Al Bond Research Articles

Direct synthesis of construction material from low-quality sand reacted with KOH and ethanol

A strong construction material was synthesised directly from low-quality sand (defined as the sand that particle size smaller than 250 μm) via the sol–gel method with ethanol as the solvent. Appropriate KOH content and ethanol concentration could improve the reaction degree and promote the compressive strength. The main results indicated that the specimen with 50 mass% KOH and 80 v/v% EtOH had the highest strength (>25 MPa) with the lowest porosity (5.79%). The high strength was attributed to microcline and tetraethoxysilane formation. Microcline was formed due to the dissolution and reorganization of Si-O-Si(Al) bonds in the raw sand, leading to a more homogenous structure and the decrease in the porosity. Formed tetraethoxysilane was a good consolidate, which could function as glue to further increase the strength. The carbon emission of the sand-based material in the construction phase was 233 kg CO2 eq/m2, which could be greatly reduced after reusing waste solution and utilizing waste heat. Therefore, a tough construction material was synthesised, which can partially substitute concrete, thus addressing the problem of insufficient concrete raw materials.

Quantitative analysis of atomic-scale local lattice distortions in high-entropy fluorite oxide (Zr0·2Ce0.2Hf0.2Y0·2Al0.2)O2-δ

Novel high-entropy oxides have attracted considerable attention as promising candidates for high-temperature structural applications. The lattice distortion effect in such materials is closely related to their microstructural evolution and thermophysical performance. In this study, the local lattice distortions in the high-entropy fluorite oxide (Zr0·2Ce0.2Hf0.2Y0·2Al0.2)O2-δ were observed at the atomic scale using aberration-corrected scanning transmission electron microscopy and studied quantitatively using geometric phase analysis. The results showed that the radius and brightness of the atomic column projections exhibit slight variations owing to the random distribution of the cations, resulting in differences in the relative contents of the five elements in each atomic column. The anions were influenced by both the random distribution of the cations and the large number of oxygen vacancies, leading to M-O-M (M = Zr, Ce, Hf, Y, and Al) bond angles of 80–105°. The distributions of strains εyy and εxx (along the lattice spacing direction and vertical direction, respectively) within the crystal structure were mainly centred around ±4%, and there was a tendency for alternating positive and negative values in strains maps without significant aggregations. In addition, strains εxx and εyy increased significantly to 26.4% and 9.2%, respectively, within the dislocation areas.

The physical, structural, elastic, optical and thermal studies on sesquioxides (Al2O3, Y2O3, Sb2O3) doped Oxy Fluoro Cobalt Borate Glasses

Sesquioxides (Al2O3, Y2O3, Sb2O3) doped Oxy fluoro Cobalt borate novel luminescent series of glasses are prepared by melt quenching method. The structural characteristics of these glasses were studied by XRD, SEM and EDS techniques. The change in physical parameters such as density of all the series of glasses prepared gives a pathway for cobalt/Alumina/Antimony/Yttrium ions to enter in to borate glass network with the enhancement in the concentration of corresponding dopants. The depolymerization of the borate glass network is evident by the decline in various elastic parameters with B-O-Co/Y/Sb/Al bonds and by the modifier role of CoO/Y2O3/Sb2O3/Al2O3 transforming a fraction of tetrahedral BO3 units into BO4 units. Both FTIR and IR spectra indicate an increase in octahedral occupancy of cations Co2+, Y3+, Sb3+and Al3+ ions in the glass network with the increase of their concentration. The conversion rate of tetrahedral BO3 units to octahedral BO4 units leading to the formation of NBOs is more in Al3+ and least in Y3+ with the increase of concentration of sesquioxides at 0.05 mol% concentration of CoO. The optical absorption spectra of all series of glasses prepared reveal that octahedral occupancy of cobalt ions is dominant due to the ligand fields created by different sesquioxide ions in the glass network produce NBOs and number of electrons trapped at the donor centers. The PL spectra of all the series of these glasses reveal the octahedral occupancy of Co2+ ions, which is evident from the two emission transitions 2T1g(H) →4T1g(F) (531–556 nm) and 2Eg→5T2g (699–718 nm).The prepared series of glasses show efficient luminescence of Cobalt ions, and Al2O3 series of glasses are better candidates for luminescence as their emission Cross-sections are highest when compared with the remaining series of glasses.

