Quadruple Bond Research Articles

On the nature of the chemical bond in valence bond theory.

This Perspective outlines a panoramic description of the nature of the chemical bond according to valence bond theory. It describes single bonds and demonstrates the existence of a "forgotten family" of charge-shift bonds (CSBs) in which the entire/most of the bond energy arises from the resonance between the covalent and ionic structures of the bond. Many of the CSBs are homonuclear bonds. Hypervalent molecules (e.g., XeF2) are CSBs. This Perspective proceeds to describe multiple bonded molecules with an emphasis on C2 and 3O2. C2 has four electron pairs in its valence shell and, hence, 14 covalent structures and 1750 ionic structures. This Perspective outlines an effective methodology of peeling the electronic structure to the minimal and important number of structures: a dominant structure that displays a quadruple bond and two minor structures with π + σ bonds, which stabilize the quadruple bond by resonance. 3O2 is chosen because it is a diradical, which is persistent and life-sustaining. It is shown that the persistence of this diradical is due to the charge-shift bonding of the π-3-electron bonds. This section ends with a discussion of the roles of π vs σ in the geometric preferences of benzene, acetylene, ethene, and their Si-based analogs. Subsequently, this Perspective discusses bonding in clusters of univalent metal atoms, which possess only parallel spins (n+1Mn), and are nevertheless bonded due to the resonance interactions that stabilize the repulsive elementary structure (all spins are up). The bond energy reaches ∼40 kcal/mol for a pair of atoms (in n+1Cun; n ∼ 10-12). The final subsection discusses singlet excited states in ethene, ozone, and SO2. It demonstrates the capability of the breathing-orbital VB method to yield an accurate description of a variety of excited states using merely 10 or few VB structures. Furthermore, the method underscores covalent structures that play a key role in the correct description and bonding of these excited states.

Poly(lactide)‐based supramolecular polymers driven by self‐complementary quadruple hydrogen bonds: construction, crystallization and mechanical properties

AbstractA series of poly(lactide) (PLA)‐based supramolecular polymers based on linear PLLA‐b‐PCL‐b‐PLLA triblock copolymers (PLLA, poly(l‐lactide); PCL, poly(ε‐caprolactone)) or/and three‐arm star (PCL‐b‐PDLA)3 block copolymers (PDLA, poly(d‐lactide)) were synthesized. The effects of the structure and composition on crystal structure, crystallization behavior, spherulite morphology and mechanical properties of the synthesized supramolecular polymers were investigated. The results of DSC and polarized optical microscopy indicated that the supramolecular polymer exhibited poor crystallization ability with respect to PCL/PLA block copolymer, and the crystallinity of the supramolecular polymer with alternating PCL/PLA multiblock structure was stronger than that with similar crosslinked network structure. The presence of molten PCL blocks disturbed the orientation of lamellae, forming spherulites with feather‐like dendrites, and ring‐banded spherulites were observed as the molecular weight of the PLA blocks increased. The results of tensile tests demonstrated that supramolecular polymers with larger molecular weight of PLA blocks showed the pronounced ductile fracture. On this basis, stereocomplexed supramolecular polymers were also synthesized, and it was found that the stereocomplex crystals had a significant impact on the crystallization and mechanical properties of the supramolecular polymers. Therefore, in this work a novel technique for manufacturing toughened PLA‐based material and tuning its performances is proposed, which may promote the application of PLA‐based materials in more fields. © 2022 Society of Industrial Chemistry.

Supramolecular Polycaprolactone-Based Polyurethanes with Thermally Activated Shape-Memory Behavior.

In this work, using supramolecular polyurethanes theories, two polycaprolactone-based polyurethanes with 2-ureido-4-[1H]-pyrimidinone (UPy) motifs capable of forming quadruple hydrogen bonds were synthetized and characterized, focusing our attention on their capability to show thermally activated shape-memory response. In particular, 1H NMR analyses confirmed the chemical structure of the supramolecular polyurethanes, while DSC showed their totally amorphous morphology. DMTA in tensile mode was used to study their thermally activated shape-memory properties. In our case, the UPy units are the switching domains while the network formed by the segregated hard segments is the permanent domain obtained materials with excellent shape-memory response at both 100 and 85 °C. These materials are promising for multi-responsive materials where bio-based and potentially recyclable polymers with excellent shape-memory properties are needed.

