Two new spin crossover complexes [FeL(py)
2] (
1) and [FeL(DMAP)
2] (
2) with L being a tetradentate N
2O
22-coordinating Schiff-base-like ligand [([3,3']-[1,2-phenylenebis(iminomethylidyne)]bis(2,4-pentanedionato)(2-)-
N,
N',
O2,
O2'], py = pyridine and DMAP =
p-dimethylaminopyridine have been investigated using temperature-dependent susceptibility and thermogravimetric and photomagnetic measurements as well as Mössbauer spectroscopyand X-ray structure analysis. Both complexes show a cooperative spin transition with an approximately 9 K widethermal hysteresis loop in the case of
2 (
T1/2 = 183 K and
T1/2 = 174 K) and an approximately 2 K wide thermalhysteresis loop in the case of the pyridine diadduct
1 (
T1/2 = 191 K and
T1/2 = 189 K). The spin transition wasadditionally followed by different temperature-scanning calorimetry and Mössbauer spectroscopy for
2, and a goodagreement for the transition temperatures obtained with the different methods was found. Results from X-ray structureanalysis indicate that the cooperative interactions are due to elastic interactions in both compounds. They aremore pronounced in the case of
2 with very short intermolecular iron-iron distances of 7.2 Å and several intenseC-C contacts. The change of the spin state at the iron center is accompanied by a change of the O-Fe-O angle,the so-called bit of the equatorial ligand, from 108
in the high-spin state to 90
in the low-spin state. The reflectivitymeasurements of both compounds give at low temperature indication that at the sample surface the light-inducedexcited spin state trapping (LIESST) effect occurs. In bulk condition using a SQUID magnetometer the complex
2displays some photomagnetic properties with an photoexcitation level of 60% and a
T(LIESST) value of 53 K.