Two new layered compounds Rb2ZnBi2Se5 and Cs6Cd2Bi8Te17 are described. Rb2ZnBi2Se5 crystallizes in the orthorhombic space group Pnma, with lattice parameters of a = 15.6509(17) angstrom, b = 4.218(8) angstrom, and c = 18.653(3) angstrom. Cs6Cd2Bi8Te17 crystallizes in the monoclinic C2/m space group, with a = 28.646(6) angstrom, b = 4.4634(9) angstrom, c = 21.164(4) angstrom, and beta = 107.65(3)degrees. The two structures are different and composed of anionic layers which are formed by inter connecting of BiQ(6) octahedra (Q = Se or Te) and MQ(4) (M = Zn or Cd) tetrahedra. The space between the layers hosts alkali metal as counter cations. The rubidium atoms of Rb2ZnBi2Se (5) structure can be exchanged with other cations (Cd2+, Pb2+ and Zn2+) in aqueous solutions forming new phases. Rb2ZnBi2Se5 is an n-type semiconductor and exhibits an indirect band gap energy of 1.0 eV. Rb2ZnBi2Se5 is a congruently melting compound(mp similar to 644 degrees C). The thermal conductivity of this semiconductor is very low with 0.38 W.m(-1). K-1 at 873 K. Density functional theory (DFT) calculations suggest that the low lattice thermal conductivity of Rb-2 ZnBi2Se5 is attributed to heavy Bi atom induced slow phonon velocities and large Gruneisen parameters especially in the a and c directions. The thermoelectric properties of Rb2ZnBi2Se (5) were characterized with the highest ZT value of similar to 0.25 at 839 K.