Ionization energies and cationic bond dissociation energies of RuB, RhB, OsB, IrB, and PtB

Two-photon ionization thresholds of RuB, RhB, OsB, IrB, and PtB have been measured using resonant two-photon ionization spectroscopy in a jet-cooled molecular beam and have been used to derive the adiabatic ionization energies of these molecules. From the measured two-photon ionization thresholds, IE(RuB) = 7.879(9) eV, IE(RhB) = 8.234(10) eV, IE(OsB) = 7.955(9) eV, IE(IrB) = 8.301(15) eV, and IE(PtB) = 8.524(10) eV have been assigned. By employing a thermochemical cycle, cationic bond dissociation energies of these molecules have also been derived, giving D0(Ru+–B) = 4.297(9) eV, D0(Rh+–B) = 4.477(10) eV, D0(Os–B+) = 4.721(9) eV, D0(Ir–B+) = 4.925(18) eV, and D0(Pt–B+) = 5.009(10) eV. The electronic structures of the resulting cationic transition metal monoborides (MB+) have been elucidated using quantum chemical calculations. Periodic trends of the MB+ molecules and comparisons to their neutral counterparts are discussed. The possibility of quadruple chemical bonds in all of these cationic transition metal monoborides is also discussed.

Self-healing artificial solid electrolyte interphase enhanced by quadruple hydrogen bonding for stable lithium metal anode

Lithium metal is considered as the ultimate anode material for lithium batteries due to its high theoretical specific capacity and lowest redox potential. However, the growth of lithium dendrites and strong side reactions seriously hinder the commercialization of Li metal anode. Here, we modify the Li metal anode with a self-healing artificial solid electrolyte interphase (SEI), where PVA-Upy with quadruple hydrogen bonds is formed on Li metal by a simple drop-coating method. This polymer artificial SEI possesses self-healing hydrogen bonds and abundant lithiophilic bonds, which can simultaneously suppress the generation of microcracks in the SEI and enable uniform deposition of Li metal. Hence, the PVA-Upy@Li symmetric cell can stably cycle for more than 2000 h (1 mA cm−2, 1 mAh cm−2) with only about 10 mV of voltage polarization. This artificial SEI provides new insight into the subsequent modification strategies of Li metal anode and can be extended to the protection of other alkali metal anodes.

Ultra-stretchable and ultra-low temperature self-healing polyurethane enabled by dual dynamic bonds strategy

The successful development of polyurethane with excellent low-temperature self-healing capability will facilitate it to find wider applications in composite solid propellants and other fields. Here, we report a design strategy that both quadruple hydrogen bonds and aliphatic disulfide bonds are introduced into polyurethane networks to achieve an ultra-stretchable and ultra-low temperature self-healing polyurethane. The polyurethane has excellent mechanical properties, including high tensile strength and elongation at breaks of 1303.56%, 1503.42%, 2381.88%, and 1814.07% at −40 °C, −20 °C, 25 °C, and 60 °C, respectively. Furthermore, after self-repair at −20 °C, the elongation at break of the cut polyurethane can reach 1120.14%, and the repair efficiency is 74.5%, whereas at −40 °C, the elongation at break and repair efficiency are 811.75% and 62.2%, respectively, which are rarely seen in the literature. In addition, the glass transition temperature of the polyurethane is extremely low (−78.34 °C), which facilitates their low-temperature application. The excellent properties of the prepared polyurethane will allow the preparation of composite solid propellants for use in a wider temperature range. More importantly, the proposed material is expected to have broader application prospects such as in cold-proof coatings, electronic devices, and so on.

Probing the Halide Effect in the δ-Bond with One- and Two-Photon Spectroscopy

Two electrons in two orbitals give rise to four states. When the orbitals are weakly coupled as in the case for the dxy orbitals of quadruple bond species, two of the states are diradical in character with electrons residing in separate orbitals and two of the states are zwitterionic with electrons paired in one orbital or the other. By measuring one-and two-photon spectra, the one-electron (ΔW) and two-electron (K) energies may be calculated, which are the determinants of the state energies of the four-state model for the two-electron bond. The K energy is thus especially sensitive to the size of the orbital as K is dependent on the distance between electrons. To this end, one- and two-photon spectra of Mo2X4(PMe3)4 are sensitive to secondary bonding interactions of the δ-orbital manifold with the halide orbitals, as reflected in decreasing K energies along the series Cl > Br > I. Additionally, the calculated one-electron energies have been verified with the spectroelectrochemical preparation of the Mo2X4(PMe3)4+ complexes, where the δ bond is a one-electron bond, and K is thus absent. The δ → δ* transition shifts over 10,000 cm-1 upon oxidation of Mo2X4(PMe3)4 to Mo2X4(PMe3)4+, establishing that transitions within the two-electron δ bond are heavily governed by the two-electron exchange energy.

