The two-d
imens
ional (2D) polymer
ic sp
in crossover (SCO) compound Fe(py)
2[Ag(CN)
2]
2 has been synthes
ized.The compound shows a two-step sp
in trans
it
ion detected by magnet
ic, heat capac
ity, and X-ray d
iffract
ionmeasurements. The magnet
ic moment shows a h
igh-temperature step (step 1) occurr
ing at 146.3 K w
ithouthysteres
is, wh
ile the low-temperature step (step 2) happens at 84 K on cool
ing and 98.2 K on heat
ing. Thesemeasurements reveal a large amount of res
idual h
igh sp
in (HS) spec
ies (23%) and that HS state trapp
ingoccurs at cool
ing rates of around 1 K m
in
-1 or h
igher. The two-step behav
ior has been conf
irmed by heatcapac
ity, wh
ich g
ives, for steps 1 and 2, respect
ively,
![](/<font color=)
images/g
ifchars/Delta.g
if" BORDER=0 >
H1 = 3.33 kJ mol
-1,
![](/<font color=)
images/g
ifchars/Delta.g
if" BORDER=0 >
S1 = 22.6 J mol
-1 K
-1, and
![](/<font color=)
images/g
ifchars/Delta.g
if" BORDER=0 >
H2 = 1.51 kJ mol
-1,
![](/<font color=)
images/g
ifchars/Delta.g
if" BORDER=0 >
S2 = 15.7 J mol
-1 K
-1. For step 2 a hysteres
is of 10 K has been determ
ined w
ithdynam
ic measurements. Powder X-ray d
iffract
ion at room temperature shows that the compound
is
isostructuralto Cd(py)
2[Ag(CN)
2]
2 prev
iously reported. Powder X-ray d
iffract
ion
ind
icates that there
is only onecrystallograph
ic s
ite for
iron(II)
in the whole temperature range, conf
irmed by Mössbauer spectroscopy. TheX-ray d
iffract
ion study at d
ifferent temperatures do not show any superstructure
in the reg
ion between thetrans
it
ions, d
iscard
ing a crystallograph
ic phase trans
it
ion as the or
ig
in of the two-step behav
ior. However, anunexpected
increase of the thermal factor
is detected on lower
ing the temperature and cons
idered as aman
ifestat
ion of a d
isordered state between the two steps, cons
ist
ing of a m
ix
ing of HS and LS spec
iesw
ithout long-range order.