Synthesis of Microporous Aluminosilicate by Direct Thermal Activation of Phenyl-Substituted Single-Source Aluminosilicate Molecular Precursors.

The construction of aluminosilicates from versatile molecular precursors (MPs) represents a promising alternative strategy to conventional processes based on monomeric molecular or polymeric Al and Si sources. However, the use of MPs often suffers from drawbacks such as the decomposition of the core structures in the presence of solvents, acids, or bases. In this work, we demonstrate a simple thermal synthesis of porous aluminosilicates from single-source spiro-7-type MPs that consist of a tetrahedral Al atom and six Si atoms functionalized with 12 phenyl (Ph) groups, (C+)[Al{Ph2Si(OSiPh2O)2}2]- (C+[AlSi6]-; C+ = pyridinium cation (PyH+), Na+, K+, Rb+, or Cs+), without using a solvent or activator. Microporous aluminosilicates synthesized via the thermal treatment of C+[AlSi6]- under a 79% N2 + 21% O2 atmosphere exhibited extremely low carbon contents (0.10-1.28%), together with Si/Al ratios of 3.9-6.7 ± 0.2 and surface areas of 103.1-246.3 m2/g. The solid-state 27Al and 29Si MAS NMR spectra suggest that the obtained aluminosilicates with alkali cations retain a tetrahedral Al site derived from the spiro-7-type core structure. After a proton-exchange reaction, the aluminosilicates showed almost 1.5 times higher reactivity in the catalytic ring-opening of styrene oxide than the aluminosilicate before proton exchange due to the catalytically active OH site being predominantly bridged by tetrahedral Al and Si atoms. These results suggest that the present MP strategy is a promising method for the introduction of key structures into active inorganic materials.

Tunable Synchronicity of Molecular Valence Tautomerism with Macroscopic Solid-Liquid Transition by Molecular Lattice Engineering.

The combination of a cobalt-dioxolene core that exhibits valence tautomerism (VT) with pyridine-3,5-dicarboxylic acid functionalized with chains bearing two, four, or six oxyethylene units led to new complexes ConEGEspy (n = 2, 4, and 6). These complexes commonly form violet crystals of the low-spin (ls)-[CoIII (nEGEspy)2 (3,6-DTBSQ)(3,6-DTBCat)] (ls-[CoIII ], 3,6-DTBSQ = 3,6-di-tert-butyl semiquinonato, 3,6-DTBCat = 3,6-di-tert-butyl catecholato). Interestingly, violet crystals of Co2EGEspy in the ls-[CoIII ] transitioned into a green liquid, accompanied by an almost complete VT shift (94 %) to the high-spin (hs)-[CoII (nEGEspy)2 (3,6-DTBSQ)2 ] (hs-[CoII ]) upon melting. In contrast, violet crystals of Co4EGEspy and Co6EGEspy in the ls-[CoIII ] exhibited partial VT (33 %) and only a 9.3 % VT shift after melting, respectively. These data demonstrate the tunability of the synchronicity of the molecular VT and macroscopic solid-liquid transitions by optimizing the tethered chains, thus establishing a new strategy for coupling bistable molecules with the macroscopic world.

Functional Group-Directed Photochemical Reactions of Aromatic Alcohols, Amines, and Thiols Triggered by Excited-State Hydrogen Detachment: Additive-free Oligomerization, Disulfidation, and C(sp2)-H Carboxylation with CO2.

Exploring new types of photochemical reactions is of great interest in the field of synthetic chemistry. Although excited-state hydrogen detachment (ESHD) represents a promising prospective template for additive-free photochemical reactions, applications of ESHD in a synthetic context remains scarce. Herein, we demonstrate the expansion of this photochemical reaction toward oligomerization, disulfidation, and regioselective C(sp2)-H carboxylation of aromatic alcohols, thiols, and amines. In the absence of any radical initiators in tetrahydrofuran upon irradiation with UV light (λ = 280 or 300 nm) under an atmosphere of N2 or CO2, thiols and catechol afforded disulfides and oligomers, respectively, as main products. Especially, the photochemical disulfidation proceeded highly selectively with the NMR and quantum yields of up to 69 and 0.46%, respectively. In stark contrast, the photolysis of phenylenediamines and aminophenols results in photocarboxylation in the presence of CO2 (1 atm). p-Aminophenol was quantitatively carboxylated by photolysis for 17 h with a quantum yield of 0.45%. Furthermore, the photocarboxylation of phenylenediamines and aminophenols proceeds in a highly selective fashion on the aromatic C(sp2)-H bond next to a functional group, which is directed by the site-selective ESHD of the functional groups for the formation of aminyl and hydroxyl radicals.

