Structural and thermal properties of three cyano-substituted azoderivatives of β-diketones

3-(2-Cyanophenylhydrazo)pentane-2,4-dione (HL1), 3-(4-cyanophenylhydrazo)pentane-2,4-dione (HL2) and 1-ethoxy-2-(4-cyanophenylhydrazo)butane-1,3-dione (HL3), and the Pd(II) complex [Pd(L2)2] were synthesized and characterized by IR, 1H and 13C NMR spectroscopies, ESI-MS, elemental and X-ray diffraction analyses (for HL1). HL3 derived from the unsymmetric 1-ethoxybutane-1,3-dione exists in solution as a mixture of the enol-azo and hydrazo tautomeric forms and a decrease of the solvent polarity shifts the tautomeric balance to the hydrazo form, while for HL1 and HL2, derived from the symmetric pentane-2,4-dione, the hydrazo form is dominating under all the studied conditions. HL1–3 and [Pd(L2)2] show a high thermal stability with well-defined peaks of phase transition at 438 (HL1), 462 (HL2), 392 (HL3) and 404 K ([Pd(L2)2]).