted octahedral geometry. Magnetic susceptibility was measured for 1 and 2 over a temperature range of 4.5–300 K. The optimized magnetic data were Jxa0=xa01.75 cm−1, zJ′xa0=xa0−0.234 cm−1, gxa0=xa02.21, Dxa0=xa015.1 cm−1, and TIPxa0=xa0370xa0×xa010−6 cm−1 for complex 1 and Jxa0=xa03.55 cm−1, zJ′xa0=xa0−0.238 cm−1, gxa0=xa02.23, Dxa0=xa021.8 cm−1, and TIPxa0=xa0470xa0×xa010−6 cm−1 for complex 2. The data revealed ferromagnetic interactions between the two nickel(II) ions.

Manganese(II) complexes of an acyclic phenol-based dinucleating ligand with four methoxyethyl chelating arms: synthesis, structure, magnetism and electrochemistry

Abstract Dinuclear manganese(II) complexes [Mn 2 (bomp)(PhCO 2 ) 2 ]BPh 4 ( 1 ), [Mn 2 (bomp)(MeCO 2 ) 2 ]BPh 4 ( 2 ), and [Mn 2 (bomp)(PhCO 2 ) 2 ]PF 6 ( 3 ) were synthesized with a dinucleating ligand 2,6-bis[bis(2-methoxyethyl)aminomethyl]-4-methylphenol [H(bomp)]. Dinuclear zinc complex [Zn 2 (bomp)(PhCO 2 ) 2 ]PF 6 ( 4 ) was also synthesized for the purpose of comparison. X-ray analysis revealed that the complex 1 ·CHCl 3 contains two manganese ions bridged by the phenolic oxygen and two benzoate groups, forming a μ-phenoxo-bis(μ-benzoato)dimanganese(II) core. Magnetic susceptibility measurements of 1 – 3 over the temperature range 1.8–300xa0K indicated antiferromagnetic interaction ( J =−4 to −6xa0cm −1 ). Cyclic voltammograms of 3 showed a quasi-reversible oxidation process at +0.9xa0V versus a saturated sodium chloride calomel reference electrode, assigned to Mn II Mn II /Mn II Mn III .

Preparation, spectroscopic properties, and dynamic behavior of a μ-oxo dirhenium(III) complex [Re2(μ-O)Cl2(tpa)2](PF6)2 (tpa=tris(2-pyridylmethyl)amine)

Abstract An oxo-bridged dirhenium(III,III) complex of tris(2-pyridylmethyl)amine (tpa) and its one-electron oxidized (III,IV) species, [Re2(μ-O)Cl2(tpa)2]3+,4+ have been prepared. They are new members to a series of rhenium tpa complexes in various oxidation states. X-ray structural determination of the Re2(III,IV) complex revealed practically linear Reue5f8Oue5f8Re bridge (178(1)°) with short Reue5f8O distances of 1.85(2) A indicative of some multiple bonded character. The 1H NMR spectrum disclosed the relatively slow rotation around the Reue5f8Oue5f8Re axis in CH3CN solution in the timescale of 1H NMR. The complex undergoes two consecutive reversible one electron oxidations Re2(III,III)/(III,IV) and Re2(III,IV)/(IV,IV) at E1/2=0.23 and 0.90 V vs Ag/AgCl, respectively. Strong visible absorption bands are observed for the Re2(III,III) species at 448 (e=31u2008160) and 563 nm (19u2008550) which are tentatively assigned to MLCT transitions. A unique oxidation product, Re2(μ-O)(O)2Cl2(bpaO2)2 (bpaO2H=1,3-bis(2-pyridyl)-2-aza-propanedione) has also been isolated and its crystal structure was determined. The complex is dirhenium(V) species with linear Oue605Reue5f8Oue5f8Reue605O moiety. Ligand tpa has been oxidized to ketone with simultaneous dissociation of one of the 2-pyridylmethyl arms.

