Rafał Czerwieniec
"Structural, spectroscopic and electrochemical studies of Re(CO)₃⁺ complexes with bidentate ligands - selected derivatives of benzoxazole, benzothiazole and benzimidazole"

Abstract

In this study the structural, spectroscopic and electrochemical properties of a series of the Re(CO)₃⁺ complexes were investigated. The studied heteroaromatic ligands (the derivatives of benzoxazole, benzothiazole and benzimidazole) belong to four different chelating types: the N^N (the 2-(2'-pyridyl) derivatives), N^O^- (the 2-(2'-hydroxyphenyl) derivatives), N^S^- (the 2-(2'-thiohydroxyphenyl) derivatives) and N^C^- (the 2-phenyl derivatives), respectively. The undertaken investigations were aimed at evaluation of the potential applicability of each coordination compound class in the light emission processes (OLED and ECL)

The results of the performed syntheses demonstrate, that the direct reactions between Re(CO)5Cl and the respective chelating reagent N^N, N^OH, N^SH and N^CH can be considered as a convenient method for obtaining the investigated Re(CO)₃⁺ complexes. An unexpected result is the observation, that the N^OH, N^SH reagents tend (in reactions carried out in the non-coordinating media) to form the dimeric compounds, Re2(CO)6(N^O)2 and Re2(CO)6(N^S)2, respectively, which constitute a new class of Re(CO)₃⁺ complexes. According to our results this tendency seems to be a general feature of the N^O^- and N^S^--type ligands coordinated to the Re(CO)₃⁺ core.

The physico-chemical properties of the investigated complexes depend on their molecular structures, in particular on the nature of the N^N, N^O^-, N^S^- and N^C^- ligand. For instance, their luminescence properties are governed by the relative energetic position of the lowest excited states 3IL (intraligand) and 3MLCT (with the charge transfer from Re(CO)₃⁺ to the N^N, N^O^-, N^S^- or N^C^- ligand). Similarly, the redox potentials corresponding to the electrochemical oxidation and reduction of the investigated complexes (and the character of the respective electrode reactions) are determined by their molecular structures.

The advantageous combination of the luminescence and electrochemical properties of the complexes with the N^N ligands: Re(CO)3(N^N)Cl and Re(CO)3(N^N)(CH3CN)+ allowed us to investigate the electrochemically generated luminescence (ECL) processes of these compounds. Prototype OLEDs (organic light emitting devices) with the Re(CO)4(N^C^-)-type complex: Re(CO)4(2-phenylobenzothiazole), showing extremely high luminescence quantum yield, were also constructed.