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Lanthanide/actinide separation is a worldwide challenge for atomic energy and nuclear waste treatment. Separation of americium (Am), a critical actinide element in the nuclear fuel cycle, from lanthanides (Ln) is highly desirable for minimizing the long-term radiotoxicity of nuclear waste, yet it is extremely challenging given the chemical similarity between trivalent Am(III) and Ln(III). Selective oxidation of Am(III) to a higher oxidation state (OS) could facilitate this separation, but so far, it is far from satisfactory for practical application as a result of the unstable nature of Am in a high OS. Herein, we find a novel strategy to generate stable pentavalent Am (Am(V)) through coordination of Am(III) with a diglycolamide ligand and oxidation with Bi(V) species in the presence of an organic solvent. This strategy leads to efficient stabilization of Am(V) and an extraordinarily high separation factor (10

Structural characterization of neutral water clusters is crucial to understanding the structures and properties of water, but it has been proven to be a challenging experimental target due to the difficulty in size selection. Here, we report the size-specific infrared spectra of confinement-free neutral water nonamer (H

Nature 616(7957), 482 - 487 (2023). doi:10.1038/s41586-023-05840-z, Published by Nature Publ. Group, London [u.a.]

We present here a set of scalar-relativistic norm-conserving 4f-in-core pseudopotentials, together with complementary valence-shell Gaussian basis sets, for the lanthanide (Ln) series (Ce-Lu). The Goedecker, Teter, and Hutter (GTH) formalism is adopted with the generalized gradient approximation (GGA) for the exchange-correlation Perdew-Burke-Ernzerhof (PBE) functional. The 4f-in-core pseudopotentials are built through attributing 4f-subconfiguration 4f

We report the smallest 4f-metalla-aromatic molecule of PrB2− exhibiting σ and π double aromaticity and multiple Pr–B bond characters.

Rare-earth metal boroxides are not only rare and of great synthetic challenge but also important theoretically due to their unrevealed bonding characteristics. In this paper, we report the synthesi...

We present here a set of norm-conserving 4f-in-core pseudopotentials, together with complementary valence-shell Gaussian basis sets, for the lanthanide (Ln) series (Ce - Lu). The Goedecker, Teter and Hutter (GTH) formalism is adopted with the generalized gradient approximation (GGA) for exchange-correlation functional of Perdew, Burke and Ernzerhof (PBE). The 4f-in-core pseudopotentials are built through attributing 4f-subconfiguration 4fn (n = 1 – 14) for Ln (Ln = Ce – Lu) into the atomic core region, making it possible to circumvent the difficulty of description of open 4fn valence shell. A wide variety of computational benchmarks and tests have been carried out on lanthanide systems including Ln3+-containing molecular complexes, aqueous solutions, and bulk solids, to validate the accuracy, reliability and efficiency of the optimized 4f-in-core GTH pseudopotentials and basis sets. The 4f-in-core GTH pseudopotentials successfully replicate main features of lanthanide structural chemistry and reaction energetics, particularly for non-redox reactions. The chemical bonding features of selected lanthanide systems are also discussed in details by utilizing these new 4f-in-core GTH pseudopotentials. This work bridges the idea of keeping highly localized 4f electrons in atomic core and efficient pseudopotential formalism of GTH, thus providing a highly efficient approach for studying lanthanide chemistry in multi-scale modeling of constituent-wise and structurally complicated systems, including electronic structures of condensed phase and first-principles molecular dynamics simulations.

Selective cleavage of C-C linkages is the key and a challenge for lignin degradation to harvest value-added aromatic compounds. To this end, electrocatalytic oxidation presents a promising technique by virtue of mild reaction conditions and strong sustainability. However, the existing electrocatalysts (traditional bulk metal and metal oxides) for C-C bond oxidative cleavage suffer from poor selectivity and low product yields. We show for the first time that atomically dispersed Pt-N3C1 sites planted on nitrogen-doped carbon nanotubes (Pt1/N-CNTs), constructed via a stepwise polymerization-carbonization-electrostatic adsorption strategy, are highly active and selective toward Cα-Cβ bond cleavage in β-O-4 model compounds under ambient conditions. Pt1/N-CNTs exhibits 99% substrate conversion with 81% yield of benzaldehyde, which is exceptional and unprecedented compared with previously reported electrocatalysts. Moreover, Pt1/N-CNTs using only 0.41 wt % Pt achieved a much higher benzaldehyde yield than those of the state-of-the-art bulk Pt electrode (100 wt % Pt) and commercial Pt/C catalyst (20 wt % Pt). Systematic experimental investigation together with density functional theory (DFT) calculation suggests that the superior performance of Pt1/N-CNTs arises from the atomically dispersed Pt-N3C1 sites facilitating the formation of a key Cβ radical intermediate, further inducing a radical/radical cross-coupling path to break the Cα-Cβ bond. This work opens up opportunities in lignin valorization via a green and sustainable electrochemical route with ultralow noble metal usage.

