Inert Metal Ions Research Articles

Mix and match - controlling the functionality of spin-crossover materials through solid solutions and molecular alloys.

The influence of dopant molecules on the structure and functionality of spin-crossover (SCO) materials is surveyed. Two aspects of the topic are well established. Firstly, isomorphous inert metal ion dopants in SCO lattices are a useful probe of the energetics of SCO processes. Secondly, molecular alloys of iron(II)/triazole coordination polymers containing mixtures of ligands were used to tune their spin-transitions towards room temperature. More recent examples of these and related materials are discussed that reveal new insights into these questions. Complexes which are not isomorphous can also be co-crystallised, either as solid solutions of the precursor molecules or as a random distribution of homo- and hetero-leptic centres in a molecular alloy. This could be a powerful method to manipulate SCO functionality. Published molecular alloys show different SCO behaviours, which may or may not include allosteric switching of their chemically distinct metal sites.

Inert Transition Metal Ion Complexes in Organic Synthesis: Protection and Activation.

Single crystal X-ray diffraction studies for a variety of metal ion complexes of functionalised sarcophagines (sarcophagine = sar = 3,6,10,13,16,19-hexa-azabicyclo[6.6.6]icosane) have further confirmed not only that the form of the metal ion/sar unit is unique for each metal, albeit with a sensitivity of the conformation to the associated counter anions, but also that for any given metal and ligand substituent, the dimensions (bond lengths and angles) of the complex and the substituent at the secondary nitrogen centres do not differ significantly from those of the isolated components. Despite this, where the substituent contains reactive sites, the reactivity differs markedly from that of their form in an uncoordinated substrate.Rationalisations are offered for these differences, in part through the use of Hirshfeld surface analysis of the intermolecular interactions. The kinetic inertness of the complexes means that the metal ions can be considered to act as regioselective protecting groups.

Enhanced Contrast of WO3-Based Smart Windows by Continuous Li-Ion Insertion and Metal Electroplating.

The electrochromic WO3 smart window based on an aqueous electrolyte shows an excellent liquid/solid interface and thus can achieve a fast electrochromic response, while the aqueous electrolyte has a limited electrochemical window, which probably induces the H+ reduction and degrades the practical application. Here, we propose a strategy to modify the traditional Li+ acidic aqueous electrolyte by adding some selective inert metal ions, which not only improve the electrochromic performance but also avoid the possible production of hydrogen bubbles due to the broadened electrochemical window. Furthermore, reversible electroplating of inert metal ions will occur, leading to an enhanced optical transmission change of up to 77.5% at 500 nm and 70.4% at 700 nm. This combination of Li-ion insertion and metal electroplating in the ESW device makes it superior to all of the previous reports. The device also demonstrates high stability and high electrochromic efficiency after 1000 cycles. The current study not only emphasizes the rational design for aqueous electrolytes but also demonstrates a practical way to realize an excellent electrochromic window for practical applications.

Reversible On/Off Switching of Lactide Cyclopolymerization with a Redox-Active Formazanate Ligand.

Redox-switching of a formazanate zinc catalyst in ring-opening polymerization (ROP) of lactide is described. Using a redox-active ligand bound to an inert metal ion (Zn2+) allows modulation of the catalytic activity by reversible reduction/oxidation chemistry at a purely organic fragment. A combination of kinetic and spectroscopic studies, together with mass spectrometry of the catalysis mixture, provides insight in the nature of the active species and the initiation of lactide ring-opening polymerization. The mechanistic data highlight the key role of the redox-active ligand and provide a rationale for the formation of cyclic polymer.

