Size-Dependent Polymorphism in Aluminum Carbide Cluster Anions Al_nC₂^–: Formation of Acetylide-Containing Structures

Abstract

Aluminum carbide cluster anions Al n C 2 − (n = 5−13) were observed as the most dominant products in the gas-phase reactions of laser-ablated Al n − with organic molecules, such as methanol, ethanol, pentane, acetonitrile, or acetone. Density functional theory calculations predicted two possible isomeric structures for Al n C 2 − : isomers in which two carbons are dissociated (type D) as in the case of the bulk aluminum carbide and novel isomers in which two carbons form an acetylide-like C 2 unit. The latter isomers are further categorized into three types depending on the location of the C 2 unit: the C 2 unit is encapsulated within the Al cage (type I), contained in the surface of Al clusters (type S), or attached to the surface of Al clusters (type O). Size-dependent behavior of the adiabatic electron affinities of Al n C 2 determined by photoelectron spectroscopy was explained in terms of polymorphism as a function of size (n): type I for n = 5−8, type D for n = 9−11, type D or O for n = 12, and type O for n = 13. The tendency in which the position of the C 2 unit was shifted from the inside to outside with the increase in n was ascribed to the balance between the stabilizations gained by forming Al−C bonds and Al−Al bonds. The smaller Al n C 2 − clusters (n = 5−8) prefer to surround the acetylide-like C 2 unit with the Al atoms so as to maximize the number of Al−C bonds, whereas larger ones (n = 12 and 13) prefer to attach the C 2 unit onto the surface of the Al clusters so as to maximize the number of Al−Al bonds.

Anion Photoelectron Spectroscopy and Theoretical Studies of Al4C6–/0: Global Minimum Triangle-Shaped Structures and Hexacoordinated Aluminum

“…Mass spectrometry and theoretical calculations on neutral aluminum–carbon clusters indicated that the small neutral aluminum–carbon clusters prefer to form structures containing a C 2 unit . Photoelectron spectroscopy and density functional theory studies on dicarbon-doped aluminum cluster anions suggested that those clusters exhibit two structure types in terms of whether two carbon atoms dissociate or not . A series of small aluminum–carbon clusters − have been investigated using anion photoelectron spectroscopy and theoretical calculations, and it was found that the Al 4 C – anion has a planar tetracoordinate carbon (ptC) structure with D 4h symmetry .…”

“…11 Photoelectron spectroscopy and density functional theory studies on dicarbon-doped aluminum cluster anions suggested that those clusters exhibit two structure types in terms of whether two carbon atoms dissociate or not. 12 A series of small aluminum−carbon clusters 13−18 have been investigated using anion photoelectron spectroscopy and theoretical calculations, and it was found that the Al 4 C − anion has a planar tetracoordinate carbon (ptC) structure with D 4h symmetry. 19 In addition to the ptC structures, 20 aluminum−carbon clusters were predicted to form many interesting structures 21−26 such as planar pentacoordinate carbon structures, 27 starlike structures, 28 or carbon endohedral stable structures.…”

A computational investigation on the correlation of structure, stability, and reactivity of neutral and charged mono- and di-aluminium doped linear carbon chains (Al1,2C¬1-7)

“…The choice of the calculated level of theory was based competence of the method to predict the structural properties of Al-containing clusters. [4,24,29] We have also compared several experimental observables against the calculated data to validate the above method. [4,29] The optimization of each structure was further confirmed without any imaginary harmonic vibrational frequencies.…”

“…[4,24,29] We have also compared several experimental observables against the calculated data to validate the above method. [4,29] The optimization of each structure was further confirmed without any imaginary harmonic vibrational frequencies. All calculations were performed using the TURBOMOLE program.…”

“…The above structures of Al2C2and Al2C5are in good agreement with the previously reported structures backed by both computational and experimental data. [21,29] 3.2 Stability of the AlnCm, AlnCm + and AlnCm − (n=0-2; m=1-7)…”