Uranium nitride-oxide cations [NUO]

Heteronuclear BeFe(CO)4 - anion complex is generated in the gas phase, which is detected by mass-selected infrared photodissociation spectroscopy in the carbonyl stretching frequency region. The complex is characterized to have a Be-Fe bonded Be-Fe(CO)4 - structure with C3v symmetry and all of the four carbonyl ligands bonded on the iron center. Quantum chemical studies indicate that the complex has a quite short Be-Fe bond. Besides one electron-sharing σ bond, there are two additional, albeit weak, Be ← Fe(CO)4 - dative π bonding interactions. The findings imply that metal-metal bonding between s-block and transition metals is viable under suitable coordination environment.

Versatile graphene-like two-dimensional materials with s-, p- and d-block elements have aroused significant interest because of their extensive applications while there is a lack of such materials with f-block elements. Herein we report a unique one composed of the f-block element moiety of uranyl (UO

Actinoid tetroxide molecules AnO

The multiple bonds between actinide atoms and their derivatives are computationally investigated extensively and compounds with an unsupported actinide–actinide bond, especially in low oxidation states, have attracted great attention. Herein, high level relativistic quantum chemical methods are used to probe the Ac–Ac bonding in compounds with a general formula LAcAcL (L = AsH3, PH3, NH3, H, CO, NO) at both scalar and spin–orbit coupling relativistic levels. H3AsAcAcAsH3, H3PAcAcPH3 and OCAcAcCO compounds show a type of zero valence AcAc triple bond with a 1σ2g1π4u configuration, and H3AsAcAcAsH3 has been found to have the shortest Ac–Ac bond length of 3.012 A reported so far. The Ac2 unit is very sensitive to the σ donor ligands and can form triple, double and even single bonds when suitable ligands are introduced, up to 3.652 A with an Ac–Ac single bond in H3NAcAcNH3.

Inverse-sandwich samarium and ytterbium biphenyl complexes were synthesized by the reduction of their trivalent halide precursors with potassium graphite in the presence of biphenyl. While the samarium complex had a similar structure as previously reported rare earth metal biphenyl complexes, with the two samarium ions bound to the same phenyl ring, the ytterbium counterpart adopted a different structure, with the two ytterbium ions bound to different phenyl rings. Upon the addition of crown ether to encapsulate the potassium ions, the inverse-sandwich samarium biphenyl structure remained intact; however, the ytterbium biphenyl structure fell apart with the concomitant formation of a divalent ytterbium crown ether complex and potassium biphenylide. Spectroscopic and computational studies were performed to gain insight into the electronic structures and bonding interactions of these samarium and ytterbium biphenyl complexes. While the ytterbium ions were found to be divalent with a 4f14 electron configuration and form a primarily ionic bonding interaction with biphenyl dianion, the samarium ions were in the trivalent state with a 4f5 electron configuration and mainly utilized the 5d orbitals to form a δ-type bonding interaction with the π* orbitals of the biphenyl tetraanion, showing covalent character., Inverse-sandwich samarium and ytterbium biphenyl complexes were synthesized and characterized by X-ray crystallography. Combined experimental and computational studies indicated that they have distinct electronic structures and bonding interactions.

