Communications: Chain and double-ring polymeric structures: Observation of Aln H3n+1- (n=4-8) and Al4 H 14-

Abstract

A pulsed arc discharge source was used to prepare gas-phase, aluminum hydride cluster anions, Aln Hm-, exhibiting enhanced hydrogen content. The maximum number of hydrogen atoms in Al n Hm- species was m=3n+1 for n=5-8, i.e., Aln H3n+1-, and m=3n+2 for n=4, i.e., Al 4 H14-, as observed in their mass spectra. These are the most hydrogen-rich aluminum hydrides to be observed thus far, transcending the 3:1 hydrogen-to-aluminum ratio in alane. Even more striking, ion intensities for Aln Hm- species with m=3n+1 and m=3n+2 hydrogen atoms were significantly higher than those of nearby Aln Hm- mass peaks for which m<3n+1, i.e., the ion intensities for Aln H3n+1- and for Al4 H14- deviated from the roughly bell-shaped ion intensity patterns seen for most Aln Hm- species, in which m ranges from 1 to 3n. Calculations based on density functional theory showed that Aln H3n+1-/ clusters have chain and/or double-ring polymeric structures. © 2010 American Institute of Physics.