Syntheses of sulfur-bridged tungsten(V) complexes with syn-W2O2S2 cores. X-ray structures of K2[W2O2S2(cys)2]·5H2O and NaNH4[W2O2S2(edta)]·2H2O

Abstract Facile synthetic methods for sulfur-bridged tungsten(V) dimers, [W2O2S2(cys)2]2−1 are described, which were obtained directly from sodium tungstate, sodium sulfide, and L -cysteine, together with the description of another route to [W2O2S2(cys)2]2− using ammonium tetrathiotungstate and L -cysteine. Synthetic methods for the derivative compounds, W2O2S22+(aq) and [W2O2S2(edta)]2− are also described. The X-ray structures of two compounds are determined. The compound K2[W2O2S2(cys)2]·5H2O (1) crystallizes in the monoclinic space group P21, a=9.670(1), b=15.993(2), c=6.893(1) A, β=95.02(1)°, V=1062.0(3) A3, Z=2, R=2.76%. The compound NaNH4[W2O2S2(edta)]·2H2O crystallizes in monoclinic P21/a, a=24.522(8), b=12.395(6), c=7.098(2) A, β=104.21(3)°, V=2091.5(14) A3, Z=4, R=4.24%. The complex anions [W2O2S2(cys)2]2− and [W2O2S2(edta)]2− have an approximate symmetry of C2 and contain the core syn-W2(Ot)2(μ-S)2.

Cubane-Type Molybdenum-Zinc or -Cadmium Mixed-Metal Clusters with Diethyldithiophosphate or Nitrilotriacetate Ligands

The reactions of sulfur-bridged clusters, [Mo3(μ3-S)(μ-S)3(μ-dtp)(dtp)3(CH3CN)] (1) in acetonitrile or [Mo3(μ3-S)(μ-S)3(Hnta)3]2− (2) in pure water, with zinc or cadmium metal result in the formation of three novel molybdenum-zinc or molybdenum-cadmium mixed-metal clusters, [Zn{(μ3-S)4Mo3(μ-dtp)(dtp)3(CH3CN)}2] (3), [Cd{(μ3-S)4Mo3(μ-dtp)(dtp)3(CH3CN)}2] (4), and [Cd{(μ3-S)4Mo3(Hnta)3}2]4− (5), respectively. The X-ray crystal structures of 1·H2O(1′), 3, 4, and [Co(H2O)6]25·22H2O (5′) were determined, and the existence of the sandwich cubane-type cores Mo3S4MS4Mo8+3 cores (M=Zn, Cd) in 3, 4, and 5′ verified. By the change of the ligands, the peak positions at the longest wavelength in the electronic spectra are distinctly different from each other between 4 (856 nm) and 6 (1235 nm). The electronic structures of 3, 4, and 5 have been calculated by Discrete Variational (DV)-Xα method.

Dinuclear zinc(II) complex of a new acyclic phenol-based dinucleating ligand with four methoxyethyl chelating arms: first dizinc model with aminopeptidase function

A new end-off type acyclic ligand with four methoxyethyl chelating arms, 2,6-bis[bis(2-methoxyethyl)aminomethyl]-4-methylphenol (Hbomp), formed a dinuclear zinc(II) complex [Zn2(bomp)(MeCO2)2]BPh4 1. X-Ray analysis revealed that the complex 1·CHCl3 contains two zinc ions bridged by the phenolic oxygen and two acetate groups, forming a µ-phenoxo-bis(µ-acetato)dizinc(II) core. The aminopeptidase function of complex 1 was estimated using N-p-nitrophenyl-L-leucine as substrate. The release of p-nitroaniline as the result of the substrate hydrolysis is first order in both complex and substrate concentrations with kxa0=xa02.3(1)xa0×xa010–3 dm3 mol–1 s–1.

