Synthesis, characterisation and variable-temperature nuclear magnetic resonance of bis(bipyridine)ruthenium complexes containing dihydrazone ligands

A series of dihydrazone and substituted dihydrazone derivatives of biacetyl and of hydrazone and phenylhydrazone derivatives of 2-acetylpyridine bind to [Ru(bipy)₂Cl₂] to give [Ru(bipy)₂(L-L)][PF₆]₂ complexes {bipy = 2,2′-bipyridine; L-L = biacetyl di(phenylhydrazone) 1a, biacetyl di[methyl(phenyl)hydrazone] 1b, biacetyl di(o-tolylhydrazone) 1c, biacetyl di(dimethylhydrazone) 1d, biacetyl dihydrazone 1e, biacetyl di(benzaldehyde azine) 1f, 2-acetylpyridine phenylhydrazone 1g, or 2-acetylpyridine hydrazone 1h}. The structures of all complexes have been determined using IR, UV/VIS, NMR and microanalysis. The proton NMR spectra of 1a-1c show an unusual dependence on probe temperature with broadened aromatic resonances, sharpening at both high and low temperature in the case of 1b and 1c. No emission was observed for complexes with two hydrazone moieties, whereas it was observed for 1g and 1h with one hydrazone. The molecular structure of 1a has been determined and shows a hydrazone phenyl group lying over each of the bipyridyl rings: space group C2/c, a = 25.895(3), b = 10.505(1), c = 17.431(2) Å, β = 106.03(2)° and Z = 4.