Kinetic stability of metal–organic frameworks for corrosive and coordinating gas capture

Metal–organic frameworks (MOFs) have diverse applications involving the storage, separation and sensing of weakly interacting, high-purity gases. Exposure to impure gas streams and interactions with corrosive and coordinating gases raises the question of chemical robustness; however, the factors that determine the stability of MOFs are not fully understood. Framework materials have been previously categorized as either thermodynamically or kinetically stable, but recent work has elucidated an energetic penalty for porosity for all these materials with respect to a dense phase, which has implications for the design of materials for gas storage, heterogeneous catalysis and electronic applications. In this Review, we focus on two main strategies for stabilization of the porous phase — using inert metal ions or increasing the heterolytic metal–ligand bond strength. We review the progress in designing robust materials for the capture of coordinating and corrosive gases such as H2O vapour, NH3, H2S, SO2, nitrogen oxides (NOx) and elemental halogens. We envision that the pursuit of strategies for kinetic stabilization of MOFs will yield increasing numbers of robust frameworks suited to harsh conditions and that short-term stability towards these challenging gases will be predictive of long-term stability for applications in less demanding environments. Metal–organic frameworks, when evacuated, are metastable with respect to a dense phase of the same components. Here, we review methods for kinetic stabilization of the porous phase and discuss progress in designing stable frameworks for the capture of corrosive and coordinating gases.

Tuning high power impulse magnetron sputtering discharge and substrate bias conditions to reduce the intrinsic stress of TiN thin films

Ion bombardment during film growth usually induces high compressive stress in compound thin film materials, resulting in rupture and failure of coated tools used in tribological applications. Hence‚ intrinsic stress generated during film growth can drastically limit the industrial appeal of deposition technologies such as high power impulse magnetron sputtering (HiPIMS). This work investigates how to reduce high stress levels by tuning the HiPIMS discharge conditions and selecting the appropriate substrate bias configuration. The strategy is based on optimizing the process discharge parameters, leading to HiPIMS discharges containing fewer multiply charged energetic metal ions, which is combined with pulsed substrate bias synchronized to the HiPIMS pulse to control the chemical nature of the incident ions‚ i.e.‚ inert gas vs. metal ions. The study was performed during growth of TiN thin films, due to their relevance as a protective coating, and the intrinsic stress was measured in situ during film growth using the wafer curvature method and a multi-beam optical stress sensor. The results show that for standard HiPIMS discharges and biased substrates‚ the energetic metal ion bombardment results in very dense, compact microstructures, but highly stressed TiN films. On the other hand‚ when using the here proposed strategy mentioned above‚ the compressive stress was considerably reduced (by a factor 11) while retaining rather compact microstructures compared to direct current magnetron sputtered as well as non-biased HiPIMS samples.

Исследование процессов зарядки ионно-имплантированных диэлектриков под воздействием электронного облучения

AbstractThe charging kinetics of Al_2O_3 (sapphire) and SiO_2 (α-quartz) dielectrics irradiated by inert gas ions (Ar^+), metal ions (Ga^+), and protons (H^+) has been studied. It has been found that charging kinetics depends considerably on the type of irradiating ion. Also, it has been established that preirradiation of a dielectric target by an ionizing corpuscular radiation (protons, ions) substantially changes the charge characteristics of the dielectric surface. These differences depend on irradiating ion energy, which governs the depth of an accumulated negative charge layer versus the depth of ion preimplantation.

Overcoming the Inertness of Iridium(III) in a Facile Single-Crystal to Single-Crystal Reaction of Iodine Vapor with a Cyclometalated Chloride Monomer.

Iridium(III) is often considered to be one of the most inert octahedral metal ions. Herein we present a phenanthroimidazole-based bis-cyclometalated iridium(III) chloride undergoing a facile chloro ligand exchange with iodine, in a gas-solid reaction under ambient conditions. Monitoring the progress of the reaction by X-ray diffraction analysis reveals the crystal-packing-induced exceptional stereoselectivity of this topochemical transformation. The results provide excellent opportunities to modulate the geometry and kinetic properties of cyclometalated iridium(III) complexes that may be very promising in catalysis and design of anticancer agents.

