Multiply engaged molecular gears composed of a cerium(IV) double-decker of a triptycene-functionalized porphyrin.

Intramolecular gearing motions are studied in a cerium(IV) double-decker of triptycene-functionalised porphyrins using single crystal X-ray analysis and variable temperature 1H-NMR.

Excited State Engineering in Ag29 Nanocluster through Peripheral Modification with Silver(I) Complexes for Bright Near-Infrared Photoluminescence.

The optical property of an ionic metal nanocluster (NC) is affected by the ionic interaction with counter ions. Here, we report that the modification of trianionic [Ag29(BDT)12(TPP)4]3- NC (BDT: 1.3-benzenedithiol; TPP: triphenylphosphine) with silver(I) complexes led to the intense photoluminescence (PL) in the near-infrared (NIR) region. The binding of silver(I) complexes to the peripheral region of Ag29 NC is confirmed by the single-crystal X-ray diffraction (SCXRD) measurement, which is further supported by electrospray ionization mass spectrometry (ESI-MS) and nuclear magnetic resonance (NMR) spectroscopy. The change of excited-state dynamics by the binding of silver(I) complexes is discussed based on the results of a transient absorption study as well as temperature-dependent PL spectra and PL lifetime measurements. The modification of Ag29 NCs with cationic silver(I) complexes is considered to give rise to a triplet excited state responsible for the intense NIR PL. These findings also afford important insights into the origin of the PL mechanism as well as the possible light-driven motion in Ag29-based NCs.

Conglomerate, Racemate, and Achiral Crystals of Polymetallic Europium(III) Compounds of Bis- or Tris-ß-diketonate Ligands and Circularly Polarized Luminescence Study.

This work reports (a) conglomerate and racemic crystal structures of [(Δ,Δ,Δ,Δ,Δ,Δ)- or/and (Λ,Λ,Λ,Λ,Λ,Λ)-EuIII 6(TTP)8(OH2)6Na4] n coordination polymers, (b) racemic crystal structures of (Δ,Δ,Δ,Δ)-/(Λ,Λ,Λ,Λ)-EuIII 4(TTP)4(bipy)4(MEK)2(OH2)2 tetrahedral clusters, and (c) the achiral crystal structure of the [EuIII 2(BTP)4(OH2)2Na2] n coordination polymer (where BTP = dianionic bis-ß-diketonate, TTP = trianionic tris-ß-diketonate, and bipy = 2,2'-bipyridine). The screw coordination arrangement of the TTP ligand has led to the formation of homoconfigurational racemic EuIII products. The conglomerate crystallization of [EuIII 6(TTP)8(OH2)6Na4] n appears to be caused by the presence of the sodium, Na+ counterions, and interactions between oxygen atoms and the trifluoromethyl unit of the TTP ligand and Na+ ions. All the EuIII compounds exhibit characteristic red luminescence (5D0 → 7FJ, J = 0-4) in solution or in the solid crystalline state. Circularly polarized luminescence (CPL) was observed in the chiral EuIII 6(TTP)8(OH2)6Na4] n species, displaying a |g lum| value in the range of 0.15 to 0.68 at the 5D0 → 7F1 emission band. Subtle changes of the [EuIII 6(TTP)8(OH2)6Na4] n structure which may be due to selection of twinned crystals or crystals that do not correspond to a perfect spontaneous resolution, are considered to be responsible for the variation in the observed CPL values.

Thermally responsive morphological changes of layered coordination polymers induced by disordering/ordering of flexible alkyl chains.

The search for a method to control structural transformations of layered coordination polymers is highly desirable to modulate their properties and functions. Herein, we report the construction of a novel coordination polymer named ZnC16 with Zn(II) ions coordinated to isophthalate ligands bearing an n-hexadecyloxy chain (C162-). Its structure consists of a layer-by-layer structure of a rigid two-dimensional coordination network and an assembly of alkyl chains as a thermally responsive moiety. Single crystals of ZnC16 exhibit a thermal crystal-to-crystal phase transition behaviour dominated by disordering/ordering of alkyl chains, which induces the expansion and shrinkage of the distance within the rigid 2D coordination networks. Microscopic observation revealed that the thermal phase transition of ZnC16 induces a significant change in their crystal morphology: a reversible macroscopic elongation/shrinkage of crystal dimensions driven by the displacement of interlayer distances and an irreversible delamination and polycrystal slippage driven by constraints generated from this phase transition. Our result provides a new direction to modulate the dynamic behaviour and related properties and functions of layered coordination polymers where the thermally responsive character of flexible alkyl chains plays an important role in tuning interlayer interactions.

