We report the synthesis,
crystal structure, thermal response, and
electrochemical behavior of the Prussian blue analogue (PBA) K
2
Cu[Fe(CN)
6
]. From a structural perspective, this
is the most complex PBA yet characterized: its triclinic crystal structure
results from an interplay of cooperative Jahn–Teller order,
octahedral tilts, and a collective “slide” distortion
involving K-ion displacements. These different distortions give rise
to two crystallographically distinct K-ion channels with different
mobilities. Variable-temperature X-ray powder diffraction measurements
show that K-ion slides are the lowest-energy distortion mechanism
at play, as they are the only distortion to be switched off with increasing
temperature. Electrochemically, the material operates as a K-ion cathode
with a high operating voltage and an improved initial capacity relative
to higher-vacancy PBA alternatives. On charging, K
+
ions
are selectively removed from a single K-ion channel type, and the
slide distortions are again switched on and off accordingly. We discuss
the functional importance of various aspects of structural complexity
in this system, placing our discussion in the context of other related
PBAs.