Toward an Iron(II) Spin-Crossover Grafted Phosphazene Polymer

Two new cyclotriphosphazene ligands with pendant 2,2′:6′,2″-terpyridine (Terpy) moieties, namely, (pentaphenoxy)­{4-[2,6-bis­(2-pyridyl)]­pyridoxy}­cyclotriphosphazene (L1), (pentaphenoxy)­{4-[2,6-terpyridin-4-yl]­phenoxy}­cyclotriphosphazene (L2), and their respective polymeric analogues, L1P and L2P, were synthesized. These ligands were used to form iron­(II) complexes with an FeIITerpy2 core. Variable-temperature resonance Raman, UV–visible, and Mössbauer spectroscopies with magnetic measurements aided by density functional theory calculations were used to understand the physical characteristics of the complexes. By a comparison of measurements, the polymers were shown to behave in the same way as the cyclotriphosphazene analogues. The results showed that spin crossover (SCO) can be induced to start at high temperatures by extending the spacer length of the ligand to that in L2 and L2P; this combination provides a route to forming a malleable SCO material.