The Bi-NL bond distances in 1 are 2.472(2) and 2.506(2) Å and the Bi-Cl bond distances range from 2.512(7) to 2.900(8) Å. The distance between the two bismuth centers in a molecule is 4.134(6) Å (Figure ). In case of 2, the Bi-NL bond distances are 2.507(2) and 2.528(2) Å, the Bi-Br bond distances range from 2.652(5) to 3.061(5) Å while the distance between the two bismuth centres in a molecule is 4.274(6) Å (Figure ). The complex 3 consists of comparatively elongated bonds as shown in figure . The Bi-NL bond distances are 2.559 (5) and 2.601(5) Å, while the Bi-I bond distances range from 2.864(5) to 3.361(5) Å. The distance between the two bismuth centers is observed to be 4.449(8) Å. The change of the bond distances with the change in the ancillary ligand are illustrated in table and the comparison of the data suggests that change of the size of halide in the complexes weakens the Bi-NL bond thus increasing the bond length. In all the cases, the bridged bismuth-halogen bond distances are longer as compared to that of unbridged bismuth-halogen bonds, which further elongates the distance between the two bismuth center atoms from 1 to 3. Moreover, the increase in the size of the bonding orbital from Cl, Br to I based ancillary ligand further suggests the weak bismuth-halide bonds in 3 as compared to that in 1 and 2. In 1 and 2 both the thiophene rings face each other with dihedral angles of -42.8(3)°, 164.2(2)° and -46.0(3)°, 161.5(2)° between the atoms N4-C14A-C19A-S2A and N3-C13A-C15A-S1A respectively (Figure ). Interestingly, in 3 both the rings oppose each other and face towards the pyrazine moiety with the dihedral angles of 53.1(6)° and 10.9(5)° when calculated along the N4-C14-C19A-S2A and N3-C13A-C15A-S1A respectively (Figure ). The distance between the nitrogen atoms of pyrazine moiety and the sulphur atoms are observed to be 3.082(2) and 3.970(2) Å in 1, 3.127(3) and 3.967(3) Å in 2 while 2.760(5) Å and 3.127(6) Å in 3 (Figure ). Such difference in orientation and distance of the thiophene rings in 3 when compared with 1 and 2 is indicative of a stronger electronic push effect from the electron rich thiophene moiety towards that electron-deficient pyrazine ring.