On the Effect of the Internal Pressure on the Photoinduced Spin‐Crossover Behavior of [FexM1–x(1,10‐phenanthroline)2(NCS)2] Solid Solutions (M = NiII, ZnII, and CdII)

The thermal and light‐induced magnetic properties of a family of metal‐diluted spin‐crossover complexes, [FexM1–x(phen)2(NCS)2] (phen = 1,10‐phenantholine and M = NiII, CdII), are reported and compared to previous results obtained for the same series but with ZnII ions used to substitute FeII ions; the ultimate goal was to validate the influence of the size and nature of the inert metal ion on the light‐induced properties of spin‐crossover compounds. For all of the materials, we measured the thermally induced spin‐crossover temperature (T1/2) and T(LIESST) (LIESST = light‐induced excited spin‐state trapping) values systematically. We observed clearly that the dilution has a strong effect on the magnetic and photomagnetic properties. The magnitude of these effects depends strongly on the nature of the diluting metal. This comparison gives insights into the effect of the size of the diluting ion on T(LIESST) and T1/2 and completes the previous studies on the effect of internal pressure on the lifetime of the photoinduced state.

Dependence of Water Exchange Kinetics on the Size and Charge of Metal Ion

While structural and dynamical properties of water on a labile metal ion such as Na+ and Ca2+ are straightforwardly evaluated using molecular dynamics (MD) simulations, direct evaluation of water exchange kinetics on a relatively more inert metal ion, Mg2+, is computationally demanding. Here, we propose a universal relationship which allows us to determine the water exchange time on a metal ion with varying charges and hydration radii. The proposed relationship highlights the ultra-sensitivity of water lifetime to the ion size, as exemplified between two divalent ions, Ca2+ (∼100 ps) and Mg2+ (∼1.5 μs). Importantly, the current MD force fields underestimate the hydration radius of Mg2+ by ∼2.5 %, which results in ∼ 400 fold overestimation of water exchange time. Accurate determination of ion size is critical for correctly modeling the water dynamics around multivalent ions.

ChemInform Abstract: Geometric Isomerism in Coordination Cages Based on Tris‐chelate Vertices: a Tool to Control Both Assembly and Host/Guest Chemistry

AbstractReview: 77 refs.

Analytical 3D migration model of steady-state metal anodizing: the velocity fields and trajectories of inert tracers, metal and oxygen ions

A mathematical model is proposed that describes the velocity fields of metal and oxygen ions and inert tracers in the steady-state porous metal oxidation. The 3D migration model is based on the theory of field-assisted dissolution of oxide at the pore bottom and migration of ions in strong spherical electric fields. The ion motion at a constant velocity in the direction of anodic film growth and their migration in the radial direction (along the electric field lines) are taken into consideration. The effect of mechanical stresses on the motion of ions and inert tracers is ignored. The oxide flows both from the oxide/electrolyte interface and from the oxide/metal interface to the boundary between the barrier and porous layers. These two flows form the porous oxide layers adjacent to the pores and afar from them. A ratio between the volumes of these layers is determined by the transport numbers and oxide porosity. The calculated tracer trajectories agree with the experimental results of Garcia-Vergara et al. on the oxide flow in the barrier layer of porous anodic alumina film.

Geometric isomerism in coordination cages based on tris-chelate vertices: a tool to control both assembly and host/guest chemistry.

This 'Perspective' article summarises recent work from the authors' research group on the exploitation of the simple fac/mer geometric isomerism of octahedral metal tris-chelates as a tool to control the chemistry of coordination cages based on bis(pyrazolyl-pyridine) ligands, in two different respects. Firstly this geometric isomerism plays a major role in controlling the guest binding properties of cages because a fac tris-chelate arrangement of pyrazolyl-pyridine chelates around a metal ion vertex results in formation of a convergent set of inwardly-directed C-H protons in a region of high positive electrostatic potential close to a metal cation. This collection of δ+ protons therefore provides a charge-assisted hydrogen-bond donor site, which interacts with the electron-rich regions of guest molecules that are of the correct size and shape to occupy the cage cavity, and the strength of this hydrogen-bonding interaction plays a major role in guest recognition in non-aqueous solvents. Secondly the ability to prepare mononuclear complexes with either a fac or mer arrangement of ligands provides an entry into the controlled, stepwise assembly of heterometallic cages based on a combination of kinetically inert and kinetically labile metal ions at different sites. This has allowed introduction of useful physical properties such as redox activity or luminescence, commonly associated with inert metal ions which are not amenable to participation in thermodynamic self-assembly processes, to be incorporated in a predictable way into the superstructures of coordination cages at specific sites.

