Volatile Pd–Pb and Cu–Pb heterometallic complexes: structure, properties, and trans-to-cis isomerization under cocrystallization of Pd and Cu β-diketonates with Pb hexafluoroacetylacetonate

Abstract

Preparation of volatile heterometallic precursors is a significant step on the way to advanced multicomponent materials. Study of molecular transformations in solution upon precursor synthesis is of importance to optimize the preparation of the stable solid product of desired composition. Two new volatile heterobimetallic complexes, cis-PdL2*Pb(hfa)2 and cis-CuL2*Pb(hfa)2, were obtained (L = 2-methoxy-2,6,6-trimethylheptane-3,5-dionate, hfa = 1,1,1,5,5,5-hexafluoropentane-2,4-dionate) under cocrystallization of trans-bis-beta-diketonates of Pd(II) and Cu(II) with Pb(hfa)2 from organic solvents. Crystals of these compounds are built of discrete bimetallic molecules where transition metal complex isomerized from trans-to-cis form. Complexation followed by isomerization was studied by solution NMR. The bimetallic molecular species were formed early in solution. Enthalpy and activation energy of isomerization were estimated to be 49 and 93 kJ mol−1, respectively. A new synthesis technique of Pd(II) beta-diketonates which is distinguished by simplicity and selectivity as well as the crystal structure of trans-PdL2 is described. Volatility of all obtained compounds was confirmed by thermogravimetric analysis and fractional sublimation in vacuum; Pd-containing heterobimetallic complex appeared to be more volatile than both the initial monometallic complexes and Cu-containing complex.