Molecular Insights into the Ligand-Based Six-Proton- and Six-Electron-Transfer Processes Between Tris-ortho-Phenylenediamines and Tris-ortho-Benzoquinodiimines.

The global demand for energy and the concerns over climate issues renders the development of alternative renewable energy sources such as hydrogen (H2 ) important. A high-spin (hs) FeII complex with o-phenylenediamine (opda) ligands, [FeII (opda)3 ]2+ (hs-[6R]2+ ), was reported showing photochemical H2 evolution. In addition, a low-spin (ls) [FeII (bqdi)3 ]2+ (bqdi: o-benzoquinodiimine) (ls-[0R]2+ ) formation by O2 oxidation of hs-[6R]2+ , accompanied by ligand-based six-proton and six-electron transfer, revealed the potential of the complex with redox-active ligands as a novel multiple-proton and -electron storage material, albeit that the mechanism has not yet been understood. This paper reports that the oxidized ls-[0R][PF6 ]2 can be reduced by hydrazine giving ls-[FeII (opda)(bqdi)2 ][PF6 ]2 (ls-[2R][PF6 ]2 ) and ls-[FeII (opda)2 (bqdi)][PF6 ]2 (ls-[4R][PF6 ]2 ) with localized ligand-based proton-coupled mixed-valence (LPMV) states. The first isolation and characterization of the key intermediates with LPMV states offer unprecedented molecular insights into the design of photoresponsive molecule-based hydrogen-storage materials.

Impact of Group†10 Metals on the Solvent-Induced Disproportionation of o-Semiquinonato Complexes.

The oxidation of [MII (3,5-DTBCat)(DTBbpy)] (M=Ni ([Ni]), Pd ([Pd]), and Pt ([Pt]); 3,5-DTBCat=3,5-di-tert-butylcatecholato; DTBbpy=4,4'-di-tert-butyl-2,2'-bipyridine) afforded the dimeric {[NiII (3,5-DTBSQ)(DTBbpy)](PF6 )}2 ({[Ni](PF6 )}2 ; 3,5-DTBSQ=3,5-di-tert-butylsemiquinonato) and monomeric semiquinonato (SQ) complexes [MII (3,5-DTBSQ)(DTBbpy)](PF6 ) (M=Pd ([Pd](PF6 )) and Pt ([Pt](PF6 ))). The negative solvatochromic properties of the SQ complexes allowed us to estimate the relative order of their dipole moments: [Pd](PF6 )>[Pt](PF6 )>{[Ni](PF6 )}2 . The complexes [Pd](PF6 ) and [Pt](PF6 ) adopt monomeric structures and are stable in CH2 Cl2 and toluene, whereas they gradually disproportionate at room temperature to [M] and 3,5-di-tert-butylbenzoquinone (3,5-DTBBQ) in polar solvents such as THF, MeOH, EtOH, DMF, or DMSO. The results of spectroscopic studies suggested that the oxidized nickel complex adopts a monomeric structure ([Ni](PF6 )) in CH2 Cl2 , but a dimeric structure ({[Ni](PF6 )}2 ) in the other investigated solvents. In polar solvents, {[Ni](PF6 )}2 may disproportionate to [Ni] and 3,5-DTBBQ at 323 K, thereby demonstrating a significant solvent- and metal-dependence in temperature. The relative activities of {[Ni](PF6 )}2 and [M](PF6 ) toward disproportionation are related to the electrochemically estimated Kdis values in CH2 Cl2 and DMF. The present work demonstrates that solvent polarity and the dipole moments of the SQ complexes promote disproportionation, which can be controlled by a judicious choice of the metal ion, solvent, and temperature.

Tuning the Mesomorphism and Redox Response of Anionic-Ligand-Based Mixed-Valent Nickel(II) Complexes by Alkyl-Substituted Quaternary Ammonium Cations.

