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While main group elements have four valence orbitals accessible for bonding, quadruple bonding to main group elements is extremely rare. Here we report that main group element boron is able to form quadruple bonding interactions with iron in the BFe(CO)3- anion complex, which has been revealed by quantum chemical investigation and identified by mass-selected infrared photodissociation spectroscopy in the gas phase. The complex is characterized to have a B-Fe(CO)3- structure of C3v symmetry and features a B-Fe bond distance that is much shorter than that expected for a triple bond. Various chemical bonding analyses indicate that the complex involves unprecedented B≣Fe quadruple bonding interactions. Besides the common one electron-sharing σ bond and two Fe→B dative π bonds, there is an additional weak B→Fe dative σ bonding interaction. This finding of the new quadruple bonding indicates that there might exist a wide range of boron-metal complexes that contain such high multiplicity of chemical bonds.

Infrared photodissociation spectroscopy has been used to investigate CrFe(CO)n− (n = 4–9) clusters in the gas phase. Comparison of the observed spectra in the carbonyl stretching frequency region with those predicted for low-lying isomers by DFT calculations showed that the observed CrFe(CO)n− (n = 4–8) clusters could be characterized to have Cr–Fe bonded (OC)4Fe–Cr(CO)n−4 structures. The coexistence of isomers with the (OC)Fe–Cr(CO)5 and (OC)3Fe–Cr(CO)4 structures was also observed for CrFe(CO)6− and CrFe(CO)7− anions, respectively. The CrFe(CO)n− (n = 4–8) complexes were strongly bonded systems. The CrFe(CO)8− complex was a coordination-saturated cluster, and the CrFe(CO)9− anion was characterized to contain a CrFe(CO)8− core tagged by one CO molecule. Bonding analysis revealed that the Cr–Fe bonds in the CrFe(CO)n− (n = 4–8) clusters were predominantly σ-type single bonds. The iron center in the Fe(CO)4 moiety and the chromium center in the Cr(CO)5 moiety fulfilled the 18-electron configuration for the CrFe(CO)n− (n = 4–6) clusters. As in the CrFe(CO)n− (n = 7, 8) complexes, the iron center in the Fe(CO)4 moiety exhibited a 17-electron configuration, while the chromium center in the Cr(CO)4 moiety exhibited a 16-electron configuration. These findings provide valuable insights into the structure and bonding mechanism of heterometallic carbonyl clusters. [ABSTRACT FROM AUTHOR]

Heteronuclear group 15 metal–iron carbonyl cluster complexes of AmFe(CO)n− (A = Sb, Bi; m, n = 2–3) were generated in the gas phase and studied by infrared photodissociation spectroscopy in the carbonyl stretching region. Their structures were determined by comparing the experimental spectra with predicted spectra derived from DFT calculations at the B3LYP and BP86 levels. All of the AmFe(CO)n− cluster anions were determined to have Fe(CO)n− fragments with all of the CO ligands terminally bonded to the iron center, and they can be regarded as being formed via the interactions of the neutral group 15 metal clusters with the Fe(CO)n− fragments. Bonding analyses indicated that each A2Fe(CO)n− (n = 2, 3) cluster anion contained two A–Fe single bonds and one A–A double bond. Each A3Fe(CO)n− (n = 2, 3) cluster anion involved three A–Fe single bonds and three A–A single bonds. There is an isolobal relationship between the Fe(CO)3− group and the group 15 atoms. The substitution of an Fe(CO)3− group in place of one A atom in the tetrahedral A4 molecule resulted in an A3Fe(CO)3− cluster anion with the closed-shell electronic configuration for all the group 15 metals and iron atoms. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The octacarbonyl cation and anion complexes of actinide metals [An(CO)8]+/− (An=Th, U) are prepared in the gas phase and are studied by mass‐selected infrared photodissociation spectroscopy. Both the octacarbonyl cations and anions have been characterized to be saturated coordinated complexes. Quantum chemical calculations by using density functional theory show that the [Th(CO)8]+ and [Th(CO)8]− complexes have a distorted octahedral (D4h) equilibrium geometry and a doublet electronic ground state. Both the [U(CO)8]+ cation and the [U(CO)8]− anion exhibit cubic structures (Oh) with a 6A1g ground state for the cation and a 4A1g ground state for the anion. The neutral species [Th(CO)8] (Oh; 1A1g) and [U(CO)8] (D4h; 5B1u) have also been calculated. Analysis of their electronic structures with the help on an energy decomposition method reveals that, along with the dominating 6d valence orbitals, there are significant 5f orbital participation in both the [An]←CO σ donation and [An]→CO π back donation interactions in the cations and anions, for which the electronic reference state of An has both occupied and vacant 5f AOs. The trend of the valence orbital contribution to the metal–CO bonds has the order of 6d≫5f>7s≈7p, with the 5f orbitals of uranium being more important than the 5f orbitals of thorium. [ABSTRACT FROM AUTHOR]

