Toward an Iron(II) Spin-Crossover Grafted Phosphazene Polymer Ross J. Davidson, † Eric W. Ainscough,* ,† Andrew M. Brodie,* ,† Geoffrey B. Jameson, † Mark R. Waterland, † Harry R. Allcock, ‡ Mark D. Hindenlang, ‡ Boujemaa Moubaraki, § Keith S. Murray, § Keith C. Gordon, ¶ Raphael Horvath, ¶ and Guy N. L. Jameson ¶ † ChemistryInstitute of Fundamental Sciences, Massey University, Private Bag 11 222, Palmerston North 4442, New Zealand ‡ Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802, United States § School of Chemistry, Monash University, Building 23, Clayton, Victoria 3800, Australia ¶ MacDiarmid Institute for Advanced Materials and Nanotechnology, Department of Chemistry, University of Otago, Dunedin 9016, New Zealand * S Supporting Information ABSTRACT: Two new cyclotriphosphazene ligands with pendant 2,2′:6′,2″-terpyridine (Terpy) moieties, namely, (pentaphenoxy){4-[2,6-bis(2-pyridyl)]pyridoxy}- cyclotriphosphazene (L 1 ), (pentaphenoxy){4-[2,6-terpyridin- 4-yl]phenoxy}cyclotriphosphazene (L 2 ), and their respective polymeric analogues, L 1P and L 2P , were synthesized. These ligands were used to form iron(II) complexes with an Fe II Terpy 2 core. Variable-temperature resonance Raman, UV-visible, and Mö ssbauer 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 L 2 and L 2P ; this combination provides a route to forming a malleable SCO material. ■ INTRODUCTION Spin-crossover (SCO) materials have long been heralded as having a potential use for quantum computers and massive data storage among a host of other potential applications. 1,2 However, one of the key difficulties in using these materials is that they are often crystalline, making deposition difficult and expensive. This has been improved by attaching long alkyl groups, 3 which resulted in a malleable material; however, by varying the substituents to produce suitable materials, the SCO behavior is also altered. 4-6 Further work was carried out by Lemaire et al. to produce an iron(III) SCO grafted polythiophene, although iron(III) is not ideal to use because each of the spin states is paramagnetic, whereas iron(II) switches from diamagnetic (low spin, LS) to paramagnetic (high spin, HS). 7 Cyclo- and polyphosphazenes provide a promising solution to many of these problems. With a repeating unit of nitrogen and phosphorus atoms, they can be substituted at the phosphorus atom with two nucleophiles (see Chart 1), typically alcohols or amines. Unlike many organic polymers, it is possible to form the polymer first, e.g., [NPCl 2 ] n , followed by substitution of the chloride groups. This allows the substituents to be varied in both type and ratio. These properties have often proven to be useful in the development of ligands because coordinating substituents (pyridines, phosphines, nitriles, etc.) can be attached to either the cyclotriphosphazene (CTP) to form discrete metal complexes 8-11 or polyphosphazene (PP) metallopolymers. 9,12-21 Previously reported polymers produced by Ainscough et al. proved that the substitution of phosphazenes with fluorophores had little effect on their physical behavior. 12 This study examines the properties of iron bis(2,2′:6′,2″- terpyridine) ([Fe(Terpy) 2 ] 2+ ) attached to both the CTP and PP platforms and measures their photo- and magnetochemical properties. A variety of techniques have been used to characterize these novel materials such as electronic absorb- ance, solid-state resonance Raman (rR), and Mö ssbauer spectroscopies as well as magnetic susceptibility. Density Received: April 26, 2012 Published: July 10, 2012 Chart 1. Generic PP and CTP Structures Article pubs.acs.org/IC © 2012 American Chemical Society 8307 dx.doi.org/10.1021/ic300853f | Inorg. Chem. 2012, 51, 8307-8316