Effect Of Central Metal Research Articles

Three multinuclear metal–organic coordination compounds based on 8-hydroxyquinoline derivative: Syntheses, structures and fluorescence properties

By taking advantage of the synthetic 8-hydroxyquinoline derivative, (E)-2-[2-(4-chlorophenyl)vinyl]-8-hydroxyquinoline (HL), three new metal–organic coordination compounds [Zn3L6] (1), [Cd3L6] (2) and [Cu2L4] (3) have been obtained by solvothermal or solution processing methods and structurally characterized. Single crystal X-ray diffraction analysis revealed that complexes 1 and 2 have similar ‘V’-type trinuclear structures. Different from complexes 1 and 2 (trinuclear structure), complex 3 displays dinuclear structure. The effects of central metals and reaction solvents on the structures of complexes 1–3 have been discussed. Furthermore, thermogravimetric analysis and solid state fluorescence of ligand HL, 1–3 were investigated.

A series of CdII/ZnII coordination polymers containing helical chains constructed from a “V”-like bis-pyridyl-bis-amide and various dicarboxylates: Assembly, structures, photoluminescent and selective photocatalysis

Eight new CdII/ZnII coordination polymers constructed from a semi-rigid “V”-like bis-pyridyl-bis-amide ligand and different dicarboxylates, namely, {[Cd(L)(tpd)(H2O)]·H2O}n (1), {[Cd(L)(bdc)(H2O)]·H2O}n (2), {[Cd(L)(mip)(H2O)]·H2O}n (3), {[Cd(L)(hip)(H2O)]·H2O}n (4), {[Zn(L)(tpd)(H2O)]·H2O}n (5), {[Zn(L)(bdc)(H2O)]·H2O}n (6), {[Zn(L)(mip)(H2O)]·H2O}n (7), {[Zn(L)(hip)]·2H2O}n (8), [L=N,N′-bis(pyridine-3-yl)-5-methylisophthalic dicarboxamide, H2tpd=2,5-thiophenedicarboxylic acid, H2bdc=1,3-benzenedicarboxylic acid, H2mip=5-methylisophthalic acid, H2hip=5-hydroxyisophthalic acid] have been hydrothermally synthesized and structurally characterized. In complexes 1 and 3–7, the L ligands adopt μ2–bridging mode connecting adjacent CdII/ZnII ions to give rise 1D left-, right-handed helixes. In complex 2, the L ligands connect adjacent metal ions to form a 1D right-handed helix. In complex 8, the L ligands link adjacent metal ions to obtain a 1D wave-like chain. The adjacent 1D [M-L]n (M=Cd, Zn) chains are further linked by dicarboxylates anions with monodentate-chelating or bis(monodentate) bridging mode to furnish 2D layer structures. The structural features of the title complexes indicate that the semi-rigid “V”-like bis-pyridyl-bis-amide L tends to construct 1D helix. In addition, the effects of central metals on the coordination modes of the dicarboxylates and the carboxyl position of dicarboxylates on the final structures have been discussed. The thermal stability and fluorescent properties of complexes 1–8 have been investigated. In addition, the title complexes exhibit photocatalytic activity and selectivity for dye degradation under UV light.

Effect of central metals and N-donor ligands on the architectures of a series of coordination polymers based on a bis(sulfanediyl) thiadiazole diacetate

Five new transition metal coordination polymers, namely, [Co(bbbm)(BSTDA)] (1), [Co(bdmbmb)(BSTDA)(H2O)]·(H2O) (2), [Ni(bbbm)(BSTDA)(H2O)2] (3), [Ni2(3-dpyh)2(BSTDA)2(H2O)] (4) and [Cd(bbbm)1.5(BSTDA)] (5) have been synthesized from an S-/thiadiazole-containing dicarboxylate [H2BSTDA=bis(sulfanediyl) thiadiazole diacetic acid] and different flexible/semi-rigid N-donor ligands [bbbm=1,1-(1,4-butanediyl) bis-1H-benzimidazole, bdmbmb=1,4-bis(5,6-dimethylbenzimidazole-1-yl)benzene and 3-dpyh=N,N′-bis(3-pyridinecarboxamide)-1,6-hexane]. Structural analysis indicates that the title complexes present different structures although using the same S-/thiadiazole-containing dicarboxylate. Complex 1 is a 3D framework constructed from 2D (63) Co-BSTDA layers and 1D Co-bbbm chains. When the flexible bbbm in 1 was replaced by a semi-rigid bdmbmb ligand, a 2D parallelogram (4,4) network 2 derived from 1D Co-BSTDA and Co-bdmbmb single chains has been obtained. Complex 3, with NiII ion as substitute of CoII ion in 1, exhibited a 2D (4,4) network constructed form 1D Ni-BSTDA and Ni-bbbm single chains. When the bbbm in 3 was replaced by a longer and more flexible N-donor ligand 3-dpyh in 4, a 2D wave-like (4,4) layer constructed from [Ni-BSTDA]2 and [Ni-(3-dpyh)]2 double chains with bimetallic nodes was generated. While the CoII ion in 1 was substituted by CdII ion in 5, a 3D framework crossed by 2D (63) wave-like Cd-bbbm layers and 1D zigzag Cd-BSTDA chains was obtained. Structural diversity in complexes 1–5 demonstrates that the coordination characters of metal ions, the spacer length and flexibility of N-donor ligands have great influence on the final structures of the title complexes. In addition, fluorescence properties of complexes 1–5 are also reported in this paper.

