3d Metal Ions Research Articles

The crystal engineering of 3d-metal with two tetrazole-phenyl-carboxylate linkers and multiple post-synthetic metal exchange

Ligand with mixed-groups contributes to the construction of special structure motif with novel properties, yet it is challenging to understand and regulate the competitive coordination of different functional groups toward metal ions. Herein, the crystal engineering for MOF construction from two linear di-topic linkers of 4-(1H-tetrazol-5-yl)benzoic acid (H2tzba) and the longer 4′-(1H-tetrazol-5-yl)-[1,1′-biphenyl]-4-carboxylic acid (H2tzbba) featuring dual groups of phenyl-carboxylate and tetrazole, with three typical 3d metal ions (Mn2+, Fe2+ and Zn2+) were investigated. A series of five new MOFs, that are [Mn3(tzba)3(dmf)4]·11dmf (1, dmf = N,N-Dimethylformamide), [Mn(tzba)(H2O)] (2), [Zn2(tzba)2(dmf)]·0.5dmf (3), [Fe2(tzba)2(dmf)]·0.5dmf (4) and [Zn2(tzbbz)(gac)(dmf)2]·1.5dmf (5), were synthesized under solvothermal reactions. The modified solvent template and temperature effects lead to 3D framework of 1 (dmf solution under 433 K) with [Mn3(tz)3(COO)3] nodes and 1D hexagonal channels, while the 2 (water solution under 373 K) posssesses compact pillared-layer motif from [Mn2(tz)2] nodes. Under changed metal salt reactents but same solvent of dmf, the generated 3 and 4 have isoreticular and porous pillared-layer structure constituted of [M2(COO)2] nodes. The use of tzbba coupled with a crucial auxiliary ligand of glycollic acid, leads to 5 as porous pillared-layer MOFs with 1D rounded channels. The porous flexible skeleton of 1 constructed from [Mn3] node with four coordinated dmf facilitates post-synthetic metal exchange of the Mn2+ by radius similar metal ions following priority of Cu2+ < Zn2+ < Ni2+< Co2+, with maximum exchange percentage ranging from 17 % to 69 %. Time dependent ICP-AES analysis revealed the quite wide feasible solvents for post-synthetic metal exchange, as well as the fine control on substituting degree based on soaking temperature and time. Particularly, the compatible introduce of four different metal ions support the potential of preparing bi-, tri-, tetra- and penta- metal MOF crystals, that can not be obtained by traditional solvothermal reactions.

Incorporating Zinc Metal Sites in Aluminum-Coordinated Porphyrin Metal-Organic Frameworks for Enhanced Photocatalytic Nitrogen Reduction to Ammonia.

Rationally designing photocatalysts is crucial for the solar-driven nitrogen reduction reaction (NRR) due to the stable N≡N triple bond. Metal-organic frameworks (MOFs) are considered promising candidates but suffer from insufficient active sites and inferior charge transport. Herein, it is demonstrated that incorporating 3d metal ions, such as zinc (Zn) or iron (Fe) ions, into Al-coordinated porphyrin MOFs (Al-PMOFs) enables the enhanced ammonia yield of 88.7 and 65.0µggcat -1h-1, 2.5- and 1.8-fold increase compared to the pristine Al-PMOF (35.4µggcat -1h-1), respectively. The origin of ammonia (NH3) is verified via isotopic labeling experiments. Incorporating Zn or Fe into Al-PMOF generates active sites in Al-PMOF, that is, Zn-N4 or Fe-N4 sites, which not only facilitates the adsorption and activation of N2 molecules but suppresses the charge recombination. Photophysical and theoretical studies further reveal the upshift of the lowest unoccupied molecular orbital (LUMO) level to a more energetic position upon inserting 3d metal ions (with a more significant shift in Zn than Fe). The promoted nitrogen activation, suppressed charge recombination, and more negative LUMO levels in Al-PMOF(3d metal) contribute to a higher photocatalytic activity than pristine Al-PMOF. This work provides a promising strategy for designing photocatalysts for efficient solar-to-chemical conversion.