The combination of the redox-active mesogenic anion [NiII (Bdt)(BdtSQ)]- (Bdt=1,2-benzenedithiolato; BdtSQ=1,2-dithia-semi-benzoquinonato) with alkyl-substituted ammonium cations afforded a series of redox-active ionic complexes of the type [NR4 ][NiII (Bdt)(BdtSQ)] [R=nC16 H33 (NC164 Ni) and C8,10 (NC8,104 Ni); C8,10=6-octylhexadecyl] or [NMe2 R2 ][NiII (Bdt)(BdtSQ)] [R=nC16 H33 (NMe2 C162 Ni) and C8,10 (NMe2 C8,102 Ni)]. X-ray crystallographic analyses of NMe2 C162 Ni and NC164 Ni revealed the formation of cation-dependent integrated ionic layers separated by interdigittated alkyl chains. Complexes NMe2 C162 Ni and NC164 Ni commonly form crystalline phases at room temperature, whereas complexes NMe2 C8,102 Ni and NC8,104 Ni, which contain branched alkyl chains, form a metastable mesophase and an amorphous phase at the same temperature, respectively. Furthermore, complexes NMe2 C162 Ni, NMe2 C8,102 Ni, and NC164 Ni commonly form a smectic A phase (SmA) at 375, 317, and 342 K, respectively. For the four complexes, well-defined cyclic voltammetry responses, derived from ligand-based oxidation and reduction, were observed in solution and the condensed phases, that is, upon casting these complexes on an indium-doped tin oxide working electrode. The present study demonstrates the tunability of the mesomorphism of ionic molecular assemblies composed of alkyl-substituted quaternary ammonium cations, while maintaining the well-defined redox responses of the anions even in the condensed phases.

A Coordination Network with Ligand-Centered Redox Activity Based on facial-[CrIII (2-mercaptophenolato)3 ]3- Metalloligands.

The design of redox-active metal-organic frameworks and coordination networks (CNs), which exhibit metal- and/or ligand-centered redox activity, has recently received increased attention. In this study, the redox-active metalloligand (RML) [Me4 N]3 fac-[CrIII (mp)3 ] (1) (mp=2-mercaptophenolato) was synthesized and characterized by single-crystal X-ray diffraction analysis, and its reversible ligand-centered one-electron oxidation was examined by cyclic voltammetry and spectroelectrochemical measurements. Since complex 1 contains O/S coordination sites in three directions, complexation with K+ ions led to the formation of the two-dimensional honeycomb sheet-structured [K3 fac-{CrIII (mp)3 }(H2 O)6 ]n (2⋅6 H2 O), which is the first example of a redox-active CN constructed from a RML with o-disubstituted benzene ligands. Herein, we unambiguously demonstrate the ligand-centered redox activity of the RML within the CN 2⋅6 H2 O in the solid state.

Shape-Memory Platinum(II) Complexes: Intelligent Vapor-History Sensor with ON-OFF Switching Function.

A novel platinum(II)-diimine complex, [Pt(CN)2 (H2 dcphen)] (1; H2 dcphen=4,7-dicarboxy-1,10- phenanthroline), was synthesized and its vapochromic shape-memory behavior was evaluated. The as-synthesized amorphous purple solid, [Pt(CN)2 (H2 dcphen)]⋅2 H2 O (1 P), exhibited vapochromic behavior in the presence of alcoholic vapors through transformation to a red, crystalline, porous, vapor-adsorbed form, 1 R⊃vapor. The obtained 1 R⊃vapor complex released the adsorbed vapors upon heating without collapse of the porous structure. The vaporfree, porous 1 R⊃open could detect water or n-hexane vapor, although these vapors could not induce 1 P-to-1 R⊃vapor transformation, and 1 R⊃open could easily be converted to the initial 1 P by manual grinding. These results indicate that 1 is a new shape-memory material that functions through formation and collapse of the porous framework with an emission change upon vapor-adsorption and grinding; this enables it to exhibit vapor history and ON-OFF switching sensing functions.

Systematic syntheses and metalloligand doping of flexible porous coordination polymers composed of a Co(III)-metalloligand.