Effect of Central Metals on Langmuir-Blodgett Monolayers of Phthalocyanines with Flexible Substituents

Effect of Central Metals on Langmuir-Blodgett Monolayers of Phthalocyanines with Flexible Substituents

The effects of central metals on the photophysical and nonlinear optical properties of reduced graphene oxide-metal(II) phthalocyanine hybrids.

Reduced graphene oxide-metal(II) phthalocyanine (RGO-MPc, M = Cu, Zn and Pb) hybrid materials have been prepared by the covalent functionalization method. The resultant RGO-MPc hybrids are characterized by scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared, ultraviolet-visible absorption and fluorescence spectroscopy. The RGO-MPc hybrids exhibit strong fluorescence quenching by means of the photo-induced electron transfer or the energy transfer (PET/ET) process between the RGO and MPc moieties. The PET/ET process particularly depends on the fluorescence quantum yield of MPc molecules with different central metals. The nonlinear optical (NLO) properties of the RGO-MPc hybrids are investigated by using the Z-scan technique at 532 nm with 4 ns laser pulses. The results show that the NLO properties of MPc molecules increase in the order of Zn < Pb < Cu, but the RGO-MPc hybrids exhibit NLO performance in the inverse sequence of Zn > Pb > Cu, implying that the NLO response arising from the efficient PET/ET process between RGO and MPc may play a more important role in the NLO properties of RGO-MPc hybrids than that originating from the MPc moiety.

A series of coordination polymers assembled from d10 metals and a new multidentate N-donor ligand: syntheses, structures, and photoluminescent properties

Seven new coordination polymers based on d10 metals and multidentate N-donor ligands, namely [Na0.4Cd4(htpmb)(L1)3.2(Cl)2(H2O)2.4]·0.8H2L1·1.6H2O (1), [Cd4(htpmb)(L1)3(OH)2(H2O)2]·3H2O (2), [Zn2(htpmb)(L1)2]·H2L1·H2O (3), [Zn2(htpmb)(L1)2]·3H2O (4), [Zn2(htpmb)(HL2)4] (5), [Zn2(htpmb)(L3)4] (6), and [Cd4(htpmb)(L4)2(OH)2(H2O)3]·8H2O (7), where htpmb = hexakis(3-(1,3,4-triazol-1-yl)phenoxy-methyl)benzene, H2L1 = 1,4-benzenedicarboxylic acid, H2L2 = 2-hydroxy-benzoic acid, HL3 = benzoic acid and H3L4 = 5-hydroxy-1,3-benzenedicarboxylic acid, have been synthesized under hydrothermal conditions. Compounds 1 and 2 display the same 3D framework with new binodal 6-connected (45·55·65)(46·69) topology based on dinuclear Cd(II) units. Compounds 3 and 4 show identical 3D 2-fold interpenetrating frameworks with rare binodal 4-connected (4·64·8)(42·62·82) topology. Compounds 5 and 6 reveal a similar 1D chain structure. Compound 7 exhibits a 1D double chain structure. The complexes were structurally characterized by single-crystal X-ray diffraction analyses, elemental analyses, powder X-ray diffraction (PXRD), ultraviolet-visible absorption spectra (UV-vis), and infrared spectra (IR). The influences of coordination modes of the htpmb, and pH values on the structures of the coordination polymers have been discussed. The effects of central metals, carboxylate anions, and N-donor ligand on the final topologies have been discussed. The luminescent properties of the seven compounds have also been investigated in detail.