Light-fueled dissipative self-assembly at molecular and macro-scale enabled by a visible-light-responsive transient hetero-complementary quadruple hydrogen bond

The development of out-of-equilibrium self-assembly systems using light as input fuel is highly desirable and promising for the fabrication of smart supramolecular materials. Herein, we report the construction of new artificial light-fueled dissipative molecular and macroscopic self-assembly systems based on a visible-light-responsive transient quadruple H-bonding array, which consists of an azobenzene-modified ureidopyrimidinone (UPy) module (Azo-O-UPy) and a nonphotoactive diamidonaphthyridine (DAN) derived competitive binder (Napy-1). The visible light (410 nm) irradiation can induce the E to Z isomerization of the azobenzene unit of E-Azo-O-UPy to produce Z-Azo-O-UPy with an opened UPy binding site, which can complex with Napy-1 to form a quadruply H-bonded heterodimer. The heterodimer is metastable and can be quickly disassembled in dark, owing to the fast thermal relaxation of Z-Azo-O-UPy to E-Azo-O-UPy. While introducing such transient quadruple H-bonding interaction into a linear polymer system or a polymeric gel system, light-fueled out-of-equilibrium polymeric assembly both at molecular and macro-scale can be achieved.

Interaction of trans-tetrachlorodi-m-carboxylates of dirhenium(III) with dipeptides of the glycyl series

The paper reports the methods for the synthesis of new cluster compounds of trans-tetrachlorodi--carboxylates of dirhenium(III) with dipeptides of the glycyl series. The compositions and the structures were determined by electron absorption and IR spectroscopies as well as by elemental analysis for the following newly synthesized compounds: trans-[Re2(H3N+–CH2–СO–NH–CH(COO)–CH2–CH(CH3)–CH3)2Cl42СН3CN]Cl2 (І) and trans-[Re2(H3N+–CH2–СO–NH–CH(COO)–CH2–C6H5)2Cl42СН3CN]Cl2 (ІІ). Analysis of the electronic absorption spectra of the solutions of the synthesized substances showed the presence of a doublet pattern (12500 and 16129 сm–1), which corresponds to the *-electronic transition of the Re–Re quadruple bond characteristic of solutions of trans-tetrachlorodi--carboxylates of dirhenium(III). The appearance of oscillations at 1485 сm–1 for І and 1486 сm–1 for ІІ, characteristic of the s(CO) of the coordinated carboxylate group, was detected on the IR spectra, which indicates the bridging coordination of this group to the Re26+ binuclear fragment. The protonation of the amino group is indicated by the appearance of a wide band of valence oscillations (NH3+) in the range of 3400–3350 сm–1 and deformation oscillations (NH3+) at 1557 сm–1 and 1614 сm–1 for I and II, respectively. The stability of the obtained complex compounds in aqueous solutions was determined. It was shown that the hydrolysis of the synthesized substances takes place in 4–5 days, which is accompanied by a decrease in the pH of the reaction solution.

Benchmark studies on the large errors of calculated binding energies in metallophilic interactions.

Aurophilicity is a d10-d10 closed-shell interaction, which is repulsively calculated by the Hartree-Fork (HF) method, whereas binding energies (Eb) are largely overestimated under the second-order Møller-Plesset (MP2) method, compared to the coupled cluster singles and doubles with perturbative triples [CCSD(T)] method. The unusual energy errors between different wave functional methods were also verified in other closed-shell metallophilic systems and even were taken as a label of metallophilic interaction. Here, we performed a benchmark study on a collection of structures with weak interactions, sp-sp bonds, sp-d bonds, and d-d bonds, to investigate the influence factor of the errors of HF and MP2 methods. It was found that the large energy errors of HF and MP2 methods were not specified for closed-shell interactions, and the errors could also be very large for many covalent bonds, which was strongly related to the azimuthal quantum number of interaction orbitals. Compared to the CCSD(T) method, the MP2 method weakens the s-s covalent interactions slightly, strengthens the p-p covalent interactions slightly, and overestimates the d-d covalent interactions largely (can be -170 kcal/mol for the Re-Requadruple bond). This benchmark study suggests that the special energy errors in metallophilicity may result from the participation of d orbitals. Benchmark studies on various density functional methods were also given for calculating binding energies of d-d bonds.

