Geometries, dimerization energies, and harmonic vibrational frequencies have been calculated for InMH(6) and MBH(6) (M = B, Al, Ga, and In) using MP2 and DFT methods. Results for B2H6 and GaBH6 show good agreement with experimental data, with both methods giving comparable accuracy. Trends in the properties of InMH(6) and MBH(6) reflect the relative Lewis acidity of the component MH(3) moieties. The mixed MBH(6) series appears to show appreciable ionic character.