The synthesis and characterisation of one-dimensional (1D) crystals that have a well-specified chemistry, size and crystal structure have presented a formidable challenge for materials chemistry and analysis. We report here the filling of single (SWNTs) and double walled carbon nanotubes (DWNTs) by two different p-block halides, TlCl and PbI2. The nanotubes were produced either by the arc synthesis  or by a CVD method , based on the reduction of a Mg0.9Co0.1O solid solution by a hydrogen-methane mixture. In the case of TlCl, the structure of the crystals observed inside the tubes were all found to be derived from the rocksalt form and bilayer crystals were observed which exhibited reduced coordination relative to the fcc structure, as determined from high resolution transmission electron microscopy (HRTEM). In contrast, the crystal structure of bulk TlCl is a CsCl type structure. These results are consistent with the recently reported reduced coordination KI crystals formed within SWNTs . In the case of PbI2 (i.e. with the CdCl2 structure), the use of HRTEM images combined with image simulations was used to confirm the partially reduced coordination of Pb atoms within the SWNT and DWNT confined 1D crystals.