Low-Barrier Hydrogen Bonds in Negative Thermal Expansion Material H3[Co(CN)6]

The covalent nature of the low-barrier N−H−N hydrogen bonds in the negative thermal expansion material H₃[Co(CN)₆] has been established by using a combination of X-ray and neutron diffraction electron density analysis and theoretical calculations. This finding explains why negative thermal expansion can occur in a material not commonly considered to be built from rigid linkers. The pertinent hydrogen atom is located symmetrically between two nitrogen atoms in a double-well potential with hydrogen above the barrier for proton transfer, thus forming a low-barrier hydrogen bond. Hydrogen is covalently bonded to the two nitrogen atoms, which is the first experimentally confirmed covalent hydrogen bond in a network structure. Source function calculations established that the present N−H−N hydrogen bond follows the trends observed for negatively charge-assisted hydrogen bonds and low-barrier hydrogen bonds previously established for O−H−O hydrogen bonds. The bonding between the cobalt and cyanide ligands was found to be a typical donor–acceptor bond involving a high-field ligand and a transition metal in a low-spin configuration.     

B−B Bond Nucleophilicity in a Tetraaryl μ-Hydridodiborane(4) Anion

The tetraaryl μ-hydridodiborane(4) anion [ 2 H]⁻ possesses nucleophilic B−B and B−H bonds. Treatment of K[ 2 H] with the electrophilic 9-H-9-borafluorene (HBFlu) furnishes the B₃ cluster K[ 3 ], with a triangular boron core linked through two BHB two-electron, three-center bonds and one electron-precise B−B bond, reminiscent of the prominent [B₃H₈]⁻ anion. Upon heating or prolonged stirring at room temperature, K[ 3 ] rearranges to a slightly more stable isomer K[ 3 a ]. The reaction of M[ 2 H] (M⁺=Li⁺, K⁺) with MeI or Me₃SiCl leads to equimolar amounts of 9-R-9-borafluorene and HBFlu (R=Me or Me₃Si). Thus, [ 2 H]⁻ behaves as a masked [:BFlu]⁻ nucleophile. The HBFlu by-product was used in situ to establish a tandem substitution-hydroboration reaction: a 1:1 mixture of M[ 2 H] and allyl bromide gave the 1,3-propylene-linked ditopic 9-borafluorene 5 as sole product. M[ 2 H] also participates in unprecedented [4+1] cycloadditions with dienes to furnish dialkyl diaryl spiroborates, M[R₂BFlu].     

The Na⋅⋅⋅B Bond in NaBH3−: A Different Type of Bond

A newly introduced Na−B bond in NaBH₃⁻ has been a challenge for the chemical bonding community. Here, a series of MBH₃⁻ (M=Li, Na, K) species and NaB(CN)₃⁻ are studied within the context of quantum chemical topology approaches. The analyses suggest that M–B interaction cannot be classified as an ordinary covalent, dative, or even simple ionic interaction. The interactions are controlled by coulombic forces between the metals and the substituents on boron, for example, H or CN, more than the direct M–B interaction. On the other hand, while the characteristics of the (3, −1) critical points of the bonds are comparable to weak hydrogen bonds, not covalent bonds, the metal and boron share a substantial sum of electrons. To the best of the author's knowledge, the characteristics of these bonds are unprecedented among known molecules. Considering all paradoxical properties of these bonds, they are herein described as ionic-enforced covalent bonds.     

Proving and Probing the Presence of the Elusive C−H⋅⋅⋅O Hydrogen Bond in Liquid Solutions at Room Temperature

Hydrogen bonds (H bonds) play a major role in defining the structure and properties of many substances, as well as phenomena and processes. Traditional H bonds are ubiquitous in nature, yet the demonstration of weak H bonds that occur between a highly polarized C−H group and an electron-rich oxygen atom, has proven elusive. Detailed here are linear and nonlinear IR spectroscopy experiments that reveal the presence of H bonds between the chloroform C−H group and an amide carbonyl oxygen atom in solution at room temperature. Evidence is provided for an amide solvation shell featuring two clearly distinguishable chloroform arrangements that undergo chemical exchange with a time scale of about 2 ps. Furthermore, the enthalpy of breaking the hydrogen bond is found to be 6–20 kJ mol⁻¹. Ab-initio computations support the findings of two distinct solvation shells formed by three chloroform molecules, where one thermally undergoes hydrogen-bond making and breaking.     

