Thermally-induced spin transition in Fe(4,4′-Azopyridine)[Fe(CN)₅NO]

The 4,4′-Azopyridine molecule was incorporated as a pillar between adjacent layers of Fe[Fe(CN)₅NO] through a precipitation reaction. According to the solved and refined crystal structure, from powder XRD data, the pillar molecule is found occupying the axial coordination sites for the iron atom linked at the N ends of the equatorial CNs of the nitroprusside complex ion. The NO and axial CN are found unlinked at their O and N ends and oriented toward the interlayer region. The structural study, from XRD data, was complemented with spectroscopic information (IR, Raman). The hybrid solid, Fe(4,4′-Azopyridine)[Fe(CN)₅NO], shows a thermally-induced spin transition in the 75–160 ​K temperature region, with a hysteresis of 8 ​K for the magnetic data recorded at 0.25 ​K/min, with the magnetometer operated in the settle mode. The spin transition was also monitored from DSC curves, and FTIR and Raman spectra at 80 and 295 ​K. The structure for the LS phase was calculated from computational simulation relaxing the refined HS structure. This method was validated through its application to materials where for both, HS and LS phases, the refined crystal structures are known. The preparation and study of this solid have not been previously reported. Unlike previous studies on spin-crossover in pillared ferrous nitroprussides, this molecule provides a pillar of enough height (∼9 ​Å) to minimize potential interactions between unbridged CN and NO ligands in the interlayer region.