Iron(II) spin crossover complexes with a sulfur rich ligand backbone

Abstract

One goal that many scientists pursue is the unification of several interesting chemical or physical properties in one system, as only multifunctional materials will meet the challenges of today's technologies. With this background, three novel iron(II) coordination compounds with a Schiff base-like N2O2 coordinating ligand L bearing a sulfur-rich backbone are investigated in this work. Two of the complexes, the mononuclear [FeL(py)2] (py = pyridine) and the coordination polymer {[FeL(bpee)]}n [bpee = trans-1,2-bis(4-pyridyl)ethene], show spin crossover behavior followed using magnetic susceptibility measurements and Mössbauer spectroscopy. To get a closer insight into different states of the complex spin crossover behavior of {[FeL(bpee)]}n, XPS measurements were conducted at different temperatures. Furthermore, impedance spectroscopic measurements at variable temperatures were performed to get insight into the electrical conductivity of this system. All iron(II) complexes were electrochemically characterized using cyclovoltammetric measurements, supplemented by DFT computation. Apparently, the extension by a sulfur backbone leads to a stabilization of the HOMO. Due to this, the complexes are more difficult to oxidize than comparable systems. With {[FeL(azpy)]}n, another coordination polymer, this time axially decorated by the redox-active ligand azpy (azpy = 4,4′-azopyridine), is investigated, which is, however, a pure high spin complex.