Bismuth–Boron Multiple Bonding in BiB2O− and Bi2B−

Despite its electron deficiency, boron is versatile in forming multiple bonds. Transition‐metal–boron double bonding is known, but boron–metal triple bonds have been elusive. Two bismuth boron cluster anions, BiB₂O⁻ and Bi₂B⁻, containing triple and double B−Bi bonds are presented. The BiB₂O⁻ and Bi₂B⁻ clusters are produced by laser vaporization of a mixed B/Bi target and characterized by photoelectron spectroscopy and ab initio calculations. Well‐resolved photoelectron spectra are obtained and interpreted with the help of ab initio calculations, which show that both species are linear. Chemical bonding analyses reveal that Bi forms triple and double bonds with boron in BiB₂O⁻ ([Bi≡B−B≡O]⁻) and Bi₂B⁻ ([Bi=B=Bi]⁻), respectively. The Bi−B double and triple bond strengths are calculated to be 3.21 and 4.70 eV, respectively. This is the first experimental observation of Bi−B double and triple bonds, opening the door to design main‐group metal–boron complexes with multiple bonding.     

Understanding Regium Bonds and their Competition with Hydrogen Bonds in Au2:HX Complexes

A theoretical study of the regium and hydrogen bonds (RB and HB, respectively) in Au₂:HX complexes has been carried out by means of CCSD(T) calculations. The theoretical study shows as overall outcome that in all cases the complexes exhibiting RB are more stable that those with HB. The binding energies for RB complexes range between −24 and −180 kJ ⋅ mol^−1, whereas those of the HB complexes are between −6 and −19 kJ ⋅ mol⁻¹. DFT-SAPT also indicated that HB complexes are governed by electrostatics, but RB complexes present larger contribution of the induction term to the total attractive forces. ¹⁹⁷Au chemical shifts have been calculated using the relativistic ZORA Hamiltonian.     

Quantitative Assessment of B−B−B,B−Hb−B,and B−Ht Bonds: From BH3 to B12H122−

We report the thermodynamic stabilities and the intrinsic strengths of three-center-two-electron B−B−B and B−H_b−B bonds ( : bridging hydrogen), and two-center-two-electron B−H_t bonds ( : terminal hydrogen) which can be served as a new, effective tool to determine the decisive role of the intermediates of hydrogenation/dehydrogenation reactions of borohydride. The calculated heats of formation were obtained with the G4 composite method and the intrinsic strengths of B−B−B, B−H_b−B, and B−H_t bonds were derived from local stretching force constants obtained at the B3LYP-D2/cc-pVTZ level of theory for 21 boron-hydrogen compounds, including 19 intermediates. The Quantum Theory of Atoms in Molecules (QTAIM) was used to deepen the inside into the nature of B−B−B, B−H_b−B, and B−H_t bonds. We found that all of the experimentally identified intermediates hindering the reversibility of the decomposition reactions are thermodynamically stable and possess strong B−B−B, B−H_b−B, and B−H_t bonds. This proves that thermodynamic data and intrinsic B−B−B, B−H_b−B, and B−H_t bond strengths form a new, effective tool to characterize new (potential) intermediates and to predict their role for the reversibility of the hydrogenation/dehydrogenation reactions.     

Not Carbon s–p Hybridization,but Coordination Number Determines C−H and C−C Bond Length

A fundamental and ubiquitous phenomenon in chemistry is the contraction of both C−H and C−C bonds as the carbon atoms involved vary, in s–p hybridization, along sp³ to sp² to sp. Our quantum chemical bonding analyses based on Kohn–Sham molecular orbital theory show that the generally accepted rationale behind this trend is incorrect. Inspection of the molecular orbitals and their corresponding orbital overlaps reveals that the above-mentioned shortening in C−H and C−C bonds is not determined by an increasing amount of s-character at the carbon atom in these bonds. Instead, we establish that this structural trend is caused by a diminishing steric (Pauli) repulsion between substituents around the pertinent carbon atom, as the coordination number decreases along sp³ to sp² to sp.     

Density Functional Theory Study of Hydrogen Bonding Dimers with 4-Pyridinecarboxylic Acid Hydrazine

The H‐bonding dimers of 4‐pyridinecarboxylic acid hydrazine were studied using density functional theory (DFT) at B3LYP/6‐311++G** level. The results showed that the most stable dimer D1 had two same linear N H···O hydrogen bonds, and the interaction energy between them was 51.038 kJ·mol⁻¹ which was corrected by the basis set superposition error and zero‐point. The stretching vibration frequency of N H bond had a red shift because of the hydrogen bonds. The natural bond orbital analysis showed that each N H···O hydrogen bond in D1 had the biggest interaction stabilization energy of 69.078 kJ·mol⁻¹. Thermodynamic analysis indicated that the formation process of D1 was exothermic and spontaneous at low and room temperatures.     

