Abstract The covalent derivatives [Et 2 M-PEt 2] 3 (M= Ga, In) have been prepared from Lewis acid-base complexes, R 3 M. PHEt 2, by alkane elimination and characterized by elemental analyses, IR, 1 H and 31 P NMR spectroscopy. Features of the mass spectra reveal a trimeric form and the strength of the [MP] n ring. For the compound [ClMeGa-PEt 2] n, spectral data are consistent with a weakening of the [Ga-P] n chain, in good agreement ...