Enhanced Performance of Organic/Inorganic Hybrid Nanomaterials bearing Impregnated [PdL2] Complexes as Counter‐Electrode Catalyst for Dye‐Sensitized Solar Cells

N‐coordinate Pd²⁺ complexes [PdL₂] (L: N‐N‐quinoline‐8‐yl‐R‐benzenesulfonamides) ( 6–10 ) and [PdL₂] complexes assembled on multi‐wall carbon nanotubes (MWCNTs) hybrid nanomaterials were fabricated and characterized by various techniques. The [PdL₂] impregnated MWCNTs materials ( 11–15 ) were applied as a counter electrode (CE) catalyst for triiodide to iodide reduction reaction in the dye‐sensitized solar cells (DSSC) and investigated electro‐catalytic activities. The MWCNTs‐supported [PdL₂] CEs ( 11–15 ) are exhibits as Pt‐free CE with good power conversion efficiencies (PCEs), and compared to platinum and bare MWCNTs CEs and the PCE of bare MWCNTs was clearly improved by means of [PdL₂] complexes ( 6–10 ). The DSSCs based on the hybrid counter electrodes (CEs) ( 11–15 ) and bare MWCNTs are indicated a relative efficiency ( ? _rel ) of 64.27%, 54.07%, 53.75%, 51.52% 44.82% and 27.27% concerning a Pt CE control device set at 100%. The report emphasizes that [PdL₂] impregnated MWCNTs type counter electrodes (CEs) ( 11–15 ) are promising as effectively catalyst in working device design, particularly taking into account the eco‐friendly approach of the hybrids.     

Rational Construction of an Exceptionally Stable MOF Catalyst with Metal-Adeninate Vertices toward CO2 Cycloaddition under Mild and Cocatalyst-Free Conditions

CO₂ is considered as the primary greenhouse gas, resulting in a series of serious environmental problems that affect people's life and health. Carbon capture and sequestration has been implemented as one of the most appealing pathways to control and use CO₂. Here, we rationally integrate various functional sites within the confined nanospace of a microporous metal–organic framework (MOF) material, which is constructed by mixed-ligand strategy based on metal-adeninate vertices. It not only exhibits excellent stability but also can efficiently transform CO₂ and epoxides to cyclic carbonates under mild and cocatalyst-free conditions. Additionally, this catalyst shows extraordinary recyclability for the CO₂ cycloaddition reaction.     

Solid-State NMR Spectroscopy: A Powerful Technique to Directly Study Small Gas Molecules Adsorbed in Metal–Organic Frameworks

Metal–organic frameworks (MOFs) have shown great potential in gas separation and storage, and the design of MOFs for these purposes is an on-going field of research. Solid-state nuclear magnetic resonance (SSNMR) spectroscopy is a valuable technique for characterizing these functional materials. It can provide a wide range of structural and motional insights that are complementary to and/or difficult to access with alternative methods. In this Concept article, the recent advances made in SSNMR investigations of small gas molecules (i.e., carbon dioxide, carbon monoxide, hydrogen gas and light hydrocarbons) adsorbed in MOFs are discussed. These studies demonstrate the breadth of information that can be obtained by SSNMR spectroscopy, such as the number and location of guest adsorption sites, host–guest binding strengths and guest mobility. The knowledge acquired from these experiments yields a powerful tool for progress in MOF development.     

Bridging the Green Gap: Metal–Organic Framework Heteromultilayers Assembled from Porphyrinic Linkers Identified by Using Computational Screening

In organic photovoltaics, porphyrins (PPs) are among the most promising compounds owing to their large absorption cross-section, wide spectral range, and stability. Nevertheless, a precise adjustment of absorption band positions to reach a full coverage of the so-called green gap has not been achieved yet. We demonstrate that a tuning of the PP Q- and Soret bands can be carried out by using a computational approach for which substitution patterns are optimized in silico. The most promising candidate structures were then synthesized. The experimental UV/Vis data for the solvated compounds were in excellent agreement with the theoretical predictions. By attaching further functionalities, which allow the use of PP chromophores as linkers for the assembly of metal-organic frameworks (MOFs), we were able to exploit packing effects resulting in pronounced redshifts, which allowed further optimization of the photophysical properties of PP assemblies. Finally, we use a layer-by-layer method to assemble the PP linkers into surface-mounted MOFs (SURMOFs), thus obtaining high optical quality, homogeneous and crystalline multilayer films. Experimental results are in full accord with the calculations, demonstrating the huge potential of computational screening methods in tailoring MOF and SURMOF photophysical properties.     

