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Homoleptic dinuclear beryllium carbonyl cation complexes have been produced and characterized in the gas phase. Infrared photodissociation spectroscopic and theoretical results confirm that Be2 (CO)5 + is a coordination saturated complex that can be assigned to a mixture of two almost isoenergetic structural isomers. Besides a beryllium-beryllium single-bonded (OC)2 Be-Be(CO)3 + isomer, another structure involving an unusual end-on and side-on bridging carbonyl ligand with very low carbonyl stretching frequency is identified.

Homoleptic Group 4 metal carbonyl cation and neutral complexes were prepared in the gas phase and/or in solid neon matrix. Infrared spectroscopy studies reveal that both zirconium and hafnium form eight‐coordinate carbonyl neutral and cation complexes. In contrast, titanium forms only the six‐coordinate Ti(CO)6 + and seven‐coordinate Ti(CO)7. Titanium octacarbonyl Ti(CO)8 is unstable as a result of steric repulsion between the CO ligands. The 20‐electron Zr(CO)8 and Hf(CO)8 complexes represent the first experimentally observed homoleptic octacarbonyl neutral complexes of transition metals. The molecules still fulfill the 18‐electron rule, because one doubly occupied valence orbital does not mix with any of the metal valence atomic orbitals. Zr(CO)8 and Hf(CO)8 are stable against the loss of one CO because the CO ligands encounter less steric repulsion than Zr(CO)7 and Hf(CO)7. The heptacarbonyl complexes have shorter metal−CO bonds than that of the octacarbonyl complexes due to stronger electrostatic and covalent bonding, but the significantly smaller repulsive Pauli term makes the octacarbonyl complexes stable., Bonding discoveries: The coordinatively saturated mononuclear carbonyl complexes of Group 4 elements, TM(CO)8 (TM=Zr, Hf) and Ti(CO)7, were prepared in the gas phase and/or in solid neon matrix. The analysis of the bonding situation shows that the formal 20‐electron complexes observe the 18‐electron rule and that Ti(CO)8 is unstable for the loss of one CO because of steric repulsion.

The carbon chain cations HnC4O+ (n = 1, 2) were generated via pulsed laser vaporisation of a graphite target in supersonic expansions of helium seeded with carbon monoxide and acetylene. The infrared spectra were measured via mass-selected infrared photodissociation spectroscopy of their CO-tagged complexes [HnC4O·CO]+ (n = 1, 2). Their geometric and electronic structures were determined by gas-phase infrared photodissociation spectra combined with theoretical calculations. The results show that the HnC4O+ (n = 1, 2) core cations are linear carbon chain derivatives which are terminated with hydrogen/dihydrogen and oxygen atoms. The HC4O+ cation has 3Σ− electronic ground state with cumulene-like carbon chain structure, while H2C4O+ cation has 2B1 electronic ground state with polyyne-like carbon chain structure. The CH and CH2 terminal groups have different influence on the type of carbon-carbon bonds in the carbon chain derivatives, due to the sp and sp2 hybridisation property. The carbon chain cations HnC4O+ (n = 1, 2) are studied by gas-phase infrared photodissociation spectra of CO-tagged complexes [HnC4O·CO]+ (n = 1, 2) combined with theoretical calculations. Studies show that the structures of the HnC4O+ (n = 1, 2) core cations are linear carbon chain derivatives which are terminated with hydrogen/dihydrogen and oxygen atoms. The spectrum of [HC4O·CO]+ shows two bands above 3000 cm−1, suggesting possible isomers.

Two structural isomers containing five second‐row element atoms with 24 valence electrons were generated and identified by matrix‐isolation IR spectroscopy and quantum chemical calculations. The OCBNO complex, which is produced by the reaction of boron atoms with mixtures of carbon monoxide and nitric oxide in solid neon, rearranges to the more stable OBNCO isomer on UV excitation. Bonding analysis indicates that the OCBNO complex is best described by the bonding interactions between a triplet‐state boron cation with an electron configuration of (2s)0(2pσ)0(2pπ)2 and the CO/NO− ligands in the triplet state forming two degenerate electron‐sharing π bonds and two ligand‐to‐boron dative σ bonds., Two of five: Two isomers of five‐atom BCNO2 were synthesized and identified by matrix‐isolation IR spectroscopy and quantum chemical calculations. OCBNO, which is produced by the reaction of boron atoms with CO/NO in solid neon, rearranges to the more stable OBNCO isomer on UV excitation. Bonding analysis indicates that OCBNO is best described by the bonding interactions of triplet‐state B+ and the CO/NO− ligands in the triplet state forming two degenerate electron‐sharing π bonds and two ligand‐to‐boron dative σ bonds.