The Periodic Table, and the unique chemical behavior of the first element in a column (group), were discovered simultaneously one and a half centuries ago. Half a century ago, this unique chemistry of the light homologs was correlated to the then available atomic orbital (AO) radii. The radially nodeless 1s, 2p, 3d, 4f valence AOs are particularly compact. The similarity of r (2s)≈r(2p) leads to pronounced sp‐hybrid bonding of the light p‐block elements, whereas the heavier p elements with n≥3 exhibit r (ns) ≪ r (np) of approximately −20 to −30 %. Herein, a comprehensive physical explanation is presented in terms of kinetic radial and angular, as well as potential nuclear‐attraction and electron‐screening effects. For hydrogen‐like atoms and all inner shells of the heavy atoms, r (2s) ≫ r (2p) by +20 to +30 %, whereas r (3s)≳r(3p)≳r(3d), since in Coulomb potentials radial motion is more radial orbital expanding than angular motion. However, the screening of nuclear attraction by inner core shells is more efficient for s than for p valence shells. The uniqueness of the 2p AO is explained by this differential shielding. Thereby, the present work paves the way for future physical explanations of the 3d, 4f, and 5g cases., 2p or not 2p? Similarity of radii (and energies) of the atomic valence orbitals is the precondition for hybridization and hybrid bonding. In the Coulomb potential of H‐like atoms, the 2p orbital without a radial node is much smaller than 2s (2s≫2p), whereas higher p orbitals are comparably less contracted (ns≳np). The screening of nuclear attraction by the core shells is more effective for the core penetrating s orbitals, so that for the valence orbital radii of ordinary many‐electron atoms of the 2nd row, 2s≈2p, whereas in rows n>2, hybridization is less pronounced owing, i.a., to ns≪ np.

The development of the uranyl cation as a powerful photocatalyst is seriously delayed in comparison with the advances in its fundamental and structural chemistry. However, its characteristic high oxidative capability in the excited state ([UO2 ]2+ * (+2.6 V vs. SHE; SHE=standard hydrogen electrode) combined with blue-light absorption (hv=380-500 nm) and a long-lived fluorescence lifetime up to microseconds have reveals that the uranyl cation approaches an ideal photocatalyst for visible-light-driven organic transformations. Described herein is the successful use of uranyl nitrate as a photocatalyst to enable C(sp3 )-H activation and C-C bond formation through hydrogen atom transfer (HAT) under blue-light irradiation. In particular, this operationally simple strategy provides an appropriate approach to the synthesis of diverse and valuable diarylmethane motifs. Mechanistic studies and DFT calculations have provided insights into the detailed mechanism of the photoinduced HAT pathway. This research suggests a general platform that could popularize promising uranyl photocatalytic performance.

Heteronuclear Group 3 metal/iron carbonyl anion complexes ScFe(CO)3 - , YFe(CO)3 - , and LaFe(CO)3 - are prepared in the gas phase and studied by mass-selective infrared (IR) photodissociation spectroscopy as well as quantum-chemical calculations. All three anion complexes are characterized to have a metal-metal-bonded C3v equilibrium geometry with all three carbonyl ligands bonded to the iron center and a closed-shell singlet electronic ground state. Bonding analyses reveal that there are multiple bonding interactions between the bare group-3 elements and the Fe(CO)3 - fragment. Besides one covalent electron-sharing metal-metal σ bond and two dative π bonds from Fe to the Group 3 metal, there is additional multicenter covalent bonding with the Group 3 atom bonded to Fe and the carbon atoms.

The Periodic Law, one of the great discoveries in human history, is magnificent in the art of chemistry. Different arrangements of chemical elements in differently shaped Periodic Tables serve for different purposes. “Can this Periodic Table be derived from quantum chemistry or physics?” can only be answered positively, if the internal structure of the Periodic Table is explicitly connected to facts and data from chemistry. Quantum chemical rationalization of such a Periodic Tables is achieved by explaining the details of energies and radii of atomic core and valence orbitals in the leading electron configurations of chemically bonded atoms. The coarse horizontal pseudo-periodicity in seven rows of 2, 8, 8, 18, 18, 32, 32 members is triggered by the low energy of and large gap above the 1s and nsp valence shells (2 ≤ n ≤ 6 !). The pseudo-periodicity, in particular the wavy variation of the elemental properties in the four longer rows, is due to the different behaviors of the s and p vs. d and f pairs of atomic valence shells along the ordered array of elements. The so-called secondary or vertical periodicity is related to pseudo-periodic changes of the atomic core shells. The Periodic Law of the naturally given System of Elements describes the trends of the many chemical properties displayed inside the Chemical Periodic Tables. While the general physical laws of quantum mechanics form a simple network, their application to the unlimited field of chemical materials under ambient ‘human’ conditions results in a complex and somewhat accidental structure inside the Table that fits to some more or less symmetric outer shape. Periodic Tables designed after some creative concept for the overall appearance are of interest in non-chemical fields of wisdom and art.