The effects of the ligand, central metal, and solvent on the O2 binding of non-precious metal catalyst model systems: An ab initio study

Non-precious metal (NPM) catalysts are currently under development to replace the expensive platinum-based materials currently utilized for oxygen reduction in PEM fuel cells. In this work, systematic studies were carried out to examine the effect of central metal, chelating ligand, and solvent on the O2 binding activity of a series of MN2 and MN4 NPM catalysts (Im)MLn where M=Cu2+, Fe2+, Fe3+, Ni2+ and Co2+, L=diaminotriazole or porphyrin, and a support ligand imidazole (Im). O2 and H2O binding energies were calculated for all the catalysts. Cu2+-based catalysts exhibit no activity toward O2 regardless of the ligand, Fe2+- and Co2+-based catalysts show the strongest O2 binding, and the rest fall in between. This is in alignment with the energy gap between the metal 3dz2 and the in-plane anti-bonding π* orbital on the O2 with the larger the energy gap, the weaker the interaction. Porphyrin-based catalysts bind weakly with H2O compared to their diaminotriazole counterparts, which is attributed to the larger energy gap between the HOMO of H2O and the higher lying LUMO of Porphyrin-based catalysts resulted from a stronger anti-bonding interaction between their metal d orbitals and the σN orbitals of porphyrin. We propose that the initial O2 absorption activity of MN4 or MN2 catalysts in the oxygen reduction reaction be considered on the basis of the relative binding of O2 to H2O.

Synthesis and physicochemical behavior of new low symmetry Ge, Ti and Sn phthalocyanines: Effect of central metal

The synthesis and photophysicochemical properties of new low symmetrically Ge, Sn and Ti phthalocyanines substituted with one carboxy containing group are reported. Broading and splitting in the absorption spectra were observed for some of the complexes in particular for both the titanium Pcs due to loss of symmetry. Higher fluorescence quantum yields and lifetimes were obtained for the Pcs substituted with three benzyloxy (5–7) compared to their corresponding counterparts substituted with six 2-diethylaminoethylthiol groups (9–11). The germanium Pc complexes gave the highest triplet and singlet oxygen quantum yields compared to all the other complexes studied in DMF. All the complexes showed reasonable ability to generate singlet oxygen with quantum yields ranging from 0.54 to 0.69.

Synthesis, characterization, photophysical and photochemical properties of tetra-2-[2-(benzothiazolylthio)]ethoxy substituted phthalocyanine derivatives

The metal-free and zinc (II) phthalocyanine compounds tetra substituted with 2-(2-benzothiazolylthio)ethoxy groups have been synthesized for the first time in this study for comparison central metal effect on photophysical and photochemical properties. The new compounds have been characterized by IR, 1H NMR, 13C NMR and MS spectra data. These compounds showed excellent solubility in most common organic solvents. The photophysical and photochemical properties of metal-free and zinc (II) phthalocyanine compounds have been studied in DMF and toluene in order to investigate of polar and non-polar solvent effect on these properties. The fluorescence quenching behaviour of the studied compounds by 1,4-benzoquinone (BQ) have also been studied in DMF and toluene.

Electronic structures, spectroscopic properties, and reaction activities of porphyrins with alkali metal ions: density functional theory approach to the central metal effects

Density functional theory (DFT) calculation method was employed to investigate a series of nine alkali metal porphyrins (alk-Pors), namely HLiPor , HNaPor , HKPor , Li2Por , LiNaPor , LiKPor , Na2Por , NaKPor , and K2Por . These molecules show different configurations depending on different metal ions which locate over the central hole of the porphyrin ligand. Alk-Pors with larger-radius metal ion have smaller binding energy and thus is more difficult to keep stable. Further detailed molecular stability analysis was carried out by noncovalent interaction and electrostatic interaction via RDG and NBO charge distribution. UV-vis spectra of these nine compounds also show different spectral shapes depending on the central metals, and the dominant state transitions with high degeneracy are revealed to be influenced by high molecular symmetric order. Finally their difference in reactivity due to the electronegativity of central metals and the nature of porphyrin rings are predicted by electrostatic potential and Fukui functions.