Carbonyls in the s block Conventional wisdom in chemistry distinguishes transition metals from other elements by their use of d orbitals in bonding. Wu et al. now report that alkaline earth metals can slide their electrons from s- to d-orbital bonding motifs as well (see the Perspective by Armentrout). Calcium, strontium, and barium all form coordination complexes with a cubic arrangement of eight carbonyl ligands and an 18-electron valence shell. The compounds were characterized in frozen neon matrices by vibrational spectroscopy and in gas phase by mass spectrometry. Science , this issue p. 912 ; see also p. 849

The boron carbonyl cluster cations in the form of B3(CO)n+ (n = 4–6) are produced and studied by infrared photodissociation spectroscopy in the carbonyl stretching frequency region in the gas phase. Their geometric structures are determined with the aid of density functional theory calculations. The B3(CO)4+ cation is characterized to have a D2d (OC)2B═B═B(CO)2 structure and 1A1 electronic ground state with a linear boron skeleton. The B3(CO)5+ cation is determined to have a chain boron framework with C2v symmetry. The B3(CO)6+ cation is a weakly bound CO-tagged complex involving a B3(CO)5+ ion core. Bonding analysis reveals that B3(CO)4+ has a chemical bonding pattern similar to allene, while bonding in B3(CO)5+ is similar to that in allyl anion.

Recent studies on boron carbonyl complexes show their intriguing structural and bonding properties, enriching our knowledge on main group coordination chemistry. The isolobal relationships between BCO and CH and the more generally applicable CO/H- and B-/C analogies are employed to understand the structure and bonding of boron carbonyl complexes, bridging the boron carbonyl chemistry to the well-known hydrocarbon analogues.

The cation complexes [ArB3O4]+, [ArB3O5]+, [ArB4O6]+ and [ArB5O7]+ were prepared via a laser vaporization supersonic ion source in the gas phase. Their vibrational spectra were measured via mass-selected infrared photodissociation spectroscopy. Spectroscopy combined with quantum chemical calculations revealed that the [ArB3O5]+, [ArB4O6]+ and [ArB5O7]+ cation complexes have planar structures each involving an aromatic boroxol ring and an argon–boron covalent bond. In contrast, the [ArB3O4]+ cation is characterized to be a weakly bound complex with a B3O4+ chain structure.

The boron carbonyl cation complexes B(CO)3+, B(CO)4+ and B2(CO)4+ are studied by infrared photodissociation spectroscopy and theoretical calculations. The B(CO)4+ ions are characterized to be very weakly bound complexes involving a B(CO)3+ core ion, which is predicted to have a planar D3h structure with the central boron retaining the most favorable 8-electron configuration. The B2(CO)4+ cation is determined to have a planar D2h structure involving a B−B one and half bond. The analysis of the B-CO interactions with the EDA-NOCV method indicates that the OC→B σ donation is stronger than the B→CO π back donation in both ions.

The carbon chain cations, HC2n+1O+ (n = 2-5), are produced via pulsed laser vaporization of a graphite target in supersonic expansions containing carbon monoxide and hydrogen. The infrared spectra are measured via mass-selected infrared photodissociation spectroscopy of the CO "tagged" [HC2n+1O·CO]+ cation complexes in the 1600-3500 cm-1 region. The geometries and electronic ground states of these cation complexes are determined by their infrared spectra compared to the predications of theoretical calculations. All of the HC2n+1O+ (n = 2-5) core cations are characterized to be linear carbon chain derivatives terminated by hydrogen and oxygen, which have the closed-shell singlet ground states with polyyne-like carbon chain structures.

The carbon suboxide cation C3O2+ and the protonated carbon suboxide HC3O2+/DC3O2+ were produced in the gas phase. The vibrational spectra were measured via infrared photodissociation spectroscopy of their argon- or CO-tagged complexes. Spectroscopic evidence combined with state-of-the-art quantum chemical calculations indicate that both cations have a bent C2v symmetry and can be designated as dicarbonyls of a carbon cation and methylidyne cation, respectively.