Electronic structure of molecular superconductors containing paramagnetic3dions

Abstract

The results of x-ray fluorescence measurements of the molecular superconductors ͑ET͒ 4 ͓͑H 3 O͒Fe͑C 2 O 4 ͒ 3 ͔•C 6 H 5 CN (T c ϭ8.5 K) and ͑ET͒ 4 ͓͑H 3 O͒Cr͑C 2 O 4 ͒ 3 ͔•C 6 H 5 CN (T c ϳ6 K) and molecular conductor ͑ET͒ 4 ͓͑H 3 O͒Fe͑C 2 O 4 ͒ 3 ͔•C 5 H 5 N containing paramagnetic 3d ions are presented. The following transition of the x-ray emission valence spectra are monitored: C K␣, N K␣ (2p→1s transition͒ and Fe L 2,3 , Cr L 2,3 (3d4s→2p 3/2,1/2 transition͒. It is found that the electronic structure of the solvents ͑benzonitrile, pyridine͒ that occupy the hexagonal cavities formed by the anionic layer is close to that of the neutral molecule. The ratio of the emission intensities of the peaks L 2 to L 3 for Fe and Cr is found to be 2.8-3.1 times higher for ͑ET͒ 4 ͓͑H 3 O͒Fe͑C 2 O 4 ͒ 3 ͔•C 6 H 5 CN and ͑ET͒ 4 ͓͑H 3 O͒Cr͑C 2 O 4 ͒ 3 ͔•C 6 H 5 CN than for pure metals. This indicates that the paramagnetic 3d ions are situated in highly insulating anionic layers. We did not find any changes in the C K␣ emission for different solvent molecules.The charge transfer salts based on the donor ET molecule ͓bis ͑ethylenedithio͒ tetrathiafulvalene͔ cover a wide range of electrical conductivity from highly conducting metallic and superconducting to wide band gap semiconducting and insulating.

Electronic structure of thiophenes and phtalocyanines

“…Nitrogen K␣ XES is found to be identical for CuPc and F 16 CuPc, which is not unexpected because emitting atoms, in this case, have the same local surrounding in both compounds. On the other hand, these spectra resemble N K␣ XES of pyridine (C 6 H 5 N) 16 ͓see Fig.…”

“…On the other hand, these spectra resemble N K␣ XES of pyridine (C 6 H 5 N) 16 ͓see Fig. 1͑c͔͒ in spite of some differences in the chemical structure.…”

“…We have found that the electronic structure of such systems as thipohenes is characterized by the delocalized character of C 2p wave functions along the polymer backbone and is not affected by the presence of the side group. The ratio of the emission intensities CuL 2 /CuL 3 is found to be two times less for CuPc and F 16 CuPc than for Cu metal, which evidences strong covalency effects in phtalocyanines.…”

“…1͑c͔͒ in spite of some differences in the chemical structure. Figure 1͑b͒ shows that the fine structure of C K␣ emission is very different for CuPc and F 16 CuPc. The spectral features for F 16 CuPc are broader than for CuPc but both compounds disclose the same three-peak structure typical for phenyl rings as showcased by the spectrum of benzene in Figure 4 shows the comparison between x-ray emission spectra of constituents and UPS of F 16 CuPc.…”

“…21͒ due to increasing covalency. The low ratio of L 2 /L 3 for CuPc and F 16 CuPc is likely to be due to strong covalency in phtalocyanines. This interpretation is in a good agreement with measurements of fluorine K␣ XES of F 16 CuPc as displayed in Fig.…”