Added as crystallisation additive. In the article I read:
Purification and crystallization were carried out as described (14) although Zn2" were found to be necessary for crystallization (15). The crystals produced in the presence of zinc were iden- tical to those reported earlier (14, 16) with space group bladeebla etcetera ..... |
If you load the 1ppt_Zn.sce scene that is stored under 'Exercise files' under 'Miscellaneous' you see that the zinc also makes contacts with a series of atoms in the crystal environment that is shown as thin lines.