Porphyrin-appended phosphapalladacycle precatalysts: effects of central metals on the catalytic activity in a high-temperature Heck reaction

The synthesis and the catalytic activity of bis(μ-chloro)-bridged, phosphapalladacycle-fused diporphyrins (M-porphyrin-appended phosphapalladacycles: M = Zn , Ni , free-base), as well as the coordinating ability of their precursors, meso-phosphanylporphyrins are reported. Treatment of meso-phosphanylporphyrinatozinc(II) with an equimolar amount of PdCl2(NCPh)2 caused regioselective β-C–H activation of the porphyrin ring to produce bis(μ-chloro)-bridged Zn -porphyrin-appended phosphapalladacycle, which was further converted to the free-base- and Ni -porphyrin-appended analogs. The UV-vis absorption spectra of these palladium complexes showed weak exciton coupling between two porphyrin chromophores connected by the μ-chloro bridges. The M-porphyrin-appended phosphapalladacycles behaved as precatalysts for a high temperature Heck reaction between p-bromobenzaldehyde and butyl acrylate. In a range of the catalyst-loading of 0.05–0.005 mol.%, the catalytic activity was found to significantly depend on the central metal incorporated at the porphyrin core. The Ni -porphyrin-appended phosphapalladacycle showed considerably higher turnover frequency than did the Zn -porphyrin- and free-base-porphyrin-appended counterparts. This trend in the catalytic activity does not simply correlate with the σ-donating ability of the phosphorus center and the electron-donating ability of the porphyrin π-systems. Instead, it is related to the durability of the precatalysts under the reaction conditions employed. The observed results corroborate that the central metal of the meso-phosphanylporphyrin ligands plays a crucial role in the active Pd(0) catalyst-loading from the porphyrin-appended phosphapalladacycles at constant efficiency.

Application of metalloporphyrins as new catalysts for the efficient, mild and regioselective synthesis of quinoxaline derivatives

A simple, highly efficient and green procedure for the condensation of aryl and alkyl 1,2-diamines with α-diketones in the presence of catalytic amounts of metalloporphyrins at room temperature is described. Using this method, quinoxaline derivatives as biologically interesting compounds are produced in high to excellent yields and short reaction times. In this report, the effects of central metal in porphyrin core and substituents on tetraphenylporphyrin skeleton have been studied.

Solvent and central metal effects on the photophysical and photochemical properties of 4-benzyloxybenzoxy substituted phthalocyanines

The synthesis and characterization of new peripherally tetra-4-benzyloxybenzoxy substituted metal-free, zinc and lead phthalocyanines are described for the first time in this study. The influence of various organic solvents and the nature of the central metal ion on the spectroscopic, photophysical and photochemical properties has been investigated. General trends are described for photodegradation, singlet oxygen and fluorescence quantum yields, and fluorescence lifetimes of these compounds in different solvents. Photophysical and photochemical properties of phthalocyanine compounds are very useful for photodynamic therapy applications. Especially high singlet oxygen quantum yields are very important for Type II mechanism. The studied phthalocyanine compounds showed good singlet oxygen generation and these compounds show potential as Type II photosensitizers. The fluorescences of the studied compounds are effectively quenched by 1,4-benzoquinone in different solvents.

Effect of Central Metals in the Porphyrin Ring on Photocurrent Performance of Cellulose Langmuir-Blodgett Films

Role-sharing functionalized cellulose derivatives having Mg, Zn, Cu, and Pd porphyrins are used for photocurrent generation system fabricated by the LB technique, mimicking the array of natural photosynthetic light-harvesting systems. These polymers exhibited different absorption and redox properties in solution depending on the central metal ions. On visible light illumination, the LB film generated anodic photocurrent in the order of Pd > free base > Zn > Cu > Mg. By inserting Pd ion, using myristoyl group, and adjusting the DS, the photocurrent quantum yield was 6.9 times as great as that of conventional porphyrin cellulose. These findings may provide opportunities for the design of a new class of organic solar cells, based on cellulose molecular characteristics.

Theoretical study on nonlinear optical properties of metalloporphyrin using elongation method

A quantum-chemical analysis of the central metal effect on the (hyper)polarizabilities of meso-meso-linked metalloporphyrin (MP) oligomers was carried out using elongation finite-field (ELG-FF) method. It is found that meso-meso-linked MPs exhibit evident evolution of the third-order nonlinear optical (NLO) response (γ) along with an increasing number of porphyrin units N. The order of γ values is as following: γMg > γZn > γNi. In contrast to the polarizability, the γ values of meso-meso-linked MPs are sensitive to the metals, that is, the nature of the metal can influence the third-order NLO response of MPs. However, the band structures for three MPs are similar to each other, and the differences on the band gaps of three MPs are very small. The local density of states (LDOSs) shows that the central metal gives the significant contributions for unoccupied bands in meso-meso-linked MPs.