An overview on copper based heterometallic complexes in combination with d10 metal ions derived from N2O2 donor di-Schiff base ligands

A good number of heterometallic complexes based on various Cu(II) bound “metalloligands” of N2O2 donor di-Schiff bases and some of their reduced counterpart along with group 12 metal ions have been synthesized and characterized by different research groups in the literature. This review focuses on an overview of the synthetic strategies, X-ray crystallographic structures and a few important properties of these complexes. These have been discussed in three major sub-classes: Cu(II)-Zn(II), Cu(II)-Cd(II) and Cu(II)-Hg(II) heterometallic complexes. Judicious combinations of carbonyls and di-amines in an easy and effective manner gives 14 selected di-Schiff base ligands (symmetrical and unsymmetrical) with particular shape, geometry and denticity that direct the synthesis of these metal complexes totally or preferentially towards di-, tri- or poly-nuclear entities. Moreover, owing to their ability to assemble three metal ions in close proximity, these resulting oxido-bridged flexible coordination clusters adapted to various other ligand functionalities with particular shape and sometimes unusual coordination modes with certain degree of control. Such unique structural aspect of this system is immensely important in inorganic synthesis. The inherent flexibility of the di-oxido bridged trinuclear coordination cluster led to produce isomeric linear and bent structures that usually depend upon various factors e.g. the nature of the Schiff base, anionic co-ligands, temperature, solvent etc. The structural aspects of resulting discrete and polymeric self-assemblies have enriched the coordination library that extended to develop numerous heterometallic systems with significant applications and new scopes

Metal (Mn2+, Co2+ and Cd2+) ions induced differentiation in mixed-ligands MOFs constructed from H3btb and H2bdc: Highly porous Structures, new topology nets and two-step gate-opening behaviors

Mix-ligands strategy is highly efficient for the rational construction of MOFs with particular structure motifs and high porosity, yet challenging and requiring matching in hierarchical coordination assembly and synergetic crystallization. The solvothermal reactions of 1,3,5-tris[4-carboxyphenyl]benzene (H3btb) and 1,4-benzenedicarboxylic acid (H2bdc) with different 3d metal ions, generated highly porous mixed-ligands MOFs of [(CH3)2NH2]2[Mn3(btb)2 (bdc)]·12DMF·3MeOH (Mn-btb-bdc) having anionic 3D frameworks constructed from linear [Mn3(COO)8] nodes, [Co4(btb)2(bdc)(H2O)3]·15DMF·7H2O (Co-btb-bdc) processing neutral frameworks constituted by linear [Co3(COO)6(H2O)4] and paddle-wheel [Co2(COO)4(H2O)2] nodes, as well as one single-ligand MOFs of [(CH3)2NH2][Cd(btb)(H2O)]·8DMF (Cd-btb-2fold) exhibiting 2-fold interpenetrated ths net frameworks due to the unsuccessful introduce of the coexisted bdc ligand. Two new topology net of 2,3,8-connected net with point symbol of (42·6)2(44·66·812·105·12)(6) and 2,3,4,6-connected net with Point Symbol of (4·82)4(42·811·102)2(84·122)(82) were found for Mn-btb-bdc and Co-btb-bdc. All these three MOFs are highly porous with void fractions of 60.9%, 52.2% and 61.4%, stemming from 3D-penetrated, 3D-penetrated and 1D channels, respectively. Such structural differentiations are attributed to the diversified electronic structure and coordination preference of different 3d metal ions, as well as the solvent template and temperature effects. Two-steps gate-opening behaviour in gas sorption isotherms was found in the flexible Mn-btb-bdc MOFs.

