| Variable temperature absorption Mossbauer, magnetic susceptibility, and infrared studies of Fe(phen)(,2)(NCBH(,3))(,2) reveal the occurrence of a reversible, gradual singlet/quintet intersystem crossing above room temperature (359 K). The Mossbauer spectra of the complex in the transition region are interpreted as showing the occurrence of a novel (for Fe(II)) fast singlet/quintet interconversion.;A time resolved emission Mossbauer spectrophotometer was constructed and a testing sequence was developed. In the procedure the instrument was checked for resolution in the time and energy domains and single line source (Co/Pd) and single line absorber (K(,4)(Fe(CN)(,6))(.)3H(,2)O) spectra were taken. This data exhibited the expected timefiltering effects, demonstrated that the instrument has time and energy domain resolution equal to or better than the instrument designs reported in the literature, and permitted development of data software for time domain spectral analysis. The compound ('57)Co(phen)(,3)(ClO(,4))(,2) (as source) was then studied with inconclusive results: the experimentally obtained time integral spectrum shows emission from three electronic excited states, with values for the center shifts and quadrupole splittings which agree with literature values, but the relative emission intensities for these states are not in agreement with literature values. The reasons for the disagreement between our emission intensities and those of the literature have not been established; however, we suspect that the electronic excited state lifetimes are sensitive to crystallite size and lattice water content.;Variable temperature magnetic moment data for Fe(phen)(,2)X(,2), X = NCS('-), NCSe('-) and NCBH(,3)('-) have been analyzed for cooperativity contributions to singlet/quintet intersystem crossing. To account for the curve shape characteristics of the magnetic data, use is made of a simple, generalized thermodynamic formulation of intermolecular and domain interactions, including lattice continuity terms. This formalism is applied to the Fe(phen)(,2)X(,2) series with the discovery that the differential quintet:singlet and quintet:quintet intermolecular interaction (Gibbs) energies, (gamma)(,c), span a narrow range, while the transition cooperativities, (gamma)(,c)/2RT(,c), markedly vary; the latter reflect the importance of the singlet/quintet electronic energy gap and differential quintet:quintet, singlet:singlet interaction energies to T(,c) and to the sharpness of the transition. |
