Co-ordination compounds of gallium (I) tetrachlorogallate, Ga[GaCl 4], and gallium (I) tetrabromogallate, Ga[GaBr 4], have been prepared with sulphur, selenium and arsenic donor ligands. Co-ordination compounds of gallium (I) chloride, GaCl, and gallium (I) bromide, GaBr, have been prepared with dioxan, morpholine and acetylacetone. Electrical conductivity and molecular weight measurements indicate that the two classes of complexes should be formulated as GaL 4 +GaX 4 − and GaL 4 +X −, where L represents a monodentate ligand and X a halogen. The crystal structure of Ga(diox) 2Cl has been examined by single crystal X0ray diffraction methods. The orthorhombic unit cell has the space-group symmetry Pnma, and contains four formula units. The arrangement of donor atoms around Ga + forms a distorted trigonal pyramid.