Infrared Spectra of the η2-M(NC)-CH3, CH3-MNC, and CH2═M(H)NC Complexes Prepared by Reactions of Thorium and Uranium Atoms with Acetonitrile

Beryllium Dimer Reactions with Acetonitrile: Formation of Strong Be-Be Bonds

Laser ablated Be atoms have been reacted with acetonitrile molecules in 4 K solid neon matrix. The diberyllium products BeBeNCCH3 and CNBeBeCH3 have been identified by D and 13C isotopic substitutions and quantum chemical calculations. The stabilization of the diberyllium species is rationalized from the formation of the real Be-Be single bonds with bond distances as 2.077 and 2.058 Å and binding energies as -27.1 and -77.2 kcal/mol calculated at CCSD (T)/aug-cc-pVTZ level of theory for BeBeNCCH3 and CNBeBeCH3, respectively. EDA-NOCV analysis described the interaction between Be2 and NC···CH3 fragments as Lewis "acid-base" interactions. In the complexes, the Be2 moiety carries positive charges which transfer from antibonding orbital of Be2 to the bonding fragments significantly strengthen the Be-Be bonds that are corroborated by AIM, LOL and NBO analyses. In addition, mono beryllium products BeNCCH3, CNBeCH3, HBeCH2CN and HBeNCCH2 have also been observed in our experiments.

M←NCCH3, M-η2-(NC)-CH3, and CN-M-CH3 Prepared by Reactions of Ce, Sm, Eu, and Lu Atoms with Acetonitrile: Matrix Infrared Spectra and Theoretical Calculations

The reactions of laser-ablated Ce, Sm, Eu, and Lu atoms with acetonitrile were studied by matrix infrared spectra in a neon matrix, and M←NCCH₃, M-η²-(NC)-CH₃, and CN-M-CH₃ were identified with isotopic substitution and quantum chemical calculations. The major product is the insertion complex (CN-M-CH₃), while the end-on and side-on complexes (M←NCCH₃ and M-η²-(NC)-CH₃) are also trapped in the matrix. The CCN antisymmetric stretching mode for Ce-η²-(NC)-CH₃ was observed at 1536.9 cm^-1, which is much lower than the same modes observed for other lanthanides. NBO analysis reveals that Ce exhibits a remarkable 4f-orbital contribution in bonding to N and to C, reconfirming an active 4f-orbital contribution of cerium in bonding in the side-on complex, while the 4f contributions of Sm and Eu to the M-N and M-C bonds are much lower and the 4f orbital of Lu is not involved in bonding.

Infrared Spectra of CH3CN→M, M-η2-(NC)-CH3, CH3-MNC Prepared by Reactions of Laser-Ablated Fe, Ru, and Pt Atoms with Acetonitrile in Excess Argon

Reactions of laser-ablated Fe, Ru, and Pt atoms with acetonitrile have been carried out in excess argon, and the products identified in the matrix spectra. CH₃CN→Fe and Fe-η²-(NC)-CH₃ observed in the original deposition spectra converted to CH₃-FeNC on uv irradiation. CH₃CN→Ru, the only product detected in the Ru system, dissociated on uv irradiation, but was partly reproduced on subsequent visible irradiation and annealing. Similar behavior was found for CH₃CN→Pt. The major products (CH₃-FeNC, CH₃CN→Ru, and CH₃CN→Pt) are the most stable constituents in the previously proposed reaction path for Group 4, 5, 6, and 7 metal atoms and acetonitrile, parallel with the previous results. The Group 8 metal π-coordination products are weakly bound complexes due to limited back-donation to the π*-orbitals of CH₃CN. Calculations show that the Fe insertion product has a much less bent structure than the Ru analogue, in line with its higher s-character from the first row transition-metal to the C-Fe bond, and the group 8 metal methylidenes are not agostically distorted. The Pt to N bond in CH₃CN→Pt is the strongest of all the metals we have investigated owing in large part to its higher electron affinity, which prevents nitrogen lone pair density from entering the pi* orbitals of the C-N group.