Robust, dimensional stable, and self-healable anion exchange membranes via quadruple hydrogen bonds

Quadruple hydrogen bonds have been introduced in anion exchange membranes (AEMs) to form supramolecular network. Specifically, 2-((3-(dimethylamino) propyl) carbonyldiamino)-6-methyl-4-[1H]-pyrimidinone (DCMP) and polystyrene-b-poly(ethylene-co-butylene)-b-polystyrene (SEBS) with quaternary ammonium cations as well as pendant DCMP are synthesized via Friedel-Crafts acylation, ketone reduction, and quaternization sequentially. Finally, a new type of anionic conducting membranes based-on functionalized SEBS, which is cross-linked via quadruple hydrogen bonds provided by pendant DCMP moieties, is obtained. The prepared AEMs have good thermal and chemical stability, significantly improved mechanical properties without sacrificing ionic conductivity and easily realized self-healing ability, which make the anion exchange membranes have the potential of long-term stable use.

High-Strength, Large-Deformation, Dual Cross-Linking Network Liquid Crystal Elastomers Based on Quadruple Hydrogen Bonds.

Liquid crystal elastomers (LCEs) with large deformation under external stimuli have attracted extensive attention in various applications such as soft robotics, 4D printing, and biomedical devices. However, it is still a great challenge to reduce the damage to collimation and enhance the mechanical and actuation properties of LCEs simultaneously. Here, we construct a new method of a double cross-linking network structure to improve the mechanical properties of LCEs. The ureidopyrimidinone (UPy) group with quadruple hydrogen bonds was used as the physical cross-linking unit, and pentaerythritol tetra(3-mercaptopropionate) was used as the chemical cross-link. The LCEs showed a strong mechanical tensile strength of 8.5 MPa and excellent thermally induced deformation (50%). In addition, the introduction of quadruple hydrogen bonds endows self-healing ability to extend the service life of LCEs. This provides a generic strategy for the fabrication of high-strength LCEs, inspiring the development of actuators and artificial muscles.

Probing the Nature of the Transition-Metal-Boron Bonds and Novel Aromaticity in Small Metal-Doped Boron Clusters Using Photoelectron Spectroscopy.

Photoelectron spectroscopy combined with quantum chemistry has been a powerful approach to elucidate the structures and bonding of size-selected boron clusters (Bn-), revealing a prevalent planar world that laid the foundation for borophenes. Investigations of metal-doped boron clusters not only lead to novel structures but also provide important information about the metal-boron bonds that are critical to understanding the properties of boride materials. The current review focuses on recent advances in transition-metal-doped boron clusters, including the discoveries of metal-boron multiple bonds and metal-doped novel aromatic boron clusters. The study of the RhB- and RhB2O- clusters led to the discovery of the first quadruple bond between boron and a transition-metal atom, whereas a metal-boron triplebond was found in ReB2O- and IrB2O-. The ReB4- cluster was shown to be the first metallaborocycle with Möbius aromaticity, and the planar ReB6- cluster was found to exhibit aromaticity analogous to metallabenzenes.

UV‐Curable Polyurethane Elastomer with UV‐Irradiation/Thermo Dual‐Activated Self‐Healability

AbstractSelf‐healable polyurethane elastomers have potential applications in many fields, however, their use is limited by single self‐healing mechanism, intricate preparation process, and long curing time. Herein, a UV‐irradiation/thermo dual‐induced self‐healing polyurethane elastomer is prepared by UV‐curing two kinds of acrylates, where one includes a quadruple hydrogen bond (PU‐UPy‐HEA) and the other contains a disulfide bond (SS‐MA). UV‐curing kinetics indicate that the conversion of acrylates is significantly improved by tuning the irradiation intensity, photoinitiator dosage, and SS‐MA content. A maximum conversion of 80% is achieved within 10 s under 200 mW cm−2 in the case of the 1.5 wt% photoinitiator. The tensile strength of UV‐cured polyurethane elastomer is notably improved by SS‐MA, whereas its elongation at break decreases. Tensile shear tests demonstrates that the bisected samples can be re‐bonded when they are repaired at 100 °C for 15 min, or under 200 mW cm−2 irradiation for 1 h. After that, ≈90% of shear strength is recovered and the strength is only slightly reduced after two healing cycles. Self‐healing mainly relies on thermally reversible hydrogen bonding interactions and UV‐induced disulfide metathesis. This UV‐cured self‐healable polyurethane elastomer can be used in smart coatings as well as in other fields.

Crystal structure of a tri-fluoro-methyl benzoato quadruple-bonded dimolybdenum complex.