Kinetic simulation of complex decomposition as a tool for the ion chromatographic determination of elemental speciation of less inert metal ions

Species decomposition is an often occurring artefact during the chromatographic determination of elemental speciation. The decomposition follows a simple path to lower coordinated compounds. Therefore a simulation is developed for those decomposition reactions. The simulation separates the isochronal processes of the separation itself and the ongoing reaction and delivers thermodynamic and kinetic information about the species present in the original sample. This shifts the boundaries of separation based elemental speciation to less inert metal ions which are typically not analyzable by this approach. The less inert gallium monooxalato complex [GaOx]+ is used as example for testing the simulation software as this complex decomposes only to Ga3+ and both species are retained on cation exchange columns. We extracted thermodynamic and kinetic information from flow rate experiments by the analysis of the peak areas in the chromatogram. The results show that some of our assumptions such as the irreversibility under the applied chromatographic conditions are not ultimately true, but good accordance of simulation and measured data was achieved.

Hexaamminecobalt(III) – Probing Metal Ion Binding Sites in Nucleic Acids by NMR Spectroscopy

AbstractHexaamminecobalt(III), an octahedral, inert metal ion complex, has lately gained increasing attention of structural biologists and bioinorganic chemists due to its use in structure determination of nucleic acids. This complex mimics outer‐sphere binding events of the physiologically relevant magnesium(II)hexaaqua ion; hexaamminecobalt(III) often finds usage either in NMR spectroscopy, where cross‐peaks between the complex ammines and the nucleic acid protons near the binding site are observed, in X‐ray spectroscopy as heavy metal derivative for phasing, or in other techniques. In this review, we discuss the basic hexaamminecobalt(III) binding modes and give an overview on the most recent findings on [Co(NH3)6]Cl3–nucleic acid complexes. The various techniques that are applied in combination with this complex are mentioned and briefly summarized. Special attention is given to the application of [Co(NH3)6]Cl3 in nuclear magnetic resonance spectroscopy of nucleic acids, where it is used to reveal potential outer‐sphere magnesium binding sites.

A convenient and eco-friendly way to synthesize Pt(II) and Pd(II) porphyrins in ionic liquids by microwave activation

Due to the slow rate of incorporation of inert-metal ions into free-base porphyrins compared to other transition metals, several methods have been proposed to accelerate the rate of metalation. However, these methods have disadvantages such as low yields, difficulties of purification of final products, and environmental effects. To avoid those disadvantages, we reacted Pt(II) and Pd(II) salts with H2(TPP), H2(TMPyP)4+, and their β-pyrrole derivatives, H2(Br8TPP) and H2(Br8TMPyP)4+, in 1-butyl-3-methylimidazolium bromide ([bmim]+Br−) under microwave irradiation. The combination of microwave heating and ionic liquids provides efficient thermal energy transfer among the porphyrins and metal salts. In addition, ionic liquids stabilize charged species as well as their intermediates, due to their high dipole moment and high boiling point. This not only shortens the reaction time but also gives high yields of products at relatively low temperatures, of about 100°C compared to conventional synthesis methods: 150°C for DMF, 190°C for DMSO. Here, we demonstrate that Pt(II)/Pt(II) metalloporphyrins are synthesized at high rates, e.g. 6–30 min for 100% metalation, with high yields of 79–93% in [bmim]+Br− by microwave activation.