The effects of central metals and peripheral substituents on the photophysical properties and optical limiting performance of phthalocyanines with axial chloride ligand

A series of peripherally substituted phthalocyanines (Pcs) with different central metals (Al, Ga and In) and axial chloride ligand were synthesized and their photophysical and optical limiting properties were investigated. The Q band absorption of the Pc shifts to longer wavelength with the central metals changing from Al to In, and the fluorescence quantum yields of S 1 emission decrease remarkably from Al to In. Transient absorption spectra of the Pcs in THF were measured in determination of the photophysical parameters. The optical limiting properties were investigated by a nanosecond pulse laser at 532 nm. All of these compounds exhibit good optical limiting performance, and the optical limiting behaviors of solid solution in glass obtained by sol–gel technique are much better than that of liquid solution. Several factors which affect the optical limiting performance of the Pcs with different central metals and substituents are discussed.

Solvent and central metal effects on the photophysical and photochemical properties of peripherally tetra mercaptopyridine substituted metallophthalocyanines

The synthesis of peripherally tetra 2-mercaptopyridine substituted phthalocyanines containing Si, Ga, Sn and In as central metal ions is reported for the first time in this study. Photophysical and photochemical studies were carried out on these compounds in order to determine the potential of the complexes as photosensitizers for use in photodynamic therapy. Fluorescence quantum yields ( Φ F ) ranged from 0.012 to 0.2 and triplet quantum yields ( Φ T ) from 0.54 to 0.89 in dimethylformamide (DMF) and from 0.65 to 0.93 in dimethylsulfoxide (DMSO). The triplet lifetimes ranged from 20 to 130 μs, the low values are due to the heavy atom effects of the central metal. The triplet lifetimes were larger in DMSO when compared with DMF.

Highly active double metal cyanide complexes: Effect of central metal and ligand on reaction of epoxide/CO 2

Various novel double metal cyanide (DMC) catalysts were successfully prepared by modifying the central metal (M) and one of cyanide ion (CN −) in Zn a [M(CN) b ] c complex. Such modifications have significant impact on the catalytic efficiency as well as the polymer selectivity for the reaction of PO/CO 2. Zn–Ni(II) DMC is a potential catalyst for alternating copolymerization of PO/CO 2, and DMC catalysts based on Zn 3[Co(CN) 5X] 2 (X = Br − and N 3 −) exhibit moderate efficiency for the production of polycarbonates. This research presents the preliminary exploration of novel DMC complex via chemical modification of its central metal and ligand.

Density Functional Theory Study of Transitional Metal Macrocyclic Complexes' Dioxygen-Binding Abilities and Their Catalytic Activities toward Oxygen Reduction Reaction

In this paper, density functional theory method is applied to study the dioxygen-binding abilities of transition metal macrocyclic complexes and their electrocatalytic activities toward oxygen reduction reaction. Both end-on and side-on binding modes are examined. Electronic properties, such as ionization potential and Mulliken charge, are evaluated. The effects of central metal, ligand, and substituents on catalyst's dioxygen-binding ability and catalytic activity are investigated. The binding nature of dioxygen adduct is analyzed based on structure property. The general activity trend observed for phthalocyanines and porphyrins is rationalized with the calculated properties. It is illustrated that the catalyst's oxygen reduction activity is related to its ionization potential and dioxygen-binding ability. Cobalt porphyrin derivatives have high ionization potentials, which make them better catalysts than the corresponding iron derivatives, whereas for phthalocyanine systems, iron derivatives have large ionization potential and better dioxygen-binding ability, which make them good catalysts.

Effect of central metal on intra-molecular exciplex of porphyrin–fullerene double linked dyad

The photoinduced electron transfer reaction of porphyrin–fullerene dyads occurs through an intermediate state, previously identified as a preformed intramolecular exciplex, emitting in the near infrared region (NIR). It can also be seen as a weak absorption band in NIR commonly called the charge transfer absorption band. A detailed analysis of the absorption and emission features of a series of double-linked dyads reported in this Letter leads to the conclusion that the state is characterized by a shift of 40% of the electron density from the porphyrin donor to the fullerene acceptor.