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 A≡Fe 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. [ABSTRACT FROM AUTHOR]

The alkali metal‐nickel carbonyl anions ENi(CO)3− with E=Li, Na, K, Rb, Cs have been produced and characterized by mass‐selected infrared photodissociation spectroscopy in the gas phase. The molecules are the first examples of 18‐electron transition metal complexes with alkali atoms as covalently bonded ligands. The calculated equilibrium structures possess C3v geometry, where the alkali atom is located above a nearly planar Ni(CO)3− fragment. The analysis of the electronic structure reveals a peculiar bonding situation where the alkali atom is covalently bonded not only to Ni but also to the carbon atoms. [ABSTRACT FROM AUTHOR]

The alkali metal‐nickel carbonyl anions ENi(CO)3− with E=Li, Na, K, Rb, Cs have been produced and characterized by mass‐selected infrared photodissociation spectroscopy in the gas phase. The molecules are the first examples of 18‐electron transition metal complexes with alkali atoms as covalently bonded ligands. The calculated equilibrium structures possess C3v geometry, where the alkali atom is located above a nearly planar Ni(CO)3− fragment. The analysis of the electronic structure reveals a peculiar bonding situation where the alkali atom is covalently bonded not only to Ni but also to the carbon atoms. 18‐electron transition‐metal complexes: ENi(CO)3− with E=Li, Na, K, Rb, Cs have been produced and characterized by mass‐selected infrared photodissociation spectroscopy in the gas phase. The calculated equilibrium structures possess C3v geometry and the analysis of the electronic structure reveals a peculiar bonding situation where the alkali atom is covalently bonded not only to Ni but also to the carbon atoms. [ABSTRACT FROM AUTHOR]

The alkali metal‐nickel carbonyl anions ENi(CO)3− with E=Li, Na, K, Rb, Cs have been produced and characterized by mass‐selected infrared photodissociation spectroscopy in the gas phase. The molecules are the first examples of 18‐electron transition metal complexes with alkali atoms as covalently bonded ligands. The calculated equilibrium structures possess C3v geometry, where the alkali atom is located above a nearly planar Ni(CO)3− fragment. The analysis of the electronic structure reveals a peculiar bonding situation where the alkali atom is covalently bonded not only to Ni but also to the carbon atoms. 18‐electron transition‐metal complexes: ENi(CO)3− with E=Li, Na, K, Rb, Cs have been produced and characterized by mass‐selected infrared photodissociation spectroscopy in the gas phase. The calculated equilibrium structures possess C3v geometry and the analysis of the electronic structure reveals a peculiar bonding situation where the alkali atom is covalently bonded not only to Ni but also to the carbon atoms. [ABSTRACT FROM AUTHOR]

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Heteronuclear transition-metal-main-group-element carbonyl complexes of AsFe(CO)3−, SbFe(CO)3−, and BiFe(CO)3− were produced by a laser vaporization supersonic ion source in the gas phase, and were studied by mass-selected IR photodissociation spectroscopy and advanced quantum chemistry methods. These complexes have C3v structures with all of the carbonyl ligands bonded on the iron center, and feature covalent triple bonds between bare Group 15 elements and Fe(CO)3−. Chemical bonding analyses on the whole series of AFe(CO)3− (A=N, P, As, Sb, Bi, Mc) complexes indicate that the valence orbitals involved in the triple bonds are hybridized 3d and 4p atomic orbitals of iron, leading to an unusual (dp-p) type of transition-metal-main-group-element multiple bonding. The σ-type three-orbital interaction between Fe 3d/4p and Group 15 np valence orbitals plays an important role in the bonding and stability of the heavier AFe(CO)3− (A=As, Sb, Bi) complexes. [ABSTRACT FROM AUTHOR]

Infrared photodissociation spectroscopy of mass-selected heteronuclear cluster anions in the form of OMFe(CO)5− (M=Sc, Y, La) indicates that all these anions involve an 18-electron [Fe(CO)4]2− building block that is bonded with the M center through two bridged carbonyl ligands. The OLaFe(CO)5− anion is determined to be a CO-tagged complex involving a [Fe(CO)4]2−[LaO]+ anion core. In contrast, the OYFe(CO)5− anion is characterized to have a [Fe(CO)4]2−[Y(η2-CO2)]+ structure involving a side-on bonded CO2 ligand. The CO-tagged complex and the [Fe(CO)4]2−[Sc(η2-CO2)]+ isomer co-exist for the OScFe(CO)5− anion. These observations indicate that both the ScO+ and YO+ cations supported on [Fe(CO)4]2− are able to oxidize CO to CO2. Theoretical analyses show that [Fe(CO)4]2− coordination significantly weakens the MO+ bond and decreases the energy gap of the interacting valence orbitals between MO+ and CO, leading to the CO oxidation reactions being both thermodynamically exothermic and kinetically facile. [ABSTRACT FROM AUTHOR]