Construction of crystal structures of metal(II)–benzoates (M = Mn, Ni, Co, Cu, Zn, and Cd) and 1,2-bis(4-pyridyl)ethane: Effects of metal coordination modes and their catalytic activities

Five polymeric metal(II)–benzoate complexes of formula [Mn(O 2CPh) 2(CH 3OH) 2(bpa)] n ( 1-Mn), [Co(O 2CPh) 2(H 2O)(bpa) 1.5] n ( 2-Co), [Ni(O 2CPh) 2(H 2O)(bpa) 1.5] n ( 3-Ni), [Cu(O 2CPh) 2(CH 3OH) 2(bpa)] n ( 4-Cu), and [Cd(O 2CPh) 2(bpa) 1.5] n ( 6-Cd) have been synthesized and characterized (bpa = 1,2-bis(4-pyridyl)ethane). They showed two kinds of structures: parallelogram-like two-dimensional sheets for Co, Ni, and Cd, and one-dimensional chains for Mn, Cu, and Zn. Since similar structures provide similar coordination geometries, the structures depend on the coordination geometries of metal ions. The compounds 1-Mn, 2-Co, 4-Cu, 5-Zn, and 6-Cd have catalyzed efficiently the transesterification of a variety of esters, while 3-Ni has displayed a very slow conversion. The reactivity of catalyst 6-Cd containing Cd ion, well known as an inert metal ion for the ligand substitution, was found to be comparable to that of 5-Zn. The reactivities of the compounds used in this study are in the order of 5-Zn > 6-Cd > 1-Mn > 4-Cu > 2-Co ≫ 3-Ni, indicating that the non-redox metal-containing compounds ( 5-Zn and 6-Cd) show better activity than the redox-active metal-containing compounds ( 1-Mn, 4-Cu, 2-Co, and 3-Ni).

Metal-directed supramolecular assembly of metal(II) benzoates (M = Co, Ni, Cu, Zn, Mn, and Cd) with 4,4′-bipyridine: Effects of metal coordination modes and novel catalytic activities

Six polymeric metal(II)-benzoate complexes of formula [Co 2(O 2CPh) 4(4,4′-bpy) 2] n ( 1-Co), [Ni(O 2CPh) 4(H 2O) 2(4,4′-bpy)] n ( 2-Ni), [Cu 2(O 2CPh) 4(4,4′-bpy)] n ( 3-Cu), [Zn 2(O 2CPh) 2(OH) 2(4,4′-bpy) 2] n ( 4-Zn), [Zn 3(O 2CPh) 4(μ-OH) 2(4,4′-bpy) 2] n ( 5-Zn), and [Cd 2(O 2CPh) 4(4,4′-bpy) 2] n ( 6-Cd) have been synthesized and characterized (4,4′-bpy = 4,4′-bipyridine). 1-Co and 6-Cd show ladder-type double chains, 2-Ni does a helical structure, 3-Cu does a one-dimensional chain containing paddle-wheel units, 4-Zn does a zigzag chain, and 5-Zn does two-dimensional sheets. Since different structures provide different coordination geometry of each metal ion, it is clear that selection of appropriate metal ions can control the coordination geometry of each metal ion to form different crystal structures. Reactivity study of the compounds 1– 7 for the transesterification of a variety of esters has shown that 4-Zn and 5-Zn are very efficient and the best among them. The catalyst 6-Cd containing Cd ion, well known as an inert metal ion for the ligand substitution, also catalyzed efficiently the transesterification of a variety of esters, and its reactivity is comparable to 4-Zn and 5-Zn. Moreover, the redox-active metal-containing polymers, 1-Co, 3-Cu, and 7-Mn, have shown efficient catalytic reactivities for the transesterification reactions, while 2-Ni has displayed a very slow conversion. The reactivities of the compounds used in this study are in the order of 5-Zn > 4-Zn > 6-Cd > 7-Mn ∼ 3-Cu > 1-Co > 2-Ni, indicating that the non-redox metal-containing compounds ( 5-Zn, 4-Zn, and 6-Cd) show better activity than the redox-active metal-containing compounds ( 7-Mn, 3-Cu, 1-Co, and 2-Ni). These results suggest that it is possible to tune the catalytic activities by changing from Zn to those metals such as Cd, a kinetically inert metal, or Cu, Mn, and Co, the redox-active metals.

