Development of a novel heteroleptic BODIPY-tetrazole-Fe(II) SCO-fluorescence coordination compound with T½ tunability

Abstract

Multifunctional spin crossover (SCO) compounds combine classical SCO properties with additional features (e.g. non-linear optics, bulk magnetic ordering, …), thus opening the possibility for prospective and versatile applications. Besides the usually performed magnetic measurements concerning SCO nanomaterials a more straightforward spin state detection method, which allows a precise tracking even in small clusters, is required. The spin state dependent modulation of photoluminescence (PL) is one approach fulfilling these demands. In addition to the development of SCO-PL systems for feasible applications, investigations on the only partially understood mechanism of this phenomenon still need to be conducted. We recently developed a heteroleptic octahedral Fe(II)-complex consisting of four 1,3,5,7-tetramethyl-8-((1H-tetrazol-1-yl)methyl)-BODIPY (2TzBODIPY) ligands and two apically arranged acetonitrile (MeCN) ligands. The structure of [Fe(2TzBODIPY)4(MeCN)2](ClO4)2 was confirmed by single crystal XRD analysis as shown in Figure 1. This novel SCO-PL system exhibits a spin transition at T½ = 265 K and shows strong fluorescence in solid state at room temperature. This multifunctional compound allows a straightforward tuning of the spin transition temperature by replacing the apical ligands with various nitrile (R-CN) species. This paves the way for detailed investigations – regarding the electronic and steric influence of the apical ligands on the Fe(II) coordination center – and for its possible future applications as multifunctional materials. The magnetic behavior of the developed system with varying apical ligands (R-CN) is depicted in Figure 2.