Improved hydrothermal stability of Cu-SAPO-18 by Sm modification in the selective catalytic reduction of NOx with NH3

The Cu-SAPO-18 catalyst is efficient for the selective reduction of NOx with NH3 reaction. Nonetheless, enhancement of the hydrothermal stability of the Cu-SAPO-18 catalyst is needed to satisfy the stringent emission regulations. Sm with partially occupied 4 f orbitals and unoccupied 5d orbitals exhibits excellent physical and chemical properties and is often used as a catalyst promoter in catalytic reactions. In this study, we introduced Sm to Cu-SAPO-18 by a hydrothermal method, and when the added amount of Sm was 0.78 wt%, there was a significant improvement in hydrothermal stability. After Sm introduction, there was a decrease in Si(4Si, 0Al) amount and in unstable Cu(OH)+-Z concentration, thus inhibiting the formation of CuO species during hydrothermal aging. Simultaneously, the Sm replaced the hydrogens of a certain amount of Si–OH–Al bonds, stabilizing the Si–O–Al bonds and alleviating the Cu-SAPO-18 dealumination. Besides, after hydrothermal aging, there was an increase of isolated Cu2+ content in Sm0.78/Cu-SAPO-18, consequently promoting the adsorption of NH3 and NOx species and enhancing the Langmuir–Hinshelwood reaction rate.

High Robustness of Coated-Ag Wire Bonding

Formation of free air ball (FAB) within the range of certain processing parameters leads to excellent bondability (distributed intermetallic coverage (IMC) at the center and periphery of the bonded ball interface, bonded ball concentricity, etc.) on bonding to aluminum (Al) bond pad and Au/Ag plated surfaces. The wire revealed zero stoppage and 0.8M bond touchdowns when tested under laboratory conditions. Thermal aging of bonded interface showed absence of Kirkendall voids until 192h at 250°C where Al diffuses into Ag bonded ball up to a depth of 5.3µm, consuming the complete Al bond pad and thus transforming into silver-aluminide containing 5 to 12wt% of Al and rest silver (Ag). Traces of coated gold (Au) and alloyed palladium (Pd) are noticed at the bond interface.

A Comprehensive Evaluation of Al Heavy Wire Bonding and Ribbon Bonding Application in high power WBG Power Modules

Targeting at a comprehensive Multiphysics evaluation for Al wire and ribbon bonding technologies for WBG power module, this paper investigates and compares the stray inductance, heat dissipation and fatigue life between these two bonding schemes in an XHP packaging designed in house. During calculation, it was tried to keep equivalent volume for the Al ribbon when substituting local Al wires for fair comparison. Results of stray inductance show extremely limit bonding-type dependence in ranges from 1 kHz to 10 MHz, and further expanding ribbon size to varied levels still presents negligible impact. The two bonding technologies do not prove their capability in sharing either static or transient thermal loads when the baseplate bottom is efficiently liquid cooled. Detailed study confirms that heat dissipates dominantly in vertical direction to the Cu baseplate rather than through Al bonds. Ultimately, the only noticeable benefit of Al ribbon in our multiscale analysis is its improved reliability during temperature cycling, with data supporting a 2.17× times longer lifetime of Al ribbon when comparing to its Al wire counterpart.

Investigation of CuAl IMCs Corrosion in Chloride Environment and its Prevention Strategy

Abstract In most current wire-bonding applications, electrical interconnection is accomplished by fine Cu wires bonded to Al bonding pads microfabricated on an IC chip and external contact pins of the PCB board. Corrosion-related failure defects between the Cu wire and Al bond pad have been an ongoing un-trackable reliability issue plaguing the IC packaging industry for the past ten years, despite approaching ppb levels. Most prior studies hypothesized that intermetallic compounds (IMCs) like Cu9Al4, and CuAl2 were responsible for the observed acute wire-bond lift-off corrosion defects. Further studies sought to quantify the rates of corrosion of these IMCs and explore the effects of mitigation efforts of adding Pd, relevant to Pd-coated Cu wire-bonding. However, utilizing a novel real-time corrosion screening approach, we previously established that peripheral bimetallic contact between Cu ball-bonds and Al bond pads also plays a substantial role in the aggressive Al pad corrosion, induced by chloride ion penetration, which often leads to device failure. In this work, we further explored the role of IMCs corrosion in wire-bond lift-off failure utilizing fundamental electrochemical studies to quantify rates of galvanic-induced corrosion of IMCs within the broader context of an interconnected stack of Al bond pad, Cu-Al IMCs and Cu bonding wire. We also explored the use of a corrosion inhibitor to suppress the galvanic corrosion currents of Al bond pad, and Al-rich IMCs when electrically connected to Cu wire or Cu-rich IMCs.

