  We report on a new iron selenide superconductor with a TC onset of 45K and
the nominal composition Lix(C5H5N)yFe2-zSe2, synthesized via intercalation of
dissolved alkaline metal in anhydrous pyridine at room temperature. This
superconductor exhibits a broad transition, reaching zero resistance at 10K.
Magnetization measurements reveal a superconducting shielding fraction of
approximately 30%. Analogous phases intercalated with Na, K and Rb were also
synthesized and characterized. The superconducting transition temperature of
Lix(C5H5N)yFe2-zSe2 is clearly enhanced in comparison to the known
superconductors FeSe0.98 (Tc ~ 8K) and AxFe2-ySe2 (TC ~ 27-32K) and is in close
agreement with critical temperatures recently reported for Lix(NH3)yFe2-zSe2.
Post-annealing of intercalated material (Lix(C5H5N)yFe2-zSe2) at elevated
temperatures drastically enlarges the c-parameter of the unit cell (~44%) and
increases the amount of superconducting shielding fraction to nearly 100%. Our
findings indicate a new synthesis road leading to possibly even higher critical
temperatures in this class of materials by intercalation of organic compounds
between Fe-Se layers.
