pubs.acs.org/IC Published on Web 07/14/2009 r 2009 American Chemical Society Inorg. Chem. 2009, 48, 7953–7961 7953 DOI: 10.1021/ic900997p Kinetic and Thermodynamic Stability of the Group 13 Trihydrides Brian Vest, † Karl Klinkhammer, ‡ Christian Thierfelder, † Matthias Lein, † and Peter Schwerdtfeger* ,† † Centre for Theoretical Chemistry and Physics (CTCP), New Zealand Institute for Advanced Study (NZIAS), Massey University Albany, Private Bag 102904, North Shore MSC, Auckland, New Zealand, and ‡ Institut f :: ur Anorganische und Analytische Chemie, Johannes-Gutenberg-Universit :: at Mainz, Duesbergweg 10-14, D-55128 Mainz, Germany Received May 21, 2009 The kinetic and thermodynamic stabilities of the group 13 hydrides EH 3 (E = B, Al, Ga, In, Tl, E113) are investigated by relativistic density functional and wave function based theories. The unimolecular decomposition of EH 3 f EH þ H 2 becomes energetically more favorable going down the Group 13 elements, with the H 2 -abstraction of InH 3 , TlH 3 , and (E113)H 3 (E113: element with nuclear charge 113) being exothermic. In accordance with the Hammond-Leffler postulate, the activation barrier for the dissociation process decreases accordingly going down the group 13 elements in the periodic table shifting to an early transition state, with activation energies ranging from 88.4 kcal/mol for BH 3 to 41.3 kcal/mol for TlH 3 and only 21.6 kcal/mol for (E113)H 3 at the scalar relativistic coupled cluster level of theory. For both TlH 3 and (E113)H 3 we investigated spin-orbit effects using Dirac-Hartree-Fock and second-order Møller- Plesset theory to account for electron correlation. For (E113)H, spin-orbit coupling results in a chemically inert closed 7p 1/2 -shell, thus reducing the stability of the higher oxidation state even further. We also investigated the known organothallium compound Tl(CH 3 ) 3 , which is thermodynamically unstable similar to TlH 3 , but kinetically very stable with an activation barrier of 57.1 kcal/mol. Introduction The stability and chemical properties of the group 13 hydrides EH 3 (E=B, ..., Tl) have been a topic of intense discussion and debate for many decades. 1 More than 60 years ago, Egon Wiberg and co-workers claimed the synthesis and isolation of the group 13 trihydrides EH 3 (E=B-Tl). 2 However, the last confirmed successful synthesis was gallane by Downs et al. 1 who were able to isolate GaH 3 as a white solid which melts at -50 °C. Any other attempts to reproduce Wiberg’s results in the synthesis of InH 3 and TlH 3 have been unsuccessful. 3 According to several authors, 4-8 it seems unlikely that InH 3 and TlH 3 are stable enough to be isolated in the solid phase under normal conditions. Unlike the group 13 monohydrides (EH), whose gas-phase stabilities have allowed them to be studied extensively by spectroscopic methods, 9 the gas-phase stability of the heavier InH 3 and TlH 3 has been problematic as well. Even two more recent review articles listed these compounds as being non- existent in the gas-phase. 10 Until very recently, only the lighter EH 3 and E 2 H 6 (E=B, Al, Ga) have been studied extensively through spectroscopy. 5,11-19 InH 3 and TlH 3 were *To whom correspondence should be addressed. E-mail: p.a.schwerdtfeger@ massey.ac.nz. (1) Downs, A. J.; Goode, M. J.; Pulham, C. R. J. Am. Chem. Soc. 1989, 111, 1936. (2) (a) Wiberg, E.; Johannsen, T. Naturwissenschaften 1941, 29, 320. (b) Stecher, O.; Wiberg, E. Ber. Dtsch. Chem. Ges. 1942, 75, 2003. (c) Wiberg, E.; Johannsen, T. Angew. Chem. 1942, 55, 38. (d) Wiberg, E.; Johannsen, T.; Stecher, O. Z. Anorg. Allg. Chem. 1943, 251, 114. (e) Wiberg, E.; Schmidt, M. Z. Naturforsch. B 1951, 6, 171. 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