First-principles study the mechanical, electronic, and thermodynamic properties of Mg-Al-Mn ternary compounds

In recent years, magnesium alloys have been used more and more widely due to their excellent lightweight and good plasticity. But correspondingly, the requirements for the elastic modulus (E) are more demanding. Therefore, to improve the deficiency, we are committed to find a way to increase the E. In this work, the mechanical, electronic, and thermodynamic properties of the Mg-Al-Mn ternary compounds were explored effectively based on first-principles calculations. It was found that the stabilities of these six structures were verified by the phonon spectrum, cohesive energy, and density of state, which showed that Mg3(MnAl9)2 possessed the best stability. Furthermore, Mg3(MnAl9)2 also had the largest bulk modulus, shear modulus, and E with values of 78.39, 50.94, and 125.6 GPa, respectively, due to the high bond strength of Al-Al bonds, and this was also verified by Mulliken's population analysis. Not only that, the largest hardness was reflected in Mg3(MnAl9)2 with a value of 9.04 and 9.11 GPa in Chen's and Tian's models. Similarly, the thermodynamic results showed that Mg3(MnAl9)2 had the highest Debye temperature as a value of 540.29 K and the highest limiting thermal conductivity with values of 1.216 W m−1K−1 in Clarke's model and 0.945 W m−1K−1 in Cahill's model.

Controllable Al2O3 coating makes TiO2 photocatalysts active under visible light by pulsed chemical vapor deposition

TiO2 catalysts, modified by coating Al2O3, presented high visible-light photocatalytic activity. Al2O3 nano-films were successfully deposited onto TiO2 particles using AlCl3 as a precursor via the pulsed chemical vapor deposition process. And, the alumina was anchored onto TiO2 surface via Ti–O–Al bonds. The morphology, constitution, photocatalytic activity and photoelectrochemical performance of the Al2O3-coated TiO2 were characterized. Controllable Al2O3 coating increased the oxygen vacancies and hydroxyl groups, and induced the formation of surface disordered TiO2 layer, which enhanced light absorption, increased charge carrier separation and transfer efficiency, and surface redox efficiency. Therefore, the TiO2/Al2O3 catalyst obtained via the pulsed chemical vapor deposition technique may break through the limitation of the band gap, and the pulsed chemical vapor deposition provided an effective strategy for the TiO2 production with active defective sites.

On the Reactivity of Mes*P(PMe3 ) towards Aluminum(I) Compounds - Evidence for the Intermediate Formation of Phosphaalumenes.

Phosphaalumenes are the heavier isoelectronic analogs of alkynes and have eluded facile synthesis until recently. We have reported that the combination of a phosphinidene transfer agent, Ar TerP(PMe3 ) (Ar Ter=2,6-Ar2 -C6 H3 ), with (Cp*Al)4 (Cp*=C5 (CH3 )5 ) afforded the phosphaalumenes Ar TerPAlCp* as isolable, violet, thermally stable compounds. In here we describe attempts to utilize Mes*P(PMe3 ) (Mes*=2,4,6-tBu3 -C6 H2 ) as a phosphinidene source in combination with different Al(I) precursors, namely Dip NacnacAl (Dip Nacnac=HC[C(Me)NDip]2 , Dip=2,6-iPr2 -C6 H3 ), (Cp*Al)4 and Cp3t Al (Cp3t =1,2,4-tBu3 -C5 H2 ). In all cases the formation of phosphaalumenes was not observed, however, their intermediate formation is indicated by formation of the dimer [Cp*Al(μ-PMes*)]2 (2) and C-H-bond activation products along the putative P=Al bond, giving unusual 1,2-P,Al-tetrahydronaphtalene derivatives 1 and 4, clearly underlining the role the sterically demanding group on phosphorus plays in these transformations. The reactivity studies are supported by theoretical studies, demonstrating a thermodynamic preference for the C-H activation products. Additionally, we show that there are potential pitfalls in the synthesis of Cp*2 AlH, the precursor to make (Cp*Al)4 and give recommendations how to circumvent these.

