Axial Pyridyl Research Articles

Isolation and Identification of Pseudo Seven-Coordinate Ru(III) Intermediate Completing the Catalytic Cycle of Ru-bda Type of Water Oxidation Catalysts

Isolation and Identification of Pseudo Seven-Coordinate Ru(III) Intermediate Completing the Catalytic Cycle of Ru-bda Type of Water Oxidation Catalysts

Light-Absorbing Pyridine Derivative as a New Electrolyte Additive for Developing Efficient Porphyrin Dye-Sensitized Solar Cells

To fabricate efficient dye-sensitized solar cells (DSSCs), 4-tert-butylpyridine (TBP) is commonly used as an additive in the electrolytes for improving the photovoltages (VOC). However, TBP cannot play a positive role in improving the photocurrent (JSC) because of the lack of absorption in the visible-wavelength range. We herein report a light-absorbing pyridine derivative N1 as an additive for the axial coordination with porphyrin dyes. N1 was synthesized by introducing a (bis(4-methoxyphenyl)amino)anthryl moiety into the para-position of pyridine via an acetylene bridge, and porphyrin dye XW64 containing meso-3,5-disubstituted phenyl groups was synthesized considering that the meta-substituted phenyl groups may induce weaker steric hindrance with the axial pyridyl ligand, as compared with wrapped and strapped porphyrin dyes. Thus, N1 was used as an electrolyte additive together with TBP. When optimized concentrations of 6 mM N1 and 0.5 M TBP were used for fabricating DSSCs based on XW64, enhanced photovoltaic performance was achieved, with JSC, VOC, and efficiency of 15.65 mA·cm-2, 0.701 V, and 7.35%, respectively, superior to those of the corresponding DSSCs without using the additives (JSC = 14.86 mA·cm-2, VOC = 0.599 V, and efficiency = 5.94%). The enhancement of JSC can be ascribed to the improved light-harvesting ability induced by the axially coordinated N1. Furthermore, the two additives also can be used to fabricate efficient solar cells based on the wrapped porphyrin dye XW42, achieving high efficiency of 10.3%, indicative of their general applicability in fabricating high-performance DSSCs. These results indicate that the simultaneous employment of the traditional TBP additive and a pyridyl ligand with light-harvesting ability in the electrolyte for the axial coordination to a porphyrin dye is a promising approach for developing efficient DSSCs.

Two-dimensional structure of poly[[[μ2-1,4-bis(pyridin-4-yl)butane]bis(μ4-pentanedioato)dicopper(II)] acetonitrile disolvate

In the title compound, {[Cu2(μ4-C5H6O4)2(μ2-C14H16N2)]·2CH3CN}n, the Cu2dinuclear units are connected by glutartate ligands, forming one-dimensional double chains. These chains, are in turn bridged by 1,4-bis(pyridin-4-yl)butane ligands to form a two-dimensional layer structure parallel to (112). The carboxylate groups of the glutarate ligand bridge two copper(II) ions, forming a paddle-wheel-type Cu2(CO2)4dinuclear secondary building unit. A crystallographic inversion centre is located midway between two CuIIions, with a Cu...Cu distance of 2.639 (3) Å. The coordination geometry of the unique CuIIion is slightly disorted square pyramidal, formed by four equatorial carboxylate O atoms and an axial pyridyl N atom.

Design and synthesis of a cyclitol-derived scaffold with axial pyridyl appendages and its encapsulation of the silver(I) cation.

Conversion of a myo-inositol derivative into a scyllo-inositol-derived scaffold with C3v symmetry bearing three axial pyridyl appendages is presented. This pre-organized hexadentate ligand allows complexation of silver(I). The crystal structure of the complex was established.

Preparation, Spectroscopic Properties, and Stability of Water‐Soluble Subphthalocyanines

A series of subphthalocyanines containing an axial pyridyl, amino, or carboxy group have been prepared. They undergo N-methylation or deprotonation readily to give a new series of water-soluble subphthalocyanines. All the compounds have been characterized with various spectroscopic methods and elemental analysis. The molecular structure of the amino analogue SPc(OCH(2)CH(2)NMe(2)) (6) has also been determined by X-ray diffraction analysis. All these compounds are essentially non-aggregated in DMF as shown by the strong Q-band absorption. The low aggregation tendency of these compounds also results in strong fluorescence emission and high efficiency in generating singlet oxygen. In the presence of Cremophor EL, these compounds also remain in the monomeric form in aqueous media and can sensitize the formation of singlet oxygen. The carboxy and carboxylate derivatives exhibit a relatively higher photostability than the amino and cationic pyridinium and ammonium counterparts, making them potentially useful as photosensitizers in aqueous media.

