Two new spin crossover complexes [FeL(py)
2] (
1) and [FeL(DMAP)
2] (
2) wit
h L being a tetradentate N
2O
22-coordinating Sc
hiff-base-like ligand [([3,3']-[1,2-p
henylenebis(iminomet
hylidyne)]bis(2,4-pentanedionato)(2-)-
N,
N',
O2,
O2'], py = pyridine and DMAP =
p-dimet
hylaminopyridine
have been investigated using temperature-dependent susceptibility and t
hermogravimetric and p
hotomagnetic measurements as well as M&
ouml;ssbauer spectroscopyand X-ray structure analysis. Bot
h complexes s
how a cooperative spin transition wit
h an approximately 9 K widet
hermal
hysteresis loop in t
he case of
2 (
T1/2 = 183 K and
T1/2 = 174 K) and an approximately 2 K wide t
hermal
hysteresis loop in t
he case of t
he pyridine diadduct
1 (
T1/2 = 191 K and
T1/2 = 189 K). T
he spin transition wasadditionally followed by different temperature-scanning calorimetry and M&
ouml;ssbauer spectroscopy for
2, and a goodagreement for t
he transition temperatures obtained wit
h t
he different met
hods was found. Results from X-ray structureanalysis indicate t
hat t
he cooperative interactions are due to elastic interactions in bot
h compounds. T
hey aremore pronounced in t
he case of
2 wit
h very s
hort intermolecular iron-iron distances of 7.2 Å and several intenseC-C contacts. T
he c
hange of t
he spin state at t
he iron center is accompanied by a c
hange of t
he O-Fe-O angle,t
he so-called bit of t
he equatorial ligand, from 108
in t
he
hig
h-spin state to 90
in t
he low-spin state. T
he reflectivitymeasurements of bot
h compounds give at low temperature indication t
hat at t
he sample surface t
he lig
ht-inducedexcited spin state trapping (LIESST) effect occurs. In bulk condition using a SQUID magnetometer t
he complex
2displays some p
hotomagnetic properties wit
h an p
hotoexcitation level of 60% and a
T(LIESST) value of 53 K.