Iodine Clathrated: A Solid-State Analogue of the Iodine–Starch Complex

Co-crystallizing iodine with a simple dicationic salt (1,8-diammoniumoctane chloride) results in the clathration of the iodine (I₂) molecules inside trigonal and hexagonal helical channels of the crystal lattice with 72 wt % overall I₂ loading. The I₂ inside the bigger trigonal channel forms a I−I⋅⋅⋅I−I⋅⋅⋅I−I halogen-bonded infinite helical chain, while the I₂ in the smaller hexagonal channel is disordered. In both channels the I₂ interaction with the channel wall happens through I−I⋅⋅⋅Cl⁻ halogen bonds. The helical channels in the crystal lattice are constructed via the strong charge-assisted H₂N⁺H⋅⋅⋅Cl⁻ hydrogen bonds between the dications and the chloride anions. The structure shows a marked similarity with the well-known starch–I₂ system, and thus may provide insight for the yet unresolved structure of the I₂ in the helical starch channel.     

Observation of Transition-Metal–Boron Triple Bonds in IrB2O− and ReB2O−

Multiple bonds between boron and transition metals are known in many borylene (:BR) complexes via metal d_π→BR back-donation, despite the electron deficiency of boron. An electron-precise metal–boron triple bond was first observed in BiB₂O⁻ [Bi≡B−B≡O]⁻ in which both boron atoms can be viewed as sp-hybridized and the [B−BO]⁻ fragment is isoelectronic to a carbyne (CR). To search for the first electron-precise transition-metal-boron triple-bond species, we have produced IrB₂O⁻ and ReB₂O⁻ and investigated them by photoelectron spectroscopy and quantum-chemical calculations. The results allow to elucidate the structures and bonding in the two clusters. We find IrB₂O⁻ has a closed-shell bent structure (C_s, ¹A′) with BO⁻ coordinated to an Ir≡B unit, (⁻OB)Ir≡B, whereas ReB₂O⁻ is linear (C_∞v, ³Σ⁻) with an electron-precise Re≡B triple bond, [Re≡B−B≡O]⁻. The results suggest the intriguing possibility of synthesizing compounds with electron-precise M≡B triple bonds analogous to classical carbyne systems.     

Hydrogen bonding in two ammonium salts of 5‐sulfosalicylic acid: ammonium 3‐carboxy‐4‐hydroxybenzenesulfonate monohydrate and triammonium 3‐carboxy‐4‐hydroxybenzenesulfonate 3‐carboxylato‐4‐hydroxybenzenesulfonate

The structures of two ammonium salts of 3‐carboxy‐4‐hydroxybenzenesulfonic acid (5‐sulfosalicylic acid, 5‐SSA) have been determined at 200 K. In the 1:1 hydrated salt, ammonium 3‐carboxy‐4‐hydroxybenzenesulfonate monohydrate, NH₄⁺·C₇H₅O₆S⁻·H₂O, (I), the 5‐SSA⁻ monoanions give two types of head‐to‐tail laterally linked cyclic hydrogen‐bonding associations, both with graph‐set R₄⁴(20). The first involves both carboxylic acid O—H...O_water and water O—H...O_sulfonate hydrogen bonds at one end, and ammonium N—H...O_sulfonate and N—H...O_carboxy hydrogen bonds at the other. The second association is centrosymmetric, with end linkages through water O—H...O_sulfonate hydrogen bonds. These conjoined units form stacks down c and are extended into a three‐dimensional framework structure through N—H...O and water O—H...O hydrogen bonds to sulfonate O‐atom acceptors. Anhydrous triammonium 3‐carboxy‐4‐hydroxybenzenesulfonate 3‐carboxylato‐4‐hydroxybenzenesulfonate, 3NH₄⁺·C₇H₄O₆S²⁻·C₇H₅O₆S⁻, (II), is unusual, having both dianionic 5‐SSA²⁻ and monoanionic 5‐SSA⁻ species. These are linked by a carboxylic acid O—H...O hydrogen bond and, together with the three ammonium cations (two on general sites and the third comprising two independent half‐cations lying on crystallographic twofold rotation axes), give a pseudo‐centrosymmetric asymmetric unit. Cation–anion hydrogen bonding within this layered unit involves a cyclic R₃³(8) association which, together with extensive peripheral N—H...O hydrogen bonding involving both sulfonate and carboxy/carboxylate acceptors, gives a three‐dimensional framework structure. This work further demonstrates the utility of the 5‐SSA⁻ monoanion for the generation of stable hydrogen‐bonded crystalline materials, and provides the structure of a dianionic 5‐SSA²⁻ species of which there are only a few examples in the crystallographic literature.     