The emergence of intense near-infrared photoluminescence by photoactivation of silver nanoclusters.

Photoirradiation of a pyridine solution of Ag29 nanoclusters (NCs) with red photoluminescence (PL) at 680 nm activated intense PL in the near infrared (NIR) region, giving a PL quantum yield (PLQY) of 33% at 770 nm. The use of Au-doped silver NCs further boosted the PLQY to more than 45% at 800 nm. Photoirradiation is considered to induce a change in the charge localization in the NCs, leading to the formation of NIR emitting sites.

Visible Circularly Polarized Luminescence of Octanuclear Circular Eu(III) Helicate.

This work reports on the structural and photophysical characterization of D4-symmetrical octanuclear circular LnIII helicates, [(R)- or (S)-iPr-Pybox]8(LnIII)8(THP)8 (where Ln = Eu and Tb, THP = trianionic tris-ß-diketonate, and iPr-Pybox = chiral bis(4-isopropyl-2-oxazolinyl)pyridine). X-ray crystallographic analysis revealed that the octanuclear circular helicate possesses square antiprism architecture and consists of four [(R)- or (S)-iPr-Pybox]2LnIII2(THP)2 asymmetric units arranged in a closed ring form. Ligand-to-ligand interactions between the THP and the iPr-Pybox ligands have successfully directed formation of enantiopure, homoconfigurational (Δ,Δ,Δ,Δ,Δ,Δ,Δ,Δ)-R and (Λ,Λ,Λ,Λ,Λ,Λ,Λ,Λ)-S isomers. All of the nonacoordinated LnIII ions are identical and exhibit a distorted capped square antiprism (CSAP) geometry. Upon excitation of the ligand absorption band (λ = 360 nm), the circular helicates display characteristic EuIII (red, 5D0 → 7FJ, J = 0-4) or TbIII (green, 5D4 → 7FJ, J = 6-3) core f-f luminescence. The overall emission quantum yields of the circular EuIII and TbIII helicates are 0.145 and 0.0013, respectively, in chloroform. The EuIII and TbIII complexes exhibit remarkable circularly polarized luminescence (CPL) activity at their magnetic dipole transition with observed luminescence dissymmetry factors |glum| of 1.25 (5D0 → 7F1, λ = 592 nm) and 0.25 (5D4 → 7F5, λ = 541 nm), respectively. Exceptional |glum| values of the circular EuIII helicates highlight the visible intensity difference between left and right circularly polarized emissions of R and S isomers in chloroform and PMMA thin film.

Self-assembled Tetranuclear EuIII Complexes with D2- and C2h-Symmetrical Square Scaffold.

Three new tetranuclear europium(III) alternating circular helicates, (2-PhRRRR/2-PhSSSS) [(R)- or (S)-Ph-Pybox]4EuIII4(BPP)6, (2-iPrRRRR/2-iPrSSSS) [(R)- or (S)-iPr-Pybox]4EuIII4(BPP)6, and (3-PhRRRR/3-PhSSSS) [(R)- or (S)-Ph-Pybox]4EuIII4(BHP)6, are presented with their structural and chiroptical characterization (BPP and BHP = bis-ß-diketonates; Pybox = chiral bis(oxazolinyl) pyridine ligand). X-ray crystallographic analysis revealed that different extents of interligand-contacting interactions between bis-ß-diketonates and Pybox ligands produce different bis-ß-diketonates arrangements around four EuIII ions and, thus, their specific symmetry in the final tetranuclear complexes. 2-PhRRRR/2-PhSSSS and 3-PhRRRR/3-PhSSSS are recognized as D2-symmetry, while 2-iPrRRRR/2-iPrSSSS self-assemblies possess pseudo C2h-symmetry. Due to different molecular symmetry, 2-PhRRRR/2-PhSSSS and 2-iPrRRRR/2-iPrSSSS crystals display different ligands orientation in their EuIII coordination spheres. The presence of pseudo σh-mirror symmetry in 2-iPrRRRR/2-iPrSSSS promotes a pair of distinguishable EuIII geometries. All the chiral self-assemblies exhibit almost identical photoluminescence emission spectra patterns of f-f transitions in the EuIII core. The EuIII self-assemblies exhibit intense CPL with different observed |glum| values (2-PhRRRR/2-PhSSSS ∼ |0.31|, 2-iPrRRRR/2-iPrSSSS ∼ |0.08|, 3-PhRRRR/3-PhSSSS ∼ |0.31| in chloroform).

