Thermolabile Noble Metal Precursors: (NO)[Au(NO3)4], (NO)2[Pd(NO3)4], and (NO)2[Pt(NO3)6]

摘要

Noble metals play a crucial role in various fields of application, for example, as optical and electrical devices and as heterogeneous catalysts. For most of these applications, the metals have to be provided in a well-defined form to address the desired properties. For example, catalytic activity is usually strongly surface-dependent and the production of nanoparticles of the metals is often mandatory.A second example is the use of metals in electronic devices as conductor pathways, which requires well-defined depositions of the metals. Owing to this significant impact, several physical and chemical processes have been developed to allow for the deposition of noble metals in different shapes. Among these, chemical vapor deposition (CVD) is the most common chemical procedure, and numerous precursors are known, especially for the element gold. The drawback of CVD techniques is that organometallic compounds are usually used, leading to significant carbon contamination of the deposited metals. Recently we have shown that the nitrylium nitrate (NO2)[Au(NO3)4] is a suitable thermolabile precursor for gold; this species was obtained from the reaction of elemental gold with N2O5. The use of nitrogen oxides for the preparation of anhydrous nitrates can be traced back to the 1970s when Addison et al. reported first investigations, mainly based on N2O4. The advantage of (NO2)[Au(NO3)4] as a precursor is that it does not contain carbon or chlorine, and that its decomposition leads only to volatile products besides the metal. Moreover, the nitrate can be dissolved in N2O5, so that deposition of the precursor for example on surfaces is easy to perform. Interestingly, this precursor can not only be decomposed thermally but also using an electron beam, which allows the simple "writing" of gold structures. These results led us to investigate whether noble metals can generally be transformed into thermolabile nitrates using N2O5. In the course of these investigations, we were able to prepare the palladium and platinum compounds (NO)2[Pd(NO3)4] and (NO)2[Pt(N03)6], and furthermore a new gold nitrate, (NO)[Au(NO3)4].