A series of flexible porous coordination polymers (PCPs) RE-Co, composed of a Co(III)-metalloligand [Co(dcbpy)3](3-) (Co; H2dcbpy = 4,4'-dicarboxy-2,2'-bipyridine) and lanthanide cations (RE(3+) = La(3+), Ce(3+), Pr(3+), Nd(3+), Sm(3+), Eu(3+), Gd(3+), Tb(3+), Er(3+)), was systematically synthesized. X-ray crystallographic analysis revealed that the six carboxylates at the top of each coordination octahedron of Co(III)-metalloligand were commonly bound to RE(3+) cations to form a rock-salt-type porous coordination framework. When RE-Co contains a smaller and heavier RE(3+) cation than Nd(3+), the RE-Co crystallized in the cubic Fm-3m space group, whereas the other three RE-Co with larger RE(3+) crystallized in the lower symmetrical orthorhombic Fddd space group, owing to the asymmetric 10-coordinated bicapped square antiprism structure of the larger RE(3+) cation. Powder X-ray diffraction and vapor-adsorption isotherm measurements revealed that all synthesized RE-Co PCPs show reversible amorphous-crystalline transitions, triggered by water-vapor-adsorption/desorption. This transition behavior strongly depends on the kind of RE(3+); the transition of orthorhombic RE-Co was hardly observed under exposure to CH3OH vapor, but the RE-Co with smaller cations such as Gd(3+) showed the transition under exposure to CH3OH vapors. Further tuning of vapor-adsorption property was examined by doping of Ru(II)-metalloligands, [Ru(dcbpy)3](4-), [Ru(dcbpy)2Cl2](4-), [Ru(dcbpy)(tpy)Cl](-), and [Ru(dcbpy)(dctpy)](3-) (abbreviated as RuA, RuB, RuC, and RuD, respectively; tpy = 2,2':6',2″-terpyridine, H2dctpy = 4,4″-dicarboxy-2,2':6',2″-terpyridine), into the Co(III)-metalloligand site of Gd-Co to form the Ru(II)-doped PCP RuX@Gd-Co (X = A, B, C, or D). Three Ru(II)-metalloligands, RuA, RuB, and RuD dopants, were found to be uniformly incorporated into the Gd-Co framework by replacing the original Co(III)-metalloligand, whereas the doping of RuC failed probably because of the less number of coordination sites. In addition, we found that the RuA doping into the Gd-Co PCP had a large effect on vapor-adsorption due to the electrostatic interaction originating from the negatively charged RuA sites in the framework and the charge-compensating Li(+) cations in the porous channel.

Vapochromic luminescence and flexibility control of porous coordination polymers by substitution of luminescent multinuclear Cu(I) cluster nodes.

Two luminescent porous coordination polymers (PCPs), i.e., [Cu2(µ2-I)2ctpyz]n and [Cu4(µ3-I)4ctpyz]n (Cu2 and Cu4, respectively; ctpyz = cis-1,3,5-cyclohexanetriyl-2,2',2″-tripyrazine), were successfully synthesized and characterized by single-crystal X-ray diffraction and luminescence spectroscopic measurements. Cu2 consists of rhombus-type dinuclear {Cu2I2} cores bridged by ctpyz ligands, while Cu4 is constructed of cubane-type tetranuclear {Cu4I4} cores bridged by ctpyz ligands. The void fraction of Cu4 is estimated to be 48.0%, which is significantly larger than that of Cu2 (19.9%). Under UV irradiation, both PCPs exhibit red luminescence at room temperature in the solid state (λem values of 660 and 614 nm for Cu2 and Cu4, respectively). Although the phosphorescence of Cu2 does not change upon removal and/or adsorption of EtOH solvent molecules in the porous channels, the solid-state emission maximum of Cu4 red-shifts by 36 nm (λem = 650 nm) upon the removal of the adsorbed benzonitrile (PhCN) molecules from the porous channels (and vice versa). This large difference in the vapochromic behavior of Cu2 and Cu4 is closely related to the framework flexibility. The framework of Cu2 is sufficiently rigid to retain the porous structure without solvated EtOH molecules, whereas the porous structure of Cu4 collapses easily after removal of the adsorbed PhCN molecules to form a nonporous amorphous phase. The original vapor-adsorbed porous structure of Cu4 is regenerated by exposure of the amorphous solid to not only PhCN vapor but also tetrahydrofuran, acetone, ethyl acetate, and N,N-dimethylformamide vapors. The Cu4 structures with the various adsorbed solvents showed almost the same emission maxima as the original PhCN-adsorbed Cu4, except for DMF-adsorbed Cu4, which showed no luminescence probably because of weak coordination of the DMF vapor molecules to the Cu(I) centers of the tetranuclear {Cu4I4} core.

Photoinduced dimerization reaction coupled with oxygenation of a platinum(II)-hydrazone complex.

