Group 2 Element Chemistry and its Role in OMVPE of Electronic Ceramics

Abstract

AbstractCoordination compounds of alkaline-earth metals with simple monodentate ligands were mentioned in the literature as early as 1820, when Faraday reported ‘metal-ammonias’.[1] The number of heavy alkaline earth element coordination compounds remained limited for many years, however, as it was thought to be unlikely for the large earth alkaline cations to form such complexes. In 1967 Pedersen discovered that cyclic oligoethers (crown ethers) can serve as suitable ligands for divalent alkaline earth cations.[2] His findings were extended a few years later by Lehn who found that macrobicyclic multidentate ligands (cryptands) are efficient ligands for alkaline earth cations.[3] In each of these examples, the primary mode of metal-ligand interaction is electrostatic in origin. These examples demonstrate the lack of well-defined covalent bonding for Ca, Sr and Ba compounds. In the 25 years which have passed since Pedersen's seminal discovery, a large number of coordination compounds containing alkaline earth metals have been synthesized. In recent years, the emphasis has shifted towards the preparation of group 2 element-containing compounds which potentially can be used as precursors in the preparation of metal oxides by chemical vapor deposition [4–8]. In light of the general agreement that no “perfect” barium source presently exists for OMVPE purposes, this article will focus on general themes in group 2 element chemistry and, where relevant, correlate those themes within an integrated approach to design of new compounds of greater potential utilization for the preparation of electronic materials in thin film form.