Bis(1,3,5-trimethylbenzene)gallium(I) tetrachloridoaluminate(III), [(1,3,5-(CH 3 ) 3 C 6 H 3 ) 2 Ga][AlCl 4 ] ( 1 ), bis(1,3,5-trimethylbenzene)gallium(I) tetrabromidoaluminate(III), [(1,3,5-(CH 3 ) 3 C 6 H 3 ) 2 Ga][AlBr 4 ] ( 2 ) and (1,3,5-trimethylbenzene)gallium(I) tetraiodidoaluminate(III), [1,3,5-(CH 3 ) 3 C 6 H 3 Ga][AlI 4 ] ( 3 ) were synthesized from the corresponding subvalent Ga I /Al III mixed metal halides and characterized via C,H analysis, Raman spectroscopy, X-ray powder diffraction and X-ray single crystal diffraction. Compound 1 crystallizes in the noncentrosymmetric monoclinic space group Cc isotypic to [(1,3,5-(CH 3 ) 3 C 6 H 3 ) 2 Ga][GaCl 4 ]. For 2 and 3 the monoclinic space group P 2 1 / n is found, however, they are neither isotypic nor homotypic. While 2 is isotypic to [(1,3,5-(CH 3 ) 3 C 6 H 3 ) 2 In][InBr 4 ], 3 establishes a new structure type. In the solids of all three title compounds coordination polymeric chains are found, in 1 and 2 built up from bis(arene)-coordinated, in 3 from mono(arene)-coordinated Ga + ions and the corresponding Al X 4 − anions in a 1κCl:2κCl′ ( 1 ), 1κCl,Cl′:2κCl″ ( 2 ) or 1κCl,Cl′:2κCl″:3κCl‴ ( 3 ) bridging mode. Taking into account the weaker coordinating character of the AlCl 4 − as compared to the AlBr 4 − anion, in line with expectations the number of gallium halogen contacts is increased and the strength of the π -arene bonding is reduced in the bromide 2 as compared to the chloride 1 . Finally, with the even more strongly coordinating AlI 4 − anion the arene coordination is limited to one molecule. Considering mesitylene complexes of gallium, the formation of a mono(arene) complex is unprecedented and even considering group 13 elements in general, the formation of a mono(mesitylene) complex like 3 is unusual. Furthermore, compound 3 is the first structurally characterized arene solvate of a main group metal tetraiodidometallate.