Photoreactivities of Ni(II)- and Pt(II)-hydrazone complexes, [NiCl(L)] (Ni1) and [PtCl(L)] (Pt1), respectively [HL = 2-(diphenylphosphino)benzaldehyde-2-pyridylhydrazone], were investigated in detail via UV-vis absorption, (1)H nuclear magnetic resonance (NMR) spectroscopy, and electrospray ionization time-of-flight (ESI-TOF) mass spectrometry; the two photoproducts obtained from the photoreaction of Pt1 were also successfully identified via X-ray analysis. The absorption bands of the Ni1 and Pt1 complexes were very similar, centered around 530 nm, and were assigned as an intraligand charge transfer transition of the hydrazone moiety. The absorption spectrum of Pt1 in a CH3CN solution changed drastically upon photoirradiation (λ = 530 nm), whereas no change was observed for Ni1. (1)H NMR and ESI-TOF mass spectra under various conditions suggested that the photoexcited Pt1* reacts with dissolved dioxygen to form a reactive intermediate, and the ensuing dark reactions afforded two different products without any decomposition. In contrast to the simple photo-oxidation of HL to form a phosphine oxide HL(P═O), the X-ray crystallographic analyses of the photoproducts clearly indicate the formation of a mononuclear Pt complex with the oxygenated hydrazone ligand (Pt1O) and a dinuclear Pt complex with the oxygenated and dimerized hydrazone ligand (Pt2). The photosensitized reaction in the presence of an (1)O2-generating photosensitizer, methylene blue (MB), also produced Pt1O and Pt2, indicating that the reaction between (1)O2 and ground-state Pt1 is the important step. In a highly viscous dimethyl sulfoxide solution, Pt1 was slowly, but quantitatively, converted to the mononuclear form, Pt1O, without the formation of the dinuclear product, Pt2, upon photoirradiation (and in the reaction photosensitized by MB), suggesting that this photoreaction of Pt1 involves at least one diffusion-controlled reaction. On the other hand, the same complexes Pt1O and Pt2 were also produced in the degassed solution, probably because of the reaction of the photoexcited Pt1* with the biradical character and H2O.

Flexible coordination polymers composed of luminescent ruthenium(II) metalloligands: importance of the position of the coordination site in metalloligands.

Coordination polymerization reactions between ruthenium(II) metalloligands [Ru(n,n'-dcbpy)](4-) ([nRu]; n = 4, 5; n,n'-dcbpy = n,n'-dicarboxy-2,2'-bipyridine) and several divalent metal salts in basic aqueous solutions afforded porous luminescent complexes formulated as [Mg(H2O)6]{[Mg(H2O)3][4Ru]·4H2O} (Mg2[4Ru]·13H2O), [Mg2(H2O)9][5Ru]·10H2O (Mg2[5Ru]·19H2O), {[Sr4(H2O)9][4Ru]2·9H2O} (Sr2[4Ru]·9H2O)2, {[Sr2(H2O)8][5Ru]·6H2O} (Sr2[5Ru]·14H2O), and {[Cd2(H2O)2][5Ru]·10H2O} (Cd2[5Ru]·12H2O). Single-crystal X-ray structural analyses revealed that the divalent metal ions were commonly coordinated by the carboxyl groups of the [nRu] metalloligand, forming porous frameworks with a void fraction varying from 11.4% Mg2[4Ru]·13H2O to 43.9% Cd2[5Ru]·12H2O. M2[4Ru]·nH2O showed a reversible structural transition accompanied by water and methanol vapor adsorption/desorption, while the porous structures of M2[5Ru]·nH2O were irreversibly collapsed by the removal of crystal water. The triplet metal-to-ligand charge-transfer emission energies of M2[4Ru]·nH2O were lower than those of [4Ru] in aqueous solution, whereas those of M2[5Ru]·nH2O were close to those of [5Ru] in aqueous solution. These results suggested that the position of the coordination site in the metalloligand played an important role not only on the structure of the porous framework but also on the structural flexibility involving the guest adsorption/desorption properties.

Nonprecious-metal-assisted photochemical hydrogen production from ortho-phenylenediamine.