Tailored coordination chemistry: A novel Zn(II)-fluorescent coordination material for highly selective and sensitive detection of Hg2+ ions in aqueous environments

The pursuit of advanced sensing materials for precisely detecting heavy metal ions remains a critical imperative in environmental science. This manuscript deal with a novel fluorescent material, ZU-1, designed for the selective and sensitive detection of Hg2+ ions in aqueous suspension. Employing the Hard-Soft Acid-Base (HSAB) concept, Zn2+ serves as the d10 metal ion, and ZU-1 is synthesized with a −S donor ligand (NaSCN) and 2-pyridine methanol (Hhmp). The fluorescence sensing elucidates a unique detection mechanism, unveiling the distinctive coordination facilitated by the larger ionic radius and soft acid characteristics of Hg2+ with the −S donor sites in ZU-1. Fluorescence titration experiments validate ZU-1’s outstanding ability to selectively quench fluorescence intensity in the presence of Hg2+, even amidst interference from other metal ions. The quantitative analysis yields a Stern-Volmer constant (Ksv) of 7.5 × 108 M−1 and an exceptional limit of detection for Hg2+ at ∼0.60 ppm. ZU-1 further distinguishes itself through outstanding recyclability over four cycles, underscoring its potential as a sustainable and reusable sensor for real-time Hg2+ detection. Beyond its practical implications, this research contributes fundamental insights into design principles for materials exhibiting heightened selectivity and sensitivity to heavy metal ions.

Synthesis, characterization, crystal structures and biological activity of 4-chloro-2-(2-hydroxy-3-ethoxybenzylideneamino)phenol and complexes

Molecular nanoclusters comprising a heterometallic 3d-4f stoichiometry are an interesting class of compounds. In this paper, a chloro-containing Schiff base 4-chloro-2-(2-hydroxy-3-ethoxybenzylideneamino)phenol (H2L) was prepared by condensation reaction of 3-ethoxysalicylaldehyde with 2-amino-4-chlorophenol in methanol. The Schiff base is predisposed to chelate within a cluster core both 3d and 4f metal ions. Reaction of H2L with nickel salts afforded a tetranuclear NiII complex [Ni4L4(MeOH)4] (1), while with nickel salts and lanthanide(III) nitrate three tetranuclear NiII-LnIII complexes [Ni2Eu2L4(NO3)2(DMF)2] (2), [Ni2Er2L4(NO3)2(DMF)2] (3), [Ni2Tb2L4(CH3COO)2(DMF)2]·4DMF (4) were obtained. H2L and the complexes have been characterized by elemental analysis, IR, UV–Vis spectra. H2L has also been characterized by 1H and 13C NMR spectra. Molecular structures of the compounds have been determined by single crystal X-ray determination. In the complexes, the Schiff base ligands coordinate to the metal atoms via ether oxygen, imino nitrogen and two phenolate oxygen atoms. All the Ni atoms in the complexes are in octahedral coordination. The rare earth metal atoms are eight coordinated by the phenolate and ether oxygen of the Schiff base ligands, and anionic and solvent oxygen atoms, forming square antiprismatic coordination. The compounds were evaluated for their antibacterial activities on Bacillus subtilis, Staphylococcus aureus, Escherichia coli and Pseudomonas fluorescens, and antifungal activities on Candida albicans and Aspergillus niger, and gave interesting results.

STUDY OF THE MECHANISM OF SORPTION OF Cu2+, Co2+, AND Mn2+ IONS ON A MODIFIED NATURAL POLYMER – PECTIN

Sorption materials based on apple pectin modified with biologically active organic acids (salicylic, anthranilic, 5-aminosalicylic, nicotinic) capable of effectively extracting Cu2+, Co2+ and Mn2+ ions from aqueous solutions of their salts have been obtained. The regularities of the sorption kinetics of Cu2+, Co2+ and Mn2+ ions by modified pectin samples were studied. An increase in the efficiency of extraction of d-metal ions by modified pectin sorbents compared to the original polysaccharide was revealed. Sorption isotherms of Cu2+, Co2+, Mn2+ ions by modified pectins have been obtained and analyzed for compliance with known theoretical models. Integral kinetic curves have been obtained, and the values of the experimental sorption capacity of biosorbents have been calculated. It was found that the process of sorption of Cu2+, Co2+ and Mn2+ ions on the studied biosorbents proceeds in the diffusion mode. The predominance of the external diffusion nature of the limiting stage of the process of extracting transition metal ions with modified pectins was established. The rate constants of sorption processes are calculated. The values of the apparent activation energy of the sorption process are determined. The thermodynamic parameters of the extraction of Cu2+, Co2+ and Mn2+ ions by pectin sorbents have been calculated. It has been established that the sorption of Cu2+, Co2+, and Mn2+ ions by modified polysaccharide materials is an exothermic process, which can be considered as physical adsorption of metal ions due to solvation and complex formation with the participation of sorbent sorption centers and solvent (water) molecules. The obtained new highly active biosorbents can be recommended as enterosorbents for detoxification of the human body.&#x0D; Keywords: sorption, d-metal ions, pectin, modification, kinetic curves, thermodynamic parameters.