First-Row Transition-Metal Complexes of a New Pentadentate Ligand, α,α,α′,α′-Tetra(pyrazolyl)lutidine

A new pentadentate ligand, alpha,alpha,alpha',alpha'-tetra(pyrazolyl)lutidine, pz 4lut, has been prepared by a CoCl 2-catalyzed rearrangement reaction between 2,6-pyridinedicarboxaldehyde and dipyrazolylthione. The coordination chemistry with some divalent first-row transition metal (Mn, Fe, Co, Ni, Cu, and Zn) chlorides has been explored. The electronic properties indicate that the new kappa (5)N ligand is a slightly stronger-field donor to Ni (2+) and Co (2+) than a related pentadentate ligand with five pyridyl donors presumably because of greater interaction between the metal and axial pyridyl.

A Two-Dimensional Iron(II) Carboxylate Linear Chain Polymer that Exhibits a Metamagnetic Spin-Canted Antiferromagnetic to Single-Chain Magnetic Transition

A two-dimensional iron(II) carboxylate coordination polymer, [Fe(pyoa)2]infinity, where pyoa is 2-(pyridin-3-yloxy)acetate, has been prepared by hydrothermal synthesis. Its crystal structure reveals a single iron(II) site with an elongated octahedral coordination environment containing four equatorial carboxylate oxygens and two axial pyridyl nitrogens; the iron(II) sites are linked by syn-anti micro-carboxylates to form chains along the b axis that have an Fe...Fe separation of 4.910 A. The shortest interchain and interlayer Fe...Fe distances are 6.453 and 11.125 A, respectively. The 4.2-295 K Mössbauer spectra of [Fe(pyoa) 2] infinity consist of a single paramagnetic high-spin iron(II) quadrupole doublet. The axial Fe-N bond direction defines the Jahn-Teller axis at an iron(II) site and, consequently, the orientation of the single-ion magnetic anisotropy. Thus, along the b axis in a given chain, the spins are collinear and parallel to the Jahn-Teller axis. The Jahn-Teller axes of adjacent intralayer chains have different orientations with an angle of 79.2 degrees between the axes in adjacent chains in a bc layer. [Fe(pyoa)2]infinity exhibits field-induced metamagnetic behavior such that, in an applied field smaller than the critical field, the iron(II) spin-canted moments experience intrachain ferromagnetic interactions and weak interchain antiferromagnetic interactions; the spin canting yields weak ferromagnetism. In an applied field larger than the critical field, the weak antiferromagnetic interchain interactions are overwhelmed to yield superparamagnetic-like slow-magnetic relaxation with an energy barrier of 23(3) K. Single-crystal magnetic studies reveal a quasi-uniaxial magnetic anisotropy with the a axis as the easy-magnetic axis and the b axis as the hard-magnetic axis; the susceptibility measured along the easy a axis may be fit with the Glauber model to yield an effective intrachain exchange coupling constant of 2.06(8) K. A dynamic analysis of the susceptibility yields a 6.3(1) K energy barrier for intrachain domain wall creation. The observed field-assisted superparamagnet-like behavior is consistent with the dynamics of a single-chain magnet. Thus, [Fe(pyoa)2]infinity is best considered as a "metamagnetic-like" single-chain magnet.

Synthesis of supramolecular fullerene–porphyrin–Cu(phen)2–ferrocene architectures. A heteroleptic approach towards tetrads

Four supramolecular fullerene-porphyrin-Cu(phen)(2)-ferrocene architectures were accessed by a twofold coordination strategy. At first, the phenanthroline-linked zinc porphyrins , conceived as supramolecular synthons, were combined with a ferrocene module, 3,8-(diferrocenylethynyl)phenanthroline, by a Cu(i)-mediated heteroleptic bisphenanthroline complexation (HETPHEN) protocol to furnish the porphyrin-Cu(phen)(2)-ferrocene aggregates . Subsequently, the fullerene module was incorporated by axial pyridyl coordination to the zinc porphyrin, affording . Their suitability as tetrads was interrogated using electrochemical and photophysical data.