Spectroscopic and Crystallographic Characterization of the R3N+−C−H⋅⋅⋅X Interaction

As appreciation for nonclassical hydrogen bonds has progressively increased, so have efforts to characterize these interesting interactions. Whereas several kinds of C−H hydrogen bonds have been well-studied, much less is known about the R₃N⁺−C−H⋅⋅⋅X variety. Herein, we present crystallographic and spectroscopic evidence for the existence of these interactions, with special relevance to Selectfluor chemistry. Of particular note is the propensity for Lewis bases to engage in nonclassical hydrogen bonding over halogen bonding with the electrophilic F atom of Selectfluor. Further, the first examples of ¹H NMR experiments detailing R₃N⁺−C−H⋅⋅⋅X (X=O, N) hydrogen bonds are described.     

Supramolecular interactions in salts/cocrystals involving pyrimidine derivatives of sulfonate/carboxylic acid

The crystal structures of three compounds involving aminopyrimidine derivatives are reported, namely, 5-fluorocytosinium sulfanilate–5-fluorocytosine–4-azaniumylbenzene-1-sulfonate (1/1/1), C₄H₅FN₃O⁺·C₆H₆NO₃S⁻·C₄H₄FN₃O·C₆H₇NO₃S, I , 5-fluorocytosine–indole-3-propionic acid (1/1), C₄H₄FN₃O·C₁₁H₁₁NO₂, II , and 2,4,6-triaminopyrimidinium 3-nitrobenzoate, C₄H₈N₅⁺·C₇H₄NO₄⁻, III , which have been synthesized and characterized by single-crystal X-ray diffraction. In I , there are two 5-fluorocytosine (5FC) molecules (5FC-A and 5FC-B) in the asymmetric unit, with one of the protons disordered between them. 5FC-A and 5FC-B are linked by triple hydrogen bonds, generating two fused rings [two R₂²(8) ring motifs]. The 5FC-A molecules form a self-complementary base pair [R₂²(8) ring motif] via a pair of N—H…O hydrogen bonds and the 5FC-B molecules form a similar complementary base pair [R₂²(8) ring motif]. The combination of these two types of pairing generates a supramolecular ribbon. The 5FC molecules are further hydrogen bonded to the sulfanilate anions and sulfanilic acid molecules via N—H…O hydrogen bonds, generating R₄⁴(22) and R⁶₆(36) ring motifs. In cocrystal II , two types of base pairs (homosynthons) are observed via a pair of N—H…O/N—H…N hydrogen bonds, generating R₂²(8) ring motifs. The first type of base pair is formed by the interaction of an N—H group and the carbonyl O atom of 5FC molecules through a couple of N—H…O hydrogen bonds. Another type of base pair is formed via the amino group and a pyrimidine ring N atom of the 5FC molecules through a pair of N—H…N hydrogen bonds. The base pairs (via N—H…N hydrogen bonds) are further bridged by the carboxyl OH group of indole-3-propionic acid and the O atom of 5FC through O—H…O hydrogen bonds on either side of the R₂²(8) motif. This leads to a DDAA array. In salt III , one of the N atoms of the pyrimidine ring is protonated and interacts with the carboxylate group of the anion through N—H…O hydrogen bonds, leading to the primary ring motif R₂²(8). Furthermore, the 2,4,6-triaminopyrimidinium (TAP) cations form base pairs [R₂²(8) homosynthon] via N—H…N hydrogen bonds. A carboxylate O atom of the 3-nitrobenzoate anion bridges two of the amino groups on either side of the paired TAP cations to form another ring [R₃²(8)]. This leads to the generation of a quadruple DADA array. The crystal structures are further stabilized by π–π stacking ( I and III ), C—H…π ( I and II ), C—F…π ( I ) and C—O…π ( II ) interactions.     

