Showing papers by "Lester Andrews published in 2021"

Cyanides and Isocyanides of Zinc, Cadmium and Mercury: Matrix Infrared Spectra and Electronic Structure Calculations for the Linear MNC, NCMCN, CNMNC, NCMMCN, and CNMMNC Molecules

Abstract: Cadmium atoms from laser ablation react with cyanogen, NC=CN, in excess argon during co-deposition at 4 K, and even more on UV irradiation of the cold samples. Final annealing to 35 K increases bands at 2187.3 and 2089.2 cm-1 at the expense of weaker bands at 2194.6 and 2092.2 cm-1 through addition of another cadmium atom. Reaction products were identified by comparison with B3LYP and CCSD(T) computed frequencies and energies, through frequency differences between Zn and Cd products, and by cyanogen isotopic substitution. The CN radical, ZnNC, and CdNC were observed on sample deposition. Hg arc ultraviolet (UV) irradiation activates the insertion of Cd and Zn to form the NCCdCN, CNCdNC, NCZnCN and CNZnNC molecules. Next annealing increased the dimetal products NCCdCdCN, CNCdCdNC, NCZnZnCN, and CNZnZnNC at the expense of their single metal analogs. Laser ablated mercury amalgam also produced NCHgCN, NCHg-HgCN, CNHgNC and CNHg-HgNC. The Group12 metals form both cyanide and isocyanide products, and the argon matrix also traps the higher energy but much more intensely absorbing isocyanides. In the isocyanide case bond polarity results in very intense infrared absorptions. Group 12 metals produce shorter M-M bonds in the dimetal cyanides NCM-MCN and isocyanides CNM-MNC than in the M-M itself, and their computed M-M bond lengths compare favorably with those measured for dimetal complexes stabilized by large ring containing molecular ligands.

Matrix Infrared Spectroscopic and Theoretical Investigations of M···NCCN, M···CNCN, M···C(N)CN, NCMCN, CNMNC, CNMCN, and [M···NCCN]+ Produced in the Reactions of Group 11 Metal Atoms with Cyanogen.

Abstract: Reactions of group 11 metals with cyanogen, N≡C–C≡N, in excess argon and neon have been carried out, and the products were identified via examination of the matrix spectra and their variation upon ...

Cyanides, Isocyanides, and Hydrides of Zn, Cd and Hg from Metal Atom and HCN Reactions: Matrix Infrared Spectra and Electronic Structure Calculations.

Abstract: Zinc and cadmium atoms from laser ablation of the metals and mercury atoms ablated from a dental amalgam target react with HCN in excess argon during deposition at 5 K to form the MCN and MNC molecules and CN radicals. UV irradiation decreases the higher energy ZnNC isomer in favor of the lower energy ZnCN product. Cadmium and mercury atoms produce analogous MCN primary molecules. Laser ablation of metals also produces plume radiation which initiates H-atom detachment from HCN. The freed H atom can add to CN radical to produce the HNC isomer. The argon matrix also traps the higher energy but more intensely absorbing isocyanide molecules. Further reactions with H atoms generate HMCN and HMNC hydrides, which can be observed by virtue of their C-N stretches and intense M-H stretches. Computational modeling of IR spectra and relative energies guides the identification of reaction products by providing generally reliable frequency differences within the Zn, Cd and Hg family of products, and estimating isotopic shifts using to 13 C and 15 N isotopic substitution for comparison with experimental data.

Matrix Infrared Spectroscopic Studies of B-NCCN, B-η2-(NC)-CN, NCBCN, CNBCN, CNBNC, and High-Order Products Produced in Reactions of Boron Atoms with Cyanogen.

Abstract: The products in reactions of laser-ablated boron atoms with cyanogen in excess argon have been identified via investigation of the matrix spectra and their variation on photolysis, annealing, and isotopic substitutions. DFT calculations have been performed for the plausible products and reaction paths, providing helpful guides. B-NCCN and B-η2-(NC)-CN were observed in the original deposition spectra, but they disappear on photolysis with λ > 220 nm while more stable NCBCN, CNBCN, and CNBNC were produced. Besides these primary products, high-order products [(NC)2B-NCCN, (CN)(NC)B-NCCN, (CN)2B-NCCN, and (NC)2B-B(CN)2] were also observed, which increased in the later stage of annealing. Our calculations show that initially produced B-NCCN is interconvertible to B-η2-(NC)-CN and the more stable boron cyanide and isocyanide, consistent with the observed results. The formation of high-order products demonstrates that boron highly prefers the trivalent state in reactions with cyanogen, similar to aluminum.

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.

Abstract: 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.