Compounds featuring a bond between a Group 13 (M) and a Group 15 element (N or P) and with the formulae HmMNHn and HmMPHn: structural aspects and bonding

Following studies of the thermal and photoactivated reactions of the Group 13 metal atoms Al, Ga or In (M) with NH3 or PH3 in solid argon matrices, the properties of the observed or potential reaction products are discussed. These are molecules with the general formula HmMEHn, where M=Al, Ga or In, E=N or P, and m, n=0-3. All the molecules have been characterised structurally, energetically and vibrationally by Density Functional Theory (DFT) calculations. The following products have been identified experimentally by their IR spectra: the adducts M . EH3, the metal(II) insertion products HMEH2, the metal(III) derivatives H2MNH2 and H2MPH, and the metal(I) amides MNH2. The observation of most of the IR-active fundamentals for different isotopic forms of the molecules MNH2 and H2MNH2 allowed normal coordinate analysis calculations to be performed, thereby endorsing the vibrational assignments and affording reliable force constants. Observed and hypothetical HmMEHn molecules have been compared with particular reference to structural and energetic differences according to whether E=N or P. Questions of bonding have been addressed through calculations of barriers to rotation of planar molecules and of barriers to inversion for molecules containing pyramidal MPH2 moieties. pi -Type interactions play only a minor part in the bonding of planar molecules like H2MNH2. The much larger barrier to inversion of PH3 compared with NH3 results in pyramidal MPH2 but planar MNH2 fragments. With the help of an appropriate MO scheme it is possible to rationalise how the inversion barrier changes when one hydrogen of PH3 is replaced by an MHm group.