X線吸収スペクトルにおける見かけ上の化学シフトを利用した半経験的価数評価

様々な3d遷移元素V，Cr，Mn，Co，Ni，Cu化合物のK吸収端，希土類元素Ce，Pr，Eu，Tb化合物及び5d，5pブロック元素Pt，Pb，Bi化合物のL1，3吸収端X線吸収スペクトルを測定し，見かけ上の化学シフトについて包括的な検討を行った．酸化数に対する見かけ上の吸収端エネルギーに関する元素間，吸収端ごとのシフト量及びその線形性に関する傾向を評価するとともに，XANESの化学シフトを半経験的な価数評価に利用する際の留意点について言及した．希土類元素ではいずれもL1吸収端のシフトがL3吸収端のものより大きく，二価三価の酸化数を取り得る元素のシフト値は三価四価を取り得る元素より大きかった．3d遷移金属及び5d，5pブロック元素では同一グループ内でシフト量に大きなばらつきはみられなかった．

X-ray absorption spectra of 3d transition elements at K-edge, lanthanoides and the other period 6 elements at L-edges for 105 compounds were recorded by a laboratory-type X-ray absorption spectrometer to elucidate the chemical shift comprehensively for empirical oxidation state analysis. Apparent absorption edge energies were determined at a half of the normalized XANES, and each the chemical shifts were estimated by a slope of the edge energy plotted as a function of the oxidation number. Evaluated apparent chemical shifts, linearity of the valence dependency, and the deviations were discussed based on chemical element groups, each element being within the group, and absorption edges. The apparent chemical shifts for K-edge of 3d transition elements lay within 2±0.5 eV/valences except for Cu. The chemical shifts for L-edges of lanthanoid compounds were about 2-4 times larger than those for K-edges of 3d transition elements, and shifts for Pt, Pb and Bi of the same period elements at L-edges were at most 1.3 eV/valences. Chemical shifts for lanthanoid elements at L1-edge were 1.5 times larger than those for corresponding L3-edges.

© The Japan Society for Analytical Chemistry 2013