Regulating electrical conductivity and Schottky nature of d10 metal ion-based nanoarchitectonics in coordination polymers

This study emphasizes the impact of a d10 metal ion [Cd(ii)/Zn(ii)] on the charge transportation and Schottky barrier diode behavior of coordination polymers based on a highly conjugated ligand 4-(1-naphthylvinyl)pyridine.

STUDY OF METAL SORPTION BY COVALENTLY IMMOBILIZED POLYAMPHOLYTES BASED ON AMINO ACIDS

In the presented article, the sorption properties were studied for the first time of polyampholyte, obtained by polycondensation - covalent fixation of ortho-aminobenzoic acid on a matrix of epoxy resin "epoxymol" and polyethylene polyamine. In particular, this polymer was complexed with copper, nickel, zinc, cobalt, and silver ions. The structure of both the resulting polyampholyte itself and its metal complexes with the indicated metals (d-elements) was determined by IR spectroscopy. For the first time, the IR spectra of ligand-polyampholyte complexes with copper, nickel, zinc, cobalt, and silver ions were recorded and studied. These spectra are compared with the spectra of the polyampholyte itself. Scanning electron microscopy (SEM) (photography, elemental analysis) was used to study the microscopic structure of the O-ABA:ED-20:PEPA ligand (ortho-aminobenzoic acid, epoxy resin, polyethylenepolyamine) and its coordination compound with copper ions Cu2+. According to the results of elemental analysis, the gross formulas of the obtained polyampholyte coordination compounds with all coordinated (adsorbed) metals are given. According to the experimental data, obtained as a result of studying the thermal stability of polyampholyte, it was shown that the sorbent is stable up to a temperature of 200 °C. The resulting sorbent is recommended for practical use in the sorption of some d-metal ions from solutions. The dependence of the sorption of some d-metals on the pH of the medium was also studied, and were constructed graphs that describe the dependence of the sorption of metals on pH in the synthesized complexing ligand, showing that the sorption of ions is higher in slightly acidic media.