Infrared photodissociation spectroscopy of mass-selected heteronuclear cluster anions in the form of OMFe(CO)5− (M=Sc, Y, La) indicates that all these anions involve an 18-electron [Fe(CO)4]2− building block that is bonded with the M center through two bridged carbonyl ligands. The OLaFe(CO)5− anion is determined to be a CO-tagged complex involving a [Fe(CO)4]2−[LaO]+ anion core. In contrast, the OYFe(CO)5− anion is characterized to have a [Fe(CO)4]2−[Y(η2-CO2)]+ structure involving a side-on bonded CO2 ligand. The CO-tagged complex and the [Fe(CO)4]2−[Sc(η2-CO2)]+ isomer co-exist for the OScFe(CO)5− anion. These observations indicate that both the ScO+ and YO+ cations supported on [Fe(CO)4]2− are able to oxidize CO to CO2. Theoretical analyses show that [Fe(CO)4]2− coordination significantly weakens the MO+ bond and decreases the energy gap of the interacting valence orbitals between MO+ and CO, leading to the CO oxidation reactions being both thermodynamically exothermic and kinetically facile. [ABSTRACT FROM AUTHOR]

Infrared photodissociation spectroscopy of mass-selected heteronuclear cluster anions in the form of OMFe(CO)5− (M=Sc, Y, La) indicates that all these anions involve an 18-electron [Fe(CO)4]2− building block that is bonded with the M center through two bridged carbonyl ligands. The OLaFe(CO)5− anion is determined to be a CO-tagged complex involving a [Fe(CO)4]2−[LaO]+ anion core. In contrast, the OYFe(CO)5− anion is characterized to have a [Fe(CO)4]2−[Y(η2-CO2)]+ structure involving a side-on bonded CO2 ligand. The CO-tagged complex and the [Fe(CO)4]2−[Sc(η2-CO2)]+ isomer co-exist for the OScFe(CO)5− anion. These observations indicate that both the ScO+ and YO+ cations supported on [Fe(CO)4]2− are able to oxidize CO to CO2. Theoretical analyses show that [Fe(CO)4]2− coordination significantly weakens the MO+ bond and decreases the energy gap of the interacting valence orbitals between MO+ and CO, leading to the CO oxidation reactions being both thermodynamically exothermic and kinetically facile. [ABSTRACT FROM AUTHOR]

Infrared photodissociation spectroscopy of mass-selected heteronuclear cluster anions in the form of OMFe(CO)5− (M=Sc, Y, La) indicates that all these anions involve an 18-electron [Fe(CO)4]2− building block that is bonded with the M center through two bridged carbonyl ligands. The OLaFe(CO)5− anion is determined to be a CO-tagged complex involving a [Fe(CO)4]2−[LaO]+ anion core. In contrast, the OYFe(CO)5− anion is characterized to have a [Fe(CO)4]2−[Y(η2-CO2)]+ structure involving a side-on bonded CO2 ligand. The CO-tagged complex and the [Fe(CO)4]2−[Sc(η2-CO2)]+ isomer co-exist for the OScFe(CO)5− anion. These observations indicate that both the ScO+ and YO+ cations supported on [Fe(CO)4]2− are able to oxidize CO to CO2. Theoretical analyses show that [Fe(CO)4]2− coordination significantly weakens the MO+ bond and decreases the energy gap of the interacting valence orbitals between MO+ and CO, leading to the CO oxidation reactions being both thermodynamically exothermic and kinetically facile. [ABSTRACT FROM AUTHOR]

We report the preparation of UFe(CO)3− and OUFe(CO)3− complexes using a laser-vaporization supersonic ion source in the gas phase. These compounds were mass-selected and characterized by infrared photodissociation spectroscopy and state-of-the-art quantum chemical studies. There are unprecedented triple bonds between U 6d/5f and Fe 3d orbitals, featuring one covalent σ bond and two Fe-to-U dative π bonds in both complexes. The uranium and iron elements are found to exist in unique formal U(I or III) and Fe(−II) oxidation states, respectively. These findings suggest that there may exist a whole family of stable df-d multiple-bonded f-element-transition-metal compounds that have not been fully recognized to date. [ABSTRACT FROM AUTHOR]