Volatile Heterobimetallic Complexes from PdIIand CuIIβ-Diketonates: Structure, Magnetic Anisotropy, and Thermal Properties Related to the Chemical Vapor Deposition of Cu-Pd Thin Films

A novel approach for preparing volatile heterometallic complexes for use as precursors for the chemical vapor deposition of various materials is reported. New Cu¢Pd complexes based on b-diketonate units were prepared, and their structures and compositions were determined. [PdL2*CuL2] (1) and [PdL2*Cu(tmhd)2] (2) (L=2-methoxy-2,6,6-trimethylheptane-3,5-dionate; tmhd=2,2,6,6- tetramethylheptane-3,5-dionate) are 1D coordination polymers with alternating metal complexes, which are connected through weak interactions between the Cu atoms and the OCH3 groups from the ligand of the Pd complexes. The volatility and thermal stability were studied using thermogravimetric and differential thermal analyses and mass spectrometry. Compound 1 vaporizes without decomposition into monometallic complexes. It exhibits magnetic anisotropy, which was revealed from the angular variations in the EPR spectrum of a single crystal. The vapor thermolysis process for 1 was investigated using mass spectrometry, allowing the process to be framed within the temperature range of 200–3508C. The experimental data, supported by QTAIM calculations of the allowed intermolecular interactions, suggest that 1 likely exists in the gas phase as bimetallic molecules. Compound 1 proved to be suitable as a single-source precursor for the efficient preparation of Cu¢Pd alloy films with tunable Cu/Pd ratio. A possible mechanism for the film growth is proposed based on the reported data

Synthesis, structure, and magnetic properties of the tetranuclear complex [Cu(tmhd)₂Pb(hfa)₂]₂. Influence of temperature-dependent rotation of CF₃ groups upon EPR spectra

<p>A tetranuclear copper–lead complex based on 2,2,6,6-tetramethylheptane-3,5-dionate and 1,1,1,5,5,5-hexafluoropentane-2,4-dionate ligands was prepared. X-ray diffraction study of the crystal structure of the complex was performed at 296, 240, 120, 100, and 85 K. It was shown that the unit cell parameters do not substantially change, but the intramolecular angles and distances significantly changed. A polycrystalline powder of the complex was characterized by continuous wave X- and Q-band electron paramagnetic resonance (EPR) spectroscopy in the 10-350 K temperature range and by magnetic susceptibility based on the Faraday balance technique in the 77-350 K temperature range. The exchange interaction between the two copper ions was not observed which allowed recording the hyperfine interaction (HFI) with one copper nucleus and super HFI with two nonequivalent outer sphere fluorine nuclei. The outer sphere interaction results in the stabilization of the CF₃ group. Lowering the temperature resulted in the rotation of the CF₃ group and that led to the observation of super HFI from only one fluorine nucleus.</p

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

<div><p>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, <i>cis</i>-PdL₂*Pb(hfa)₂ and <i>cis</i>-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 <i>trans</i>-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 <i>trans</i>-to-<i>cis</i> 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 <i>trans</i>-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.</p></div

Isomerization as a tool to design volatile heterometallic complexes with methoxy-substituted β-diketonates

<p>A series of new heterometallic compounds have been obtained by the co-crystallization of Cu(II) methoxy-substituted β-diketonates and Pb(II) hexafluoroacetylacetonate (hfac) from organic solvents. Their crystal structures were established by X-ray analysis. It is shown that the formation of heterometallic compounds proceeds with geometrical isomerization of the initial copper complexes, which can be controlled by varying terminal substituents in the ligand. Due to the ability of copper complexes to isomerize, the structure of the resulting heterocomplexes can be flexibly and purposefully changed from polymeric to discrete molecular forms. The study of the thermal properties shows that all the reported compounds are volatile and can be re-sublimed in a vacuum, with their composition and structure being retained.</p