Structure and properties of bivalent nickel and copper complexes with pyrazine-amide-thioether coordination: stabilization of trivalent nickel

Two Coordination Polymers Synthesized from Various N-Donor Clusters Spaced by Terephthalic Acid for Efficient Photocatalytic Degradation of Ibuprofen in Water under Solar and Artificial Irradiation

Two coordination polymers CP1 {[Zn(II)(BIPY)(Pht)] _n } and CP2 {[Zn(HYD)(Pht)] _n } (BIPY = 4,4'-bipyridine, Pht = terephthalic acid, and HYD = 8-hydroxyquinoline) have been successfully synthesized by a hydrothermal process using zinc aqueous solution. The so-prepared compounds were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, UV-visible spectroscopy, thermogravimetric analysis (TGA), and cyclic voltammetry. XRD pointed to a crystalline phase for CP1, while CP2 required recrystallization, FTIR spectroscopy established the presence of characteristic bands for all the ligands, and TGA showed thermal stability up to 100 °C. The electrochemical study showed a good charge transfer between the ligands and Zn metal for both materials. The UV-vis spectra displayed a strong absorption band spreading over a wide wavelength range, encompassing UV and visible light, with a band gap of 2.69 eV for CP1 and 2.56 eV for CP2, both of which are smaller than that of ZnO. This provides an advantageous alternative to using ZnO. The 5 × 10^-5 mol L^-1 ibuprofen decomposition kinetics under solar and UV light were studied under different irradiation conditions. Good photocatalytic properties were observed due to their high surface area.

Correlation between Second Ionization Potential and Nonlinear Optical Properties of Bivalent Transition-Metal Complexes: A Quantum Chemical Study

Discovering new materials with excellent nonlinear optical responses has recently become a very interesting research topic in the different domains of materials science. Currently, density functional theory (DFT) has been shown to be a powerful tool in the explanation and prediction of the performance of novel nonlinear optical (NLO) materials. Quantum chemical calculations using DFT/TD-DFT with the B3LYP exchange-correlation functional are reported to study the NLO properties of 26 bivalent transition-metal (TM) complexed by six acyclic hexadentate ligands providing pyridyl/pyrazine-amide-thioether/ether coordination and differing by the nature of the methylene dichalcogenate spacer between the rings. However, the geometry parameters and the theoretically predicted UV-vis absorption spectra of the optimized compounds M(II)Lⁱ are in excellent agreement with the experiment, when available, the trends among the nature of the TM, the importance of the ligand spacer, and of the substituents of the pyridine/pyrazine amide ligand are discussed. To the best of our knowledge, our work evidences for the first time that the hyper-polarizability, second harmonic generation, and hyper-Rayleigh scattering response of TM coordination complexes can be correlated to the second ionization potential of metal and spin state of complexes.

Copper (ii) dimers stabilized by bis(phenol) amine ligands: theoretical and experimental insights

Comparative structural and magnetic studies on the binuclear Cu complexes of ¹L(2−)/²L(2−) have been done and their electronic structures and observed electronic transitions (DFT and TD-DFT calculations) rationalized. The dimer complex can be converted into the corresponding monomeric Cu(ii) complex, [¹L₂CuII2(X)] (X = py), by adding an exogenous ligand such as pyridine (py).

Polycarboxylate-directed semi-rigid pyridyl-amide-based various NiII complexes: electrochemical properties and enhancements of photocatalytic activities by calcination

Four different pyridyl-amide-based Ni-complexes were synthesized by tuning polycarboxylates, displaying bifunctional electrocatalytic properties and enhancements of photocatalytic activities by calcination.

