Naoto Kuwamura

Anion-Controlled Assembly of Four Manganese Ions: Structural, Magnetic, and Electrochemical Properties of Tetramanganese Complexes Stabilized by Xanthene-Bridged Schiff Base Ligands

The reaction of manganese(II) acetate with a xanthene-bridged bis[3-(salicylideneamino)-1-propanol] ligand, H(4)L, afforded the tetramanganese(II,II,III,III) complex [Mn(4)(L)(2)(μ-OAc)(2)], which has an incomplete double-cubane structure. The corresponding reaction using manganese(II) chloride in the presence of a base gave the tetramanganese(III,III,III,III) complex [Mn(4)(L)(2)Cl(3)(μ(4)-Cl)(OH(2))], in which four Mn ions are bridged by a Cl(-) ion. A pair of L ligands has a propensity to incorporate four Mn ions, the arrangement and oxidation states of which are dependent on the coexistent anions.

Carbene–carbanion equilibrium for tris(2-pyridylthio)methanido Fe(II) complexes

A reaction of FeCl(2) with tris(2-pyridylthio)methane (tptmH) produced the carbanion complex [Fe(tptm)(CH(3)CN)(2)](FeCl(4)){(C(2)H(5))(3)NH}. When FeI(2) was used instead of FeCl(2), the carbene complex [FeI(pyt)(bptmd)] (pyt = 2-pyridinethiolate, bptmd = bis(2-pyridylthio)methylidene) was isolated. The carbene forms [FeX(pyt)(bptmd)](n+) (n = 1 for X = CH(3)CN, n = 0 for X = I) were observed for [Fe(tptm)(CH(3)CN)(2)](FeCl(4)){(C(2)H(5))(3)NH} and [FeI(pyt)(bptmd)] in chloroform, whereas the carbene-carbanion equilibrium was observed in acetonitrile by NMR measurements. The thermodynamic parameters were evaluated by variable temperature (1)H NMR measurements using the diamagnetic salt [Fe(tptm)(CH(3)CN)(2)]PF(6) for [Fe(tptm)(CH(3)CN)(2)](+)⇆ [Fe(pyt)(bptmd)(CH(3)CN)](+) + CH(3)CN (ΔH = 23 kJ mol(-1), ΔS = 55 J mol(-1) K(-1)).

pH‐Controlled Multiple Chiral Inversion That Induces Molecular Dimerization in a Gold(I)–Cobalt(III) Coordination System with L‐Cysteinate

Herein, a unique coordination system that exhibits multiple chiral inversions and molecular dimerization in response to a subtle pH change is reported. Treatment of (Δ)2-H3[Au3Co2(L-cys)6] (H3[1 a]) with [Co3(aet)6](NO3)3 (aet=2-aminoethanethiolate) in water at pH 7 gave a 1:1 complex salt of [Co3(aet)6](3+) and [1 a](3-), retaining the Au(I)3Co(III)2 structure and chiral configurations of [1 a](3-). Similar treatment at pH 9 led to not only the inversion of all of the chiral Co(III) and S centers but also the dimerization of [1 a](3-), giving a 2:1 complex salt of [Co3(aet)6](3+) and (Λ)4(R)12-[Au6Co4(L-cys)12](6-) ([2](6-)). When dissociated from [Co3(aet)6](3+) in solution, [2](6-) was converted to (Λ)2(R)6-[Au3Co2(L-cys)6](3-) ([1 b](3-)) with retention of the chiral configurations.

Mimicking the photosynthetic system with strong hydrogen bonds to promote proton electron concerted reactions.

A Copper(2+) complex with a CuII–C bond containing sp3 configuration was used to investigate the role of strong hydrogen bonds in proton coupled electron transfer (PCET) reactions. The only example of a CuII–C system realized so far is that using tris-(pyridylthio)methyl (tptm) as a tetradentate tripodal ligand. Using this ligand, [CuF(tptm)] and [Cu(tptm)(OH)] have been prepared. The former complex forms supra-molecular arrays of layers of the complex between which hydroquinone is intercalated in the crystalline phase. This hydroquinone intercalation crystal was prepared via the photochemical conversion of quinone during the crystallization process. This conversion reaction probably involves a proton coupled electron transfer process. The nuclear magnetic resonance spectroscopic analysis of the reaction mixture shows the presence of Cu(III) during the conversion reaction. These results strongly suggest the presence of the molecular aggregate of the [CuF(tptm)] complex, water and quinone in the solution phase during the quinone to hydroquinone conversion. The presence of this type of aggregate requires a strong hydrogen bond between the [CuF(tptm)] complex and water. The presence of this particular hydrogen bond is a unique character of such a complex that has the CuII–C bond. This complex is used as a model for photosynthetic water splitting since the photoconversion of quinone to hydroquinone also involves the production of oxygen from water.