Theoretical predict the structure, elastic anisotropy and thermodynamic properties of Al5W in Al-rich region

Al5W compound is a promising high-temperature material due to the high melting point, good mechanical properties and good corrosion resistance. However, the structural feature of Al5W remains controversy. To solve these problems, we apply the first-principles calculations to study the structural stability, elastic properties, elastic anisotropy and melting point of Al5W. Four possible Al5W phases are discussed based on the similar A5B-type structure. The results show that two novel Al5W phases: orthorhombic (Cmma) and rhombohedral (R-3c) structures are predicted. The hexagonal (P6/mmm) Al5W has better thermodynamic stability. The bulk modulus of the predicted Cmma and R-3c phases is close to the known P63 phase. The result demonstrates the brittle behavior of the P63 Al5W. However, the hexagonal (P6/mmm) Al5W shows lower deformation resistance in comparison to the other Al5W. Importantly, the hexagonal (P63) Al5W has the stronger degree of shear anisotropy along the (100) and (010) plane. But the orthorhombic (Cmma) Al5W has the stronger degree of shear anisotropy along the (001) plane compared to the other three Al5W. Finally, the calculated melting point follows the order of P63 > R-3c > Cmma > P6/mmm. Naturally, the Al5W shows high melting point is related to the vibration of Al atom and Al–Al bond.

29Si and 27Al NMR study of the structural transformation of calcined kaolin residue-based geopolymer using low alkali activator content for sustainable construction materials

Geopolymer commercialization efforts in parallel with unconventional research are the only pathway to achieve the large-scale deployment of geopolymer technology. Geopolymers with a low quantity of alkali activator produced by the compression process are one way to bring this technology to industry because of the higher strength and lower efflorescence of the product. In this work, calcined kaolin residue-based geopolymers with a low alkali activator content were synthesized by various Si/Al mole ratios with soluble silicate from Na2SiO3 to adjust the Si ratio. The effects of Si/Al mole ratios on the structural transformation, microstructure, and compressive strength of geopolymers containing low alkali activator content were studied. The structural transformation and microstructure of geopolymers were characterized by NMR, SEM, and BET, and the compressive strength was assessed using a mechanical testing machine. The results present that geopolymer synthesized with various Si/Al mole ratios of precursor materials impacted the change in polymerization degree of silicate species (Qn(mAl)) and aluminate species. The Q4(4Al) and Q4(3Al) structures were transformed into the Q4(2Al) structure, and the content of the AlIV structure decreased when the Si/Al mole ratio of geopolymer was increased to 1.58. However, the contents of Q4(4Al) and AlIV structures increased again when the geopolymer had a Si/Al mole ratio of 1.62. SEM/EDX and BET results of geopolymers presented denser matrices, more amorphous aluminosilicate gels, and higher Si/Al ratios in aluminosilicate gels, while the pore size and pore volume were quite small when the Si/Al mole ratio of precursor materials was increased. In contrast, the highest Si/Al mole ratio of 1.62 showed different properties. The compressive strength of geopolymer was maximized at a Si/Al mole ratio of 1.58, and the decline in compressive strength of geopolymer with higher Si/Al mole ratio was related to the contents of Si–O–Si, Si–O–Al, and Al–O–Al bonds, content of aluminosilicate gels, and properties of the microstructure. The geopolymer synthesis using calcined kaolin residue and low alkali activator content is considered an eco–friendly process, which uses waste materials and less chemicals, and obtains high-strength products.

Preparation of aluminium-hydroxide-modified diatomite and its fluoride adsorption mechanism