Printable 2D Materials for Thin Film Batteries and Supercapacitors

Two-dimensional transition metal oxide (TMO) nanosheets are the oxide equivalents of the well-known 2D graphene phase. Compared with graphene, a much wider range of compositions, structures and properties can be realized from TMOs. 2D metal oxides typically have thicknesses of 0.45-2.5 nm, and lateral dimensions between 50 nm and tens of micrometers. Interestingly, although they are oxides, they are very flexible and bendable owing to their thinness. So far, several dozen nanosheet phases have been reported in literature, but many more compositions are possible.Dispersions of TMO nanosheets can be made following one of several solution-phase strategies. Often, they are prepared by chemical delamination of isomorphous layered metal oxide parent phases. In a few cases, the 2D TMO phase can be grown directly bottom-up from an aqueous chemical solution. Either way, the resulting colloidal solutions of 2D single crystal nanosheets can serve in subsequent process step as the basis of a chemical ink suitable for ink jet printing on arbitrary substrates like paper, silicon or flexible polymers. Redox-active nanosheets may also be used as active electrode elements for micro-supercapacitors and flexible thin film batteries.For example, 2D MnO2 nanosheets that are isomorphous to the layered δ-MnO2 (birnessite) phase exhibit high pseudocapacance owing to their beneficial redox properties, relatively high in-plane conductivity and very large specific surface area. Ink-jet printed 2D MnO2 based thin film microsupercapacitors were realized that showed comparable performance with other state of the art systems. However, undoped MnO2 nanosheets exhibit relatively low sheet conductivity. Substitutional doping of 3d metal ions (Co, Fe and Ni) into MnO2 nanosheets improved the volumetric energy density to 1.13 mWh cm−3 at a power density of 0.11 W cm−3. The dopants introduced new electronic states near the Fermi level which enhanced the electronic conductivity within the nanosheets and contributed to the further formation of redox-active 3d surface states. Among these, Fe-doped MnO2 exhibited a significant increase in the carrier density and conductivity, while doping with Ni or Co had a much more limited effect on conductivity. These Fe-doped MnO2 nanosheet-based microsupercapacitors show long cycle life and bendability without performance loss on flexible plastic substrates [1].Following a similar inkjet printing approach, thin film cathodes for Li ion batteries were made using V2O5 nanosheets as charge-storage medium. In this case the conductivity of the electrode was improved by addition of highly conductive 2D MXene (Ti3C2) platelets derived from the parent MAX phase Ti3AlC2. Using LiPF6 in EC/DMC as electrolyte, the hybrid V2O5-MXene electrodes showed a high capacity of 321 mAh g-1 at 1C, 112 mAh g-1 at 10.5C and 92% capacity retention after ~700 cycles [2].As third example, an all inkjet-printed MXene/graphene oxide (GO)/MXene thin film supercapacitor with GO as solid electrolyte phase will be discussed. Here, free water molecules trapped between GO layers enabled proton transport through the electrolyte. The as-made capacitor showed high areal capacitance, good cyclability and power densities comparable with state of the art printed supercapacitors. The specific capacitance could be increased further by addition of liquid electrolyte [3].[1] Y. Wang, Y.-Z. Zhang, Y.-Q. Gao, G. Sheng, J.E. ten Elshof, Nano Energy 68 (2020) 104306.[2] Y. Wang, T. Lubbers, R. Xia, Y.-Z. Zhang, M. Mehrali, M. Huijben, J.E. ten Elshof, J. Electrochem. Soc. 168 (2021) 020507[3] Y. Wang, M. Mehrali, Y.-Z. Zhang, M.A. Timmerman, B.A. Boukamp, P.-Y. Xu, J.E. ten Elshof, Energy Storage Mater. 36 (2021) 318-325.

A hard molecular nanomagnet from confined paramagnetic 3d-4f spins inside a fullerene cage

Reducing inter-spin distance can enhance magnetic interactions and allow for the realization of outstanding magnetic properties. However, achieving reduced distances is technically challenging. Here, we construct a 3d-4f metal cluster (Dy2VN) inside a C80 cage, affording a heretofore unseen metallofullerene containing both paramagnetic 3d and 4f metal ions. The significantly suppressed 3d-4f (Dy-V) distances, due to the unique cage confinement effect, were observed by crystallographic and theoretical analysis of Dy2VN@Ih(7)-C80. These reduced distances result in an enhanced magnetic coupling (Jtotal, Dy-V = 53.30 cm−1; Jtotal, Dy-Dy = −6.25 cm−1), leading to a high magnetic blocking temperature compared to reported 3d-4f single-molecule magnets and strong coercive field of 2.73 Tesla. Our work presents a new class of single-molecule magnets with both paramagnetic 3d and 4f metals confined in a fullerene cage, offering superior and tunable magnetic properties due to the unique cage confinement effect and the diverse composition of the entrapped magnetic core.

Aggregation-Induced Emission via the Restriction of the Intramolecular Vibration Mechanism of Pinacol Lanthanide Complexes.

Pinacol lanthanide complexes PyraLn (Ln = Dy and Tb) with the restriction of intramolecular vibration were obtained for the first time via an in situ solvothermal coordination-catalyzed tandem reaction using cheap and simple starting materials, thereby avoiding complex, time-consuming, and expensive conventional organic synthesis strategies. A high-resolution electrospray ionization mass spectrometry (HRESI-MS) analysis confirmed the stability of PyraLn in an organic solution. The formation process of PyraLn was monitored in detail using time-dependent HRESI-MS, which allowed for proposing a mechanism for the formation of pinacol complexes via in situ tandem reactions under one-pot coordination-catalyzed conditions. The PyraLn complexes constructed using a pinacol ligand with a butterfly configuration exhibited distinct aggregation-induced emission (AIE) behavior, with the αAIE value as high as 60.42 according to the AIE titration curve. In addition, the PyraLn complexes in the aggregated state exhibit a rapid photoresponse to various 3d metal ions with low detection limits. These findings provide fast, facile, and high-yield access to dynamic, smart lanthanide complex emissions with bright emission and facilitate the rational construction of molecular machines for artificial intelligence.