Chiral Scrambling and Independent Crystallization of d4, l4, and d2l2 Isomers of an AuI4CoIII2 Hexanuclear Complex with Mixed Penicillaminate and Bis(diphenylphosphino)ethane

The 1:1 mixing of a pair of enantiomers of a cyclic Au(I)4Co(III)2 hexanuclear complex having penicillaminate (pen) and 1,2-bis(diphenylphosphino)ethane (dppe), [Au4Co2(dppe)2(d-pen)4](2+) (d4-[1](2+)) and [Au4Co2(dppe)2(l-pen)4](2+) (l4-[1](2+)), in solution produced an additional stereoisomer, [Au4Co2(dppe)2(d-pen)2(l-pen)2](2+) (d2l2-[1](2+)), because of the scrambling of [Co(d-pen)2](-) and [Co(l-pen)2](-) units between d4-[1](2+) and l4-[1](2+). Upon crystallization with NO3(-), the three stereoisomers were independently crystallized to form three different kinds of crystals, homochiral crystals of d4-[1](NO3)2, homochiral crystals of l4-[1](NO3)2, and heterochiral crystals of d2l2-[1](NO3)2, showing a unique example of the self-recognition and organization of three stereoisomers upon crystallization.

Valence Interconversion of Octahedral Nickel(II/III/IV) Centers

Three oxidation states (+2, +3, +4) of an octahedral nickel center were stabilized in a newly prepared RhNiRh trinuclear complex, [Ni{Rh(apt)3 }2 ]n+ (apt=3- aminopropanethiolate), in which the nickel center was bound by six thiolato donors sourced from two redox-inert fac-[RhIII (apt)3 ] octahedral units. The three oxidation states of the octahedral nickel center were fully characterized by single-crystal X-ray crystallography, as well as spectroscopic, electrochemical, and magnetic measurements; all three were interconvertible, and the conversion was accompanied by changes in color, magnetism, and Jahn-Teller distortion.

Bis(μ2-4,7-dimethyl-4,7-diazadecane-1,10-dithiolato)trinickel(II) bis(perchlorate)

In the title compound, [Ni3(C10H22N2S2)2](ClO4)2, the complex cation consists of a nickel(II) ion and two [Ni(C10H22N2S2)] units with an N2S2 tetradentate ligand, 3,3′-[1,2-ethanediylbis(methylimino)]bis(1-propanethiolate). The central NiII ion is located on a crystallographic inversion centre and is bound to the four S atoms of the two [Ni(C10H22N2S2)] units to form a linear sulfur-bridged trimetallic moiety. The dihedral angle between the central NiS4 plane and the terminal NiN2S2 plane is 145.71 (5)°. In the [Ni(C10H22N2S2)] unit, the two methyl groups on the chelating N atoms are cis to each other, and the two six-membered N,S-chelate rings adopt a chair conformation. The Ni—S bond lengths and the S—Ni—S bite angles in the central NiS4 group are similar to those in the [Ni(C10H22N2S2)] unit.

Creation of Optically Pure Crystals from a Meso-type Gold(I) Metalloligand with D- and L-Amino Acids: A Coordination Trick

A unique example of a coordination system that creates optically pure crystals from a meso compound with d- and l-amino acids is reported. The 1:1 reaction of a newly prepared meso digold(I) complex, [Au2 (dcpe)(d-Hpen)(l-Hpen)] ([H2 1]), with Co(OAc)2 under aerobic conditions yielded a cationic AuI2 CoIII trinuclear complex, [Au2 Co(dcpe)(d-pen)(l-pen)]+ [2]+ , in which [1]2- acts as a hexadentate-N2 ,O2 ,S2 metalloligand to a CoIII center. Similar reactions with M(OAc)2 (M=Ni and Zn) produced analogous but neutral AuI2 MII complexes, [Au2 M(dcpe)(d-pen)(l-pen)] ([3M ]). Complexes [2]+ and [3M ] are chiral (C vs. A) at the octahedral CoIII and MII centers due to the arrangement of the N2 ,O2 ,S2 donor set. In addition, through spontaneous resolution, [3M ] gave optically pure C-[3M ] and A-[3M ] crystals, showing the creation of homochirality from meso-[1]2- and achiral M2+ through crystallization. Such a phenomenon was not observed for [2]+ , which gave a racemic compound containing both C-[2]+ and A-[2]+ .

Crystal structure of (2S,4S)-5,5-dimethyl-2-(pyridin-2-yl)-1,3-thia­zolidine-4-carb­oxy­lic acid

In the title compound, C11H14N2O2S, the thiazolidine ring has an envelope conformation with the C atom bonded to the carboxylic acid group at the flap. Two C atoms of the thiazolidine ring adopt S conformations. In the crystal, O—H⋯N hydrogen bonds between the amine and carboxylic acid groups construct a helical chain structure along the a-axis direction. The chains are further connected via weak C—H⋯π contacts, forming a layer parallel to the ac plane.