The present paper reports the first comprehensive study on the synthesis, structures, optical and electrochemical properties, and peripheral functionalizations of nickel(II) and copper(II) complexes of β-unsubstituted 5,15-diazaporphyrins (M-DAP; M = Ni, Cu) and pyridazine-fused diazacorrinoids (Ni-DACX; X = N, O). These two classes of compounds were constructed starting from mesityldipyrromethane by a metal-template method. Ni-DAP and Cu-DAP were prepared in high yields by the reaction of the respective metal-bis(dibromodipyrrin) complexes with NaN(3)-CuX (X = I, Br), whereas Ni-DACN and Ni-DACO were formed as predominant products by the reaction with NaN(3). In both cases, the metal centers change their geometry from tetrahedral to square planar during the aza-annulation; X-ray crystallographic analyses of M-DAPs showed highly planar diazaporphyrin π planes. The Q band of Ni-DAP was redshifted and intensified compared with that of a nickel-porphyrin reference, due to the involvement of electronegative nitrogen atoms at the meso positions. It was found that the peripheral bromination of Ni-DAP and Ni-DACO occurred regioselectively to afford Ni-DAP-Br(4) and Ni-DACO-Br, respectively. These brominated derivatives underwent Stille reactions with tributyl(phenyl)stannane to give the corresponding phenylated derivatives, Ni-DAP-Ph(4) and Ni-DACO-Ph. On the basis of the absorption spectra and X-ray analysis, it has been concluded that the attached phenyl groups efficiently conjugate with the diazaporphyrin π system. The present results unambiguously corroborate that the β-unsubstituted DAPs and DACXs are promising platforms for the development of a new class of π-conjugated azaporphyrin-based materials.
The intermolecular correlation due to electrostatic repulsion in flexible polyelectrolyte solutions as a function of ionic strength has been studied using small-angle neutron and X-ray scattering (SAXS and SANS) techniques. The ionic strength was changed by adding low molecular weight salts at a fixed polyion concentration (C ) 0.25 mol/L). To solve the controversy about the added salt effect on the characteristic maximum in small-angle scattering of polyelectrolyte solutions, separation of the total scattering function into the intra-and intermolecular parts has been performed. With increasing the ionic strength of the solution the maximum position q m in the total scattering function of SAXS and SANS slightly shifts toward the lower scattering vector and subsequently disappears, whereas the maximum position q m 0 in the intermolecular scattering function slightly shifts to the higher scattering vector, but the peak itself does not disappear even for the highest ionic strength of the present study though it becomes weaker. The intramolecular scattering function is enhanced in the lower scattering vector (q < q m 0 ) when the ionic strength increases. Thus, it turned out that the apparent shift of the maximum in the total scattering function is caused by the combination of the intra-and intermolecular scattering functions.
The synthesis, structures, optical and electrochemical properties, and aromaticity of a series of 5,15-diaza-10,20-dimesitylporphyrins (M-DAP; M = Pb, H(2), Ni, Pd, Pt, Zn; mesityl = 2,4,6-trimethylphenyl) are reported. Treatment of mesityl-substituted bis(5,5'-dibromodipyrrin) with sodium azide in the presence of lead(II) acetylacetonate afforded Pb-DAP, which was quantitatively converted to H(2)-DAP by acidolysis. The free base H(2)-DAP reacted with palladium(II), platinum(II), and zinc(II) salts to give Pd-DAP, Pt-DAP, and Zn-DAP, respectively. The crystal structures, optical and electrochemical properties, and aromaticities of these β-unsubstituted M-DAPs were comprehensively investigated by X-ray crystallography, UV-vis absorption/fluorescence spectroscopy, nanosecond flash photolysis, cyclic and differential pulse voltammetry, NMR spectroscopy, and density functional theory calculations. The obtained data show that replacement of the 5- and 15-methine carbons with nitrogen atoms alters the intrinsic properties of the porphyrin 18π system as follows: (i) the coordination spheres at the N(4) core become contracted while keeping high planarity; (ii) the Q bands are red shifted and largely intensified; (iii) the electron-accepting ability is enhanced, whereas the electron-donating ability is reduced; (iv) the radiative decay rates from the S(1) state are enhanced; and (v) the aromaticity of the 18π circuit is slightly reduced in terms of both geometric and magnetic criteria. These optical and electrochemical properties of M-DAPs stem from their characteristic frontier orbitals; two HOMOs and two LUMOs are nondegenerate as a result of the incorporation of the electronegative nitrogen atoms at the two meso positions. In addition, the group 10 metals incorporated at the core finely tune the fundamental properties of DAP π systems through inductive effects as well as dπ-pπ antibonding orbital interactions; the HOMO-LUMO gaps of the group 10 metal complexes increase in the order Ni-DAP < Pd-DAP < Pt-DAP.
This study proves that a small amount of Pd loading (1 wt%) on SrFeO can dramatically enhance the oxygen-storage properties of SrFeO. The topotactic oxygen intake and release between SrFeO and SrFeO takes place in response to gas switching between an O flow and H flow, regardless of the presence or absence of Pd loading. The effect of Pd loading is significant for the oxygen-release process under H atmosphere; that is, highly dispersed Pd metal nanoparticles sized less than 1 nm formed on Pd/SrFeO to promote H dissociation, resulting in the improvement of the oxygen-release temperature and rate. Pd/SrFeO with a layered perovskite structure has a higher oxygen-release property at lower temperature than Pd/SrFeO with a perovskite phase without the layered structure. These facts indicate that the surface reaction as well as the crystal structure are responsible for the oxide ion mobility in perovskite structure, and also provide guidelines for designing novel oxygen-storage materials.
The first examples of β-β directly linked, acetylene-bridged, and butadiyne-bridged 5,15-diazaporphyrin dimers have been prepared by palladium-catalyzed coupling reactions of nickel(II) and copper(II) complexes of 3-bromo-10,20-dimesityl-5,15-diazaporphyrin (mesityl=2,4,6-trimethylphenyl). The effects of the linking modes and meso-nitrogen atoms on the structural, optical, electrochemical, and magnetic properties of the distributed π systems were investigated by using X-ray crystallography, UV/Vis absorption spectroscopy, DFT calculations, cyclic voltammetry, and ESR spectroscopy. Both the electronic and steric effects of the meso-nitrogen atoms play an important role in the highly coplanar geometry of the directly linked dimers. The direct β-β linkage produces enhanced π conjugation and electron-spin coupling between the two diazaporphyrin units.
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