  Post-annealing effects on the crystal structure and superconductivity of the
lithium- and hexamethylenediamine (HMDA)-intercalated superconductor
Lix(C6H16N2)yFe2-zSe2 have been investigated. Through the post-annealing, a
two-step reduction of the interlayer spacing between neighboring Fe layers, d,
has been observed. It has been found that a new phase of Lix(C6H16N2)yFe2-zSe2
with d= 10.30(2) {\AA} and Tc = 41 K different from the as-intercalated phase
is stabilized owing to the possible stable inclination of HMDA intercalated
between FeSe layers. This result supports the domic relation between Tc and d
in the FeSe-based intercalation superconductors. The reason why Tc increases
with a decrease in d through the post-annealing is discussed.