Formation of Cerium and Neodymium Isocyanides in the Reactions of Cyanogen with Ce and Nd Atoms in Argon Matrices

Laser ablation of metallic Ce and Nd reacting with cyanogen in excess argon during codeposition at 4 K forms Ce(NC)_x and Nd(NC)_x for x = 1-3, which are identified from their matrix infrared spectra using cyanogen substituted with ¹³C and ¹⁵N. The electronic structure calculations were performed for isocyano and cyano Cd and Nd compounds for up to n = 4. The frequencies were calculated at the density functional theory level with three different functionals as well as correlated molecular orbital theory (MP2) and are consistent with the experimental assignments and the corresponding ¹²C/¹³C isotopic frequency ratios for the isocyano species. The computed frequencies for the analogous cyanide complexes are significantly higher than those for the isocyano isomers, and they are not observed in the spectra. The high spin isocyano complexes are the lowest energy structures. On the basis of the natural population analysis results, the bonding in ⁴CeNC and ⁶NdNC is essentially purely ionic with the Ce/Nd in the +I-oxidation state. The bonding for disocyano (³Ce(NC)₂ and ⁵Nd(NC)₂) and triisocyano (²Ce(NC)₃ and ⁴Nd(NC)₃) complexes is still quite ionic with the lanthanide in the +II and +III formal oxidation states, respectively. For ¹Ce(NC)₄, the oxidation state is best described as being between +III and +IV. Formation of ⁵Nd(NC)₄ does not really change the electron configuration on the Nd from that in ⁴Nd(NC)₃ and the oxidation state on the Nd remains at +III. Although Nd compounds with up to 3 NC^- groups have more ionic binding than do the corresponding Ce compounds, Ce(NC)₄ has more ionic binding than does Nd(NC)₄. The ionic nature of isocyano Ce and Nd complexes decreases as the number of isocyano groups increases. The energetics of formation of the isocyano Ce and Nd complexes using cyanogen or CN radicals are calculated to be mostly due to exothermic processes, with the exothermicity decreasing as the number of isocyano groups increases.

A cyano-bridged Cu(i)-based organic framework coupled with the C-C bond cleavage of acetonitrile for selective and sensitive sensing of Fe3+ ions

A cyano-bridged Cu(i) organic framework based on [Cu6(CN)6]n was synthesized, in which cyano anions were generated in situ from the C-C bond cleavage of acetonitrile. The as-synthesized compound displays orange-red luminescence and is further proven to be a promising Fe3+ luminescent sensor with high selectivity and sensitivity.

Uranium(III)-carbon multiple bonding supported by arene δ-bonding in mixed-valence hexauranium nanometre-scale rings

Despite the fact that non-aqueous uranium chemistry is over 60 years old, most polarised-covalent uranium-element multiple bonds involve formal uranium oxidation states IV, V, and VI. The paucity of uranium(III) congeners is because, in common with metal-ligand multiple bonding generally, such linkages involve strongly donating, charge-loaded ligands that bind best to electron-poor metals and inherently promote disproportionation of uranium(III). Here, we report the synthesis of hexauranium-methanediide nanometre-scale rings. Combined experimental and computational studies suggest overall the presence of formal uranium(III) and (IV) ions, though electron delocalisation in this Kramers system cannot be definitively ruled out, and the resulting polarised-covalent U = C bonds are supported by iodide and δ-bonded arene bridges. The arenes provide reservoirs that accommodate charge, thus avoiding inter-electronic repulsion that would destabilise these low oxidation state metal-ligand multiple bonds. Using arenes as electronic buffers could constitute a general synthetic strategy by which to stabilise otherwise inherently unstable metal-ligand linkages.