Infrared spectroscopy of closed s-shell gas-phase M+(N2O)n (M = Li,Al) ion-molecule complexes*

ABSTRACT

We present the results of a combined experimental and computational study of the structures of gas-phase M⁺(N₂O)_n (M?=?Li, Al) complexes. Infrared spectra were recorded in the region of the N₂O asymmetric (N?=?N) stretch using photodissociation spectroscopy employing the inert messenger technique. Unlike in our previous studies on M⁺(N₂O)_n (M?=?Cu, Ag, Au and M?=?Co, Rh, Ir) complexes, N– and O–bound isomers in this case are near isoenergetic and are not distinguished spectroscopically at this resolution. In the case of Li⁺ complexes, there is, however, evidence for the presence of bound N₂ moieties, indicating the presence of inserted, OLi⁺N₂(N₂O)_n–type structures. The weak N₂ band lies to the blue of the signature of molecularly N– and O–bound ligands and is well–reproduced in the simulated spectra of energetically low-lying structures computed from density functional theory. No such inserted isomers are observed in the case of Al⁺(N₂O)_n complexes whose infrared spectra can be understood on the basis of molecularly-bound N₂O ligands. The differences in M⁺(N₂O)_n structures observed for these closed–shell, ns², metal centres relative to other metal cations are discussed in terms of the likely bonding motifs.     

Invariant discrete flows

In this paper, we investigate the evolution of joint invariants under invariant geometric flows using the theory of equivariant moving frames and the induced invariant discrete variational complex. For certain arc length preserving planar curve flows invariant under the special Euclidean group , the special linear group , and the semidirect group , we find that the induced evolution of the discrete curvature satisfies the differential‐difference mKdV, KdV, and Burgers' equations, respectively. These three equations are completely integrable, and we show that a recursion operator can be constructed by precomposing the characteristic operator of the curvature by a certain invariant difference operator. Finally, we derive the constraint for the integrability of the discrete curvature evolution to lift to the evolution of the discrete curve itself.     

Oxotitanium(IV) complexes of some bis‐unsymmetric Schiff bases: Synthesis,structural elucidation and biomedical applications

A number of oxotitanium(IV) complexes of the type TiOL with bis‐unsymmetric dibasic tetradentate Schiff base (LH₂) containing ONNO donor atoms have been synthesized. Mono‐Schiff base (OPD‐HNP) was prepared by the condensation of 1:3 molar ratio of 2‐hydroxy‐1‐naphthaldehyde (HNP) with o‐phenylenediamine (OPD). Dibasic unsymmetric tetradentate diamine Schiff bases were prepared by the reaction of OPD‐HNP with 2‐hydroxyacetophenone, 2‐hydroxypropeophenone, benzoylacetone, acetylacetone and ethylacetoacetate. Further, titanylacetylacetonate was reacted with these ligands to obtain their metal complexes. On the basis of analytical and physiochemical data, the formation of complexes as TiOL was suggested having square pyramidal geometry. Quantum mechanical approach also confirmed this geometry. The assessment of the synthesized ligands and their complexes showed that some behave as good inhibitors of mycelial growth against selected phytopathogic fungi but weak inhibitors against some selected bacteria. A few of them also showed antioxidant properties.     

Conformational Changes and Redox Properties of Bimetallic Single Helicates of Hexapyrrole-α,ω-dicarbaldehydes

The hexapyrrole-α,ω-dicarbaldehydes 1 a and 1 b were metallated with Cu^II, Ni^II, and Pd^II to give bimetallic complexes where a pair of 3 N+O four-coordinate metal planes are helically distorted and the central 2,2′-bipyrrole subunit adopts a cis or trans conformation. X-ray crystallographic analysis of the bisCu complex revealed a closed form with a cis-2,2′-bipyrrole subunit and an open form with a trans-2,2′-bipyrrole subunit. The bisPd complexes took a closed form both in the solid state and in solution. They are regarded as single helicates of two turns and the energy barrier for the interchange between an M helix and a P helix was remarkably influenced by the bulky 3,3′-substituent of the central 2,2′-bipyrrole subunit. Although the bisNi complexes adopt a closed form in the solid state, they exist as a homohelical open C₂-symmetric form or a heterohelical open C_i-symmetric form in solution. A theoretical study suggested that the closed form of 1 a Pd was stabilized by the Pd–Pd interaction. Compound 1 a Pd was reversibly oxidized by one electron at 0.14 V versus ferrocene/ferrocenium (Fc/Fc⁺) and this oxidized species showed Vis/NIR absorption bands at λ=767 and 1408 nm.     

Attaching tweezers like ionophore to a proton crane: theoretical design of new tautomeric sensors

ABSTRACT

The tautomeric optical sensors based on 4-(phenyldiazenyl)naphthalen-1-ol exist in their pure enol tautomeric form as free ligands, while the addition of metal ion fully shifts the equilibrium towards the keto tautomer allowing a red shift in the measured absorbance. This effect is achieved when a side ionophore group is connected to a tautomeric backbone by a spacer in a way that stabilizes the enol form via hydrogen boding. When the ionophore captures the metal ion the keto form is stabilized due to C─O tautomeric group participation in the complex. In the current study, we model theoretically the effect of symmetric tweezer like ionophores (RCOXCOR, where X, being CH or N, is the linker to the tautomeric backbone) on the tautomeric state and complexation ability of 4-(phenyldiazenyl)naphthalen-1-ol containing ligands. It was found that enol form stabilisation is achieved when R?=?NMe₂, independing on the linker. Both ligands are unsuitable for capturing alkali metal ions. The calculations predict that the complexation with alkali earth metal ions could lead to a full shift of the tautomeric equilibrium towards keto tautomer.