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The effects of backbone amine functionalization in three new homoleptic C^N^C type ruthenium(II) complexes bearing a tridentate bis‐imidazole‐2‐ylidene pyridine ligand framework are characterized and studied by single crystal diffraction, electrochemistry, optical spectroscopy and transient absorption spectroscopy in combination with ab initio DFT calculations. Functionalization by dimethylamine groups in 4‐position of the pyridine backbone significantly influences the properties of the complexes as revealed by comparison with the unfunctionalized references. As a result of the amine functionalization, a higher molar absorption coefficient of the MLCT bands, a decreased photoluminescence quantum yield at room temperature together with a shortened excited state lifetime but an improved photostability is observed. Introduction of electron donating and withdrawing groups at the NHC unit modifies the electronic and optical properties, such as the oxidation potential, absorption and emission properties, and the lifetimes of the excited states. [ABSTRACT FROM AUTHOR]

The unique core portion of Janus head pro‐ligands based on a tailored phenanthroline‐bis(guanidine) architecture has been utilized to generate a multiplicity of homometallic copper(II), nickel(II) and zinc(II) complexes terminated by halide constituents. The bis‐bidentate nitrogen donor ligands provide coordination sites with metal‐differentiating properties which can be loaded successively starting with the phenanthroline interface as can be demonstrated by mononuclear species which form under metal deficient conditions. Furthermore, depending on both the alkylation and metalation stage of the guanidine residues comprising variants with tetramethyl‐, tetraethyl‐, dimethylethylene‐, and dipentylene‐guanidino functionalities, a unique diversity of bi‐ and tetranuclear complexes with multifarious coordination geometries is accessible. The resulting complexes were characterized by low‐temperature X‐ray crystallography, and their redox behavior and magnetochemical properties in solution were analyzed via cyclic voltammetric and NMR techniques (Evans method). In this way, a remarkable equilibrium between the neutral phenanthroline‐bis(guanidine) copper(II) complex (X2CuII‐phenGua‐CuIIX2) and the radical monocationic phenanthroline‐bis(guanidine) copper(I)/copper(II) [X2CuII‐phenGua+·‐(CuIX2)–] species was identified which affects the chemical characteristics of the presented compounds in solution. Based on the unique phenanthroline‐bis(guanidine) architecture of Janus head pro‐ligands, a variety of homometallic CuII, NiII and ZnII complexes assembled in multifarious coordination geometries and completed by terminal or bridging halide constituents have been synthesized. Structural configurations, redox behavior and magnetochemical properties of the mono‐, bi‐ and tetranuclear species were characterized via X‐ray crystallographic, electrochemical and NMR techniques. [ABSTRACT FROM AUTHOR]

In search of new ligand motifs for photoactive iron(II) complexes with long-lived MLCT states, a series of six complexes with tridentate amine-functionalized bis- n -heterocyclic carbene (NHC)-pyridine ligands is presented. In the homoleptic complexes imidazole-, methylimidazole-, or benzimidazole-2-ylidene, NHC donors are employed in combination with pyridine, functionalized in the 4-position by dimethylamine or dibenzylamine. The effects of these different functionalities on the electronic structure of the complexes are examined through detailed ground state characterization by NMR, single crystal X-ray diffraction, as well as electrochemical and spectroscopic methods. The net influence of these different functionalities on orbital-orbital and electrostatic ligand-iron interactions is investigated thoroughly by density functional theory, and changes in the excited state behavior and lifetimes are finally examined by ultrafast optical spectroscopy. Great deviations of the initially expected effects by substitution in 4-position on the photochemical properties are observed, together with a significantly increased π-acceptor interaction strength in the benzimidazole-2-ylidene functionalized complexes.

While the Hieber anion [Fe(CO) 3 (NO)] - has been reincarnated in the last years as an active catalyst in organic synthesis, there is still a debate about the oxidation state of the central Fe atom and the resulting charge of the NO ligand. To shed new light on this question and to understand the Fe-NO interaction in the Hieber anion, it is investigated in comparison to the formal 3d 8 reference Fe(CO) 5 and the formal 3d 10 reference [Fe(CO) 4 ] 2- by the combination of valence-to-core X-ray emission spectroscopy (VtC-XES), X-ray absorption near-edge structure spectroscopy (XANES), and high-energy-resolution fluorescence-detected XANES. In order to extract information about the electronic structure, time-dependent density functional theory and ground-state density functional theory calculations are applied. This combination of experimental and computational methods reveals that the electron density at the Fe center of the Hieber resembles that of the isoelectronic [Fe(CO) 4 ] 2- . These observations challenge recent descriptions of the Hieber anion and reopen the debate about the experimentally and computationally determined Fe oxidation state and charge on the NO ligand.