Experimental and Theoretical Evidence of Spin-Orbit Heavy Atom on the Light Atom 1H NMR Chemical Shifts Induced through H⋅⋅⋅I− Hydrogen Bond

Spin-orbit (SO) heavy-atom on the light-atom (SO-HALA) effect is the largest relativistic effect caused by a heavy atom on its light-atom neighbors, leading, for example, to unexpected NMR chemical shifts of ¹H, ¹³C, and ¹⁵N nuclei. In this study, a combined experimental and theoretical evidence for the SO-HALA effect transmitted through hydrogen bond is presented. Solid-state NMR data for a series of 4-dimethylaminopyridine salts containing I⁻, Br⁻ and Cl⁻ counter ions were obtained experimentally and by theoretical calculations. A comparison of the experimental chemical shifts with those calculated by a standard DFT methodology without the SO contribution to the chemical shifts revealed a remarkable error of the calculated proton chemical shift of a hydrogen atom that is in close contact with the iodide anion. The addition of the relativistic SO correction in the calculations significantly improves overall agreement with the experiment and confirms the propagation of the SO-HALA effect through hydrogen bonds.     

Structural and computational analysis of intermolecular interactions in a new 2‐thiouracil polymorph

The crystallization and characterization of a new polymorph of 2‐thiouracil by single‐crystal X‐ray diffraction, Hirshfeld surface analysis and periodic density functional theory (DFT) calculations are described. The previously published polymorph (A ) crystallizes in the triclinic space group P , while that described herein (B ) crystallizes in the monoclinic space group P 2₁/c . Periodic DFT calculations showed that the energies of polymorphs A and B , compared to the gas‐phase geometry, were −108.8 and −29.4 kJ mol⁻¹, respectively. The two polymorphs have different intermolecular contacts that were analyzed and are discussed in detail. Significant differences in the molecular structure were found only in the bond lengths and angles involving heteroatoms that are involved in hydrogen bonds. Decomposition of the Hirshfeld fingerprint plots revealed that O…H and S…H contacts cover over 50% of the noncovalent contacts in both of the polymorphs; however, they are quite different in strength. Hydrogen bonds of the N—H…O and N—H…S types were found in polymorph A , whereas in polymorph B , only those of the N—H…O type are present, resulting in a different packing in the unit cell. QTAIM (quantum theory of atoms in molecules) computational analysis showed that the interaction energies for these weak‐to‐medium strength hydrogen bonds with a noncovalent or mixed interaction character were estimated to fall within the ranges 5.4–10.2 and 4.9–9.2 kJ mol⁻¹ for polymorphs A and B , respectively. Also, the NCI (noncovalent interaction) plots revealed weak stacking interactions. The interaction energies for these interactions were in the ranges 3.5–4.1 and 3.1–5.5 kJ mol⁻¹ for polymorphs A and B , respectively, as shown by QTAIM analysis.     

Rational Modification of the Hierarchy of Intermolecular Interactions in Molecular Crystal Structures by Using Tunable Halogen Bonds

A family of 16 isomolecular salts (3‐XpyH)₂[MX′₄] (3‐XpyH=3‐halopyridinium; M=Co, Zn; X=(F), Cl, Br, (I); X′=Cl, Br, I) each containing rigid organic cations and tetrahedral halometallate anions has been prepared and characterized by X‐ray single crystal and/or powder diffraction. Their crystal structures reflect the competition and cooperation between non‐covalent interactions: N? H???X′? M hydrogen bonds, C? X???X′? M halogen bonds and π–π stacking. The latter are essentially unchanged in strength across the series, but both halogen bonds and hydrogen bonds are modified in strength upon changing the halogens involved. Changing the organic halogen (X) from F to I strengthens the C? X???X′? M halogen bonds, whereas an analogous change of the inorganic halogen (X′) weakens both halogen bonds and N? H???X′? M hydrogen bonds. By so tuning the strength of the putative halogen bonds from repulsive to weak to moderately strong attractive interactions, the hierarchy of the interactions has been modified rationally leading to systematic changes in crystal packing. Three classes of crystal structure are obtained. In type A (C? F???X′? M) halogen bonds are absent. The structure is directed by N? H???X′? M hydrogen bonds and π‐stacking interactions. In type B structures, involving small organic halogens (X) and large inorganic halogens (X′), long (weak) C? X???X′? M interactions are observed with type I halogen–halogen interaction geometries (C? X???X′ ≈ X???X′? M ≈155°), but hydrogen bonds still dominate. Thus, minor but quite significant perturbations from the type A structure arise. In type C, involving larger organic halogens (X) and smaller inorganic halogens (X′), stronger halogen bonds are formed with a type II halogen–halogen interaction geometry (C? X???X′ ≈180°; X???X′? M ≈110°) that is electrostatically attractive. The halogen bonds play a major role alongside hydrogen bonds in directing the type C structures, which as a result are quite different from type A and B.     