Stable metal clusters that can resist both highly concentrated acid and alkali are unknown. Herein, we present a discrete neutral cluster, Hf13 (μ4 -O)8 (OCH3 )36 (1), which features extraordinary chemical stability by preserving its crystalline state in concentrated aqueous solutions of both acid (10 m HNO3 ) and alkali (20 m boiling NaOH). Importantly, 1 can serve as a luminescent probe for detecting both concentrated alkali (20 m NaOH) and strong acid (1 m HNO3 ) with high selectivity and repeatability. DFT studies of the electronic structure and bonding revealed that 1 has an extremely large HOMO-LUMO gap due to strong d π-p π bonding that accounts for the ultrahigh stability.

The multiple bonds between actinide atoms and their derivatives are computationally investigated extensively and compounds with an unsupported actinide-actinide bond, especially in low oxidation states, have attracted great attention. Herein, high level relativistic quantum chemical methods are used to probe the Ac-Ac bonding in compounds with a general formula LAcAcL (L = AsH3, PH3, NH3, H, CO, NO) at both scalar and spin-orbit coupling relativistic levels. H3AsAcAcAsH3, H3PAcAcPH3 and OCAcAcCO compounds show a type of zero valence Ac[triple bond, length as m-dash]Ac triple bond with a 1σ2g1π4u configuration, and H3AsAcAcAsH3 has been found to have the shortest Ac-Ac bond length of 3.012 Å reported so far. The Ac2 unit is very sensitive to the σ donor ligands and can form triple, double and even single bonds when suitable ligands are introduced, up to 3.652 Å with an Ac-Ac single bond in H3NAcAcNH3.

Single transition-metal site catalysts with s-, p-, or d-block atom anchor for nitrogen fixation have been extensively studied, and yet the studies of the f-block atom anchor are rarely reported. Thus, we investigate the feasibility of using a newly synthesized U-Co complex featuring a single CoI site coordinated by tetrakis(phophinoamide) and an UIV anchor for N2-to-NH3 conversion by theoretical modeling. We characterize the evolution of oxidation states of U and Co along the reaction pathways from ab initio density matrix renormalization group (DMRG) calculations, and we find that the variation of the Co → U dative bond is correlated with the changes of oxidation states. Both uranium and cobalt can serve as electron reservoirs to facilitate breaking the N-N bond. Our study demonstrates the viability of metal → metal dative bonds, particularly the df-d one, for the reduction of N2 to NH3, and thus, this opens up a new avenue to the rational design of efficient catalyst for nitrogen fixation.

Assembled from [Th48 Ni6 ] nanocages, the first transition-metal (TM)-thorium metal-organic framework (MOF, 1) has been synthesized and structurally characterized. 1 exhibits high solvent and acid/base stability, and resistance to 400 kGy β irradiation. Notably, 1 captures ReO4 - (an analogue of radioactive 99 TcO4 - , a key species in nuclear wastes) with a maximum capacity of 807 mg g-1 , falling among the largest values known to date. Furthermore, 1 can enrich methylene blue (MB) and can also serve as an effective and recyclable catalyst for CO2 fixation with epoxides; there is no significant loss of catalytic activity after 10 cycles. Theoretical studies with nucleus-independent chemical shifts and natural bond orbital analysis reveal that the [Th6 O8 ] clusters in 1 have a unique stable electronic structure with (d-p)π aromaticity, partially rationalising 1's stability.

Since the discovery of the first drum-like CoB $_{16}$ - complex, metal-doped drum-like boron nanotubular structures have been investigated with various metal dopants and different tubular size, forming a new class of novel nanostructures. The CoB $_{16}$ $.-$ cluster was found to be composed of a central Co atom coordinated by two fused B $_8$ rings in a tubular structure, representing the potential embryo of metal-filled boron nanotubes and providing opportunities to design one-dimensional metal-boron nanostructures. Here we report improved photoelectron spectroscopy and a more in-depth electronic structure analysis of CoB $_{16}$ -, providing further insight into the chemical bonding and stability of the drum-like doped boron tubular structures. Most interestingly, we find that the central Co atom has an unusually low oxidation state of $-$ 1 and neutral CoB $_{16}$ can be viewed as a charge transfer complex (Co-@B $_{16}$ +), suggesting both covalent and electrostatic interactions between the dopant and the boron drum.