As the current excessive accumulation of fluoride (F−) in the environment can be hazardous to human health, it is essential to remove fluoride from wastewater. In this study, diatomite (DA) was used as a raw material and modified using aluminum hydroxide (Al-DA) for use in the adsorption of F− from water bodies. SEM, EDS, XRD, FTIR, and Zeta potential characterization analyses were carried out; adsorption tests and kinetic fitting were performed, and the effects of pH, dosing quantity, and presence of interfering ions on the adsorption of F− by the materials were investigated. The results show that the Freundlich model effectively describes the adsorption process of F− on DA, which therefore involves adsorption-complexation interactions; however, the Langmuir model effectively describes the adsorption process of F− on Al-DA, corresponding to unimolecular layer adsorption mainly via ion-exchange interactions, that is, adsorption is dominated by chemisorption. Aluminum hydroxide was shown to be the main species involved in F− adsorption. The efficiency of F− removal by DA and Al-DA was over 91% and 97% for 2 h, and the adsorption kinetics were effectively fit by the quasi-secondary model, suggesting that chemical interactions between the absorbents and F− control the adsorption process. The adsorption of F− was highly dependent on the pH of the system, and the maximum adsorption performance was obtained at pH 6 and 4. The optimal dosage of DA and Al-DA was 4 g/L. Even in the presence of interfering ions, the removal of F− on Al-DA reached 89%, showing good selectivity. XRD and FTIR studies showed that the mechanism of F− adsorption on Al-DA involved ion exchange and the formation of F–Al bonds.

Recognizing the Minimum Structural Units Driving the Crystallization of SAPO-34 in a Top-Down Process.

Recognizing the structure and nature of the nuclei for zeolites crystallization on an atomic level is of great importance, which can provide guidance on the control of crystallization kinetics and the rational synthesis of zeolites. However, it remains a long-standing challenge due to the difficulty in characterization of amorphous precursor with limited crystal nuclei. Herein, a top-down synthesis system was designed for SAPO-34 molecular sieve and well investigated. A clear precursor solution with abundant SAPO-34 crystal nuclei was obtained under a depolymerization-dominant condition. The species in the liquid precursor were identified by FT-ICR MS, solid-state MAS NMR and atomic pair distribution function analyses. In combination with various designed experiments, it is revealed that both the formation of small species containing Si-O-Al bonds and reaching a certain concentration, is crucial for driving the crystallization of SAPO-34, rather than structural units with specific spatial conformation. This work provides an important understanding on the (pre)nucleation of SAPO-34 and sheds light on the synthesis control of SAPO molecular sieves.

Development of attapulgite based catalytic membrane for activation of peroxymonosulfate: A singlet oxygen-dominated catalytic oxidation process for sulfamethoxazole degradation

Antibiotic contamination of aquatic ecosystems has attracted growing concern over the past few years. As a novel and low-cost catalytic membrane, attapulgite-based ceramic membrane (ATPCM) impregnated with Co3O4 (Co-ATPCM) was successfully prepared for the degradation of sulfamethoxazole (SMX) under peroxymonosulfate (PMS) activation. The physical and chemical properties of ATPCM and Co-ATPCM were characterized by SEM-EDS, XRD, XPS, zeta potential, contact angle and the three-point bending test. Co was stably anchored on ATPCM via X-O-Co (X denotes Al, Si or Mg) bonds during the catalytic process, avoiding Co leaching. Approximately 70 % SMX could be removed by the optimized Co-ATPCM in batch experiments over a wide pH range from 4.0 to 10.0. Furthermore, 58 % SMX degradation was observed during filtration experiments with a high water flux of up to 774 L m−2h−1 (LMH). According to the quenching experiment and electron paramagnetic resonance (EPR) spectroscopy, SO4−, OH and 1O2 were involved in the SMX degradation process, while 1O2 played a dominant role. Density functional theory (DFT) calculation successfully predicted that the sits on SMX molecules with high Fukui index were more susceptible to attacks by free radicals, confirmed by liquid chromatography-Quadrupole-time of flight mass spectrometer (LC-MS). Consequently, a possible pathway for the catalytic oxidation process was proposed based on the results of DFT and LC-MS. This study provided a promising strategy using natural magnesium aluminum silicate clay minerals to prepare cost-effective, efficient, and eco-friendly catalytic membranes for wastewater treatment.