Solvation of quantum dots in 1-alkyl-1-methylpyrrolidinium ionic liquids: toward stably luminescent composites.

CdTe nanoparticles capped with a cationic thiolate ligand were stably dispersed in ionic liquids, 1-alkyl-1-methyl-pyrrolidinium bis(trifluoromethanesulfonyl)amides with an alkyl group of n-propyl, butyl and octyl-chain, and in an ionic plastic crystal, 1-ethyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)amide. Dispersion behavior of CdTe nanoparticles in these ionic media was evaluated, in which the solvation of nanoparticles by the ionic components was particularly interested. The ionic media showed alkyl-chain length-dependent solvation behavior, which was suggested by the thermal analysis of nanocomposites. The longer alkyl-chains led to the greater decrease in the thermal melting enthalpy of ionic media with the introduction of nanoparticles. The ionic liquid with an octyl-chain, which is considered to form a thicker solvation layer, afforded better emission durability of CdTe nanoparticles compared to the ionic liquid with a shorter alkyl chain.

Photo-Lewis Acid Generator Based on Radical-Free 6π Photo-Cyclization Reaction.

We present here a new photo-active molecule which acts as a photo-Lewis acid generator (PLAG) based on photo-chemical 6π-percyclization. Photo-illumination of the PLAG molecule produces a condensed aromatic carbocation with a triflate counteranion, which exhibits Lewis acid chemical catalytic reactivity such as initiation of the polymerization of epoxy monomers and catalysis of Mukaiyama-aldol reactions. The terminal-end structure in the epoxy polymerization was modified with the Lewis acid fragment. The carbocation induced the Mukaiyama-aldol reaction as a new photo-gated system with remarkably high catalytic reactivity and turnover numbers higher than 60. The photo-chemical quantum yield of the carbocation generation is 50%, which is considerably higher than obtained with most Brønsted photo-acid generators.

Tuning of intramolecular charge transfer properties and charge distributions in ferrocene-appended catechol derivatives by chemical substitution.

In this study, we report intramolecular charge transfer (ICT) properties and charge distributions in a series of FcC derivatives (FcC = 4-ferrocenylcatecholate where Fc = ferrocene and C = catecholate). This series consists of a previously reported complex FcV (4-ferrocenylveratrole) and newly synthesized complexes FcA (4-ferrocenylcatechol bis(acetate) and Pt((t)Bu2bpy)(FcC) ((t)Bu2bpy = 4,4'-di-tert-butyl-2,2'-dipyridyl). An electrochemical analysis of Pt((t)Bu2bpy)(FcC) using cyclic voltammetry revealed two well-defined, reversible waves which were assigned to the sequential oxidation of the Pt((t)Bu2bpy)(C) and Fc moieties. The potential splitting between the waves (524 mV) indicated that there was an electronic interaction between both moieties. ICT property and charge distribution of [Pt((t)Bu2bpy)(FcC)]˙(+) were rationalized by comparison with the [FcV]˙(+) and [FcA]˙(+) (4-ferrocenylcatechol bis(acetate)). DFT calculations and UV-vis-NIR spectroscopy revealed that [Pt((t)Bu2bpy)(FcC)]˙(+), [FcV]˙(+), and [FcA]˙(+) were ferrocenium (Fc(+))-centered rather than semiquinone ligand-centered and that these complexes exhibited ICT transition bands from the catechol-derivatized framework to the Fc(+) moiety in the near infrared (NIR) region. Both the electronic coupling parameter (HAB) and delocalization parameter (α) increased in value as the electron-donating strength of the substituent groups in the catechol-derivatized framework increased (OCOCH3 ([FcA]˙(+)) < OCH3 ([FcV]˙(+)) < O(-) ([Pt((t)Bu2bpy)(FcC)]˙(+))). The electronic interactions between the organometallic center and the non-innocent framework were tuned by changing the substituents. The potential energy surfaces of the Fc(+) derivatives, obtained using two-state Marcus-Hush theory, can be modulated by changing the energy level of the molecular orbitals of the appended catechol-derivatized moieties.