Stereochemical Analysis of Cobalt(III) Complexes with Tridentate Imino- and Amino-Oxime Ligands

The stereochemistry of a new class of models of the vitamin B12 system, containing tridentate pyridyl-imino-oxime [C6H5N(CH2)nNC(CH3)C(CH3)NO−; n = 1, L1; n = 2, L2] and pyridyl-amino-oxime [C6H5N(CH2)nNHCH(CH3)C(CH3)NO−; n = 1, L3; n = 2, L4] ligands, has been investigated through molecular mechanics calculations based on a specific force field. It is shown that, among all the possible diastereomers of the imino complexes [Co(L1,2)2]+, the minimum strain energy is exhibited in a mer configuration. For the amino complexes [Co(L3,4)(HL3,4)]2+, the minimum is exhibited in a fac configuration, with the amino nitrogen atoms all having the same chirality, opposite to that of the adjacent carbon atoms. Furthermore, comparison of the effect of five- (L1, L3) or six-membered (L2, L4) chelate rings on the complexes indicates that the strain energy decreases upon passing from L1 to L2 complexes, while it increases upon passing from L3 to L4 complexes. The effect of rotation around the axial pyridyl Co−N bond on the coordination geometry has also been studied through a conformational analysis of the methyl (R = Me) and adamantyl (R = Adam) organocobalt derivatives [RCo(L4)(HL4)]+. The most important result is that the rotation is rather hindered in the case of the bulky Adam group, while in the Me case the pyridyl group can rotate across a wide angular range. In both cases, the rotation causes a significant change in the Co−N bond length, while the Co−C distance is almost unaffected. It is also shown that the aromatic base is oriented with respect to the equatorial ligand in a fashion quite different from other B12 models. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Molecular and electronic structures of bis(dipicolylamine)copper(II) perchlorate and bis[2-(2-pyridylethyl)picolylamine]copper(II) perchlorate

The geometric isomers of bis(dipicolylamine)copper(II) perchlorate, [Cu(dipica)2](ClO4)2, and bis[2-(2-pyridylethyl)picolylamine]copper(II) perchlorate, [Cu(pepica)2](ClO4)2, have been prepared and their molecular structures determined by X-ray diffraction methods. The copper atom of cis-fac-[Cu(dipica)2](ClO4)2, is six coordinate with an amine nitrogen and a pyridyl group of each facial dipica ligand forming a cis coordination plane, and the remaining pyridyl nuclei on the axial sites completing a distorted octahedral structure. The mixed trans-fac- & square-pyramidal-[Cu(dipica)2](ClO4)2 comprises discrete hexacoordinate and pentacoordinate cations. The distorted trans-facial octahedral cation has two picolyl chelates in the equatorial plane and two slightly longer axial pyridyl groups. In the square-pyramidal cation, the basal plane is formed by a meridional tridentate dipicia and a pyridyl of another bidentate dipica ligand, of which the amine group is bound at the apex. The copper ion of trans-fac-[Cu(pepica)2](ClO4)2 is bound by two picolyl chelates in the equatorial plane and two elongated axial pyridyl groups. The electronic structures of these complexes are deduced based on their electronic and e.p.r. spectra. The bonding properties and the formation of the geometric isomers are elucidated.

Conformational analysis of the aromatase inhibitor 3-ethyl-3-(4-pyridyl)piperidine-2,6-dione (rogletimide) and discovery of potent 5-alkyl derivatives.

Analysis of the proton NMR spectra of 3-ethyl-3-(4-pyridyl)piperidine-2,6-dione (rogletimide, 1) shows that it exists in solution with the aromatic ring in an axial position; the same conformation was found for aminoglutethimide. Excess lithium diisopropylamide treatment of 1 formed a dianion which methylated at C-5. The major product with the methyl group trans to the pyridyl ring retained this ring in an axial position and had higher aromatase inhibitory potency than 1. The minor diastereoisomer with an equatorial pyridyl ring had low potency. Upon elongating the alkyl chain, particularly high inhibitory activity was found for the major product isomer having a C-5 octyl, coinciding with the high activity in C-3 and N-1 octyl derivatives of 1, but there was only a small difference in the activity between the enantiomers of 5-octyl-1 and activity was reduced rather than increased when octyl also replaced ethyl at C-3. The results partially support a previously described model comparing binding of androstenedione to aromatase in as much as an axial pyridyl ring is needed to mimic the axial C-19 methyl group of the steroid and bind to the heme component of the enzyme, but for the derivatives bearing a C-5 octyl, the function of the glutarimide ring seems to be simply as a spacer between the hydrophobic chain and the pyridyl ring.