A pyrazole-containing verdazyl radical ligand Meprv: structure of its precursor prvH3 and its bis(2,2′-bipyridine)ruthenium(II) complex

Reaction between 1,1′-dimethyl carbonic dihydrazide and pyrazole-3-carboxaldehyde gave 1,5-dimethyl-3-(3′-pyrazolyl)-6-oxotetrazane (prvH3), which crystallizes in the orthorhombic space group Pca21, with a=10.7745(4), b=8.1745(2) and c=10.6625(3) Å. Dehydrogenation of prvH3 in methanol by 1,4-benzoquinone afforded the methylated radical 1,5-dimethyl-3-(1′-methyl-3′-pyrazolyl)-6-oxoverdazyl (Meprv), which reacted with cis-[Ru(bpy)2Cl2] and NaBPh4 to yield the cation [Ru(bpy)2(Meprv)]2+ as its BPh4 salt. The absence of luminescence and the electrochemical behavior of this complex imply that the lowest 3MLCT (metal to ligand charge transfer) excited state is located on the electron-deficient Meprv ligand.