Spectroscopic and Computational pH Study of NiII and PdII Pyrrole-Imine Chelates with Human Serum Albumin.

Human serum albumin (HSA) efficiently transports drugs in vivo: most are organic. Therefore, it is important to delineate the binding of small molecules to HSA. Here, for the first time, we show that HSA binding depends not only on the identity of the d8 metal ion, NiII or PdII, of their complexes with bis(pyrrole-imine), H2PrPyrr, but on the pH level as well. Fluorescence quenching data for native and probe-bound HSA showed that sites close to Trp-214 (subdomain IIA) are targeted. The affinity constants, Ka, ranged from ~3.5 × 103 M-1 to ~1 × 106 M-1 at 37 °C, following the order Pd(PrPyrr) > Ni(PrPyrr) at pH levels of 4 and 7; but Ni(PrPyrr) > Pd(PrPyrr) at a pH level of 9. Ligand uptake is enthalpically driven, dependent mainly on London dispersion forces. The induced CD spectra for the protein-bound ligands could be simulated by hybrid QM:MM TD-DFT methods, allowing us to delineate the binding site of the ligands and to prove that the metal chelates neither decompose nor demetallate after uptake by HSA. The transport and delivery of the metal chelates by HSA in vivo is therefore feasible.

HOMO- AND HETERONUCLEAR Yb(III) AND Lu(III) COMPLEXES WITH CALIX[4]ARENE MODIFIED WITH PORPHYRIN SUBSTITUENTS.

In this work we describe the approaches for the synthesis of lanthanide-containing homo- and heteronuclear complexes using 5,11,17,23-tetra-tert-butyl-25,27-dihydroxy-26,28-bis[(N-meso-­(p-aminophenyl)-meso-triphenylporphyrincarbonyl)methoxy]-calix[4]arene (1). Such spatially preorganizedcalix[4]arene macrocycle facilitates lanthanide cation coordination, impacting the structure and analytical signal of porphyrin substituents. The study employs two synthesis stra­tegies resulting in mononuclear and homobinuclear complexes, influenced by steric effects and changes in hydrogen bonding. The complexes exhibit changes in fluorescence spectra due to intramolecular dimerization and hydrogen bonding during complex formation. Mononuclear complexes (Ln-1) are synthesized under mild conditions, while homobinuclear complexes (Ln2-1) require high-boiling solvents and specific reaction conditions, detailed synthesis procedures are described. The structural changes during complex formation were analyzed with the use of NMR analysis. The absorption spectra of lanthanide complexes demonstrate shifts in maxima, reflecting coordination changes, with notable variations between mononuclear and homobinuclear complexes. Additionally, heteronuclear compounds with copper(II), zinc(II), and palladium(II) exhibit distinctive absorption patterns, emphasizing the role of d-metal ions. Luminescence stu­dies reveal the sensitization of 4f-luminescence by both calix[4]arene and porphyrin fragments. The use of deuterated solvents enhances 4f-luminescence intensity, highlighting solvent effects. Furthermore, 4f-luminescence characteristics were investigated in both solid and solution states for heterometallic compounds, emphasizing differences between copper-containing and zinc/palladium-containing complexes. The results offer valuable insights into the design, synthesis, and spectral properties of these complexes, showcasing their potential applications in various fields, and the findings contribute to the understanding of lanthanide-porphyrin systems and their coordination behavior.

