Projector augmented wave (PAW) method of Blöch, coded in the Vienna ab initio simulation package (VASP) was used to calculate the total energy after structure relaxation for three ordered models of Ba8In3Zn2Bi10. VASP employed generalized gradient approximation (GGA) with exchange and correlation treated by the Perdew-Burke-Enzerhoff (PBE) functionals. The cutoff energy for the plane wave calculations was set to 280 eV and the Brillouin zone integrations were carried out using Comparable In-Bi exo-bonds distance of 2.912 Å is found in Ba5In4Bi5 in which additional In-Bi distances that are longer (3.322 Å), corresponding to delocalize bonds. However, the Bi1-Zn3 bond length of 3.237(4) Å is too long when compared to either the sum of atomic radii or to other reported Bi-Zn distances like in Ba2ZnBi2 and BaZnBi2 with distances of 2.857(1) and 2.803 Å, respectively. Such longer than expected bond distance is also observed in other related structures with similar double pentagonal tube, for instance in the ternary Eu10Mn6Sb13 and Sr11Cd6Sb12 (vide infra). The shortest Ba-Bi interaction distances are also within the expected range between 3.400(2) and 3.574(2) Å, when compared to the sum of covalent radius (3.77 Å). Such rather short distances indicate non-negligible contribution of Ba atoms to the covalent bonding of the system, and this is often found to have decisive impact on the stability of the corresponding Zintl phases. Two distinct 1-D polyanionic substructures of In or Zn centered Bi tetrahedra are found in the structure running along the b-direction. This resulting in a partition of the structure into two virtually independent blocks in the a-direction, that can be expressed as Ba8Zn2-xIn3+xBi10 (1) = [Ba3Zn1-yIn1+yBi4] (1A) + [Ba5Zn1-zIn2+zBi6] (1B), with x = y+z. The occurrence of two different polyanionic units in the same crystal structure have not been reported in ternary pnictide Zintl phases to the best of our knowledge. Only the co-existence of two or more oligomers is quite often observed. According to the Zintl-Klemm concept (ZKC), full electron transfer from the electropositive Ba atom to the more electronegative Zn, In and Bi networks results in the polyanions [Zn1-yIn1+yBi4] 6-in 1A block and [Zn1-zIn2+zBi10] 10-in 1B block. Since one out of four Bi atoms in 1A forms dumbbell, the 1A block is formally charge balance according to the ZKC and the 8-N rule for y = 0, with the ionic formulation 3Ba 2+ ,[Zn 2+ In 3+ (Bi 3-)3(Bi1) 2-] 6-, whereas 1B block would be charge balanced for z = 0 as well, according to 5Ba 2+ ,[Zn 2+ (In 3+ )2(Bi 3-)6] 10-. Although not yet described, these blocks are predicted to exist as simple parent structures, i.e. "Ba3ZnInBi4" and "Ba5ZnIn2Bi6", since they are formally charge balanced according to the ZKC. However, while the Zintl-Klemm concept can often rationalize an observed structure, it has rarely predicted a new compound. The complex polymeric anion in the first block (1A), consists of two condensed pentagonal rings that are rigorously planar with Bi7 at apical, In4 and Zn5 at lateral and (Bi2) dumbbells at their equatorial positions. They are stacked along the b-direction and bridged together by four additional Bi (Bi6 and Bi9 in current labelling) jumpers at their lateral positions to form 'double pentagonal tubes' leading to idealized fully ordered [Zn2In2Bi8] 12-polyanion, running in the b-direction, and filled with charge balancing Ba cations (Figure ). The unique structural feature and bonding pattern of the 'double pentagonal tube' were first described in Sr11Cd6Sb12 and later in the isostructural family of structures A11M6Sb12 (A = Sr, Ba, Eu; M = Cd, Zn). A side view of the 1A polyanion is provided in Figure ).