Organic mixed valency in quadruple hydrogen-bonded triarylamine dimers bearing ureido pyrimidinedione moieties.

Quadruple hydrogen-bonding interactions stabilized the mixed-valence states of dimers of triarylamine derivatives bearing an ureido pyrimidinedione moiety without any electronic coupling. This study represents the first example of proton-coupled "organic" mixed valency in solution with different substituents being used to control the stability.

Synthesis, structure, and properties of α,ß-linked oligothiazoles with controlled sequence.

α,ß-Linked oligothiazoles with head-to-tail connectivity are presented as a new family of helical scaffolds. Combinations of palladium-catalyzed cross-coupling reactions at the 5- and 4-positions of 2-phenylthiazole led to the synthesis of oligo(2-phenylthiazoles) with ortho linkages with a variety of defined sequences. The secondary structures of the α,ß-linked oligo(2-phenylthiazoles) showed a clear dependence on their sequences. X-ray crystallography of the trimer, tetramer, and hexamer with head-to-tail connection revealed the formation of a helical structure, which was stabilized by a combination of intramolecular forces, including interheteroatom (S⋅⋅⋅N), CH-π, and π-π interactions. The introduction of a chiral end-group successfully led to the induction of chirality into the helical conformations. Programmable sequences for controlled geometries and photofunctions have been demonstrated through the manifold connection pathways in α,ß-linked oligothiazoles.

Construction of covalent- and hydrogen-bonded assemblies from 1',1'''-biferrocenediboronic acid as a new organobimetallic building block.

1',1'''-Biferrocenediboronic acid () was synthesized from 1',1'''-dibromobiferrocene by a typical procedure of converting Br to B(OH)2 groups in 76% yield and identified by (1)H-, (13)C- and (11)B-NMR and ESI-MS. X-ray diffraction (XRD) studies showed that, in non-solvated crystals (Form I), the new organobimetallic building block formed 1D hydrogen-bonded networks (i.e., chain) with octaatomic rings composed of the neighbouring two molecules. In solvated crystals with a composition of ()3(THF)2 (Form II), exists in two conformers (Conformers A and B) with respect to the rotation of the CpB(OH)2 moieties relative to the Cp rings of the fulvalenide moieties; Conformer A formed 1D hydrogen-bonded networks laterally hydrogen-bonding with THF molecules while Conformer B formed a new planar hydrogen-bonded motif involving four B(OH)2 groups and stepwise laminated networks of the planar motif. A macrocyclic tetraferrocenyl boronate ester was synthesized by cyclocondensation between and pentaerythritol in 33% yield and identified by (1)H-, (13)C- and (11)B-NMR, ESI-MS and XRD. In electrochemical measurements, the cyclocondensed compound exhibited four defined reversible waves with a total spread of 756 mV in CH2Cl2 containing n-Bu4NBArF4 (ArF = 3,5-bis(trifluoromethyl)phenyl), displaying both intra- and inter-biferrocenyl interactions.

Construction of di- and tetra-ferrocenyl spiroborate complexes from catechol building blocks and their redox behaviors.

