The structural chemistry of alkali metal thallides shows a broad range of type structures. At an alkali metal : thallium proportion A : Tl 1 : 2 the perceived dependency on the alkali metal involved is conspicuous. Two main structure types are reported with A(15)Tl(27) (A=K, Rb, Cs) and K49Tl108. The compound K49K108 with a 3-dimensional Tl-substructure has been known since 1993 from Cordier and Muller but so far only with potassium. We here present single crystal X-Ray structure analyses of the compounds K49-yRbyTl108, and K49-yCsyTl108 (y<10) belonging to the K49Tl108 type structure. Additionally, structures of Rb49Tl109.67, Cs3.35Rb45.65Tl109.71 and Cs7.49Rb41.51Tl109.76 are introduced, which prove the possibility of Tl incorporation in the Tl-12 icosahedra in K49Tl108 type structures. The effects of the change in alkali metals on the thallium substructure are discussed as well as the preferred Wyckoff sites of the different alkali metals.