The diphosphane O-C6H4(PMe2)(2) reacts with GaX3 (X = Cl, Br, or l) in a 1:1 molar ratio in dry toluene to give trans-[GaX2{o-C6H4(PMe2)(2)}(2)][GaX4], the cations of which contain the first examples of six-coordinate gallium in a phosphane complex. The use of a 1:2 ligand/GaCl3 ratio produced [GaCl2{o-C6H4(PMe2)(2)}][GaCl4], containing a pseudotetrahedral cation, and similar pseudotetrahedral [GaX2{o-C6H4(PPh2)(2)}](GaX4] complexes are the only products isolated with the bulkier O-C6H4(PPh2)(2). On the other hand, Et2P(CH2)(2)PEt2, which has a flexible aliphatic backbone, formed [(X3Ga)(2){mu-Et2P(CH2)(2)PEt2}], in which the ligand bridges two pseuclotetrahedral gallium centers. The diarsane, O-C6H4(AsMe2)(2), formed [GaX2{o-C6H4(AsMe2)(2)}][GaX4], also containing pseudotetrahedral cations, and in marked contrast to the diphosphane analogue, no six-coordinate complexes form; a very rare example where these two much studied ligands behave differently towards a common metal acceptor. The complexes [(l(3)Ga)Au-Ph2As(CH2)(2)AsPh2}] and [GaX3(AsMe3)] are also described. The X-ray structures of trans-[GaX2{o-C6H4(PME2)(2)}(2)][GaX4] (X = Cl, Br or 1), [GaCl2{o-C6H4(PPh2)(2)}][GaCl4], [GaX(2)10-C6H4(AsMe2)2J][GaX41 (X = Cl or 1), [(l(3)Ga)(2){U-Ph2As(CH2)(2)AsPh2}], and [GaX3(AsMe3)] (X = Cl, Br or 1) are reported, and the structural trends are discussed. The solution behavior of the complexes has been explored using a combination of P-31{H-1} and Ga-71 NMR spectroscopy.