In this paper, we report a method for the construction of multi-ferrocenyl spiroborate assemblies from discrete mono- and di-ferrocenyl complexes. To prepare the building blocks for the spiroborate assemblies, 4-ferrocenylveratrole (1) and 4,5-diferrocenylveratrole (3) were first synthesized by Negishi cross-coupling between ferrocene and the corresponding aryl halides. Compounds 1 and 3 were characterized by NMR and UV-vis spectroscopies and electrochemical methods, namely cyclic voltammetry and differential pulse voltammetry. The potential splittings of 167 and 263 mV for the oxidations of the two ferrocenyl groups of 3 in CH2Cl2-n-Bu4NPF6 and n-Bu4NB(C6F5)4, together with the presence of an intervalence charge-transfer transition of 3(+) in the NIR region, indicate a strong inter-ferrocenyl interaction through the ortho connection in the veratrole bridge. The treatment of 1 and 3 with BBr3, followed by complexation with B(OH)3 in the presence of KOH, afforded potassium salts of di- and tetra-ferrocenyl spiroborate assemblies, K2 and K4, respectively. The spiroborate assemblies K2 and K4 were characterized by NMR and UV-vis spectroscopies, ESI-MS, and electrochemical methods. K2 exhibited a potential splitting value of 302 mV in DMF-n-Bu4NPF6, indicating electronic interactions over the boron center. K4 exhibited four one-electron-oxidation waves in DMF-n-Bu4NPF6 and n-Bu4NB(C6F5)4; the one-electron-oxidized species 4 is thermodynamically more stable than 4(+) and 4(2+). The overall E(1/2)(1)-E(1/2)(4) spread for K4 is 201 mV larger than the E(1/2)(1)-E(1/2)(2) splitting for 3 in DMF-n-Bu4NPF6, indicating that the spiroborate link between diferrocenyl units led to electronic interactions over the boron center.

Synthesis and structural analysis of (imido)vanadium(V) dichloride complexes containing imidazolin-2-iminato- and imidazolidin-2-iminato ligands, and their use as catalyst precursors for ethylene (co)polymerization.

A series of (imido)vanadium(V) dichloride complexes containing 1,3-imidazolin-2-iminato or 1,3-imidazolidin-2-iminato ligands of the type, V(NR')Cl2(L) [R' = 2,6-Me2C6H3, L = 1,3-R2(CHN)2C═N (1a-c,e) or 1,3-R2(CH2N)2C═N (2a-d), R = (t)Bu (a), 2,6-Me2C6H3 (b), 2,6-(i)Pr2C6H3 (c), C6H5 (d), 2,6-(Ph2CH)2-4-MeC6H2 (e); L = 1,3-(2,6-(i)Pr2C6H3)2(CHN)2C═N, R' = 1-adamantyl (Ad, 3c), C6H5 (4c); L = 1,3-(2,6-(i)Pr2C6H3)2(CH2N)2C═N, R' = Ad (5c)], were prepared and characterized. The molecular structures of 1a, 2a,c,d, 3c, 4c, and 5c were determined by X-ray crystallography. All complexes showed high catalytic activity for ethylene polymerization especially in the presence of Et2AlCl cocatalyst; the 2,6-R2C6H3 analogues (R = Me, (i)Pr; 1b,c, 2b,c) exhibited higher catalytic activities than the (t)Bu analogues (1a, 2a), which display rather unique (small) V-N-C(imido) bond angles in the solid state. A good correlation between the activity and the (51)V NMR chemical shift was found for the (arylimido)vanadium precatalysts (1a-c,e, 2a-d, and 4c). These complexes showed high catalytic activity for the copolymerization of ethylene with norbornene (NBE), affording ultrahigh molecular weight copolymers with uniform molecular weight distributions. The activities were affected by the imido ligand as well as by the substituents in the anionic ligand, and the 2,6-(i)Pr2C6H3 analogues (especially 2c and 4c) showed the higher activities. The complexes 2c and 4c also showed high activities with efficient comonomer incorporation for the ethylene copolymerization with 5-ethylidene-2-norbornene (ENB) in the presence of Et2AlCl; both the comonomer incorporation and the molecular weight in the resulting polymers were affected by the comonomer employed (NBE vs ENB).

Synthesis and structural analysis of (imido)vanadium(V) complexes containing chelate (anilido)methyl-imine ligands: ligand effect in ethylene dimerization.