Group 6 Hexacarbonyls as Ligands for the Silver Cation: Syntheses,Characterization, and Analysis of the Bonding Compared with the Isoelectronic Group 5 Hexacarbonylates

The syntheses of the two novel complexes [Ag{Mo/W(CO)₆}₂]⁺[F-{Al(OR^F)₃}₂]⁻ (R^F=C(CF₃)₃) are reported along with their structural and spectroscopic characterization. The X-ray structure shows that three carbonyl ligands from each M(CO)₆ fragment bend towards the silver atom within binding Ag−C distance range. DFT calculations of the free cations [Ag{M(CO)₆}₂]⁺ (M=Cr, Mo, W) in the electronic singlet state give equilibrium structures with C₂ symmetry with two bridging carbonyl groups from each hexacarbonyl ligand. Similar structures with C₂ symmetry (M=Nb) and D₂ symmetry (M=V, Ta) are calculated for the isoelectronic group 5 anions [Ag{M(CO)₆}₂]⁻ (M=V, Nb, Ta). The electronic structure of the cations is analyzed with the QTAIM and EDA-NOCV methods, which provide detailed information about the nature of the chemical bonds between Ag⁺ and the {M(CO)₆}₂^q (q = −2, M = V, Nb, Ta; q = 0, M = Cr, Mo, W) ligands.     

Cooperativity in a cycloalkane-1,2/1,3-polyol corona: Topological hydrogen bonding in 1,2-diol motifs

A corona, consisting of 18 carbon atoms bearing 12 hydroxy groups in a continuous hydrogen-bonded chain, is built up by alternating degenerate conformations of alternating alkane-1,2-diol and 1,3-diol motifs. Geometries, proton nuclear magnetic resonance shifts and interaction energies for the dodecahydroxycyclo-octadecane and selected fragments are determined by density functional calculations at the B3LYP/6-311+G(d,p) level. Cooperative effects of O–H⋯O–H bonding are evident from the simple juxtaposition of these two motifs with a common OH group in butane-1,2,4-triol conformers. Bracketing a 1,2-diol motif with two 1,3-diol motifs in hexane-1,3,4,6-tetrol leads to a structure in which the 1,2-diol motif displays a bond critical point for hydrogen bonding. This is associated with enhancement of the shift of the hydrogen-bonded OH proton and of the corresponding H⋯O interaction energy. The full corona has a complete outer ring of O–H⋯O–H bond paths, and an inner ring of bond paths, due to C–H⋯H–C hydrogen–hydrogen bonding, which result in a central ring critical point. The topological O–H⋯O–H hydrogen bond, never seen in simple alkane-1,2-diols, is associated with cooperative enhancement of the H⋯O interaction energy, but this is not a necessary condition for a bond path: values for topological C–H⋯H–C hydrogen–hydrogen bonds can be as low as −0.4 kcal mol⁻¹.     

Elucidating the Mechanism of Simultaneous Activation of CH4 and CO2 Mediated by Single Group 10 Metal Anions in Gas Phase

Quantum chemistry calculations predict that besides the reported single metal anion Pt⁻, Ni⁻ can also mediate the co-conversion of CO₂ and CH₄ to form [CH₃−M(CO₂)−H]^– complex, followed by transformation to C−C coupling product [H₃CCOO−M−H]⁻ ( A ), hydrogenation products [H₃C−M−OCOH]⁻ ( B ) and [H₃C−M−COOH]⁻. For Pd⁻, a fourth product channel leading to PdCO₂⁻…CH₄ becomes more competitive. For Ni⁻, the feed order must be CO₂ first, as the weaker donor-acceptor interaction between Ni⁻ and CH₄ increases the C−H activation barrier, which is reduced by [Ni−CO₂]⁻. For Ni⁻/Pt⁻, the highly exothermic products A and B are similarly stable with submerged barrier that favors B . The smaller barrier difference between A and B for Ni⁻ suggests the C−C coupling product is more competitive in the presence of Ni⁻ than Pt⁻. The charge redistribution from M⁻ is the driving force for product B channel. This study adds our understanding of single atomic anions to activate CH₄ and CO₂ simultaneously.