Heteronuclear transition-metal-main-group element carbonyl anion complexes of AFe(CO)3− (A = Ge, Sn, and Pb) are prepared using a laser vaporization supersonic ion source in the gas phase, which were studied by mass-selected infrared (IR) photodissociation spectroscopy. The geometric and electronic structures of the experimentally observed species are identified by a comparison of the measured and calculated IR spectra. These anion complexes have a 2A1 doublet electronic ground state and feature an AFe triply bonded C3v structure with all of the carbonyl ligands bonded at the iron center. Bonding analyses of AFe(CO)3− (A = C, Si, Ge, Sn, Pb, and Fl) indicate that the complexes are triply bonded between the valence np atomic orbitals of bare group-14 atoms and the hybridized 3d and 4p atomic orbitals of iron.

Lanthanide elements typically exhibit a +III oxidation state (OS) in chemical compounds with a few in +IV or even +V OS. Although lanthanides with +II OS have been observed recently in organometallic compounds, +I OS is extremely rare. Using a joint photoelectron spectroscopy and quantum theoretical study, we have found two low OS lanthanides in doped boron clusters, PrB3– and PrB4–. These two clusters are shown to have planar structures, in which the Pr atom is bonded to the aromatic boron clusters via two Pr–B σ bonds. Chemical bonding and electronic structure analyses reveal that the Pr atom is in a very low OS in the two boride clusters: +II in PrB3– and +I in PrB4–. The current finding suggests that there should exist a whole class of boride complexes featuring rather low-valent lanthanides and expands the frontier of lanthanide chemistry.

We have developed a new set of norm-conserving pseudopotentials and companion Gaussian basis sets for the actinide (An) series (Ac - Lr) using the Goedecker, Teter and Hutter (GTH) formalism with the Perdew, Burke and Ernzerhof (PBE) exchange-correlation functional of generalized gradient approximation (GGA). To test the accuracy and reliability of the newly parameterized An-GTH pseudopotentials and basis sets, a variety of benchmarks on actinide-containing molecules are carried out and compared to all-electron and available experimental results. The new pseudopotentials include both medium- ([Xe]4f14) and large-core ([Xe]4f145d10) options that have successfully reproduced structures and energetics, particularly redox processes. The medium-core size set, in particular, reproduce all-electron calculations over multiple oxidation states from 0 to VII, whereas the large-core set is suitable only for the early series elements and low oxidation states. The underlying reason for these transferability issues are discussed in detail. This work fills a critical void in the literature for studying the chemistry of 5f-block elements in condensed phase.

Superwetting porous membranes with tunable liquid repellency are highly desirable in broad domains including scientific research, chemical industry, and environmental protection. Such membranes should allow for controllable droplet bouncing or spreading, which is difficult to achieve for low surface energy organic liquids (OLs). Here we develop an interfacial physical parameter to regulate the OL wettability of nanoparticle-embedded membranes by structuring synergistic layers with reconfigurable surface energy components. Under the tunable solid-liquid interaction in the aggregation-induced process, the membranes demonstrate positive/negative liquid gating regularity for polar protic liquids, polar aprotic liquids, and nonpolar liquids. Such a membrane can be employed as self-adaptive gating for various immiscible liquid mixtures with superior separation efficiency and permeation flux, even afford successive achievement of high-performance in situ extraction-back extraction coupling. This study should provide distinctive insights into intrinsic wetting behaviors and have pioneered a rational strategy to design high-performance separation materials for diverse applications., Superwetting membranes with tunable organic liquid (OL) repellency are highly desirable but remain a challenge. Here, the authors develop a nanoparticle-embedded reconfigurable membrane with switchable wetting modes for various OLs based on a self-defined interfacial physical parameter.

Heteronuclear BeFe(CO)

Clear recognition and rational construction of suitable active center for specific reaction is always of great significance in designing highly efficient catalysts. Herein, a dual-active-site copper catalyst (DAS-Cu) containing both CuN

The water octamer, with its cubic structure consisting of six four-membered rings, presents an excellent system in which to unravel the cooperative interactions driven by subtle changes in the hydrogen-bonding topology. Although many distinct structures are calculated to exist, it has not been possible to extract the structural information encoded in their vibrational spectra because this requires size-selectivity of the neutral clusters with sufficient resolution to identify the contributions of the different isomeric forms. Here we report the size-specific infrared spectra of the isolated cold, neutral water octamer using a scheme based on threshold photoionization using a tunable vacuum ultraviolet free electron laser. A plethora of sharp vibrational bands features are observed for the first time. Theoretical analysis of these patterns reveals the coexistence of five cubic isomers, including two with chirality. The relative energies of these structures are found to reflect topology-dependent, delocalized multi-center hydrogen-bonding interactions. These results demonstrate that even with a common structural motif, the degree of cooperativity among the hydrogen-bonding network creates a hierarchy of distinct species. The implications of these results on possible metastable forms of ice are considered.

