Synthesis and magnetic characterization of transition metal porphyrinic compounds

Synthesis and purification of novel tetraazaporphyrin (TAP) square planar tetradentate ligands was performed. Insertion of transition metals via standard and air sensitive techniques provided M(II)(TAP) (M = Fe, Mn) which were investigated using SQUID magnetometry. Magnetization as a function of temperature measurements were used to explore the nature of any three-dimensional cooperative exchange interactions present.; Most notably, a needle-like crystalline phase of iron(II) octaethyltetraazaporphyrin, {dollar}alpha{dollar}-Fe(OETAP), showed a ferromagnetic transition to a three-dimensionally ordered state below {dollar}rm Tsb{lcub}c{rcub} = 2.8{dollar} K. This is truly a unique material in that all other porphyrinic iron(II) compounds show no cooperative interactions. In fact, {dollar}alpha{dollar}-Fe(OETAP) is only the second compound to show long range three-dimensional ordering among planar tetrapyrrolic metallated species. Magnetic characterization including low field measurements and ac susceptibility was performed to further explore the nature of the exchange interactions within {dollar}alpha{dollar}-Fe(OETAP). Attempts to grow a single crystal for X-ray diffraction provided a different crystalline phase, {dollar}beta{dollar}-Fe(OETAP), which showed no evidence for the ferromagnetic coupling previously observed in the {dollar}alpha{dollar}-phase. Characterization of this compound revealed an identical UV-visible solution spectrum with the {dollar}alpha{dollar}-phase but differences can be observed via solid state techniques such as powder diffraction and Mossbauer spectroscopy.; Manganese(II) octaethyltetraazaporphyrin, Mn(OETAP), also exists in two crystalline phases: an {dollar}alpha{dollar}-phase exhibiting cooperative effects and a {dollar}beta{dollar}-phase which does not. Upon further characterization through powder diffraction, the manganese phases were found to be structurally isomorphous with their respective iron analogues. Magnetic characterization showed the {dollar}alpha{dollar}-phase exhibits spin-glass-like behavior while the {dollar}beta{dollar}-phase has similar magnetic behavior to {dollar}beta{dollar}-Fe(OETAP).; In order to study a system exhibiting similarities to the well-studied phthalocyanine class of compounds, tetracyclohexenotetraazaporphyrin, H{dollar}sb2{dollar}TCHTAP, was synthesized involving the multi-step formation of a dinitrile precursor. Metallation of this free-base species proved to be more difficult than H{dollar}sb2{dollar}OETAP due to solubility problems. Direct template cyclization techniques were employed and evidence for Fe(TCHTAP) and Mn(TCHTAP) was determined spectroscopically. Preliminary magnetic data show evidence for cooperative interactions within a doubly sublimed sample of Mn(TCHTAP).; Chromium(III) tetraphenylporphyinato tetracyanoethenide, (Cr(TPP)) {dollar}sp{lcub}:.+{rcub}{dollar} (TCNE) {dollar}sp{lcub}.-{rcub}{dollar} was synthesized by a charge-transfer reaction between Cr(II)(TPP) and TCNE under extreme oxygen and moisture-free conditions. Infrared analysis showed that each TCNE molecule bridges two chromium atoms through nitrile groups trans to one another resulting in one-dimensional chains of alternating donors and acceptors. Magnetic characterization of this compound showed the onset of magnetic ordering below 100 K. Presumably, the S = 3/2 spin centers on the porphyrin units are coupling antiparallel with the S = 1/2 TCNE radical anions resulting in one-dimensional ferrimagnetism.