Date of Award
Doctor of Philosophy (PhD)
Robert V. Nauman
The conformations of the dipyrromethene molecule seem to control the spectral properties of its derivatives and its metal complexes. A sharply structured absorption band at 505nm that is red shifted relative to the broad structureless neutral ligand absorption band at 445nm when a weak base is added to hexamethyldipyrromethene in DMSO is inferred to be that of a negative ion. Another sharply structured absorption band at 489nm is observed after addition of a strong base to a solution of hexamethyldipyrromethene in DMSO and is inferred to be that of a different negative ion of hexamethyldipyrromethene. The two different negative ions of hexamethyldipyrromethene may have different degrees of rotation of one pyrrole ring out of the plane that contained both pyrrole rings of the neutral hydrogen bonded HMDPM. The Zn(HMDPM)$\sb2$, Fe(HMDPM)$\sb2$, and Co(HMDPM)$\sb2$ complexes are designated the Type 1 complexes. All three compounds are negative ion type complexes that slowly decompose. The products of decomposition may have two neutral ligands and two OH$\sp-$ counter ions attached to their metal centers. The source of the proton that forms the neutral ligand appears to be water. Cu(HMDPM)$\sb2$ has two major absorption bands and is called the Type 2 complex. The two bands represent absorptions from complexes that possibly differ only with respect to the geometry of the negative ion attached to the metal center. The higher energy band may be that of a nearly planar negative ion which resembles that of the planar hydrogen bonded neutral ligand. The lower energy band is that of a Type 1 complex. Ni(HMDPM)$\sb2$ may be a group of oligimeric negative ion type complexes. The Ni(HMDPM)$\sb2$ complex is called the Type 3 complex. The different absorptions of Ni(HMDPM)$\sb2$ may be those of different oligimers that result from different ligand geometries that are the result of the bonding of the negative ions sometimes to one and other times to more than one nickel center.
Fillingim, Timothy Gale, "Spectroscopy of Hexamethyldipyrromethene and of Metallo Hexamethyldipyrromethene Complexes." (1987). LSU Historical Dissertations and Theses. 4446.