Low-spin [MII(L)2] and [MIII(L)2]+ (M = Fe and Co) complexes of tridentate azo-containing pyridine/pyrazine amide ligands: structures, properties and redox potential correlations

Using deprotonated forms of tridentate azo-containing pyridine-2-/pyrazine-2-carboxamide 2-[N-(2-phenylazo)carbamoyl]-pyridine/pyrazine, seven bis-ligand complexes of Fe^II/Co^II and Fe^III/Co^III have been synthesized. Molecular structures of six of them reveal that these six-coordinate complexes utilize all available donor sites of the ligands and assume M^II/IIIN₂(pyridine/pyrazine)N'₂(amide)N''₂(azo) coordination. Complexes of Fe^II and Co^III are diamagnetic and those of Fe^III and Co^II are paramagnetic (S = 1/2; room-temperature magnetic data and EPR spectra). Cyclic voltammetry experiments in CH₂Cl₂ reveal facile metal-centred Fe^III/Fe^II and Co^III/Co^II redox responses, and all complexes display quasireversible-to-irreversible ligand(azo)-centred redox processes. The E_1/2 values of M^III/M^II redox processes for Fe, Co and Ni (reported earlier) complexes of the pyridine amide ligand linearly correlate with those for six-coordinate [M^III(bpy)₃]³⁺/[M^II(bpy)₃]²⁺, [M^III(terpy)₂]³⁺/[M^II(terpy)₂]²⁺, [M^III(L)]⁺/[M^II(L)]⁰ or [M^III(L')₂]⁺/[M^II(L')₂]⁰ (bpy = 2,2'-bipyridine, terpy = 2,2':6',2''-terpyridine, hexadentate L(2-) = 1,4-bis[o-(pyridine-2-carboxamidophenyl)]-1,4-dithiobutane and tridentate L'(-) = {2-[2-(arylimino)phenylazo]-pyridine}) couples. Density functional theory (DFT) at the B3LYP level and time-dependent (TD)-DFT calculations rationalize the electronic structure of the present complexes and throw light on the origin of observed electronic transitions.

Various pH-Dependent Copper(II) Coordination Architectures Constructed from N,N′-Di(3-pyridyl)succinamide and Two Different Dicarboxylates

Using a bis-pyridyl-bis-amide N,N′-di(3-pyridyl)succinamide (L) and two dicarboxylates as mixed ligands, four 2D copper(ii) metal–organic networks, formulated as [Cu(1,4-chdc)(L)]·3H2O (1), [Cu(1,4-chdc)(L)]·H2O (2), [Cu(2,5-tdc)(L)]·H2O (3), and [Cu(2,5-tdc)(L)]·2H2O (4) (L = N,N′-di(3-pyridyl)succinimide; 1,4-H2chdc = 1,4-cyclohexanedicarboxylic acid; 2,5-H2tdc = thiophen-2,5-dicarboxylic acid) have been hydrothermally synthesized under different pH conditions, and characterized by IR spectroscopy, thermogravimetric analysis, and single-crystal X-ray diffraction. Compound 1, formed at pH 5.4, contains two rare types of left-, right-handed [Cu-L]n helix chains, which are further connected by [Cu-1,4-chdc]n zigzag chains, affording a 2D wave-like polymeric network. Compound 2 was obtained at pH 5.9, and shows a 2D square-grid layer constructed from zigzag [Cu-L]n chains and linear [Cu-1,4-chdc]n chains. Compounds 3 and 4 possess a similar 2D grid layer to that of 2 with 44-sql topology, formed at pH 4.8 and 5.4 respectively, and are constructed from zigzag [Cu-L]n chains and linear [Cu-2,5-tdc]n chains. The effects of pH and secondary dicarboxylates on the diversity of structures are discussed. In addition, the thermal stabilities, photoluminescence properties, and photocatalytic activity of compounds 1–4 were also studied.

Aminopyridine derivatives controlled the assembly and various properties of Cu–BTC metal–organic frameworks

Three Cu(ii) MOFs based on three aminopyridine derivatives and 1,3,5-benzenetricarboxylic acid have been synthesized and characterized. The electrocatalytic and photocatalytic properties of complexes 1–3 have been investigated in detail.