The combination of o-phenylenediamine (opda), which possesses two proton- and electron-pooling capability, with Fe(II) leads to the photochemical hydrogen-evolution reaction (HER) in THF at room temperature without addition of photosensitizers. From the THF solution, the tris(o-phenylenediamine) iron(II) complex, [Fe(II)(opda)3](ClO4)2 (1), was isolated as a photoactive species, while the deprotonated oxidized species was characterized by X-ray crystallographic analysis, electrospray ionization mass spectrometry, and UV-vis NIR spectra. Furthermore, the HER is photocatalyzed by hydroquinone, which serves as a H(+)/e(-) donor. The present work demonstrates that the use of a metal-bound aromatic amine as a H(+)/e(-) pooler opens an alternative strategy for designing nonprecious-metal-based molecular photochemical H2 production/storage materials.

Integration of alkyl-substituted bipyridyl benzenedithiolato platinum(II) complexes with cadmium(II) ion via selective dative bond formation.

The presence of lone pairs on the Pt and S atoms of [Pt(Bdt)(DTBbpy)] (1) (Bdt = 1,2-benzenedithiolato and DTBbpy = 4,4'-di-tert-butyl-2,2'-bipyridine) and [Pt(Bdt)(C13bpy)] (2) (C13bpy = 4,4'-ditridecyl-2,2'-bipyridine) led to selective dative bond formation with Cd(II). Complexes 1 and 2 show no binding interaction with Zn(II), while they bind selectively with Cd(II) to give a twisted trinuclear complex, [Cd{Pt(Bdt)(DTBbpy)}2(ClO4)(H2O)](ClO4) (3), and a shuttlecock-shaped tetranuclear complex, [Cd{Pt(Bdt)(C13bpy)}3(H2O)](ClO4)2·CH2Cl2 (4), respectively, depending upon the alkyl groups substituted on the 2,2'-bipyridine. The two platinum moieties in 3 are connected to the seven-coordinated Cd atom through Pt → Cd (2.7331(7) and 2.7936(7) Å) and S → Cd (2.690(3), 2.940(3), and 3.067(3) Å) dative bonds, while the three moieties in 4 are connected to the tetrahedral Cd atom only by S → Cd (2.552(4) Å) dative bonds. These structural variations found in 3 and 4 are caused not only by steric hindrance of the t-Bu groups but also by the microsegregation effect derived from the tridecyl chains. The three platinum moieties in 4 align so as to form a parallel orientation of their dipole moments, in contrast to the twisted arrangement found in 3. The dative bonds formed in 3 and 4 are commonly stable in the solid state and in less coordinative solvents such as dichloromethane, while dissociation behavior of platinum moieties with Cd(II) was observed in more coordinative THF. UV-vis and NMR spectroscopy unsealed the characteristic association/dissociation properties depending on the coordination abilities of solvents. Finally, the present study revealed that the formation of dative bonds between the platinum moieties with Cd(II) plays important roles not only in stabilizing the ground states, which leads to blue shifts in both absorption and emission energies, but also in electronic interactions between the moieties, which are revealed by electrochemical studies.

Photo- and vapor-controlled luminescence of rhombic dicopper(I) complexes containing dimethyl sulfoxide.

Halide-bridged rhombic dicopper(I) complexes, [Cu2(µ-X)2(DMSO)2(PPh3)2] (X = I(-), Br(-); DMSO = dimethyl sulfoxide; PPh3 = triphenylphosphine), were synthesized, the iodide complex of which exhibited interesting photochromic luminescence driven by photoirradiation and by exposure to DMSO vapor in the solid state. Single-crystal X-ray diffraction measurements revealed that the iodo and bromo complexes (abbreviated Cu2I2-[O,O] and Cu2Br2-[O,O]) were isomorphous, and that the two DMSO ligands were coordinated to the Cu(I) ion via the O atom in both complexes. Both complexes exhibited bright blue phosphorescence at room temperature (λ(em) = 435 nm, Φ(em) = 0.19 and 0.14 for Cu2I2-[O,O] and Cu2Br2-[O,O], respectively) with a relatively long emission lifetime (τ(em) ~ 200 µs at 77 K) derived from the mixed halide-to-ligand and metal-to-ligand charge transfer ((3)XLCT and (3)MLCT) excited state. Under UV irradiation, the blue phosphorescence of Cu2Br2-[O,O] disappeared uneventfully and no new emission band appeared, whereas the blue phosphorescence of Cu2I2-[O,O] rapidly disappeared with simultaneous appearance of a new green emission band (λ(em) = 500 nm). On further irradiation, the green emission of the iodide complex gradually changed to bright yellowish-green (λ(em) = 540 nm); however, this change could be completely suppressed by lowering the temperature to 263 K or in the presence of saturated DMSO vapor. The initial blue phosphorescence of Cu2I2-[O,O] was recovered by exposure to DMSO vapor at 90 °C for a few hours. IR spectroscopy and theoretical calculations suggest that the DMSO ligand underwent linkage isomerization from O-coordination to S-coordination, and both the occurrence of linkage isomerization and the removal of DMSO result in contraction of the rhombic Cu2(µ-I)2 core to make the Cu···Cu interaction more effective. In the contracted core, the triplet cluster-centered ((3)CC) emissive state is easily generated by thermal excitation of the (3)XLCT and (3)MLCT mixed transition state, resulting in the green to yellowish-green emission. In contrast, the Cu···Cu distance in Cu2Br2-[O,O] is considerably longer than that of Cu2I2-[O,O], which destabilizes the (3)CC emissive state, resulting in the nonemissive character.

