A series of iron complexes with functionlized bipyridine ligands: Their properties and structures.

摘要

Temperature dependent color change is a useful property of iron complexes which may allow for preparation of thermo-sensors. The color change phenomenon may be driven by several processes including (1) ligand rearrangement, (2) redox chemistry, and/or (3) spin crossover. Herein presented is the synthesis of a series of iron-dialkyl-2,2'-bipryidyl-4,4'-dicarboxylate complexes including [FeL12Cl2]Cl•H2O, [FeL 13]Cl2, [FeL23]Cl•3H 2O, [FeL43]Cl2, [FeL8 2Cl2]Cl•H2O, [FeL8 3]Cl2, and [FeL16Cl3]2. These complexes have been characterized by IR spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and elemental analysis. Electron paramagnetic resonance (EPR) and Evan's method for 1H NMR spectroscopic analyses have been utilized to probe the spin states of the metal centers. During initial characterization, a reversible temperature-dependent color change, from maroon to orange and then to yellow, was observed from one of the early products. This unique phenomenon immediately attracted the attention and the research was reoriented to investigate the color change along the structure identification. The process of determining the cause of the color change is addressed in the second half of the results and discussion section.