Substituted pyridazines as ligands in homoleptic (fac and mer) and heteroleptic Ru(II) complexes.

This article reports the preparation of a range of phenyl, pyridyl and pyrazinyl substituted pyridazines via the inverse electron demand [2 + 4] Diels-Alder reaction between 3,6-di(2-pyridyl)-1,2,4,5-tetrazines (bptz) and 3,6-di(2-pyrazinyl)-1,2,4,5-tetrazines (bpztz) and suitable dienophiles including acenaphthalene. The resulting polyaromatic compounds vary systematically in the number of aromatic substituents and the number and position of N-heteroatoms. For four of these compounds, the effect of the molecular changes on the solid-state structures were investigated using single crystal X-ray crystallography. The pyridazines were used as bidentate ligands in {M(II)(bipy)(2)} and tris(homoleptic) complexes (M = Fe, Ru). The optical and electrochemical properties of these complexes reflect the electron accepting character of the new ligands. The facial and meridional isomers of the tris complexes could be separated by column chromatography (on silica), thus allowing a spectral comparison of their absorption and emission properties. The solid-state structures of several of the metal complexes are discussed, including that of the facial isomer of the tris Ru(II) complex of 3,6-bis(2-pyridyl)-4,5-bis(4-pyridyl)pyridazine--a potential preformed geometric motif for the predirected construction of supramolecular assemblies.

A dinuclear extension to constrained heteroleptic Cu(I) systems.

This article reports the synthesis and optical properties of three dinuclear, cationic copper complexes [Cu(2)(µ-dppm)(2)(µ-L)](NO(3))(2) (dppm diphenyldiphosphinomethane, L: L(A) 3,6-bis(2-pyridyl)-4,5-diphenyl-pyridazine, L(B) 3,6-bis(2-pyridyl)-4,5-di(4-pyridyl)-pyridazine and L(C) 3,6-bis(2-pyridyl)-8,9-diazafluoranthene). These were formed on the reaction of [Cu(µ-dppm)(NO(3))](2) with a series of N-donor (bppn) ligands L. The single crystal X-ray structures of [Cu(2)(µ-dppm)(2)(µ-L)](NO(3))(2)·CH(2)Cl(2) were determined and revealed that in both, the two copper atoms are held by three bridging ligands, two dppm ligands and one bppn ligand acting as a tetradentate bridge. The absorption spectra of the complexes present a MLCT [Cu → π*(N(∧)N)] band in the λ 370-425 nm region. These new complexes exhibit red-orange MLCT-based emission in the solid-state with lifetimes in the microsecond range. In oxygen-free dichloromethane solution, the complex [Cu(2)(µ-dppm)(2)(µ-L(C))](2+) has a long lifetime of 22.8 µs. The long emission lifetimes are attributed to a rigid conformation that precludes the possible distortion of the copper in the excited state.