Switching of the redox centers of a tris-2-mercaptophenolato chromium(III) metalloligand by a guest metal ion.

This work reports that the redox-active metalloligand (ML) fac-[CrIII(mp)3]3- (mp: 2-mercaptophenolato) coordinates with a Co(III) ion to afford the trianionic complex [CoIII{fac-CrIII(mp)3}2]3-. The free ML shows ligand-centered redox processes, whereas the guest-metal-bound trinuclear structure exhibited a guest-metal-centered Co(II)/Co(III) redox couple, demonstrating redox switching through guest-metal binding to the MLs.

Vapor-controlled linkage isomerization of a vapochromic bis(thiocyanato)platinum(II) complex: new external stimuli to control isomerization behavior.

We synthesized a novel Pt(II)-diimine complex with a typical ambidentate thiocyanato ligand, [Pt(thiocyanato)(2)(H(2)dcbpy)] (1; H(2)dcbpy =4,4'-dicarboxy-2,2'-bipyridine), and found that the complex 1 exhibits unique linkage isomerizations with drastic color and luminescence changes driven by exposure to volatile organic chemical (VOC) vapors in the solid state. Reaction between [PtCl(2)(H(2)dcbpy)] and KSCN in aqueous solution at 0 °C enabled successful isolation of an isomer with the S-coordinated thiocyanato ligand, [Pt(SCN)(2)(H(2)dcbpy)] (1SS·H(2)O), as a nonluminescent orange solid. Interestingly, 1SS·H(2)O was isomerized completely to one isomer with the N-coordinated isothiocyanato ligand, [Pt(NCS)(2)(H(2)dcbpy)] (1NN·3DMF) by exposure to DMF vapor, and this isomerization was accompanied by significant color and luminescence changes from nonluminescent orange to luminescent red. IR spectroscopy and thermogravimetric analysis revealed that adsorption of the DMF vapor and transformation of the hydrogen-bonded structure both played important roles in this vapor-induced linkage isomerization. Another isomer containing both S- and N-coordinated thiocyanato ligands, [Pt(SCN)(NCS)(H(2)dcbpy)] (1SN), was obtained as a nonluminescent yellow solid simply by exposure of 1SS·H(2)O to acetone vapor at room temperature, and about 80% of 1SS·H(2)O was found to be converted to 1SN. In the solution state, each isomer changed gradually to an isomeric mixture, but pure 1SS was regenerated by UV light irradiation (λ(irr.) = 300 nm) of an MeOH solution of the mixture. In the crystal structure of 1SN, the complex molecules were hydrogen-bonded to each other through the carboxyl groups of the H(2)dcbpy ligand and the N site of the thiocyanato ligand, whereas the 1NN molecules in the 1NN·4DMF crystal were hydrogen-bonded to the solvated DMF molecules. Competition of the hydrogen-bonding ability among the carboxyl groups of the H(2)dcbpy ligand, N and S atoms of the thiocyanato ligand, and the vapor molecule was found to be one of the most important factors controlling linkage isomerization behavior in the solid state. This unique linkage isomerization controlled by vapor can provide an outstanding vapochromic system as well as a new molecular switching function driven by vapor molecules.

Light-induced electron transfer/phase migration of a redox mediator for photocatalytic C-C coupling in a biphasic solution.

