Low valent and would-be multiply bonded derivatives of the Group 13 metals Al, Ga and In revealed through matrix isolation

Two aspects of Group 13 metal chemistry are surveyed in the light of recent matrix-isolation and quantum chemical studies. The first concerns derivatives of the metals Al, Ga and In (M) in formal oxidation states less than + 3: these include the M-0 derivatives MLn, where L = CO, N-2, NH3, or PH3, and n = 1 or 2; the M-1 derivatives MX, where X = H, CH3 or NH2, and M2H2; and the M-II derivatives HMX, where X = H, CH3, NH2 or PH2. The second concerns derivatives in which there is the opportunity for the metal to engage in multiple bonding, as exemplified by the cases of M2H2 and H2MNH2. Experimental studies have involved thermally or photolytically excited reactions between M atoms, or sometimes M-2 molecules, and an appropriate substrate, e.g. H-2, CO, N-2, CH4, NH3 or PH3. The reagents have been trapped in solid noble gas matrices, the IR spectra of which have been exploited to deduce the course of events and identities of the products. Confirmation of the identity and geometry of each of the products have been achieved primarily on the basis (i) of isotopic effects and (ii) of comparison of the measured spectrum with that anticipated by quantum chemical calculations. This liaison of experiments with theory has led to the characterisation not only of numerous simple molecules that are short-lived under normal conditions, but also of some of the reaction channels open to them, typically through photolytic activation, The structure, energies and reactivities of the compounds are reviewed. (C) 2002 Elsevier Science Ltd. All rights reserved.