A series of (imido)vanadium dichlorido complexes containing chelate anionic donor ligands of the type, VCl2(L)(NR) [R = 1-adamantyl (Ad), L = 2-(2,6-Me2C6H3)NCH2(C9H6N) (2), 8-(2,6-Me2C6H3)NCH2(C9H6N) (3); L = 2-(2,6-R'2C6H3)NCH2(C5H4N), R = 2-MeC6H4, R' = Me (4a), (i)Pr (4b); L = 2-(2,6-Me2C6H3)NCH2(C5H4N), R = 4-MeC6H4 (5), 3,5-Me2C6H3 (6)], have been prepared and identified. The reactions with ethylene by 2,3 in the presence of methylaluminoxane (MAO) afforded a mixture of high molecular weight polyethylene and oligomers. Reactions with ethylene by VCl2[2-(2,6-R'2C6H3)NCH2(C5H4N)](NAd) (1a,b), 4-6 afforded 1-butene with high selectivities (>92%), and the activities by 4a,b are at the same level as those in 1a,b. The activities by 5,6 were lower than 4a,b and were at the same level of that by VCl2[2-(2,6-Me2C6H3)NCH2(C5H4N)](NPh). These results thus suggest that both the chelate anionic donor and the imido ligands play a role for both the activity and the selectivity.

Pseudorotaxane structure of a fullerene derivative--cyclodextrin 1:2 complex.

X-Ray crystallography revealed that the C(60) derivative·Î³-cyclodextrin (γ-CDx) complex has a pseudorotaxane structure and the structure of the crystal clarified the importance of multi-point hydrogen bonds between two γ-CDxs for stabilising the 3·Î³-CDx complex.

Effect of ligand substituents in olefin polymerisation by half-sandwich titanium complexes containing monoanionic iminoimidazolidide ligands-MAO catalyst systems.

Various half-sandwich titanium complexes containing iminoimidazolidide ligands, CpTiCl(2)[1,3-R(2)(CH(2)N)(2)C=N] (1a-d) [R = Ph (a), 2,6-Me(2)C(6)H(3) (b), cyclohexyl (c), (t)Bu (d)], have been employed as the catalyst precursors for ethylene polymerisation, syndiospecific styrene polymerisation, and copolymerisation of ethylene with 1-hexene in the presence of MAO cocatalyst; 1d showed the highest catalytic activity for ethylene polymerisation whereas 1b showed the highest activity for syndiospecific styrene polymerisation.

Synthesis and structural analysis of half-titanocenes containing eta(2)-pyrazolato ligands, and their use in catalysis for ethylene polymerization.

Cp*TiCl(2)(L) [L = C(3)H(3)N(2) (1), 3,5-Me(2)C(3)HN(2) (2) and 3,5-(i)Pr(2)C(3)HN(2) (3)], and Cp*Ti(C(3)H(3)N(2))(3) (4) were prepared in moderate yields by treating Cp*TiCl(3) with the pyrazoles in the presence of Et(3)N or with their corresponding lithium salts in Et(2)O. The structures of 1 and 2 determined by X-ray crystallography indicate that these complexes fold a distorted tetrahedral geometry around Ti, and the pyrazolato ligands coordinate to Ti with eta(2)-N,N'-coordination mode. In contrast, one of the pyrazolato ligand in 4 coordinates to Ti with eta(1)-N-bonding, whereas the other two ligands were bound to Ti with eta(2)-N,N'-fashion. The Cp analogues, CpTiCl(2)(L) [L = C(3)H(3)N(2) (5), 3,5-Me(2)C(3)HN(2) (6), 3,5-(i)Pr(2)C(3)HN(2) (7), and 3,5-Ph(2)C(3)HN(2) (8)], were also prepared by the reaction of CpTiCl(3) with the corresponding lithium salts in Et(2)O or n-hexane. The crystallographic analyses of 5 and 6 revealed that the pyrazolato ligands coordinate to Ti with eta(2)-N,N'-coordination mode. These complexes (1-3, 5-8) exhibited moderate catalytic activities for ethylene polymerization in the presence of methylaluminoxane (MAO), and the activities were highly affected by the substituent on the pyrazolato ligand employed. Complex 1 exhibited the highest activity affording polymer with uniform molecular weight distribution, suggesting that the polymerization proceeded with uniform catalytically active species. An increase in the steric bulk in the pyrazolato ligand led to a slight decrease in the activity by the Cp* analogues, whereas the activity by the Cp analogues increased upon increasing the steric bulk in the pyrazolato ligand employed.