Since the landmark work of Heck, Negishi and Suzuki on Pd-catalyzed crossing coupling reactions, innovative discovery of new reactions forming C-C bonds and constructing functional olefins via nonmetal catalysts remains an imperative area in organic chemistry. Herein, we report a transition-metal-free arylation method of vinyl pinacolboronates with diaryliodonium salts to form C(sp2)-C(sp2) bond and provide trans-arylvinylboronates. The resulting vinylboronates can further react with the remaining aryl iodides (generated from diaryliodonium salts) via Suzuki coupling to afford functional olefins, offering an efficient use of aryliodonium salts. Computational mechanistic studies suggest radical-pair pathway of the diaryliodonium salts promoted by the multi-functional wet carbonate. The modular synthesis of crowded alkenes is a challenge. Here diaryliodonium salts are used to arylate vinyl boronates, which can then undergo Suzuki-Miyaura coupling with the aryl iodide generated in situ in the first step to yield modular trisubstituted alkenes.

Significance Spectroscopic investigation of neutral water clusters is critical in understanding the structures and properties of condensed-phase water. Because of the difficulty for size selection of neutral clusters in general, infrared spectroscopic study of structural evolution of confinement-free, neutral water clusters has been a grand challenge. In this work, we exploit recently developed, hybrid instruments that integrate infrared spectroscopy with a tunable vacuum ultraviolet free-electron laser to capture structural evolution of water clusters. Striking spectral change in the OH stretch region is observed from water tetramer to penta- and hexamer, due to appearance of three-dimensional hydrogen-bonding networks. The technique has the potential to obtain the infrared spectra of size-selected neutral clusters and to access their rich structural landscape.

While reduction reactions are ubiquitous in chemistry, it is very challenging to further reduce electron-rich compounds, especially the anionic ones. In this work, the reduction of 1,3-butadienyl dianion, the anionic conjugated olefin, has been realized by divalent rare-earth metal compounds (SmI2), resulting in the formation of novel 2-butene tetraanion bridged disamarium(III) complexes. Density functional theory (DFT) analyses reveal two features: (i) the single electron transfer (SET) from 4f atomic orbitals (AOs) of each Sm center to the antibonding π*-orbitals of 1,3-butadienyl dianion is feasible and the new HOMO formed by the bonding interaction between Sm 5d orbitals (AOs) and the π*-orbitals of 1,3-butadienyl dianion can accept favorably 2e- from 4f AOs of Sm(II); (ii) the 2-butene tetraanionic ligand serves as a unique 10e- donating system, in which 4e- act as two σ-donation bonding interactions while the rest 6e- as three π-donation bonding interactions. The disamarium(III) complexes represent a unique class of the bridged bis-alkylidene rare-earth organometallic complexes. The ligand-based reductive reactivity of 2-butene tetraanion bridged disamarium(III) complexes demonstrates that 2-butene tetraanionic ligand serves as a 3e- reductant toward cyclooctatetraene (COT) to provide doubly COT-supported disamarabutadiene complexes. The reaction of the disamarium(III) complexes with Cp*Li produces the doubly Cp*-coordinated Sm(III) complexes via salt metathesis. In addition, the reaction with Mo(CO)6 affords the oxycyclopentadienyl dinuclear complex via CO insertion.

Through reaction of beryllium dimers with carbon monoxide, a carbonyl complex BeBeCO is formed in solid neon. Upon visible light excitation, the BeBeCO complex rearranges to a BeCOBe isomer, which further isomerizes to a low-energy BeOBeC species under UV-visible light excitation. These species are identified on the basis of infrared absorption spectroscopy with isotopic substitutions and quantum chemical studies. The BeOBeC molecule is characterized to be a multiple radical species having an electronic quintet ground state featuring an unusual quartet carbyne unit with three unpaired electrons on the carbon center. Bonding analysis indicates that the strong Pauli repulsion between carbon 2s lone pair electrons and the σ electrons of the BeOBe fragment significantly weakens the Be-C bonding and destabilizes the triplet state of the BeOBeC radical with a doublet carbyne unit. The three-center π-bonding of BeOBe is also found to play a role in stabilizing the quartet carbyne.