Assembly, structures, photophysical properties and photocatalytic activities of a series of coordination polymers constructed from semi-rigid bis-pyridyl-bis-amide and benzenetricarboxylic acid

Ten metal–organic coordination polymers 1–10 based on semi-rigid bis-pyridyl-bis-amide ligands have been synthesized. The fluorescence sensing and photocatalytic properties of 1–10 have been investigated.

Hexacoordinate nickel(II)/(III) complexes that mimic the catalytic cycle of nickel superoxide dismutase

A functional model complex of nickel superoxide dismutase (NiSOD) with a non-peptide ligand which mimics the full catalytic cycle of NiSOD is unknown. Similarly, it has not been fully elucidated whether NiSOD activity is a result of an outer- or inner-sphere electron-transfer mechanism. With this in mind, two octahedral nickel(II)/(III) complexes of a bis-tridentate N2 S donor carboxamide ligand, N-2-phenylthiophenyl-2'-pyridinecarboxamide (HL(Ph)), have been synthesized, structurally characterized, and their SOD activities examined. These complexes mimic the full catalytic cycle of NiSOD. Electrochemical experiments support an outer-sphere electron-transfer mechanism for their SOD activity.

Shuttling of nickel oxidation states in N4S2 coordination geometry versus donor strength of tridentate N2S donor ligands

Seven bis-Ni(II) complexes of a N(2)S donor set ligand have been synthesized and examined for their ability to stabilize Ni(0), Ni(I), Ni(II) and Ni(III) oxidation states. Compounds 1-5 consist of modifications of the pyridine ring of the tridentate Schiff base ligand, 2-pyridyl-N-(2'-methylthiophenyl)methyleneimine ((X)L1), where X = 6-H, 6-Me, 6-p-ClPh, 6-Br, 5-Br; compound 6 is the reduced amine form (L2); compound 7 is the amide analog (L3). The compounds are perchlorate salts except for 7, which is neutral. Complexes 1 and 3-7 have been structurally characterized. Their coordination geometry is distorted octahedral. In the case of 6, the tridentate ligand coordinates in a facial manner, whereas the remaining complexes display meridional coordination. Due to substitution of the pyridine ring of (X)L1, the Ni-N(py) distances for 1~5 < 3 < 4 increase and UV-vis λ(max) values corresponding to the (3)A(2g)(F)→(3)T(2g)(F) transition show an increasing trend 1~5 < 2 < 3 < 4. Cyclic voltammetry of 1-5 reveals two quasi-reversible reduction waves that correspond to Ni(II)→Ni(I) and Ni(I)→Ni(0) reduction. The E(1/2) for the Ni(II)/Ni(I) couple decreases as 1 > 2 > 3 > 4. Replacement of the central imine N donor in 1 by amine 6 or amide 7 N donors reveals that complex 6 in CH(3)CN exhibits an irreversible reductive response at E(pc) = -1.28 V, E(pa) = +0.25 V vs saturated calomel electrode (SCE). In contrast, complex 7 shows a reversible oxidation wave at E(1/2) = +0.84 V (ΔE(p) = 60 mV) that corresponds to Ni(II)→Ni(III). The electrochemically generated Ni(III) species, [(L3)(2)Ni(III)](+) is stable, showing a new UV-vis band at 470 nm. EPR measurements have also been carried out.

catena-Poly[[bis-(pyrazine-2-carbox-amide-κN)mercury(II)]-di-μ-bromido]

In the crystal structure of the title compound, [HgBr₂(C₅H₅N₃O)₂]_n, the Hg^II cation is located on an inversion center and is coordinated by two N atoms from the pyrazine rings and four bridging Br⁻ anions in a distorted octa­hedral geometry. The Br⁻ anions bridge the Hg^II cations with significantly different Hg—Br bond distances of 2.4775 (8) and 3.1122 (8) Å, forming polymeric chains running along the a axis. Inter­molecular N—H⋯O and N—H⋯N hydrogen bonds are effective in the stabilization of the crystal structure.