Effect of Pt on diffusion-controlled growth characteristics of interdiffusion zone between CM247LC superalloy and Ni(Pt)Al bond coat

Effect of Pt on diffusion-controlled growth characteristics of interdiffusion zone between CM247LC superalloy and Ni(Pt)Al bond coat

Fabrication of hydrophobic Pd/Al2O3-phosphoric acid via P O Al bond for liquid hydrogenation reaction

Alumina (Al2O3) is widely used in the chemical industry as the catalyst and support due to its high specific surface area, abundant pore size distribution and chemical stability. However, the occurrence of hydration in water environment, result in outstanding decrease in specific surface area and collapse of pore structure. In this work, dodecyl phosphoric acid (PA) is used to modify the surface of Al2O3 to obtain a series of hydrophobic material (Al2O3-PA). Based on XPS and NMR analysis, PA is chemically bonded on Al2O3 to form POAl bond. Furthermore, BET and WCA results display that Al2O3-1PA exhibits excellent the hydrophobicity and hydrothermal stability while maintains the pore structure. Take it as the substrate to support the Pd nanoparticles, the as-prepared Pd/Al2O3-PA shows the superior catalytic performance in the hydrogenation of phenol and anthraquinone relative to Pd/Al2O3, indicating the accessibility of Pd sites after PA modification. Especially, the significantly enhanced stability is also obtained in four cycles for aqueous phenol hydrogenation. This can be ascribed that the PA modification inhibits the aggregation of Pd nanoparticles and the products adhesion in the reaction process. The extension of PA coatings to monolithic catalysts could expand their current capabilities in industrial applications and warrants ongoing investigation.

Radical-like reactivity for dihydrogen activation by coinage metal-aluminyl complexes: computational evidence inspired by experimental main group chemistry.

The computational study of an unprecedented reactivity of coinage metal-aluminyl complexes with dihydrogen is reported. In close resemblance to group 14 dimetallenes and dimetallynes, the complexes are predicted to activate H2 under mild conditions. Two different reaction pathways are found disclosing a common driving force, i.e., the nucleophilic behavior of the electron-sharing M-Al (M = Cu, Ag, Au) bond, which enables a cooperative and diradical-like mechanism. This mode of chemical reactivity emerges as a new paradigm for dihydrogen activation and calls for experimental feedback.

Structural snapshots of an Al-Cu bond-mediated transformation of terminal acetylenes.

The copper(i) alumanyl derivative, [{SiNDipp}Al-Cu(NHCiPr)] (SiNDipp = {CH2SiMe2NDipp}2; Dipp = 2,6-di-isopropylphenyl; NHCiPr = N,N'-di-isopropyl-4,5-dimethyl-2-ylidene), reacts in a stepwise fashion with up to three equivalents of various terminal alkynes. This reactivity results in the sequential formation of cuprous (hydrido)(alkynyl)aluminate, (alkenyl)(alkynyl)aluminate and bis(alkynyl)aluminate derivatives, examples of which have been fully characterised. The process of alkene liberation resulting from the latter reaction step constitutes a unique case of alkyne transfer semi-hydrogenation in which the C-H acidic alkyne itself acts as a source of proton, with the Cu-Al bond providing the requisite electrons to effect reduction. This reaction sequence is validated by DFT calculations, which rationalise the variable stability of the initially formed heterobimetallic hydrides.

Mechanistic Study of Alkyne Insertion into Cu–Al and Au–Al Bonds: A Paradigm Shift for Coinage Metal Chemistry

In this work, the mechanism of the insertion reaction of 3-hexyne into Cu-Al and Au-Al bonds in M-aluminyl (M = Cu, Au) complexes is computationally elucidated. The mechanism is found to be radical-like, with the Cu-Al and Au-Al bonds acting as nucleophiles toward the alkyne, and predicts a less efficient reactivity for the gold-aluminyl complex. The proposed mechanism well rationalizes the kinetic (or thermodynamic) control on the formation of the syn (or anti) insertion product into the Cu-Al bond (i.e., dimetallated alkene) which has been recently reported. A comparative analysis of the electronic structure reveals that the reduced reactivity at the gold site─usually showing higher efficiency than copper as a "standard" electrophile in alkyne activation─arises from a common feature, i.e., the highly stable 6s Au orbital. The relativistic lowering of the 6s orbital, making it more suitable for accepting electron density and thus enhancing the electrophilicity of gold complexes, in the gold-aluminyl system is responsible for a less nucleophilic Au-Al bond and, consequently, a less efficient alkyne insertion. These findings demonstrate that the unconventional electronic structure and the electron-sharing nature of the M-Al bond induce a paradigm shift in the properties of coinage metal complexes. In particular, the peculiar radical-like reactivity, previously shown also with carbon dioxide, suggests that these complexes might efficiently insert/activate other small molecules, opening new and unexplored paths for their reactivity.