The study of quadruple bonds between transition metals, in particular those of dimolybdenum, has revealed much about the two-electron bond. The solid-state structure of the quadruple-bonded dimolybdenum(II) complex tetra-kis-[μ-4-(tri-fluoro-methyl)-benzoato-κ2 O:O']bis[(tetra-hydro-furan-κO)molybdenum(II)] 0.762-pentane 0.238-tetra-hydro-furan solvate, [Mo2(p-O2CC6H4CF3)4·2THF]·0.762C5H12·0.238C4H8O or [Mo2(C8H4F3O2)4(C4H8O)2]·0.762C5H12·0.238C4H8O is reported. The complex crystallizes within a triclinic cell and low symmetry (P ) results from the inter-calated penta-ne/THF solvent mol-ecules. The paddlewheel structure at 100 K has inversion symmetry and comprises four bridging carboxyl-ate ligands encases the Mo2(II,II) core that is characterized by two axially coordinated THF mol-ecules and an Mo-Mo distance of 2.1098 (7) Å.

Two σ- and two π-dative quadruple bonds between the s-block element and transition metal in [BeM(CO)4; M = Fe − Os

The bonding interaction between the metal fragment M(CO)4 and beryllium in BeM(CO)4 (M = Fe, Ru, and Os) can be best described by dative quadruple bonds, viz., two σ and two π dative bonds.

Molecularly engineered dual-crosslinked elastomer vitrimers with superior strength, improved creep resistance, and retained malleability

Preparation of covalently crosslinked elastomers with an integration of high mechanical performance, enhanced creep resistance and retained malleability by incorporating quadruple hydrogen bonds into dynamic boronic ester bonds crosslinked SBR.

Assessing the Accuracy of Tailored Coupled Cluster Methods Corrected by Electronic Wave Functions of Polynomial Cost.

Tailored coupled cluster theory represents a computationally inexpensive way to describe static and dynamical electron correlation effects. In this work, we scrutinize the performance of various coupled cluster methods tailored by electronic wave functions of polynomial cost. Specifically, we focus on frozen-pair coupled cluster (fpCC) methods, which are tailored by pair-coupled cluster doubles (pCCD), and coupled cluster theory tailored by matrix product state wave functions optimized by the density matrix renormalization group (DMRG) algorithm. As test system, we selected a set of various small- and medium-sized molecules containing diatomics (N2, F2, C2, CN+, CO, BN, BO+, and Cr2) and molecules (ammonia, ethylene, cyclobutadiene, benzene, hydrogen chains, rings, and cuboids) for which the conventional single-reference coupled cluster singles and doubles (CCSD) method is not able to produce accurate results for spectroscopic constants, potential energy surfaces, and barrier heights. Most importantly, DMRG-tailored and pCCD-tailored approaches yield similar errors in spectroscopic constants and potential energy surfaces compared to accurate theoretical and/or experimental reference data. Although fpCC methods provide a reliable description for the dissociation pathway of molecules featuring single and quadruple bonds, they fail in the description of triple or hextuple bond-breaking processes or avoided crossing regions.

Photodissociation of dicarbon: How nature breaks an unusual multiple bond

The dicarbon molecule (C2) is found in flames, comets, stars, and the diffuse interstellar medium. In comets, it is responsible for the green color of the coma, but it is not found in the tail. It has long been held to photodissociate in sunlight with a lifetime precluding observation in the tail, but the mechanism was not known. Here we directly observe photodissociation of C2 From the speed of the recoiling carbon atoms, a bond dissociation energy of 602.804(29) kJ·mol[Formula: see text] is determined, with an uncertainty comparable to its more experimentally accessible N2 and O2 counterparts. The value is within 0.03 kJ·mol-1 of high-level quantum theory. This work shows that, to break the quadruple bond of C2 using sunlight, the molecule must absorb two photons and undergo two "forbidden" transitions.

Contributions of Erhard Kurras to Organochromium Chemistry – From a Historical Perspective

AbstractStarting from the fundamental organometallic research work of Franz Hein, Erhard Kurras investigated the possibility of isolating stable organochromium compounds. He studied the existence of σ‐alkyl and σ‐alkylene complexes, π‐allyl compounds, as well as dichromium complexes containing a chromium‐chromium quadruple bond. Since that time a variety of organochromium compounds have been developed by the scientific community. In this article, we highlight the scientific work of Erhard Kurras by using selected examples. Most of these examples represent very important contributions to the field of chromium complex chemistry, as they were completely new at that time in terms of bonding, activation of small molecules, and finally catalytic behavior. We believe that Kurras's fundamental work has opened a new chapter in organometallic chemistry.