Photocatalytic molecular conversions that lead to value-added chemicals are of considerable interest. To achieve highly efficient photocatalytic reactions, it is equally important as it is challenging to construct systems that enable effective charge separation. Here, we demonstrate that the rational construction of a biphasic solution system with a ferrocenium/ferrocene (Fc+/Fc) redox couple enables efficient photocatalysis by spatial charge separation using the liquid-liquid interface. In a single-phase system, exposure of a 1,2-dichloroethane (DCE) solution containing a Ru(II)- or Ir(III)-based photosensitizer, Fc, and benzyl bromide (Bn-Br) to visible-light irradiation failed to generate any product. However, the photolysis in a H2O/DCE biphasic solution, where the compounds are initially distributed in the DCE phase, facilitated the reductive coupling of Bn-Br to dibenzyl (Bn2) using Fc as an electron donor. The key result of this study is that Fc+, generated by photooxidation of Fc in the DCE phase, migrates to the aqueous phase due to the drastic change in its partition coefficient compared to that of Fc. This liquid-liquid phase migration of the mediator is essential for facilitating the reduction of Bn-Br in the DCE phase as it suppresses backward charge recombination. The co-existence of anions can further modify the driving force of phase migration of Fc+ depending on their hydrophilicity; the best photocatalytic activity was obtained with a turnover frequency of 79.5 h-1 and a quantum efficiency of 0.2% for the formation of Bn2 by adding NBu4+Br- to the biphasic solution. This study showcases a potential approach for rectifying electron transfer with suppressed charge recombination to achieve efficient photocatalysis.

Dimensionality control of vapochromic hydrogen-bonded proton-transfer assemblies composed of a bis(hydrazone)iron(II) complex.

We describe the novel synthesis of a bis(hydrazone)iron(II) complex in protonated [Fe(Hpbph)(2)]Cl(2) (1) and deprotonated [Fe(pbph)(2)] (2) forms and several hydrogen-bonded proton-transfer (HBPT) assemblies having different dimensionalities of hydrogen-bonded network structures, [Fe(Hpbph)(2)](CA)·2CH(3)OH (3), [Fe(Hpbph)(2)](HCA)(2)·2THF (4), and [Fe(Hpbph)(2)](CA)(H(2)CA)(2)·2CH(3)CN (5) (Hpbph = 2-(diphenylphosphino)benzaldehyde-2-pyridylhydrazone), consisting of a deprotonated Fe(II)-hydrazone complex (2) as a proton acceptor (A) and chloranilic acid (H(2)CA) as a proton donor (D). The deprotonated complex 2 exhibited two-step reversible protonation reactions to form the double-protonated form 1, and the acid-dissociation constants were determined to be 7.6 and 10.3 in methanol solution. Utilizing this proton-accepting ability of 2, we succeeded in synthesizing HBPT assemblies 3, 4, and 5 from the reactions in CH(3)OH, THF, and CH(3)CN, respectively, with the same D/A ratio of H(2)CA/[Fe(pbph)(2)] = 10:1. These assemblies were found to have one-dimensional (1-D), two-dimensional (2-D), and three-dimensional (3-D) hydrogen-bonded networks with D/A ratios of 1:1, 2:1, and 3:1 for 3, 4, and 5, respectively. In 3, a 1-D hydrogen-bonded chain composed of the alternate arrangement of [Fe(Hpbph)(2)](2+) and CA(2-), {···[Fe(Hpbph)(2)](2+)···CA(2-)···}(∞), was surrounded by solvated methanol molecules to form isolated 1-D hydrogen-bonded chains. In the HBPT assembly 4, a 2-D hydrogen-bonded sheet was formed from two types of hydrogen-bonded chains, {···[Fe(Hpbph)(2)](2+)···HCA(-)···HCA(-)···}(∞) and {···HCA(-)···HCA(-)···}(∞), and solvated THF molecules did not form any hydrogen bonds. In 5, two orthogonal hydrogen-bonded chains constructed from the neutral chloranilic acid molecules, {···CA(2-)···2(H(2)CA)···}(∞), were formed in addition to the 1-D hydrogen-bonded chain similar to that in 3, resulting in the formation of a rigid 3-D hydrogen-bonded network structure. By controlling the dimensionality of the hydrogen bond network, we found that the 2-D HBPT assembly 4 is sufficiently flexible to exhibit interesting vapochromic behavior in response to various organic vapors.