Sulfonato Complex Formation Rather than Sulfonate Binding in the Extraction of Base Metals with 2,2′-Biimidazole: Extraction and Complexation Studies

The application of a bidentate aromatic N,N’-donor ligand, 2,2′-biimidazole (BIIMH2), as an extractant in the form of 1-octyl-2,2′-biimidazole (OBIIMH) and related derivatives in the solvent extraction of base metal ions (Mg2+, Mn2+, Fe3+, Fe2+, Co2+, Ni2+, Cu2+ and Zn2+) from an acidic sulfonate medium using dinonylnaphthalene disulfonic acid (DNNDSA) as a synergist was investigated. OBIIMH with DNNDSA as a co-extractant showed a lack of selectivity for base metals ions (Mg2+, Mn2+, Fe3+, Fe2+, Co2+, Ni2+, Cu2+ and Zn2+) despite its similarity with a related bidentate aromatic ligand, 2,2′-pyridylimidazole, which showed preference for Ni(II) ions. The nickel(II) specificity, through stereochemical “tailor-making”, was not achieved as expected and the extracted species were isolated to study the underlying chemistry. The homemade metal sulfonate salts, M(RSO3)2·6H2O (R = Toluene and M2+ = Co2+, Ni2+, Cu2+ and Zn2+), were used as precursors of the metal complexes of BIIMH2 using toluene-4-sulfonic acid as the representative sulfonate. Spectroscopic analysis and single-crystal X-ray analysis supported the formation of similar neutral distorted octahedral sulfonato complexes through the bis coordination of BIIMH2 and two sulfonate ions rather than the formation of cationic complex species with anion coordination of sulfonates. We attributed the observation of similar complex species and the similar stability constants of the bis-complexes in solution as the cause for the lack of pH-metric separation of the later 3d metal ions.

Au13 Superatom Bearing Two Terpyridines at Coaxial Positions: Photoluminescence Quenching via Complexation with 3d Metal Ions

Abstract A gold cluster [Au13(dppe)5(EPTpy)2]3+ (dppe = 1,2-bis(diphenylphosphino)ethane, EPTpy-H = 4′-(4-ethynylphenyl)-2,2′:6′,2′′-terpyridine) was synthesized by ligand exchange reaction of [Au13(dppe)5Cl2]3+. Single-crystal X-ray diffraction analysis revealed that two terpyridyl moieties were σ-bonded to the coaxial positions of the icosahedral Au13 core. These two terpyridyl moieties were coordinated with 3d metal ions M2+ (M = Co, Ni, Cu, Zn) in acetonitrile solution under ambient conditions. The photoluminescence (PL) of [Au13(dppe)5(EPTpy)2]3+ with a quantum yield of 0.17 at ∼780 nm was almost completely quenched by coordination with Co2+, Ni2+, and Cu2+, while the PL was not affected by Zn2+ coordination. The metal-dependent PL quenching behavior is ascribed to the difference in the electronic structure of the metal ions. The energy transfer from the Au13 chromophore to the coordinated Co2+, Ni2+, or Cu2+ with an open electronic structure proceeds efficiently via an electron exchange mechanism, while the process is prohibited for Zn2+ with a closed electronic structure.

Concentration transition in Cu2(Mn,Ga)BO5 solid solutions

The effects related to the conversion of magnetic structures of a Cu2MnBO5 ferrimagnet to a Cu2GaBO5 antiferromagnet under the Mn3+ → Ga3+ substitution were studied. The properties of four single crystal samples with the gallium concentration x = 0.04, 0.11, 0.17, 0.25 were examined. The chemical composition and valence state of the samples were determined by X-ray absorption spectroscopy element-sensitive technique. Distribution of the 3d metal ions over crystallographic positions was studied using the first principle calculations by Wien2k program. The evolution of the magnetic properties was investigated by the measurements of the temperature and field dependences of magnetization, dc and ac magnetic susceptibility. In agreement with the previous study of the structure evolution of Cu2Mn1-xGaxBO5 solid solutions, the critical concentration upon a change in the magnetic ordering type was found in the range x = 0.17–0.25. The non-monotonic behavior of magnetization in terms of the gallium content was found in the concentration range of 0.04–0.17. A complex pattern of magnetic phase transitions belonging to the concentration phase boundary was obtained in the compounds with gallium being within the range x = 0.17–0.25. One could observe the splitting of the peaks of the real part of ac-susceptibility of the high-temperature phase transition in the Cu2MnBO5-like phase (x = 0.04, 0.11) and that of the low-temperature one at the concentration boundary (x = 0.17, 0.25) with different frequency and orientational dependence. The type and origin of the multiple phase transitions observed in the studied samples were analyzed.

