ESR studies of inter- and intra-lamellar cation exchange processes in Cd2P2S6

The transition metal chalcogenides, M2P2S6 (M = divalent transition metal cation), are lamellar materials that undergo an unusual cation exchange process when their crystals are placed in contact with a solution of a transition metal salt. EPR spectroscopy has been used to examine the exchange of paramagnetic Co2+ for Cd2+ in diamagnetic Cd2P2S6. It has been possible to study the uptake of ions by the lamellar lattice and to examine the cation coordination environment through its effect on the parameters of the spin-Hamiltonian. In order to extract details of the Co2+ coordination from the observed EPR spectra, theoretical values of the g-value have been computed as a function of several crystal field parameters. The results for Co2+ are compared with previous results for the insertion of Mn2+ into Cd2P2S6 by cation exchange. The relative occupancy of the inter- and intra-lamellar sites is a function of the cation type and the solvent employed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28953/1/0000790.pd

RESONANCE RAMAN STUDIES ON EXCITED STATES OF ZN(Π\Pi) OCTAETHYLPORAPHYRIN

Author Institution: Departments of Chemistry and the LASER Laboratory, Michigan State UniversityThe important biological process of charge separation in the photosynthetic reaction center is initiated by photoexcitation of a chlorophyll molecule into the excited singlet state ($S_{1}$). To better understand this process, more insight into the electronic structure and conformation of singlet excited porphyring is essential. Picosecond time resolved pump-probe Resonance Raman scattering can provide this insight by means of probing bond strengths in the molecule in the excited state. For the experiments we selected zn($\Pi$) Octachylporphyrin (ZnOEP) because it has several characteristics beneficial for the experiment. In the $S_{1}$ state the resonance Raman spectrum is dominated by totally symmetric modes at 1564, 1450, 1359, 1261, 1135 and $664 cm^{-1}$. Since nontotally symmetric modes are only weakly enbaneed, we conclude that Jahn-Teller distortion is absent in this state. In the lowest triplet state ($T_{1}$) nontotally symmetric modes dominate the spectrum. Jahn-Teller distortion in the triplet state thus appears to be important. The latter conclusion aggress with previous results on triplet states that indicated Jahn-Teller distortion in metalloporphyrins with $D_{4h}$ symmetry, Implications of our results for the efficiency of charge separation in the photosynthetic reaction center will be discussed. (Supported by NIH grant GM25480