Tailored conductivity in ion implanted polyetheretherketone

Ion implantation can be used to confer electrical conductivity upon conventional insulating polymers such as polyetheretherketone (PEEK). We have implanted PEEK films using three different types of ion implantation: conventional inert gas and metal ion implantation, and ion beam mixing. We have applied a number of analytical techniques to compare the chemical, structural and electrical properties of these films. The most effective means of increasing electrical conductivity appears to be via ion beam mixing of metals into the polymer, followed by metal ion implantation and finally, inert gas ion implantation. Our results suggest that in all cases, the conducting region corresponds to the implanted layer in the near surface to a depth of ∼750 Å (ion beam mixed) to ∼5000 Å (metal ion). This latter value is significantly higher than would be expected from a purely ballistic standpoint, and can only be attributed to thermal inter-diffusion. Our data also indicates that graphitic carbon is formed within the implant region by chain scission and subsequent cross-linking. All ion implanted samples retained their bulk mechanical properties, i.e. they remained flexible. The implant layers showed no signs of de-lamination. We believe this to be the first comparative study between different implantation techniques, and our results support the proposition that soft electronic circuitry and devices can be created by conductivity engineering with ion beams.

Intrinsic acid-base properties of purine derivatives in aqueous solution and comparison of the acidifying effects of platinum(II) coordinated to N1 or N7: acidifying effects are reciprocal and the proton "outruns" divalent metal ions.

The effect of Pt(2+) coordination, in particular of (dien)Pt(2+) or cis-(NH(3))(2)Pt(2+), on the acid-base properties of the purine ligands 9-ethylguanine (9EtG), 9-methylhypoxanthine (9MeHx), inosine (Ino), 9-methyladenine (9MeA), and N6',N6',N9-trimethyladenine (TriMeA) is quantitatively evaluated. The corresponding acidity constants of the complexes are calculated by curve-fitting procedures using previously published (1)H NMR shift data which had been measured in aqueous solution (D(2)O) in dependence on pH (pD). Comparison of the pK(a) values of the ligands with those of the Pt(2+) complexes reveals the expected behavior for the (N7)-platinated complexes; i.e., the (N1)H(0/+) sites are acidified due to charge repulsion. However, Pt(2+) coordination at (N1)(-)(/0) sites leads to an (already previously observed) apparent increase in the basicity of the N7 sites for the guanine, hypoxanthine, and adenine residues; this is also the case if Pt(2+) is bound to N3. Coordination of Pt(2+) to both the (N1)(-) and N7 sites of 9EtG results apparently in an enhanced basicity of N3 if compared with the release of the proton from the (N3)H(+) site in H(2)(9EtG)(2+). For the former cases in aqueous solution (H(2)O) it is now proven for a comprehensive set of data (seven examples), by taking into account the intrinsic basicities of the various N7 sites via micro acidity constants, that the acidifications are reciprocal and identical. This means Pt(2+) coordinated to (N1)(-)(/0) sites in guanine, hypoxanthine, or adenine residues acidifies the (N7)H(+) unit to the same extent as (N7)-coordinated Pt(2+) acidifies the (N1)H(0/+) site. In other words, the apparently increased basicity of N7 upon Pt(2+) coordination at (N1)(-)(/0) sites disappears if the micro acidity constants of the appropriate isocharged tautomers of the ligand are properly taken into account. It is further proven, on the basis of the evaluations of the nucleotide analogue 9-[2-(phosphonomethoxy)ethyl]adenine (PMEA), that these given conclusions are also valid for nucleotides. In addition, it is shown that the mentioned apparent basicity increase, which results from the use of macro acidity constants, has its origin in the fact that the proton-metal ion (Pt(2+)) interaction (the extent of which depends on the kind of metal ion involved) is less pronounced than the proton-proton interaction. Finally, the proven reciprocal behavior will now allow one to determine micro acidity constants of ligands by studying complexes formed with kinetically inert metal ions. A further result of interest is the proof that the competition of Pt(2+) (or Pd(2+)) with the proton for the (N1)(-) and N7 binding sites of inosinate results in the isomer where the metal ion is at N7 with the proton relegated to (N1)(-); this isomer is favored by a factor of about 2000 compared with the one having the metal ion at (N1)(-) and the proton at N7.