Complexities of the Interaction of NiII, PdII and PtII Pyrrole‐Imine Chelates with Human Serum Albumin**

AbstractHuman serum albumin (HSA) efficiently transports drugs in vivo: most are organic. Here, HSA binding affinity and site specificity are shown to depend on the identity of the d8 metal ion in NiII, PdII and PtII chelates of the bis(pyrrole‐imine) ligand H2PrPyrr. Fluorescence quenching data for native and probe‐bound HSA showed sites close to Trp‐214 (subdomain IIA) are targeted. The Stern‐Volmer constants, KSV, ranged from 104 M−1 to 105 M−1 while the affinity constants, Ka, ranged from ∼3.5×103 M−1 to ∼1×106 M−1 at 37 °C, following the order Pd(PrPyrr) &gt; Pt(PrPyrr) &gt; Ni(PrPyrr) &gt; H2PrPyrr. Ligand uptake is enthalpically driven, hinging mainly on London dispersion forces. Induced CD spectra for the protein‐bound ligands could be simulated by hybrid QM:MM TD‐DFT methods, proving that the metal chelates neither decompose nor demetallate after uptake by HSA. Transport and delivery of the metal chelates by HSA in vivo could therefore be feasible.

Importance of broken geometric symmetry of single-atom Pt sites for efficient electrocatalysis

Platinum single-atom catalysts hold promise as a new frontier in heterogeneous electrocatalysis. However, the exact chemical nature of active Pt sites is highly elusive, arousing many hypotheses to compensate for the significant discrepancies between experiments and theories. Here, we identify the stabilization of low-coordinated PtII species on carbon-based Pt single-atom catalysts, which have rarely been found as reaction intermediates of homogeneous PtII catalysts but have often been proposed as catalytic sites for Pt single-atom catalysts from theory. Advanced online spectroscopic studies reveal multiple identities of PtII moieties on the single-atom catalysts beyond ideally four-coordinated PtII–N4. Notably, decreasing Pt content to 0.15 wt.% enables the differentiation of low-coordinated PtII species from the four-coordinated ones, demonstrating their critical role in the chlorine evolution reaction. This study may afford general guidelines for achieving a high electrocatalytic performance of carbon-based single-atom catalysts based on other d8 metal ions.

Super-Hydrophilic Co- and Mo-Based Mix-Metallomicellar Film as an Electrocatalyst toward Hydrogen Evolution Reaction

A rational design and facile synthesis that is based upon inexpensive and earth-abundant elements is an effective strategy for electrochemical hydrogen evolution reaction (HER). Herein, we have utilized single-chain metallosurfactants (CoDDA(I) and MoDDA(I)) to develop a mix-metallomicellar film (Co-MoDDA(I)) that is used as an electrocatalyst toward HER. To our knowledge, there have been no reports on mix-metallomicellar films toward HER. Experimental results reveal that the HER activity of Co-MoDDA(I) was comparable with commercial Pt/C (20 wt %), a low Tafel slope (29.2 mV dec–1), and long-term stability. The dramatically improved HER performance of Co-MoDDA(I) was favored by the combination of the following factors: formation of reverse micelles, super-hydrophilic characteristic, and presence of Co(II) and Mo(III) ions in the micellar core. Organic media pushed the Co of CoDDA(I) toward the core of the reverse micelles, which further attracts the Mo ions of MoDDA(I) to form a mixed micellar film. The cooperative effect of Co and Mo in the reverse micellar core generates the catalytic center for efficient hydrogen production. In situ reduction of Co and the synergic effect between 3d (Co) and non 3d (Mo) metal ions in the core of micelles accelerate the HER reaction rate effectively. Several chemical changes were also observed in the material, i.e., removal of chloride ions from the surface and reduction of Co inside the core of reverse micelles as authenticated by X-ray photoelectron spectroscopy (XPS). However, surface characteristics were verified by field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). Metallosurfactants are available to provide controllable structure, orientation, and structural stability and assist to detach the bubbles from the surface.