An ab initio study on coinage atom-inserted cyanide/isocyanide: XMCN/XMNC (M = coinage atoms; X = halogen)

The coinage atom-inserted cyanide/isocyanide compounds, XMCN and XMNC (X = halogens) formed by the insertion of a coinage atom into the X-C(N) bonds of XCN (or XNC), were investigated by ab initio methods. XMCN was predicted to be more stable than XMNC, which is different from the case of XUCN/XUNC reported previously. Based on the analyses on the ionization dissociation pathways, the M-C (or M-N) bond is more easily broken than the X-M bond. Moreover, the order of the M-C (or M-N) bond energy in XMCN (or XMNC) is XAuCN (XAuNC) > XCuCN (XCuNC) > XAgCN (XAgNC). The shift characters of v C-N in XMCN (or XMNC) with respect to the concerning precursor can be used to identified XMCN and XMNC experimentally. The results of charge decomposition analysis (CDA) and atoms-in-molecule (AIM) illustrate that the X-M and M-C(N) bond behaves as a coordination bond, while the C-N bond is a typical polar covalent bond. The higher thermodynamic stability of XMCN is the result of the -CN group having better coordination ability than the -NC group.

Theoretical Insights into Halogenated Uranium Cyanide/Isocyanide Compounds

Two kinds of halogenated uranium cyanide/isocyanide compounds, XUCN and XUNC (X = halogen) formed by the insertion of uranium atom into X-C(N) bonds of XCN (or XNC), were investigated by DFT and ab initio methods. Although XNC is less stable thermodynamically than XCN, XUNC is more stable than XUCN and is expected to be prepared and characterized in matrix isolation experiments. The C-N stretching vibration mode (ν_C-N) is the primary fingerprint for the identification of these isomers due to its red-shift character with respect to the relevant precursor. Atoms-in-molecule (AIM) analysis illustrates that both X-U and U-C(N) bonds in XUCN and XUNC show closed-shell interaction character, although partial covalent character contributes to them, and can be denoted as X^-U²⁺(CN)^- and X^-U²⁺(NC)^-, respectively. Charge decomposition analysis (CDA) further reveals that the isocyanide exhibits better donation performance than the cyanide, which should be the root cause of the difference between XUCN and XUNC.

Control of cerium oxidation state through metal complex secondary structures

A series of alkali metal cerium diphenylhydrazido complexes, M _x (py) _y [Ce(PhNNPh)₄], M = Li, Na, and K, x = 4 (Li and Na) or 5 (K), and y = 4 (Li), 8 (Na), or 7 (K), were synthesized to probe how a secondary coordination sphere would modulate electronic structures at a cerium cation. The resulting electronic structures of the heterobimetallic cerium diphenylhydrazido complexes were found to be strongly dependent on the identity of the alkali metal cations. When M = Li⁺ or Na⁺, the cerium(iii) starting material was oxidized with concomitant reduction of 1,2-diphenylhydrazine to aniline. Reduction of 1,2-diphenylhydrazine was not observed when M = K⁺, and the complex remained in the cerium(iii) oxidation state. Oxidation of the cerium(iii) diphenylhydrazido complex to the Ce(iv) diphenylhydrazido one was achieved through a simple cation exchange reaction of the alkali metals. UV-Vis spectroscopy, FTIR spectroscopy, electrochemistry, magnetic susceptibility, and DFT studies were used to probe the oxidation state and the electronic changes that occurred at the metal centre.

Reactions of laser-ablated U atoms with (CN)2: infrared spectra and electronic structure calculations of UNC, U(NC)2, and U(NC)4 in solid argon

Reactions of laser-ablated U atoms with (CN)₂ produce the isocyanides UNC, U(NC)₂, and U(NC)₄ and not the corresponding cyanides.

Advances in f-element cyanide chemistry

By using the cyanide ligand, actinide compounds with unprecedented structures, U^III–CN vs. Ce^III–NC and U^III–CN vs. U^IV–NC coordination modes, and novel high-valent uranium complexes were revealed.