Synthesis, structure and reactivities of the dinuclear μ-η1:η6-arylethynyl ruthenium complexes [Cp(PR3)2Ru(μ-η1:η6-CCC6H4Me-p)RuCp*]·Cl (R=Ph, Me; Cp=η5-C5H5, Cp*=η5-C5Me5). The molecular structure of [Cp(PPh3)2Ru(μ-η1:η6-CCC6H4Me-p)RuCp*]·PF6

Abstract Treatment of [Cp(PR3)2Ru(Cue606CC6H4Me-p) (1a, R=Ph 1b, R=Me; Cp=η5-C5H5) with [Cp*Ru(μ3·Cl)]4 (Cp*=η5-C5Me5) selectively produced the novel dinuclear μ-η1:η6- arylethynyl complex Cp(PR3)2Ru(μ-η1:η6-Cue606CC6H4Me-p)RuCp*] (2·Cl: 2a, R=Ph; 2b, R=Me). Protonation of 2·OTf (OTf=OSO2CF3) by TfOH afforded the corresponding vinylidene complex [Cp(PR3)2Ru(μ-η1:η6-Cue605CHC6H4Me-p)RuCp*]·[OTf]2 (3·[OTf]2: 3a, R=Ph; 3b, R=Me), which regenerated 2·OTf upon treatment with LiBHEt3. Reaction of 2a·Cl with I2 and subsequent anion metathesis with AgBF4 produced the iodovinylidene complex [Cp(PPh3)2Ru(μ-η1:η6-Cue605CIC6H4Me-p)RuCp*]·[BF4]2 (4·[BF4]2), whereas similar treatment of 2b·PF6 yielded the iodo/arylethynyl complex [Cp(I)(PMe3)2Ru(μ-η1:η6-Cue606CC6H4Me-p)RuCp*]·[PF6]2 (5·[PF6]2). Substitution of one of the PPh3 ligands in 2a·OTf proceeded under 1 atm of CO to form [Cp(PPh3)(CO)Ru(μ-η1:η6-Cue606CC6H4Me-p)RuCp*]·OTf (6·OTf). The molecular structure of 2a·PF6 was determined by X-ray crystallography.

Magnetic Properties of a Dinuclear Nickel(II) Complex with 2,6-Bis[(2-hydroxyethyl)methylaminomethyl]-4-methylphenolate

Magnetic properties of dinuclear nickel(II) complex [Ni2(sym-hmp)2](BPh4)2·3.5DMF·0.5(2-PrOH) (1), where (sym-hmp)- is 2,6-bis[(2-hydroxyethyl)methylaminomethyl]-4-methylphenolate anion and DMF indicates dimethylformamide, were investigated using high-frequency and -field electron paramagnetic resonance (HFEPR). To magnetically characterize the mononuclear nickel(II) species forming the dimer, its two dinuclear zinc(II) analogues, [Zn2(sym-hmp)2](BPh4)2·3.5DMF·0.5(2-PrOH) (2) and [Zn2(sym-hmp)2](BPh4)2·2acetone·2H2O (2), were prepared. One of them (2) was structurally characterized by X-ray diffractometry and doped with 5% mol nickel(II) ions to prepare a mixed crystal 3. From the HFEPR results on complex 1 obtained at 40 K, the spin Hamiltonian parameters of the first excited spin state (S = 1) of the dimer were accurately determined as |D1| = 9.99(2) cm-1, |E1| = 1.62(1) cm-1, and g1 = [2.25(1), 2.19(2), 2.27(2)], and for the second excited spin state (S = 2) at 150 K estimated as |D2| ≈ 3.5 cm-1. From these numbers, the single-ion zero-field splitting (ZFS) parameter of the Ni(II) ions forming the dimer was estimated as |DNi| ≈ 10-10.5 cm-1. The HFEPR spectra of 3 yielded directly the single-ion parameters for DNi = +10.1 cm-1, |ENi| = 3.1 cm-1, and giso = 2.2. On the basis of the HFEPR results, the previously obtained magnetic data (Sakiyama, H.; Tone, K.; Yamasaki, M.; Mikuriya, M. Inorg. Chim. Acta 2011, 365, 183) were reanalyzed, and the isotropic interaction parameter between the Ni(II) ions was determined as J = -70 cm-1 (Hex = -J SA·SB). Finally, density functional theory calculations yielded the J value of -90 cm-1 in a qualitative agreement with the experiment.